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Some aspects of the geochemistry of sulphur and iodine in marine humic substances and transition metal… François, Roger 1987

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SOME ASPECTS OF THE GEOCHEMISTRY OF SULPHUR AND IODINE IN MARINE HUMIC SUBSTANCES AND TRANSITION METAL ENRICHMENT IN ANOXIC SEDIMENTS by ROGER F R A N C O I S M . S c , The University of Southampton A THESIS S U B M I T T E D IN P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S FOR T H E D E G R E E OF DOCTOR OF P H I L O S O P H Y in T H E F A C U L T Y OF G R A D U A T E STUDIES < The Department of Oceanography We accept this thesis as conforming to the required standard T H E U N I V E R S I T Y O F BRITISH C O L U M B I A 3 June 1987 ® Roger Francois, 1987 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. The University of British Columbia 1956 Main Mall Vancouver, Canada Department V6T 1Y3 DE-6(3/81) ABSTRACT. The evolution of the sulphur content of humic substances extracted from a near-shore sediment core was investigated. Special attention was taken to avoid S contamination of the humic materials during sample handling and extraction. The S/C ratios increased continuously with depth to values which strongly suggest S addition to the humic matrix during early diagenesis by reactions between organic matter and I^S or i t s oxidation products. The l i g h t isotopic composition of t h i s organic sulphur supports t h i s view; however, subsequent isotopic exchange has obscured the mechanism i n i t i a l l y involved. Since a large f r a c t i o n of the enrichment occurred above the sulphidic zone, redox boundaries, such as the interface of anoxic microniches within the more oxidized zones, or the sulphidic/suboxic boundary of the sediment column, must have been important s i t e s for S addition. The influence of sulphur enrichment on the complexing capacity of humic materials was also investigated, and i t was shown that S-addition increases s i g n i f i c a n t l y the number of s i t e s on which Cu is i r r e v e r s i b l y bound. Iodine is c h a r a c t e r i s t i c a l l y enriched at the surface of hemipelagic and nearshore sediments deposited under oxygenated conditions. In such sediments, bulk I/C ratios usually org decrease with depth to values which are c h a r a c t e r i s t i c of anoxic i i sediments, r e f l e c t i n g a p r e f e r e n t i a l release of iodine during early diagenesis. There is some debate as to whether sedimentary iodine i s associated with the iron oxyhydroxide phase or with the organic f r a c t i o n , and whether the decrease in I/C with 3 org depth i s due to the dissolution of the iron oxyhydroxides or the decomposition of l a b i l e organic matter. In this study, i t i s shown that in a s u r f i c i a l hemipelagic sediment sample and in a nearshore sediment core iodine is mainly associated with the organic f r a c t i o n and, moreover, that humic substances are involved in the s u r f i c i a l iodine enrichment. Laboratory experiments on the uptake and release of iodine by and from sedimentary humic substances also suggest a mechanism whereby humic materials reduce iodate at the sediment/water interface to an e l e c t r o p h i l i c iodine species which further reacts with the organic matter to produce iodinated organic molecules. During b u r i a l , t h i s excess iodine could be displaced from the organic matrix by nucleophiles such as sulphide ions or thiosulphate, thus providing a possible explanation for the decrease in I / c o r g r a t i o with depth observed in many nearshore and hemipelagic sediments. Bulk metal concentrations were measured in the sediments of Saanich Inlet in an attempt to es t a b l i s h the occurrence of trace metal enrichments in the anoxic central basin. Ba, Ni, V, Cr, Zn, Pb, Cu, and Mo were found to be enriched in the anoxic ooze over the possible contributions from lithogenous sources. Spatial and i i i seasonal variations in the chemical composition of the s e t t l i n g p articulates c o l l e c t e d with interceptor traps gave further indications of the mode of incorporation of these metals. Biogenic Ba and Cr appeared to be associated with opaline s i l i c a , although alternative explanations are also possible, p a r t i c u l a r l y for Ba. Zinc seemed to be added to the sediment e s s e n t i a l l y in association with planktonic materials, while Cu required an additional source d i r e c t l y linked to the anoxic environment. Si m i l a r l y , Ni, V, and Mo were added to the anoxic sediments by reactions occurring at the sediment-water interface. In the nearshore environment studied here, these metals were not associated to any s i g n i f i c a n t extent with planktonic materials, p a r t i c u l a r l y Ni and Mo. Of a l l the elements analyzed, Mo showed the largest enrichment in the anoxic sediments of Saanich In l e t . i v TABLE OF CONTENTS ABSTRACT 1 INTRODUCTION 1 1.1 A BRIEF REVIEW OF THE SIGNIFICANCE OF HUMIC SUBSTANCES IN THE MARINE ENVIRONMENT 1 1.2 SYNOPSIS OF THE PRESENT STUDY 15 2 SULPHUR IN THE HUMIC SUBSTANCES OF NEARSHORE MARINE SEDIMENTS 19 2.1 INTRODUCTION 19 2.2 EVALUATION OF THE EXTRACTION CONDITIONS OF SEDIMENTARY HUMIC SUBSTANCES NECESSARY TO ESTIMATE THEIR TRUE, IN SITU SULPHUR CONTENT 23 2.2.1 INTRODUCTION 23 2.2.2 MATERIALS AND METHODS 24 2.2.3 RESULTS AND DISCUSSION 25 2.2.3.1 CONTAMINATION OF THE HUMIC FRACTION EXTRACTED FROM A SULPHIDIC SEDIMENT BY CO-EXTRACTED PYRITE 25 2.2.3.2 SULPHUR CONTAMINATION OF THE HUMIC FRACTION DURING THE OXIDATION OF ANOXIC SEDIMENTS 26 2.2.3.3 SULPHUR CONTAMINATION OF HUMIC SUBSTANCES BY REACTIONS WITH VARIOUS SULPHUR SPECIES DURING ALKALINE EXTRACTION 30 2.2.3.3.1 SULPHUR CONTAMINATION BY SULPHIDES ... 30 2.2.3.3.1.1 REACTIONS BETWEEN FREE SULPHIDES AND HUMIC SUBSTANCES IN BASIC SOLUTIONS 30 2.2.3.3.1.2 REACTIONS BETWEEN ACID VOLATILE SULPHIDES AND HUMIC SUBSTANCES IN BASIC SOLUTIONS 34 2.2.3.3.2 SULPHUR CONTAMINATION BY ELEMENTAL SULPHUR 35 2.2.3.3.3 REACTIONS BETWEEN POLYSULPHIDES AND HUMIC SUBSTANCES IN BASIC SOLUTIONS .. 39 2.2.4 CONCLUSIONS 45 2.3 EVOLUTION OF THE SULPHUR CONTENT OF THE HUMIC FRACTION OF MARINE SEDIMENTS DURING EARLY DIAGENESIS .. 47 2.3.1 INTRODUCTION 47 2.3.2 MATERIALS AND METHODS 48 2.3.2.1 SITE DESCRIPTION AND SAMPLING PROCEDURE ... 48 2.3.2.2 EXTRACTION AND ANALYTICAL METHODS 50 2.3.3 RESULTS AND DISCUSSION 55 V 2.3.4 CONCLUSIONS 80 2.4 REACTIONS BETWEEN REDUCED SULPHUR SPECIES AND HUMIC SUBSTANCES AT SEAWATER pH, UNDER LABORATORY CONDITIONS 86 2.4.1 INTRODUCTION 86 2.4.2 METHODS 87 2.4.3 RESULTS AND DISCUSSION 87 2.5 INFLUENCE OF S-ENRICHMENT ON THE COMPLEXING CAPACITY OF HUMIC MATERIALS 89 2.5.1 INTRODUCTION 89 2.5.2 METHODS 101 2.5.3 RESULTS AND DISCUSSION 103 3 THE INFLUENCE OF HUMIC SUBSTANCES ON THE GEOCHEMISTRY OF IODINE IN NEARSHORE AND HEMIPELAGIC SEDIMENTS 109 3.1 INTRODUCTION 109 3.2 MATERIALS 112 3 . 3 METHODS 112 3.3.1 ANALYTICAL METHODS 112 3.3.2 EXPERIMENTAL METHODS 112 3.3.2.1 PARTITIONING OF IODINE IN SEDIMENTS 112 3.3.2.1.1 OXYHYDROXIDE PHASE 112 3.3.2.1.2 HUMIC MATERIALS 113 3.3.2.2 UPTAKE OF IODINE BY HUMIC SUBSTANCES 113 3.3.2.2.1 PRELIMINARY EXPERIMENT 113 3.3.2.2.2 REACTION BETWEEN HUMIC SUBSTANCES AND IODATE 114 3.3.2.2.3 RELEASE OF IODINE FROM HUMIC SUBSTANCES 115 3.4 RESULTS AND DISCUSSION 115 3.4.1 THE PARTITIONING OF IODINE IN MARINE SEDIMENTS ...115 3.4.1.1 OXYHYDROXIDES 117 3.4.1.2 HUMIC SUBSTANCES 121 3.4.2 ASSOCIATION BETWEEN HUMIC SUBSTANCES AND IODINE DURING EARLY DIAGENESIS 123 3.4.3 EXPERIMENTAL STUDIES OF THE ADSORPTION AND RELEASE OF IODINE BY SEDIMENTARY HUMIC MATERIALS..126 3.4.3.1 UPTAKE OF IODINE BY HUMIC MATERIALS 128 3.4.3.2 INVESTIGATION OF THE MECHANISM OF IODINE UPTAKE BY HUMIC MATERIALS 130 3.4.3.3 RELEASE OF IODINE FROM HUMIC MATERIALS 138 3.5 CONCLUSIONS 141 4 A STUDY OF THE REGULATION OF METAL CONCENTRATION IN SAANICH INLET SEDIMENTS 145 4.1 INTRODUCTION 145 4.2 GENERAL FEATURES OF SAANICH INLET AND SAMPLING LOCATIONS 148 4.2.1 GENERAL DESCRIPTION 148 v i 4.2.2 PHYTOPLANKTON 152 4.2.3 GENERAL GEOLOGY OF THE SAANICH REGION 153 4.2.4 SAMPLING 158 4.3 BULK COMPOSITION OF SAANICH INLET SEDIMENTS 158 4.3.1 MINERALOGY OF SAANICH INLET SEDIMENTS 162 4.3.2 GEOCHEMISTRY OF SAANICH INLET SEDIMENTS 167 4.3.2.1 ORGANIC MATTER 167 4.3.2.2 CARBONATE 178 4.3.2.3 MAJOR ELEMENTS 178 4.3.2.3.1 ALUMINIUM 178 4.3.2.3.2 SILICON 178 4.3.2.3.3 POTASSIUM 183 4.3.2.3.4 CALCIUM AND SODIUM 183 4.3.2.3.5 IRON AND MAGNESIUM 189 4.3.2.3.6 TITANIUM 198 4.3.2 3.7 CONCLUSIONS 202 4.3.2.4 PHOPHORUS 205 4.3.2.5 SULPHUR 205 4.3.2.6 MINOR ELEMENTS ..209 4.3.2.6.1 RUBIDIUM AND BARIUM 210 4.3.2.6.2 STRONTIUM 219 4.3.2.6.3 NICKEL AND CHROMIUM 223 4.3.2.6.4 VANADIUM AND MANGANESE 232 4.3.2.6.5 ZINC AND LEAD 241 4.3.2.6.6 COPPER 248 4.3.2.6.7 MOLYBDENUM 251 4.3.2.6.8 ZIRCONIUM 253 4.3.2.6.9 CONCLUSIONS 256 4.3.2.7 IODINE AND BROMINE 257 4.4 ELEMENTAL FLUXES IN SAANICH INLET FROM AUGUST 1983 TO SEPTEMBER 1984 261 4.4.1 FLUXES OF ORGANIC MATTER 266 4.4.1.1 STATION SI-9 266 4.4.1.1.1 45 M 266 4.4.1.1.2 110 M 268 4.4.1.1.3 150 M 268 4.4.1.2 STATION SN0.8 270 4.4.1.2.1 50 M 270 4.4.1.2.2 130 M AND 180 M 270 4.4.1.3 DISCUSSION 273 4.4.2 FLUXES OF MAJOR ELEMENTS 282 4.4.2.1 STATION SI-9 284 4.4.2.1 .1 45 M 284 4.4.2.1.2 110 M AND 150 M 291 4.4.2.2 STATION SN0.8 297 4.4.3 FLUXES OF MINOR ELEMENTS 301 4.4.3.1 BARIUM 301 4.4.3.2 ZINC, CHROMIUM, COPPER, VANADIUM, AND NICKEL 310 v i i 4.4.3.2.1 ZINC 310 4.4.3.2.2 CHROMIUM 315 4.4.3.2.3 COPPER 319 4.4.3.2.4 VANADIUM 322 4.4.3.2.5 NICKEL 325 4.4.3.3 MOLYBDENUM 329 4.4.3.4 RUBIDIUM 332 4.4.3.5 ZIRCONIUM 334 4.4.3.6 MANGANESE 334 4.4.4 FLUXES OF IODINE 337 4.5 CONCLUSIONS 341 5 CONCLUDING REMARKS 344 6 BIBLIOGRAPHY 348 APPENDIX I: SAMPLE COLLECTION AND INITIAL SAMPLE PREPARATION 390 1-1 BOTTOM SEDIMENTS AND PORE WATERS 390 I- 2 SETTLING PARTICULATES 391 APPENDIX I I : ANALYTICAL METHODS 399 II- 1 SOLID PHASE 399 II-1.1 ELEMENTAL ANALYSIS BY X-RAY FLUORESCENCE 399 II —1.1.1 SAMPLE PREPARATION 399 II —1.1.1.1 MAJOR ELEMENTS 399 11-1.1.1.2 MINOR ELEMENTS AND SODIUM 401 11-1.1.1.3 IODINE 405 II-1.1.1.4 CHLORINE AND SALT-CORRECTION PROCEDURE 405 11-1 .2 CARBON AND NITROGEN ANALYSIS 409 11-1.2 . 1 TOTAL CARBON AND NITROGEN 410 11-1.2.2 CARBONATE AND ORGANIC CARBON 410 II-1.2.2.1 GRAVIMETRIC DETERMINATION OF THE CARBONATES 410 11-1.2.2.2 ELEMENTAL ANALYZER 411 11-1.2.2.3 COULOMETRY 412 11-1.3 ELEMENTAL SULPHUR ANALYSIS 414 11-2 PORE WATERS 415 II-2.1 SULPHATE ANALYSIS 415 11-2.2 SULPHIDE ANALYSIS 416 11-3 HUMIC EXTRACTS 416 11-3.1 EXTRACTION OF HUMIC MATERIALS ..416 II-3.2 DISSOLVED ORGANIC CARBON IN HUMIC EXTRACTS ...416 II-3.3 POLYSULPHIDE CONCENTRATIONS IN HUMIC EXTRACTS 417 11-3.4 IODINE IN HUMIC EXTRACTS 418 11-4 HUMIC MATERIALS 418 II-4.1 ISOLATION OF HUMIC MATERIALS 418 v i i i 11-4.2 CARBON AND NITROGEN CONTENT 419 11-4.3 IODINE CONTENT 419 II- 4.4 SULPHUR CONTENT 419 11-4.4.1 TOTAL SULPHUR 419 11-4.4.2 PYRITIC SULPHUR 420 11-4.4.3 ORGANIC SULPHUR 421 11-4.4.4 ESTER SULPHATE 421 11-4.4.5 C-BONDED SULPHUR 423 APPENDIX I I I : SEDIMENTATION RATE MEASUREMENT 424 111-1 PRINCIPLES OF THE METHOD 424 II1-2 MEASUREMENT OF Po ACTIVITY IN SEDIMENT SAMPLES 424 II I - 3 SEDIMENTATION RATE CALCULATIONS 426 II I - 3.1 STATION SN0.8 426 II I - 3.2 STATION SI-9 427 APPENDIX IV: CHEMICAL DATA 430 IV- 1 CHEMICAL COMPOSITION OF SAANICH INLET SEDIMENTS ...430 IV- 1.1 CHEMICAL COMPOSITION (SALT-CORRECTED) AND DEPTH OF COLLECTION OF FINE-GRAINED SEDIMENT SAMPLES FROM THE CENTRAL BASIN OF SAANICH INLET 431 IV-1.2 CHEMICAL COMPOSITION (SALT-CORRECTED) AND DEPTH OF COLLECTION OF THE SILL AND COWICHAN ESTUARY SEDIMENT SAMPLES 434 IV-1.3 CHEMICAL COMPOSITION (SALT-CORRECTED) AND DEPTH OF COLLECTION OF THE COARSE-GRAINED NEARSHORE SEDIMENT SAMPLES 436 IV-2 CHEMICAL COMPOSITION OF SI-9 AND SN0.8 SEDIMENT CORES 438 IV-2.1 SALT-CORRECTED MAJOR ELEMENT CONCENTRATIONS: SI-9 438 IV-2.2 SALT-CORRECTED MINOR ELEMENT CONCENTRATIONS: SI-9 439 IV-2.3 SALT-CORRECTED MAJOR ELEMENT CONCENTRATIONS: SN0.8 440 IV-2.4 SALT-CORRECTED MINOR ELEMENT CONCENTRATIONS: SN0.8 441 IV-3 FLUXES OF ELEMENTS AT SI-9 AND SN0.8 442 ix LIST OF FIGURES 1 . Fractionation of humic substances on the basis of s o l u b i l i t y 6 2. Sulphur cycle 21 3. Infra-red spectra of humic acids . 43 4. Map of Jervis Inlet 49 5. Humic extraction procedure 51 6. Bulk sediment analysis 57 7. D i s t r i b u t i o n of pore water sulphide and sulphate concentrations 59 8. Concentration p r o f i l e and isotope composition of elemental sulphur 60 9. S/C ra t i o s of humic acids extracted from core A 65 10. Total sulphur content of humic acids hydrolyzed in 5N HC1, 5h at 120 C, normalized to C, , 70 ' ' hyd 11. Polysulphides ( s s n ) associated with the humic extracts obtained from core A 71 12. Isotope composition of free sulphides and hydrolyzed humic acids 74 13. Possible mechanism of sulphur addition to the organic matrix in the oxic , sub-oxic, and sulphidic zones of nearshore marine sediments 84 14. The periodic table of the elements showing the d i s t r i b u t i o n of the "class-a", "borderline", and "class-b" metal and metalloid ions (after Nieboer and Richardson, 1 980) 93 15. Chelate formation between o-hydroxycarboxylic acids, o-dicarboxylic acids, and divalent metal cations 96 16. Logarithms of t h e 2 + s t a b i l i t y 2c_onstants f ° r 1 : 1 complexes between Ba through Zn and the bidentate ligands oxalic acids, glycine, ethylene-diamine, mercaptoacetic acid and mercapto-ethylamine (after Siegel and McCormick, 1 970) 100 x 17. Procedure followed in the experiment on the influence of S-enrichment on the Cu retention by humic substances 102 2+ • . 18. Reaction between Cu and S-containing proteins, under anoxic conditions 108 19. I/C , Fe/Al, and Mn p r o f i l e s of the hemipelagic sedimint core HUD 22 (from Pedersen et a l . , 1986) 116 20. Sediment core HA-2: (a) Iodine, carbon and C /N r a t i o p r o f i l e s (C and N data from Losher, 1985) °b) I/C rat i o s in sediments and extracted humic subiiSnces 124 21. Sediment core HA-2: (a) s o l i d phase. - Mn (ppm) and S (%) p r o f i l e s , (b) pore waters - Mn and H 2S (umol/1) p r o f i l e s (from Losher, 1985) 7 125 22. Displacement of iodine from I-enriched humic substances 139 23. Map of Saanich Inlet 149 24. General geology of Southern Vancouver Island 154 25. Sampling locations 159 26. Period of deployment of the sediment trap moorings 160 27. Longitudinal transect of Saanich Inlet showing the positioning of the sediment traps 161 28. D i s t r i b u t i o n of organic carbon in Saanich Inlet sediments 168 29. D i s t r i b u t i o n of the C/N r a t i o in Saanich Inlet sediments 171 30. Relationship between organic carbon content and sedimentation rate in Saanich Inlet sediments 175 31. D i s t r i b u t i o n of CaCO^ in Saanich Inlet sediments 179 32. D i s t r i b u t i o n of Al in Saanich Inlet sediments 180 33. Relationship between S i / A l and % C o r g 182 x i 34. Di s t r i b u t i o n of the K/Al r a t i o in Saanich Inlet sediments 184 35. Di s t r i b u t i o n of the Na/Al r a t i o in Saanich Inlet sediments 185 36. Di s t r i b u t i o n of the Ca/Al r a t i o in Saanich Inlet sediments 186 37. Histogram of d i s t r i b u t i o n of the Na/Al and Ca/Al ra t i o s in Saanich Inlet sediments 187 38. Correlation between %Fe and %Mg in Saanich Inlet sediments 190 39. Correlation between %Fe and %A1 in Saanich Inlet sediments 192 40. Di s t r i b u t i o n of the Fe/Al r a t i o in Saanich Inlet sediments 193 41. Histogram of d i s t r i b u t i o n of the Fe/Al r a t i o in Saanich Inlet sediments 195 42. Correlation between %Fe and %K in Saanich Inlet sediments 196 43. Di s t r i b u t i o n of the Fe/K r a t i o in Saanich Inlet sediments 197 44. Correlation between % T i and %A1 in Saanich Inlet sediments 199 45. Correlation between % T i and %Fe in Saanich Inlet sediments 201 46. Di s t r i b u t i o n of sulphur in Saanich Inlet sediments 207 47. Correlation between %S and %C in Saanich Inlet sediments ? 208 48. Correlation between K and Rb in Saanich Inlet sediments 212 49. Di s t r i b u t i o n of the Rb/K r a t i o in Saanich Inlet sediments 213 50. Di s t r i b u t i o n of Ba in Saanich Inlet sediments 215 x i i 51. D i s t r i b u t i o n of the Ba/K r a t i o in Saanich Inlet sediments 216 52. Correlation between Ba/K and S i / A l ratios in Saanich Inlet sediments 217 53. Correlation between Sr and Ca in Saanich Inlet sediments 220 54. Di s t r i b u t i o n of Ni in Saanich Inlet sediments 224 55. Correlation between Ni and Mg in Saanich Inlet sediments 226 56. Relationship between Ni/Mg and % c o r a i - n Saanich Inlet sediments ? 227 57. Di s t r i b u t i o n of Cr in Saanich Inlet sediments 229 58. Relationship between Cr/Mg and % c o r a * n Saanich Inlet sediments .? 230 59. Di s t r i b u t i o n of "excess" Cr in Saanich Inlet sediments 231 60. Di s t r i b u t i o n of V in Saanich Inlet sediments 233 61. Correlation between V and Ni in Saanich Inlet sediments 234 62. Relationship between V/Fe and %C in Saanich Inlet sediments ?.? 235 63. Di s t r i b u t i o n of Mn in Saanich Inlet sediments 237 64. Relationship between Mn/Fe and %C in Saanich Inlet sediments ?.? 238 65. D i s t r i b u t i o n of the Mn/Fe r a t i o in Saanich Inlet sediments 239 66. Correlation between Mn and V in nearshore sands 240 67. D i s t r i b u t i o n of Zn in Saanich Inlet sediments 242 68. Relationship between Zn/Fe and %C in Saanich Inlet sediments ? 244 69. D i s t r i b u t i o n of Pb in Saanich Inlet sediments 245 x i i i 70. Relationship between Pb/K and %C in Saanich Inlet sediments ? 246 71. D i s t r i b u t i o n of Cu in Saanich Inlet sediments 249 72. Relationship between Cu/Mg and %C in Saanich Inlet sediments ?.? 250 73. D i s t r i b u t i o n of "excess" Cu in Saanich Inlet sediments 252 74. D i s t r i b u t i o n of Mo in Saanich Inlet sediments 254 75. D i s t r i b u t i o n of Zr in Saanich Inlet sediments 255 76. Correlation between Br and %C in Saanich Inlet sediments ?!;? 258 77. D i s t r i b u t i o n of the I/C r a t i o in Saanich Inlet sediments 259 78. Correlation between I and %C in Saanich Inlet sediments ?.? 260 79. Fraser and Cowichan River discharge from August 1983 to September 1984 262 80. S°/oo and 0 2/H 2S p r o f i l e s in the water column over the time of sampling of the s e t t l i n g particulates 264 81. Comparison between the S°/oo and 0 2 p r o f i l e s measured in the water column on June 18 and August 24, 1984 265 82. Seasonal fluxes of organic carbon at SI-9 267 83. Variations in the organic carbon fluxes with depth at SI-9 269 84. Seasonal fluxes of organic carbon at SN0.8 271 85. Variations in the organic carbon fluxes with depth at SN0.8 ,.272 86. Seasonal fluxes of major elements (SI-9, 45 m) 283 87. Seasonal variations in the S i / A l r a t i o of s e t t l i n g p a r t i c u l a t e s (SI-9) 285 xiv 88. Seasonal fluxes of opaline s i l i c a 286 89. Seasonal variations in the K/Al and Fe/Al ratios of s e t t l i n g particulates (SI-9, 45 m) 287 90. Seasonal variations in the Fe/K ra t i o of s e t t l i n g p a r t i c u l a t e s (SI-9, 45 m) 289 91. XRD scan of sediment trap samples c o l l e c t e d at SI-9: (a) in August 1984; (b) in November 1983 290 92. Seasonal fluxes of major elements (SI-9, 110 m) 292 93. Seasonal fluxes of Al (SI-9, 150 m) 293 94. Variations in Al fluxes with depth at station SI-9 294 95. Seasonal variations in the C /Al r a t i o of s e t t l i n g particulates (SI-9, 110 and 150gm) 295 96. Seasonal variations in the Fe/K ra t i o of s e t t l i n g p a r t i c u l a t e s (SI-9, 110 and 150 m) 296 97. Variations in Al fluxes with depth at station SN0.8 ....300 98. Correlation between K and Ba in the s e t t l i n g particulates c o l l e c t e d at SI-9 (at the 3 depths) 304 99. Seasonal variations in the Ba/K ra t i o of s e t t l i n g particulates at SI-9 305 100. Variations in the Ba/K and S i / A l ratios of s e t t l i n g particulates at SN0.8 306 101. Fluxes of biogenic Ba at SN0.8 307 102. Seasonal variations in the Zn/Fe r a t i o of s e t t l i n g particulates ....311 103. Seasonal variations in the C /Fe r a t i o of s e t t l i n g p a r t i c u l a t e s ?.? 312 104. Relationship between Zn/Fe and %C in sediments and s e t t l i n g p a r t i c u l a t e s ? 314 105. Seasonal variations in the Cr/Fe r a t i o of s e t t l i n g particulates 316 xv 106. Relationship between Cr/Fe and %C in sediments and s e t t l i n g p a r t i c u l a t e s 7 318 107. Seasonal variations in the Cu/Fe r a t i o of s e t t l i n g particulates at SI-9 320 108. Relationship between Cu/Fe and %C_ in sediments and s e t t l i n g p a r t i c u l a t e s ? 321 109. Seasonal variations in the V/Fe r a t i o of s e t t l i n g particulates 323 110. Relationship between V/Fe and %C in sediments and s e t t l i n g particulates ? 324 111. Seasonal variations in the Ni/Fe r a t i o of s e t t l i n g particulates 327 112. Relationship between Ni/Fe and % c o r a * n t h e sediments and s e t t l i n g particulates ? 328 113. Seasonal variations in the Rb/K r a t i o of s e t t l i n g particulates 333 114. Seasonal variations in the Zr/Al r a t i o of s e t t l i n g p articulates 335 115. Seasonal variations in the Mn/Fe r a t i o of s e t t l i n g p articulates 336 116. Comparison between the Mn fluxes measured at SN0.8 (130 m) with and without NaN^ poisoning 338 117. Seasonal variations in the I / C Q r a r a t i o of s e t t l i n g particulates ? 339 2 1 0 118. Po p r o f i l e s in gravity cores c o l l e c t e d from station SI-9 and SN0.8 429 xv i LIST OF TABLES 1. Some chemical c h a r a c t e r i s t i c s of humic substances . 2 2. C and S content of planktonic materials 20 3. Contamination of humic acids extracted from an anoxic sediment by pyrite 27 4. S/C r a t i o of humic acids extracted from an anoxic sediment after d i f f e r e n t intervals of a i r exposure 29 5. Sulphur contamination by sulphides during a l k a l i n e extraction of humic acids 31 6. Sulphur enrichment of humic acids by sulphide ions in alk a l i n e solutions 33 7. Influence of the presence and removal of the A.V.S on the sulphur content of extracted humic acids 36 8. Sulphur enrichment of humic acids by elemental sulphur in alk a l i n e solutions 40 9. Sulphur enrichment of humic acids by polysulphides in alka l i n e solutions 42 10. D i a l y s i s of polysulphides present in humic extracts...... . 46 1 1 . Bulk sediment analysis 56 12. Amount of C and S extracted by NaOH 0.5N from s e t t l i n g p a r t i c u l a t e materials (% c o r a = 5.14%) col l e c t e d from an interceptor trap deployed in Je r v i s Inlet (station JV11.5) 66 13. Microbial S/C ra t i o s 67 14. C and S content of humic acids extracted from core A ........ 68 15. C and S content of humic acids extracted from core A after hydrolysis in 5N HC1, 120 C, 5h ... 73 16. Sulphur isotope composition of free sulphides, elemental sulphur , and hydrolyzed humic acids 75 17. Isotope mass balance 78 x v i i 18. Sulphur enrichment of humic acids by various sulphur species after I8h. of contact at seawater pH (8.2) 88 19. Unidentate ligands l i k e l y to be found in humic materials 90 20. Some examples of bidentate ligands possibly present in humic materials (after Houghton, 1979) 92 21. Influence of S enrichment on the Cu retention of acid-washed t e r r e s t r i a l humic materials 104 22. Chemical composition of HUD 22 (bulk surface sample) ....118 23. Influence of resorcinol on the extraction of iodine from HUD 22 by hydroxylamine hydrochloride 120 24. Extraction of iodine from HUD 22 by 0. 5N NaOH 122 25. Uptake of iodine by marine sedimentary humic substances 129 26. Uptake of iodine by marine sedimentary humic substances at pH 7.4-8 131 27. Rf values of resorcinol and i t s iodinated derivatives during T.L.C. on S i 0 2 with 80% CHCl 3/20% CH3COOCH2CH3 ...133 28. Influence of the presence of resorcinol on the iodine uptake by humic substances at pH 2.5-3 135 29. Displacement of iodine from humic materials extracted from HUD 22 by OH and HS 140 30. Major element composition (wt %) of the gneisses and granodiorite found in the Saanich area (from Clapp, 1913) 157 31. Peak intensity r a t i o s . Quartz / c h l o r i t e and kao l i n i t e 1 64 32. Peak intensity r a t i o s . Plagioclase / c h l o r i t e and kao l i n i t e 165 33. Peak intensity r a t i o s . Hornblende / c h l o r i t e and kao l i n i t e 1 66 34. C/N r a t i o of organic materials of marine and xv i i i t e r r e s t r i a l o r i g i n 169 35. Sediment accumulation rate (w) and %C in Saanich Inlet 174 36. Carbon accumulation rates in the deep basin of Saanich Inlet 176 37. Average Sr/Al r a t i o in the d i f f e r e n t types of sediment present in Saanich Inlet 222 38. Annual carbon and aluminium fluxes and accumulation rates in sediment at station SI-9 274 39. Seasonal carbon and aluminium fluxes at station SN0.8 ...279 40. Annual C fluxes and accumulation rates in sediment at station SN0.8 281 41. Average C /Al and S i / A l ratios in sediment trap materials colSected at station SI-9 and SN0.8 from May 5 to August 24, 1 984 299 42. Fluxes of biogenic Ba at station SN0.8 (50 m) 303 43. Evaluation of the extent of flushing which occurred during deployment of the sediment traps 396 44. Instrumental conditions for elemental analysis of sediment samples by X-ray fluorescence 400 45. XRF a n a l y t i c a l precision for major elements 402 46. XRF a n a l y t i c a l precision for minor elements and sodium 404 47. Comparison of the results obtained from the analyses of 1 g and 0.5 g sediment p e l l e t s using the same c a l i b r a t i o n curve 406 48. Correction for seasalt 408 49. Comparison of C analyses by Leco and Carlo Erba CHN analyzer > 413 50. Sulphur recovery by CrCl 2/HCl treatment 422 xix Acknowledgements. I would l i k e to thank my supervisor, Dr. S.E. Calvert, for his constant guidance and encouragement throughout t h i s work, and Dr. T.F. Pedersen for many hours of enlightening and cheerful discussions. I am also grateful to the other members of my committee, Dr. Andersen, Dr. Lewis, and Dr. Lowe for their willingness to answer questions and grant valuable advice. F i n a l l y , very special thanks go to my wife, Michaela, for drafting the 118 figures present in thi s d i s s e r t a t i o n and for her unwavering support during the past two years. xx 1 . INTRODUCTION. 1 . 1 A BRIEF REVIEW OF THE SIGNIFICANCE OF HUMIC SUBSTANCES IN THE MARINE ENVIRONMENT. "Humic substances" i s a general term used to describe that assemblage of refractory, s t r u c t u r a l l y complex, ac i d i c polymers which constitute the bulk of the organic matter in aquatic, t e r r e s t r i a l , and marine environments. They result from random reactions between biogenic molecules released by the biosphere. They are not assemblages of some r e p e t i t i v e , s t r u c t u r a l l y well-defined units, and consequently no two samples w i l l be exactly i d e n t i c a l . For descriptive purposes, one must therefore work in terms of their general structure and, in order to understand their significance for environmental problems, variations in their bulk structural features must be correlated with their d i s t i n c t i v e properties. Some of .the main chemical c h a r a c t e r i s t i c s of humic substances are well established (Table 1). They consist of a polydispersed system of polymers displaying a wide range of molecular (or miscellar) weights extending from a few hundreds to several hundred thousands. Their a c i d i c character i s attributed mainly to the presence of O-containing f u n c t i o n a l i t i e s , primarily carboxyl and phenolic hydroxyl groups, and the occurrence of 1 Table 1: Some chemical c h a r a c t e r i s t i c s of humic substances, - Elemental composition C: 40 0: 32 H: 4 N: 1 S: .1 58 50 8 8 4 - Polydisperse system i . e . mixture of organic molecules with a wide range of molecular (miscellar) weights from a few hundreds to several hundred thousands. Acidic Attributed mainly to their -Carboxylic groups: R-C=0 NOH -Phenolic groups: - Other s t r u c t u r a l groups often recognized in humic molecules Amino -NH„ Unsaturated -CH=CH-CH=0 carbonyl Amide Alcohol R-C=0 R-CH20H Aldehyde R-C=0 Enol Ketone R-CH=CH-0H R-C=0 R' Keto acids R-C=0 COOH Anhydride Imino Ether Ester Quinone Peptide R-C-O-C-R' I I IT 0 0 =NH R-CH2~0-CH2-R' R-C=0 o-< O-R' R-C=0 H-N-R' 2 quinones and polyhydroxy phenols i s thought to be, at least in part, responsible for the i r reducing a b i l i t i e s . Also, protein and carbohydrate residues are often found chemically attached to the humic matrix. The set of chemical reactions which leads to the formation of humic substances ( i . e . the humification process) and therefore their general structure and composition w i l l , in broad terms, be influenced by the setting of the environment in which they are being formed. Elemental analysis, functional group analysis and various spectroscopic methods show some clear d i s t i n c t i o n s between humic substances derived from d i f f e r e n t environments(e.g. t e r r e s t r i a l vs marine, oxic vs anoxic, forest s o i l vs grassland, e t c . ) . Some of these differences w i l l be mainly the result of the nature of their biogenic precursors (e.g. t e r r e s t r i a l vs marine), while in some other cases the environmental conditions during their formation w i l l be the overriding factor (e.g. oxic vs anoxic). Humic substances of marine o r i g i n are enriched in N and H compared with their t e r r e s t r i a l counterparts (Vandenbroucke et al.,1985). Also, t o t a l a c i d i t y and p a r t i c u l a r l y phenolic a c i d i t y tend to be much lower in the-marine materials (Vandenbroucke et al.,1985). This i s consistent with the higher a l i p h a t i c and lower aromatic character generally displayed by these substances (Stuermer and Payne, 1976; Stuermer et a l . , 1978; Hatcher et a l . , 1980), which would r e f l e c t the lack of aromatic precursors in the 3 marine environment and the r e l a t i v e importance of planktonic l i p i d s in their formation (Harvey and Boran, 1985). Differences are less well documented between humic substances or i g i n a t i n g from the same material but formed under d i f f e r e n t environmental conditions. However, i t seems that s i g n i f i c a n t differences can be distinguished between marine humus extracted from oxic or anoxic sediments. Humic substances formed under anoxic conditions tend to have a greater reducing character ( i . e . with a higher H content) and to be enriched in l i p i d s (Demaison and Moore, 1980). They also contain more sulphur (Nissenbaum and Kaplan, 1972; Stuermer et a l . , 1978). On the other hand, humic substances formed under oxic conditions contain more oxygen, possibly through oxidative cleavage during the humification process (Vandenbroucke et al.,1985). Because of the random factor involved in humus formation, i t is very d i f f i c u l t to characterize humic substances by simple, well-defined, r e l i a b l e parameters. Their properties and structures w i l l vary in subtle ways from sample to sample and, when studying the influence of environmental parameters on their formation or the influence of s t r u c t u r a l c h a r a c t e r i s t i c s on their properties, i t i s often d i f f i c u l t to d i s t i n g u i s h d i r e c t causal v a r i a t i o n s . This i s further complicated by the d i f f i c u l t y of i s o l a t i n g them from their inorganic matrices. The structure and properties of the isolated product are always more or less 4 modified by the extraction procedure. Since many di f f e r e n t extraction procedures which a l t e r the extracted humic materials to varying degree are being used, i t i s very d i f f i c u l t to obtain r e l i a b l e inter-laboratory comparisons. Hence, there i s a wide divergence of views concerning even fundamental questions such as the broad p r i n c i p l e s of the humification process. T r a d i t i o n a l l y , humic substances are extracted from s o i l s , peats or sediments by f a i r l y strong alkaline solutions. This extraction procedure leads to an empirical fractionation scheme based on their pH-dependent s o l u b i l i t y behaviour (Fig. 1). Humic acids are that material which i s extractable (generally by alkaline aqueous solutions, although other solvent systems are being used (e.g. Bremner and Lees, 1949; Hayes, 1985)) and precipitated at low pH, while f u l v i c acids remain in solution under the same conditions. Humin refers to that part of the humic material which i s not extractable. Although convenient as a crude fractionation technique, t h i s approach i s a r t i f i c i a l . These operationally-defined fractions represent only a r b i t r a r y delineations which mainly r e f l e c t the extraction and fractionation procedures. Moreover, since there are no conventional ways to perform these operations, a given molecule could be found in any of these three fractions, depending on the actual method used. Also, i t i s now accepted that humic substances are a family of macromolecules exhibiting continuous spectra of molecular properties. The s o l u b i l i t y c h a r a c t e r i s t i c s 5 H U M U S E x t r a c t with alkal i i 1 } ( Insoluble ) ( So lub le ) HUMIN I T r e a t with a c i d * 1 * ( P r e c i p i t a t e d ) ( Not p r e c i p i t a t e d ) HUMIC ACIDS F U L V I C ACIDS F i g . 1: Fractionation of humic substances on the basis of thei r pH-dependent s o l u b i l i t y properties. 6 of these molecules are determined by the interactions of a variety of more fundamental properties, such as molecular weight, p o l a r i t y , ionization constant of functional groups, etc. Many di f f e r e n t combinations of these fundamental properties could result in i d e n t i c a l s o l u b i l i t y behaviour. Therefore, the same generic term, according to the fractionation scheme presented in F i g . 1, could refer to widely d i f f e r e n t molecules. For instance, f u l v i c acids are generally considered to be of lower molecular weight (e.g. Hayes and Swift, 197,8). However, the occurrence of high molecular weight f u l v i c acid i s occasionally reported (e.g. Naik and Poutanen, 1984). Considering these two points ( i . e . that the presence of a humic molecule in any of the three classes of humic substances w i l l be strongly dependent upon the extraction and fractionation procedure used, and that these classes w i l l also encompass molecules with widely d i f f e r e n t chemical characte-r i s t i c s ) , one may f e e l j u s t i f i e d in questioning the s u i t a b i l i t y of using s p e c i f i c terms for such i l l - d e f i n e d groups of molecules. Such practice may, in part, be the source of the vagueness c h a r a c t e r i s t i c of a l l discussions of humic substances (e.g. Aiken et a l . , 1985). A l t e r n a t i v e l y , i t may seem more appropriate to work within a conceptual framework where humic substances are considered as one family of molecules displaying a continuous spectrum of any - given property which can be investigated using modern a n a l y t i c a l techniques (e.g. Swift, 1985), rather than a r b i t r a r i l y subdividing these spectra solely 7 on s o l u b i l i t y properties. Accordingly, most of the work presented here w i l l be done on what would be conventionally c a l l e d a humic acid f r a c t i o n , because i t i s the easiest fraction to i s o l a t e . However, the conclusions drawn w i l l be applied in a more general sense to humic substances which i s meant to encompass the bulk of the organic matter not readily s t r u c t u r a l l y characterizable. The environmental importance of humic substances has been appreciated for some time. They are known to be a major reservoir in the carbon biogeochemical cycle which i s in a state of r e l a t i v e l y rapid turnover (Bolin, 1983). As such, they may have a s i g n i f i c a n t impact on the l e v e l of C0 2 in the atmosphere. For instance, i t has been reported that the amount of C0 2 released to the atmosphere by the oxidation of humic substances occurring during deforestation could be of the same order of magnitude as the amount released due to f o s s i l fuel burning (Woodwell et a l . , 1978). Also, humic substances are the precursor of kerogen, the inert macromolecules found in a l l sedimentary rocks. Kerogens, along with reduced sulphur, represent one of the major pools of "reducing equivalent" in our oxidizing environment ( i . e . each mole of electrons buried mainly as reduced C or S corresponds to 1/4 mole of 0 2 produced by photosynthesis and accumulated in the atmosphere or locked in oxides). Therefore, humification processes in sediments, by determining the amount and oxidation state of the organic carbon which was f i n a l l y 8 buried, may have had an important effect in determining the steady-state amount of oxygen present in the atmosphere and may be d i r e c t l y involved in some feedback mechanism for i t s maintenance at levels suitable for the existence of complex organisms through geological time (Garrels and Perry, 1974). Humification is also of relevance to the study of f o s s i l fuel formation. The amount and nature of hydrocarbons which can be generated depends on the composition of the organic matter which was f i r s t accumulated on the sea floor (Tissot et a l . , 1974). The composition of t h i s organic matter w i l l be partly determined by the humification processes which w i l l be c h a r a c t e r i s t i c of the environment of deposition. The study of the evolution of humic substances as a function of the environment of formation w i l l therefore be very important for our understanding of the generation of f o s s i l fuels and w i l l help in predicting the occurrence of petroleum source rocks. Also, the sulphur content of f o s s i l fuels has been recently a subject of concern, due to the environmental problems associated with the formation of acid r a i n . It has been argued that t h i s sulphur i s being incorporated at a very early stage of coal formation (Casagrande et a l . , 1977; Casagrande and Ng, 1979; Casagrande et a l . , 1979; Altschuler et a l . , 1983; Lowe and Bustin, 1985), i . e . during the peat-forming, humification stage. A study of t h i s phenomenon w i l l have an important bearing on the development of techniques for the removal of sulphur from coal. 9 Besides these long-term considerations, a l l humic substances have common properties which confer on them the a b i l i t y to have immediate effects on the environment in which they are found. Among these properties, their a b i l i t y to complex metals and the i r behaviour in redox reactions are the best documented. The reducing properties of humic substances are well established ( S z i l a g y i , 1973). The reduction of Mo04~ to Mo0 2 + ( S z i l a g y i , 1967), V0 3~ to V 0 2 + (Szalay and S z i l a g y i , 1967; Wilson 3+ 2 + and Weber, 1979; Templeton and Chasteen, 1980), Fe to Fe (S z i l a g y i , 1971) and Hg 2 + to Hg° (Alberts et a l . , 1974) by humic substances have been reported. Also, Schnidler et a l . (1976) and Zimmermann (1983) have demonstrated that humic acids could f a c i l i t a t e the electron transfer between redox couples which would otherwise be discrete. They also argue that anaerobic organisms could a c t u a l l y use humic acids as an e x t r a c e l l u l a r electron transport system which would allow them to use terminal electron acceptors otherwise unavailable to them. Photo-reduction of Mn oxides by humic substances occurs readily in surface seawater. Sunda et a l . (1983) argued that t h i s 2 + reduction is responsible for the higher Mn concentration found in the euphotic zone of the oceans. Since manganese i s an essential micronutrient for photosynthetic organisms, such a process may be p a r t i c u l a r l y important in maintaining a pool of Mn in a more readily available form to phytoplankton. Also, a 10 s i m i l a r mechanism i n v o l v i n g a f e r r o u s - f e r r i c c y c l e was proposed by M i l e s and B r e z o n i c (1981) to e x p l a i n the s u b s t a n t i a l 0 2 consumption found i n the p h o t i c zone of h u m i c - c o l o u r e d l ake waters . Another important p r o p e r t y of humic substances i s t h e i r a b i l i t y to i n t e r a c t w i th meta l i o n s , p a r t i c u l a r l y a l k a l i n e -e a r t h and t r a n s i t i o n m e t a l s . S i n c e these ions are not t o t a l l y exchangeable by n e u t r a l s a l t e x t r a c t i o n ( e . g . S tevenson , 1982), s imple ion-exchange e q u i l i b r i a cannot a d e q u a t e l y d e s c r i b e these i n t e r a c t i o n s . T h i s p r o p e r t y has t h e r e f o r e been main ly a t t r i b u t e d to the presence of f u n c t i o n a l groups i n the o r g a n i c m a t r i x which are a b l e to form c o v a l e n t bonds wi th the meta l ions e i t h e r v i a e l e c t r o n - d o n a t i n g atoms (O, N, S, P , A s , e t c . ) or v i a TJ -e l e c t r o n - d o n a t i n g systems ( o l e f i n i c bonds, aromat ic r i n g s e t c . ) ( e . g . Saxby, 1969). I t seems l i k e l y tha t most of these c o o r d i n a t i o n compounds w i l l be u n i d e n t a t e complexes; however, i n some i n s t a n c e s , haphazard s t e r i c c o n f i g u r a t i o n w i l l a l l o w the format ion of more s t a b l e m u l t i d e n t a t e complexes , a l s o known as c h e l a t e s . C h e l a t e f o r m a t i o n has been very o f t e n p o s t u l a t e d to e x p l a i n the s t r o n g i n t e r a c t i o n o f t e n observed between humic substances and v a r i o u s m e t a l s , p a r t i c u l a r l y Cu ( e . g . Gamble et a l . , 1 9 7 0 ) , a l t h o u g h the o c c u r r e n c e of such compounds i n the n a t u r a l environment has never been unambiguously demons tra ted . The most o f t e n c i t e d model invokes the f o r m a t i o n of p h t h a l a t e and s a l i c y l a t e - t y p e r i n g s t r u c t u r e s ( S c h n i t z e r and S k i n n e r , 1965; 1 1 B o y d e t a l . , 1 9 8 1 ) . O t h e r O - c o n t a i n i n g f u n c t i o n a l g r o u p s , s u c h a s c o n j u g a t e d k e t o n i c s t r u c t u r e s , h a v e a l s o b e e n s u g g e s t e d ( P i c c o l o a n d S t e v e n s o n , 1 9 8 1 ) , a n d some e v i d e n c e i n d i c a t e s t h a t NH g r o u p s may a l s o be i n v o l v e d ( R a s h i d , 1 9 7 2 ; V i n k l e r e t a l . , 1 9 7 6 ; B o y d e t a l . , 1 9 7 9 ) . C o n s i d e r i n g t h e i r l o w d e g r e e o f a r o m a t i c i t y ( e . g . B r e g e r , 1 9 6 0 ; S t u e r m e r e t a l . , 1 9 7 8 ) a n d t h e i r r e l a t i v e l y h i g h N c o n t e n t ( e . g . V a n d e n b r o u c k e e t a l . , 1 9 8 5 ) , t h e i n v o l v e m e n t o f N - c o n t a i n i n g g r o u p s may be p a r t i c u l a r l y i m p o r t a n t f o r h u m i c m a t e r i a l s o f m a r i n e o r i g i n ( R a s h i d , 1 9 7 2 ) . A l s o , t h e i r h i g h e r S c o n t e n t ( N i s s e n b a u m a n d K a p l a n , 1972) c o u l d h a v e a s i g n i f i c a n t i n f l u e n c e on t h e c o m p l e x a t i o n o f t r a n s i t i o n m e t a l s s i n c e C a + + a n d M g + + , w h i c h o c c u r i n s e a w a t e r a t much h i g h e r c o n c e n t r a t i o n s , w i l l be much l e s s a b l e t o c o m p e t e f o r a S - c o n t a i n i n g c o m p l e x i n g g r o u p t h a n f o r an O - c o n t a i n i n g g r o u p ( A h r l a n d , 1 9 6 6 ; A h r l a n d e t a l . , 1 9 5 8 ; P e a r s o n , 1 9 6 8 ) . Some m e t a l s , m a i n l y f o u n d i n t h e f i r s t t r a n s i t i o n p e r i o d ( W h i t f i e l d , 1 9 8 1 ) , p l a y a c r u c i a l r o l e i n v a r i o u s m e c h a n i s m s o f l i f e p r o c e s s e s a n d t h e r e f o r e a r e e s s e n t i a l n u t r i e n t s . B e c a u s e a t o x i c l e v e l i s q u i c k l y a t t a i n e d , a n a c c u r a t e e n v i r o n m e n t a l m o n i t o r i n g o f t h e i r c o n c e n t r a t i o n i s n e c e s s a r y . B e i n g a d y n a m i c s y s t e m , t h i s c a n o n l y be a c h i e v e d by a s e t o f n e g a t i v e f e e d b a c k p r o c e s s e s whose i n t r i c a c i e s h a v e t o be u n r a v e l l e d i n o r d e r t o f u l l y u n d e r s t a n d a n d p r e d i c t t h e c o n s e q u e n c e s o f a n y m o d i f i c a t i o n o f t h e p r e s e n t s t a t e o f t h e n a t u r a l b a l a n c e . O w i n g t o t h e i r 1 2 potential complexing capacity with regard to the "nutrient metals", humic materials may have played a primordial role in such processes. They would be p a r t i c u l a r l y suitable as metal buffers (Mantoura, 1981; Saar and Weber, 1982), and so dampen the influence of any e r r a t i c supply of metals to a given biotope. Various laboratory experiments have demonstrated the detoxifying a b i l i t y of natural organic matter, p a r t i c u l a r l y with respect to Cu (e.g. Lewis et al.,1973; Sunda and Lewis, 1978), and a similar mechanism has been suggested to explain the increase in primary production observed upon addition of a zooplankton extract to upwelled water r i c h in nutrients but low in DOC (Barber and Ryther, 1969). The complexation of metals by humic substances w i l l also af f e c t their geochemical mobility. It has been shown experimentally that humic material can readily leach metals from their mineral matrices, thus enhancing the weathering process (Kononova et a l . , 1964; Ponomoreva and Ragim-Zade, 1969; Baker, 1973; Kodama and Schnitzer, 1973; Tan, 1975; Antweiller and Drever, 1983). Once leached, these metals may be either transported as soluble complexes, or adsorbed on a s o l i d phase, p a r t i c u l a r l y on the humic f r a c t i o n of s o i l s or sediments which could then act as a metal reservoir (Stevenson and Ardakani, 1972). It has been argued that humic substances may constitute the most important pool of micronutrients available in the t e r r e s t i a l ecosystems (Zunino and Martin, 1977). Competition 13 between soluble and insoluble ligands w i l l determine the b i o a v a i l a b i l i t y and mobility of t r a n s i t i o n metals in s o i l s . They w i l l eventually be transported to the oceans where the removal of their dissolved fracti o n can also be mediated by metal-organic associations (Revelle et a l . , 1955; Greenslate et. a l . , 1973; Turekian, 1977; Bostrom et a l . , 1978). This is supported by sequential leaching of s e t t l i n g particulate materials c o l l e c t e d from sediment traps deployed in the Eastern Tropical North P a c i f i c Ocean (Fischer et a l . , 1986) which showed that the amount of Cu associated with organic matter increases with depth, presumably through scavenging. In marine sediments, there are indications that a large proportion of some t r a n s i t i o n metals, and p a r t i c u l a r l y Cu, i s associated with the humic fr a c t i o n (Volkov and Fomina, 1972; Cooper and Harris, 1974; Nissenbaum and Swaine, 1976; Calvert and Morris, 1977; Knezevic and Chen, 1977; Nriagu and Coker, 1980; Hallberg et a l . , 1980; Hirata, 1985; Calvert et a l . , 1985). Whether this metal content i s acquired from the overlying water (e.g. Nriagu and Coker, 1980) or through post-depositional diagenetic processes (e.g. Nissenbaum and Swaine, 1976; Calvert and Morris, 1977) i s s t i l l a matter of debate. Here again, metal-humic association w i l l be important in regulating the mobility and b i o a v a i l a b i l i t y of t r a n s i t i o n metals. There i s evidence for metal-humic associations in sedimentary pore waters (Nissenbaum and Swaine, 1976; Krom and Sholkovitz, 14 1978; Lyons et al.,1979; E l d e r f i e l d , 1981) and thi s has been used by some authors to explain the occurrence of metals in anoxic pore waters at concentrations higher than predicted from sulphide mineral e q u i l i b r i a (Brooks et a l . , 1968; Piper, 1971; Presley et a l . , 1972; E l d e r f i e l d and Hepworth, 1975). As discussed throughout th i s brief review, humic substances are of paramount importance in many aspects of environmental biogeochemistry. However, our knowledge of their role i s , in many instances, s t i l l far from adequate. This should j u s t i f y the recent escalating interest in humic substances by s c i e n t i s t s from a wide d i v e r s i t y of d i s c i p l i n e s . To quote a leading authority in the f i e l d : "... working with humic materials i s often f r u s t r a t i n g , always laborious and seldom rewarding.' Yet, these materials, so widely dis t r i b u t e d on the earth's surface, control d i r e c t l y or i n d i r e c t l y many reactions that af f e c t man's survival on t h i s planet and they continue to challenge the c u r i o s i t y and ingenuity of s c i e n t i s t s of many d i s c i p l i n e s . " (Schnitzer, 1978). I s h a l l present here a somewhat f r u s t r a t i n g , c e r t a i n l y laborious, yet hopefully rewarding attempt at solving a few of the many problems s t i l l to be addressed in the geochemistry of humic materials. 1.2 SYNOPSIS OF THE PRESENT STUDY. In the present work, three d i f f e r e n t but related topics are investigated: 15 1.2.1 SULPHUR IN THE HUMIC FRACTION OF MARINE SEDIMENTS. The evolution of the sulphur content in the humic fraction of a near-shore marine sediment was investigated. An appropriate extraction procedure designed to meet the p a r t i c u l a r requirements of this study was developed. Chemical and isotopic analyses were performed on the extracted material to constrain the possible mechanisms involved in the observed sulphur enrichment. 1.2.2 THE INFLUENCE OF HUMIC SUBSTANCES ON THE GEOCHEMISTRY OF IODINE IN MARINE SEDIMENTS. Iodine is c h a r a c t e r i s t i c a l l y enriched in surface near-shore and hemipelagic sediments (Vinogradov,1939; Shishkina and Pavlova, 1965; Price et a l . , 1970; Price and Calvert, 1977; Pedersen and Price, 1980). This aspect of iodine geochemistry was investigated by determining the p a r t i t i o n i n g of iodine in marine sediments and by performing laboratory experiments on the uptake and release of iodine by and from sedimentary humic substances. Based on these results, a mechanism for iodine uptake by humic substances at the sediment/water interface and i t s subsequent release upon bu r i a l i s proposed. 16 1.2.3 METAL ENRICHMENT IN SEDIMENTS DEPOSITED IN ANOXIC BASINS. An enrichment of certain trace metals has often been observed in modern organic-rich anoxic sediments (Calvert and Price, 1970; Volkov and Fomina, 1972, Calvert, 1976). The mechanism of enrichment, considered to be associated with oxygen-depletion , is s t i l l e s s e n t i a l l y unknown. Bulk sediment analyses often show a d i s t i n c t s t a t i s t i c a l c o r r e l a t i o n between metal concentrations and organic carbon content and t h i s has sometimes been taken as an indication of a d i r e c t association with organic matter (Curtis, 1966; Volkov and Fomina, 1972). However, i t was recognized that t h i s c o r r e l a t i o n could also be the result of a set of conditions leading to the simultaneous accumulation of organic matter and metals without d i r e c t association. A similar d i s t r i b u t i o n pattern has been sought in the surface sediment of Saanich Inlet, an intermittently anoxic f j o r d on the coast of B r i t i s h Columbia. S t a t i s t i c a l analysis has been used to determine which are the elements whose d i s t r i b u t i o n pattern cannot be solely explained in terms of sediment mineralogy. S e t t l i n g particulate materials have also been col l e c t e d in Saanich Inlet using interceptor traps deployed monthly over an 18 month period at three d i f f e r e n t depths. The seasonal variations in the fluxes of organic matter and various metals were determined. These samples were also compared with the 1 7 sediment data in an attempt to evaluate the d i f f e r e n t factors which regulate the metal concentrations in these sediments. Although each of these sections addressed d i f f e r e n t problems, I have been able to demonstrate a certain degree of interdependence between the various processes involved. 18 2. SULPHUR IN THE HUMIC SUBSTANCES OF NEARSHORE MARINE SEDIMENTS. 2.1 INTRODUCTION. It has been argued that the sulphur content of sedimentary humic substances from marine environments r e f l e c t s the redox conditions prevailing during their formation (Nissenbaum and Kaplan, 1972; Stuermer et a l . , 1978). While the S/C r a t i o (by weight) of marine plankton l i e s in the range 0.010-0.030 (Table 2), s i g n i f i c a n t l y higher values (up to 0.10) have been reported in sedimentary humic materials, p a r t i c u l a r l y from anoxic sediments. The most commonly accepted pathway for incorporation of sulphur into organic matter i s biosynthesis. The organic sulphur so formed i s found at a l l oxidation states, from +6, as in polysaccharide sulphate esters, to -2, as in t h i o l s and thioethers (Kharasch and Aurora, 1976). The main process involved is assimilatory sulphate reduction, with subsequent formation of amino acids and proteins. However, considering the r e a c t i v i t y of inorganic sulphur species, p a r t i c u l a r l y HS and polysulphides, and their abundance in sedimentary marine environments, three alternative pathways through which sulphur can be chemically added to the organic matrix should also be considered (Fig. 2). 19 Table 2: C and S content of planktonic materials. % C % S S/C References Marine plankton 22.5 0.6 0.027 Vinogradov* (1953) Dinoflagellate (G. polyhedra) - 0.3 -0.013 Kaplan et a l .1 (1963) Blue-green algae (N. muscorum, A. nidulans, P. luridium) 45.4-49.7 0.5-0.7 0.010-0.015 Philp and Calvin (1976) Green algae (C. pyrenoidosa) 51.4 0.7 0.014 Philp and Calvin (1976) Diatom _ (T. pseudonana) 35.1 0.82 0.023 This work Near-shore marine plankton 3 (mixed population) 18.7 0.37 0.020 This work "Humic acids" extracted from 4 a mixed population 53.5 55.7 0.72 0.76 0.013 0.014 This work This work 1 - Cited i n Bowen (1979) 2 - T. pseudonana was grown to early senescence in batch culture using a r t i f i c i a l seawater (Harrison et a l . , 1980). After concentration i n a continuous centrifuge, the sample was dialysed against deionized water to eliminate seawater sulphates, freeze-dried and homogenized before elemental analysis. 3 - This sample was obtained by v e r t i c a l haul during a spring bloom in Saanich Inlet. It had been freeze-dried and storedseveral months before being dialyzed. 4 - The above freeze-dried plankton population was treated with 0.5N NaOH under nitrogen for 18hrs. The material extracted was a c i d i f i e d to pH 1.5-2 with HC1. HP (0.1M) was added to reduce the ash content of the pr e c i p i t a t e . After centrifugation and several rinsings, the sample was freeze-dried and analyzed. The two sets of figures correspond to two succesive extractions of the same sample. 20 oxidation ( b a d ./chem.) F i g . 2: S u l p h u r c y c l e . 21 The l i g h t isotopic composition which has been found in sedimentary humic substances would support the hypothesis that a sulphur enrichment of the organic matter is occurring via reactions between the organic matrix and H2S- (or i t s oxidation products) produced by diss i m i l a t o r y sulphate reduction during early diagenesis (Nissenbaum and Kaplan, 1972). However, a great potential exists for sulphur contamination of the humic matrix during sample handling and extraction from anoxic sediments. Pyrite i s an ubiquitous component of such sediments and a wide range of chemical reactions are possible between organic matter and various inorganic sulphur species (sulphides, elemental sulphur, polysulphides), most of which are base-catalyzed (e.g. Pryor, • 1962; Mango, 1983). Although these reactions may occur naturally during early diagenesis and may explain the high sulphur content and l i g h t isotopic composition of sedimentary humics, they w i l l be greatly accelerated during humic extraction, which i s generally performed under f a i r l y strongly alkaline conditions. Therefore, some s i g n i f i c a n t a r t i f i c i a l enrichment of the humics could result during the extraction step and the extent of the natural sulphur enrichment could be obscured. Confirmation of sulphur-enrichment in humic substances formed in marine sediments using an extraction procedure which w i l l minimize these contamination problems i s s t i l l required. If confirmed, the mechanism(s) of such an enrichment would complement our knowledge of sulphur transformations during early 22 diagenesis and the importance of d i f f e r e n t reaction mechanisms involved in the incorporation of sulphur in coal (Casagrande et a l . , 1979; Casagrande and Ng, 1979). Moreover, i t may provide a basis for explaining the marked contrast observed between kerogen types derived from d i f f e r e n t organic facies (Demaison et a l . , 1984). Understanding sulphur incorporation into marine organic matter may also have a bearing on explanations for the marked metal enrichment observed in many anoxic sediments (Calvert, 1976), since t h i o l groups are p a r t i c u l a r l y suitable complexing f u n c t i o n a l i t i e s for t r a n s i t i o n and class "B" metals (e.g. Emerson et a l . , 1982; Boulegue et a l . , 1982). 2 . 2 EVALUATION OF THE EXTRACTION CONDITIONS OF SEDIMENTARY HUMIC SUBSTANCES NECESSARY TO ESTIMATE THEIR TRUE, IN-SITU SULPHUR CONTENT. 2.2.1. INTRODUCTION. The d i f f i c u l t y in estimating the true, i n - s i t u sulphur content of marine sedimentary humic substances resides in the presence, in the sediments, of large amounts of reduced inorganic sulphur species which w i l l react readily with the organic matrix during an a l k a l i n e extraction step. This section describes a series of observations and 23 e x p e r i m e n t s d e s i g n e d t o t e s t the s u l p h u r c o n t a m i n a t i o n of a n o x i c marine sedimentary humic s u b s t a n c e s d u r i n g sample h a n d l i n g and e x t r a c t i o n . An e x t r a c t i o n scheme i s o u t l i n e d which a v o i d s a s e r i e s of c h e m i c a l r e a c t i o n s i n d uced by the e x t r a c t i o n c o n d i t i o n s which l e a d t o the c o n t a m i n a t i o n . 2.2.2 MATERIALS AND METHODS. Sediment samples were c o l l e c t e d from two B r i t i s h Columbia i n l e t s u s i n g the l i g h t w e i g h t g r a v i t y c o r e r d e s c r i b e d by Pedersen et a l . (1985). The c o r e s were e x t r u d e d i n a n i t r o g e n - f i l l e d g love-box and p a r t i t i o n e d i n t o a p p r o p r i a t e subsamples f o r subsequent a n a l y s i s or e x p e r i m e n t a t i o n . Sediments from S a a n i c h I n l e t , c o l l e c t e d a t a depth of 220 m, accumulated under a n o x i c c o n d i t i o n s and c o n t a i n h i g h l e v e l s of hydrogen s u l p h i d e , a c i d -v o l a t i l e s u l p h i d e s (AVS) and p y r i t e . The sediments from J e r v i s I n l e t accumulated a t a depth of 650 m under permanently oxygenated c o n d i t i o n s and c o n s i s t of a t h i n (~1 cm) o x i d i z e d s u r f a c e l a y e r o v e r l y i n g a s u b o x i c and a s u l p h i d i c l a y e r . Both sediment t y p e s c o n t a i n r o u g h l y e q u i v a l e n t amounts of o r g a n i c carbon (~3-4%). The humic s u b s t a n c e s were e x t r a c t e d by 0.5 N NaOH, under a n i t r o g e n atmosphere, on an a u t o m a t i c shaker f o r 18 h o u r s . The humic a c i d f r a c t i o n (HA) was f u r t h e r i s o l a t e d by a c i d i f i c a t i o n 24 to pH2 with HC1, and the p r e c i p i t a t e was freeze-dried. The carbon content of the extracted fractions was determined by gas chromatography using a Carlo Erba Model 1106 Elemental Analyzer and using acetanilide as a standard. Precision was +2.5% at the 95% confidence l e v e l . Total sulphur was determined by amperometric t i t r a t i o n after combustion of the sample , using a Fisher Model 475 Sulfur Analyzer (Guthrie and Lowe, 1984). The precision was +5% at the 95% confidence l e v e l . P y r i t i c sulphur, co-extracted with the humic acids, was estimated by treating a few mg of the humic material with 1ml of a freshly prepared C r C l 2 solution according to Zhabina and Volkov (1978) (Appendix I I ) . The precision was +8% at the 66% confidence l e v e l . The D.O.C. of the humic extracts was measured by dry-combustion using the Carlo Erba Analyzer (Appendix I I ) . Elemental sulphur was extracted by benzene and measured by cyanolysis according to B a r t l e t t and Skoog (1953) (Appendix I I ) . Fourier-Transform Infra-Red spectra of humic acids were made on a Nujol mull with a Nicolet 5-DX A n a l y t i c a l Spectrophotometer. 2.2.3 RESULTS AND DISCUSSION 2.2.3.1 CONTAMINATION OF THE HUMIC FRACTION EXTRACTED FROM A SULPHIDIC SEDIMENT BY CO-EXTRACTED PYRITE. If pyrite i s present in the examined sediment in a fine-25 grained, highly dispersed form, i t could be co-extracted with the humic acids. This potential contamination problem was investigated by treating the humic acids extracted from an anoxic sediment with a freshly prepared C r C l 2 solution. Such treatment was shown by Zhabina and Volkov (1978). to produce H 2S from FeS 2 while leaving the organic sulphur unaffected. The recoveries obtained when using t h i s method on pyrite of known stochiometry (ground and mixed with granite) and some planktonic material are shown in Table 50. An anoxic sediment sample co l l e c t e d from Saanich Inlet was treated, within two hours after c o l l e c t i o n , with HC1 0.1N at room temperature under a stream of nitrogen u n t i l no further H2S was produced. Elemental sulphur was removed from the dried sediment with benzene and f i n a l l y the humic acids were extracted with 0.5N NaOH. After measuring their S and C contents, the humic acids were subjected to the C r C l 2 treatment and their p y r i t i c sulphur estimated from the amount of H2S produced. The results presented in Table 3 show that pyrite contamination can be a substantial source of error in the determination of the sulphur content of humic acids extracted from sulphidic sediments. 2.2.3.2 SULPHUR CONTAMINATION OF THE HUMIC FRACTION DURING THE OXIDATION OF ANOXIC SEDIMENTS. When an anoxic sediment i s in contact with the oxygen of the atmosphere during storage or drying , some H 2S and acid v o l a t i l e 26 Table 3. Pyrite contamination of humic acids extracted from an anoxic sediment. % wt in humic acids^ C S 2 S 3  b t bpy S4 34.8+0.4 3.01+0.07 1.00+0.08 2.01+0.11 1. Not ash corrected 2. Total sulphur 3. P y r i t i c sulphur 4. Organic sulphur (S.-S ) 27 sulphides (A.V.S.) w i l l be oxidized to elemental sulphur and polysulphides w i l l be formed as an intermediate (Chen and Morris, 1972; Chen and Gupta, 1973). Polysulphides are readily cleaved homolytically and produce free r a d i c a l s which could conceivably react with organic matter to form organic polysulphides and eventually t h i o l groups. The possible contamination of humic acids via such processes was evaluated in the following experiment. A fresh anoxic sediment sample from Saanich Inlet was thoroughly homogenized in a blender, in a i r , and s p l i t into two subsamples. One subsample was treated within two hours after c o l l e c t i o n with 0.1N HC1, at room temperature, under a nitrogen stream u n t i l ^ S stopped being produced. This treatment removed the A.V.S.. After drying, the elemental sulphur produced i_n s i t u and by the acid treatment was removed with benzene and the humic acids were extracted with NaOH 0.5N under nitrogen. The second subsample was l e f t in a i r for a t o t a l of 50 hours and freeze-dried before being treated with HCl, dried and the humic acids extracted as before. If the addition of sulphur to the organic matrix by reaction with polysulphides formed during storage was s i g n i f i c a n t , an increase in the S/C r a t i o of the humic substances extracted after 50 hours would be recorded. The results shown in Table 4 indicate that under the conditions of storage which were used (room temp., 50 hours) such contamination is neg l i g i b l e since the S/C r a t i o (after correction for p y r i t i c sulphur) stayed e s s e n t i a l l y constant. However, the 28 Table 4. S/C r a t i o of humic acids extracted from an anoxic sediment after d i f f e r e n t intervals of a i r exposure. Wt% in HA C S1 S/C 2 hrs a i r exposure 34.8+0.4 2.01+0.11 0.058+0.003 50 hrs a i r exposure 39.1+0.4 2.37+0.20 0.061+0.005 1. Corrected for p y r i t i c sulphur. 29 p o s s i b i l i t y that an a r t i f i c i a l sulphur enrichment would occur after a longer time of storage or at higher temperature cannot be ruled out. 2.2.3.3 SULPHUR CONTAMINATION OF HUMIC SUBSTANCES BY REACTIONS WITH VARIOUS SULPHUR SPECIES DURING ALKALINE EXTRACTION. 2.2.3.3.1 SULPHUR CONTAMINATION BY SULPHIDES: As a preliminary test, a freshly collected anoxic sediment from Saanich Inlet was thoroughly homogenized under nitrogen and s p l i t into two subsamples. One subsample was immediately extracted with NaOH 0.5N (18 hours, under nitrogen) while the other was f i r s t subjected to an acid pre-treatment (HC1 0.1N,room temperature) before a similar a l k a l i n e extraction. The elemental composition of these humic acids, shown in Table 5, demonstrates the extent of sulphur contamination when humic acids are extracted in the presence of sulphides ( H 2S and/or A.V.S.). Further tests to investigate the possible reactions responsible for t h i s sulphur enrichment were undertaken. 2.2.3.3.1.1 REACTIONS BETWEEN FREE SULPHIDES AND HUMIC ACIDS IN BASIC SOLUTIONS: Sulphide anions are powerful nucleophiles which w i l l readily react with organic f u n c t i o n a l i t i e s containing a carbon atom with 30 Table 5. Sulphur contamination by sulphides during the alkaline extraction of humic acids. Wt% in HA C S S/C No HC1 pretreatment 37.2+0.4 7.48+0.19 0.201+0.006 With HC1 pretreatment 43.6+0.4 3.50+0.09 0.080+0.003 1. Not ash corrected. 31 an electron deficiency, e s p e c i a l l y at high pH, viz HS: + X=Z > C > C=S + HZ , (1) ^ ^ / c T SH ' where Z represents an electron-withdrawing fu n c t i o n a l i t y producing a p a r t i a l positive charge (h+) on the adjacent carbon. This type of reaction w i l l take place with f u n c t i o n a l i t i e s containing carbonyl groups such as aldehydes (Campaigne, 1961) or perhaps ketones and quinones (Boulegue and Michard, 1974). In addition, such a reaction could take place on a carbon-carbon double bond, activated by conjugation to an electron-withdrawing f u n c t i o n a l i t y such as ino(, unsaturated ketones, aldehydes or lactones (Kharasch and Aurora, 1976; Boelens et a l . , 1979). A set of experiments was performed to check for evidence of reactions involving free sulphides, by allowing sulphide anions to react with a humic acid extracted from an a i r - d r i e d anoxic sediment from which elemental sulphur had been previously removed. The humic fr a c t i o n s o l u b i l i z e d from this sediment was s p l i t into two parts. N a 2 S w a s added to one part while the other was kept as a control. The two solutions were kept under nitrogen overnight and a c i d i f i e d to pH2 under a vigorous nitrogen stream. The pre c i p i t a t e d humic acids were then analyzed for their C and S contents. The results (Table 6) show that the sulphur content of the humic acids increases s i g n i f i c a n t l y in the Na2S-treated samples. This occurs with humic acids which have already been exposed to naturally high lev e l s of sulphide. The degree of 32 Table 6. Sulphur enrichment of humic acids by sulphide ions in al k a l i n e solutions. Wt% in HA C S S/C HA - no Na2S 30.2+0.4 1.79+0.05 0.059+0.002 HA + 2mM Na,S 13.2+0.2 1.02+0.03 0.083+0.003 HA - no Na 2S 51.8+0.5 3.37+0.08 0.065+0.002 HA + 20mM Na9S 46.8+0.5 9.84+0.25 0.210+0.006 HA - no Na 2S 49.3+0.5 2.80+0.07 0.057+0.002 HA + 20mM Na2S 43.5+0.5 15.45+0.39 0.355+0.010 1. Not ash corrected. 33 enrichment c l e a r l y depends on the ambient sulphide l e v e l s , as shown by the treatments with 2 and 20 mmol/1 sulphide solutions. In addition, the sulphur enrichment observed in the humic materials with low ash content confirms that the organic rather than the inorganic fraction is responsible for t h i s sulphur enrichment. 2.2.3.3.1.2 REACTIONS BETWEEN ACID VOLATILE SULPHIDES (A.V.S.) AND HUMIC ACIDS IN BASIC SOLUTIONS: Since a l l the sulphides present in the A.V.S. are bound to metals, i t i s unlikely that they would be able to react chemically with the organic matrix. However, co-extraction of A.V.S. with humic materials i s occurring to a certain extent. E a s i l y decomposable A.V.S., such as mackinawite, w i l l be decomposed during the acid p r e c i p i t a t i o n of humic acids. However, more resistant sulphide minerals (e.g. greigite) w i l l require a more dra s t i c acid treatment (HC1 1N,boiling) for their elimination. Sulfate-esters, which are known to be present in humic materials (e.g. Tabatabai and Bremner, 1972; Altschuler et a l . , 1983) are susceptible to acid hydrolysis (e.g. King and Klug, 1980), and therefore such a strong acid pre-treatment must 3 + be avoided. Also, during the removal of A.V.S., Fe i s released from the sediment and oxidizes some of the H 2S produced into elemental sulphur, possibly v i a polysulphides. These polysulphides could then react with humic materials and 34 a r t i f i c i a l l y increase their sulphur content. An anoxic sediment c o l l e c t e d from Saanich Inlet was freeze-dried and divided into two subsamples. One of the samples was treated with 0.1N HC1, at room temperature, to remove the A.V.S. prior to humic acid extraction (which was performed after the removal of elemental sulphur produced by the acid treatment) while the other sample had the humic acids extracted with the A.V.S. present. After p r e c i p i t a t i o n , freeze-drying and elemental analysis, the humic acids were further subjected to a C r C l 2 treatment (Zhabina and Volkov, 1978) in order to estimate the amount of co-extracted p y r i t e . This determination also included sulphide produced by the decomposition of co-extracted g r e i g i t e . The r e s u l t s - presented in Table 7 show no s i g n i f i c a n t difference in the sulphur content of humic acids extracted either in the presence of A.V.S. or after a 0.1N HC1 pre-treatment. This would seem to indicate that, under the conditions used, the processes discussed ( i . e . contamination by A.V.S., ester sulphate hydrolysis and contamination by polysulphides) are either n e g l i g i b l e or, which i s less l i k e l y , exactly compensate each other. The large amount of sulphur released by the C r C ^ treatment further i l l u s t r a t e s the need for the determination of the amount of co-extracted acid-resistant sulphide species. 2.2.3.3.2 SULPHUR CONTAMINATION BY ELEMENTAL SULPHUR: Elemental sulphur i s present in most marine sediments. It i s 35 Table 7. I n f l u e n c e of the presence and removal of the A.V.S. on the sulphur content of e x t r a c t e d humic a c i d s . Wt% in HA Humic a c i d s e x t r a c t e d from: C S S S/C - F r e e z e - d r i e d sediment 35.2+0.4 2.11+0.17 2.28+0.20 0.065+0.006 (with A.V.S. p r e s e n t ) . - F r e e z e - d r i e d and a c i d - 39.1+0.5 1.93+0.15 2.37+0.19 0.061+0.005 t r e a t e d sediment (no A.V.S. p r e s e n t ) . 1. Not ash c o r r e c t e d . 36 also formed by the oxidation of t^S and A.V.S. during storage, drying or acid treatment of sulphide-bearing sediments. It was therefore necessary to investigate the p o s s i b i l i t y of sulphur contamination of humic substances by reactions with elemental sulphur under strongly basic conditions. The S-S bonds of the stable S g rings of elemental sulphur can be attacked by: (a) nucleophilic species, v i z Nu:~ + S g > Nu-S7-S~ (2) (b) e l e c t r o p h i l i c species, v i z E + + Sg > E-S ?-S + (3) or (c) free r a d i c a l s , v iz R• + Sg > R-S?-S- (4) The most l i k e l y reaction in the present case would be (2). Because of the presence of free d-orbitals and despite the 16 electron doublets on the Sg ring, elemental sulphur acts more l i k e a Lewis acid ( i . e . an electron acceptor) than a base, as i l l u s t r a t e d by the cyanolysis reaction of Sg (Pryor, 1962). Accordingly, reactions between Sg and nucleophilic groups of humic acids such as amines and t h i o l s might be possible as follows (see Schumann, 1972): R ' — S R ^NH +*I^Sfc > /N-S~ + H + (5) 37 Furthermore, the polysulphides so formed could readily produce free r a d i c a l s , through homolytic cleavage, v i z R R R > S 8 — " > R > S 8 - X + *SX ( 7 ) which could in turn react with organic matter, v i z A A + *s~ > A A + HS~ (8) SY A A +*Sy > A / V (9) Reactions between amines and elemental sulphur have been shown experimentally (Martin and Hodgson, 1977) and a rapid reaction between Sg and humic acids has been demonstrated at room temperature (Casagrande and Ng, 1979). Another possible reaction involving elemental sulphur and humic acids is via free radicals (reaction (4)). Humic acids are known to contain free radicals which appear to be related to the aromatic character of these substances (Stuermer et a l . , 1978). Of p a r t i c u l a r relevance here i s the reported increase in free radical number for sodium humate (Schnitzer and Skinner, 1969). These free radicals could conceivably open the Sg rings to produce open-chain organic polysulphides. ESR studies show that 1 7 marine humic acids contain approximately 2x10 spins/g.C 38 (Stuermer e_t a l . , 1978). Therefore, even i f every free radical s i t e was associated with 8 sulphur atoms, this would produce only an enrichment o f , v i z 2X10 1 7 x 8 x 32 _ = _o.OOOlg.S/g.C 6X10V;-This simple c a l c u l a t i o n indicates that there are not enough free r a d i c a l s in humic substances to produce a s i g n i f i c a n t sulphur enrichment by th i s mechanism. In order to check possible reactions between elemental sulphur and organic matter during the extraction of humic acids with NaOH, the sulphur content of humic materials extracted from an a i r - d r i e d anoxic sediment sample, before and after elemental sulphur removal from the sediment, was determined. The humic acids extracted in the presence of S contain twice as much sulphur, r e l a t i v e to carbon, as the humic acids extracted after an exhaustive removal of S (Table 8). This sulphur was chemically bound to the humic matrix, since i t could not be removed by benzene extraction. 2.2.3.3.3 REACTIONS BETWEEN POLYSULPHIDES AND HUMIC SUBSTANCES IN BASIC SOLUTIONS: In the experiment conducted to investigate the reactions between polysulphides and humic acids, Na 2S and S° were allowed to react in the presence of an oxic, freeze-dried sediment (collected from J e r v i s Inlet) during the humic acid extraction in 39 Table 8. Sulphur enrichment of humic acids by elemental sulphur in a l k a l i n e solutions. Wt% in HA C S S/C HA extracted after elemental 34.1+0.4 2.4+0.1 0.070+0.002 sulphur extraction. HA extracted in presence of 42.5+0.5 5.8+0.2 0.136+0.004 elemental sulphur. 1. Not ash corrected. 40 NaOH. The results are shown in Table 9. As already noted, the presence of elemental sulphur can s i g n i f i c a n t l y a l t e r the sulphur content of the extracted humic acids. The presence of Na2S alone had a smaller although s t i l l s i g n i f i c a n t e f f e c t , presumably due to i t s rapid oxidation by the iron oxides. However, the largest increase in the S/C ra t i o was produced by the combined presence of S° and Na 2S during the extraction. This i s interpreted as being the result of the formation of inorganic polysulphides producing free radicals which then react with the organic matrix. Since these humic acids were precipitated by a c i d i f i c a t i o n , the newly-formed organic sulphur groups could not have been organic polysulphides, which are decomposed at low pH, but instead must have been acid resistant S-containing functional groups formed by the hydrolysis and/or homolytic cleavage of organic polysulphides produced as an intermediate. I.R. spectra of humic acids extracted from 1 and 3 (Table 9) are shown in F i g . 3. These samples displayed the usual I.R. features generally reported from such spectra. The strong absorptions at 1720 cm 1 and 1640 cm 1 have been attributed to C=0 stretching vibrations of carboxylic and amide groups (Stevenson and Goh, 1971; Ishiwatari, 1972), while the absorption bands in the 1200-1090 cm 1 region have been interpreted as C-0 stretch of polysaccharides (Hatcher e_t a l . , 1980) or Si-0 stretching vibrations (Whitby and Schnitzer, 1978). The prominent peaks at 2900, 1460, 1390 and 700 cm"1 are from the Nujol mull used to mount the samples. However, two addi t i o n a l , 41 Table 9. Sulphur enrichment of humic acids by polysulphides in alkaline solutions. 1 2 3 HA extracted from: mg C extracted SSn(mg) S S r / c s / c 1.sediment alone, 335 0.030+0.001 2.sediment spiked with 338 n .„ co (4) 0.4% S . 0.392 0.001 0.059+0.002 3.sediment spiked with ,o (4) 0.4% S and 1.5% Na 2S.9H 2o: (4) 185 3.325 0.018 0.211+0.007 4.sediment spiked with 217 1.5% Na 2S.9H 20: (4) 0.557 0.003 0.039+0.002 1.Amount of elemental sulphur produced by acid hydrolysis of polysulphides during humic acid p r e c i p i t a t i o n . 2.SS normalized to carbon extracted (HA + FA), n 3.S/C r a t i o of humic acids after a c i d i f i c a t i o n (and decomposition of the polysulphides). 4.% dry weight sediment. 42 F i g . 3: Infrared spectra of humic acids extracted : (a ) from a marine sediment deposited under oxic conditions (S/C of extracted HA: 0.030+0.007). (b) from the same sediment spiked with Na2S a n d elemental sulphur (S/C of the extracted HA: 0.211+0.001). 43 well-defined peaks appeared in the spectrum of the humic acids extracted in the presence of polysulphides ( Fig.3, curve b). The peak at 1260 cm 1 corresponds to the absorption band of thiocarbonyl ( S i l v e r s t e i n et a l . , 1981), while the peak at 800 cm 1 i s tentatively ascribed to a C-S stretching band. There was no evidence for the S-H stretching band near 2600 cm 1. However, thi s band is known to be very weak and may not be detectable in t h i s complex matrix. An attempt was made to determine the amount of polysulphides produced in these reactions. The alkaline humic acid solutions were f i r s t checked for the presence of elemental sulphur and then were a c i d i f i e d while being under a vigorous nitrogen stream to drive off the excess H 2 S . Any elemental sulphur found in the extracts after a c i d i f i c a t i o n was assumed to come from the decomposition of the polysulphides present in the humic extracts. The amount of polysulphide S associated with the humic extracts was then expressed as the ratio of elemental sulphur extracted by benzene from the a c i d i f i e d extracts to the dissolved organic carbon (DOC) of the extract before a c i d i f i c a t i o n (SS n/C). Table 9 shows that treatment #3 produced humic acids with a s i g n i f i c a n t l y higher polysulphide S to carbon r a t i o (SS n/C) than the other treatments, confirming the conclusions drawn e a r l i e r . Part of the extracts from treatments #3 and #4 (Table 9) were dialysed, p r i o r to a c i d i f i c a t i o n , against d i s t i l l e d water, under a nitrogen atmosphere. E s s e n t i a l l y a l l the polysulphides passed through the 44 membrane (Table 10), showing that they were not chemically associated with the organic matrix. I conclude that they were present as low molecular weight inorganic polysulphides (HS^, HS 4) which were reacting rapidly with the organic matter. The rapid reaction between polysulphides and organic matter i s further supported by the decrease in polysulphides during d i a l y s i s . The amount of polysulphides found in the dialysates (Table 10, LMwt SS n) was much smaller than the amount dialysed (Table 10, expected). Since no elemental sulphur was formed before a c i d i f i c a t i o n , this decrease could not be due to t h e i r oxidation or decomposition. Therefore, i t must be a result of their reaction with organic matter during d i a l y s i s . 2.2.4 CONCLUSIONS It has been shown that certain precautions are necessary in order to extract the humic acid frac t i o n from anoxic marine sediments without a r t i f i c i a l l y r a i s i n g i t s sulphur content. Elemental sulphur and free sulphides must be removed from the sample before proceeding with the a l k a l i n e extraction. Also, the extent of sulphur contamination from co-extracted pyrite and gr e i g i t e must be estimated. Although these requirements can be met in various ways, i t was found convenient to freeze-dry the sediment samples 45 Table 10. D i a l y s i s of polysulphides present in humic extracts. HA extracted from: mgC HMwt LMwt expected dialysed SSn(mg) SSn(mg) (mg) Sedt. spiked with 134.6 0.002 1.60 2.40 S and Na 2S. Sedt. spiked with 140.4 0.003 0.12 0.36 Na 2S. 1. Elemental sulphur recovered upon a c i d i f i c a t i o n of the humic acid solution after d i a l y s i s . 2. Elemental sulphur recovered upon a c i d i f i c a t i o n of the dialysate. 3. Amount of elemental sulphur expected i f the amount of polysulphides had stayed constant during d i a l y s i s ( i . e . = mgC dialysed (Table 10) x SS n/C (Table9)). 46 immediately after their extrusion under a nitrogen atmosphere, on board ship. The humic substances were extracted by NaOH 0.5N after removal of the elemental sulphur from the dried sediment with benzene. The humic acids were precipitated from the alkaline solutions by a c i d i f i c a t i o n to pH2 with HC1. In order to minimize the formation of elemental sulphur by the oxidation of H2S produced by the decomposition of co-extracted A.V.S., the p r e c i p i t a t i o n of humic acids was done under a vigorous stream of nitrogen. The precipitates were freeze-dried and their elemental composition determined. Subsequently, the samples were treated with a freshly prepared C r C l 2 solution and the amount of H2S produced was measured to estimate the sulphur contribution of co-extracted pyrite and g r e i g i t e . This procedure i s thought to y i e l d sulphur values for sedimentary humic acids close to their true ijn s i t u values and was used to study the diagenetic changes in the organic sulphur fractio n in anoxic sediments. A more detailed presentation of th i s extraction procedure i s given in section 2.3.2.2. 2.3 EVOLUTION OF THE SULPHUR CONTENT OF THE HUMIC FRACTION OF MARINE SEDIMENTS DURING EARLY DIAGENESIS. 2.3.1 INTRODUCTION. The evolution of the sulphur content of the humic substances extracted from a nearshore sediment core was investigated. 47 Special attention was taken to avoid sulphur contamination of the humic materials during the extraction which was performed according to the method outlined above and presented in more d e t a i l s in section 2.3.2.2.. 2.3.2 MATERIALS AND METHODS. 2.3.2.1 SITE DESCRIPTION AND SAMPLING PROCEDURE. Sediment samples were c o l l e c t e d from Jervis Inlet on the coast of B r i t i s h Columbia. It i s a t y p i c a l long, narrow and deep fjor d (Fig. 4) with a r e l a t i v e l y deep s i l l , allowing deep water v e n t i l a t i o n . Its sediments are deposited under well-oxygenated conditions and support a variety of macro-benthic organisms. They contain on average 3-4% organic carbon with a r e l a t i v e l y high C/N r a t i o (10-13) suggesting some t e r r e s t i a l input from the steep wooded flanks on both sides of the i n l e t . Three cores were taken from the same location (JV11, 49°53.9'N, 123°54.1'W. F i g . 4) from a depth of 650m. Two were c o l l e c t e d with a lightweight gravity corer described by Pedersen et a l . (1985)." One core (core A) was used for chemical analyses and the other (core B) for stable isotope analysis. A t h i r d core (core C) was taken with a box-corer for bulk sediment analysis. S e t t l i n g particulates were also c o l l e c t e d using an interceptor trap deployed at JV11.5 (660m deep, F i g . 4), 60m 48 F i g . 4: Map of J e r v i s I n l e t . 49 above the sea f l o o r , over a 6 week period (August 8th to September 18th, 1985). The c o l l e c t o r trap consisted of a PVC cylinder with an internal diameter of 12.5 cm and a height of 48cm. Baffle grids were placed at the opening of the cylinder and in the sampling chamber (Iseki et a l . , 1980). A saturated NaCl solution (500ml) containing 0.5% NaN^ was used as a preservative. 2.3.2.2 EXTRACTION AND ANALYTICAL METHODS. CORE A: The sediment samples from th i s core ( i . e . for chemical analyses) were processed according to the diagram shown in F i g . 5. After core extrusion and subsampling, the subsamples were centrifuged (step (1)). The pore waters were coll e c t e d and H 2S measured immediately (step (2)) using the methylene blue procedure of Cline (1969). Sulphate concentrations were measured a few weeks later by gravimetry (Appendix I I ) . The s o l i d phase was quickly frozen with a mixture of dry ice and acetone and immediately freeze-dried (step (3)). This procedure dried the samples while avoiding their oxidation, and also removed the free sulphides present. Subsequently, a known volume of benzene was used to extract elemental sulphur from the freeze-dried sediments (step (4)). Since a second benzene extract did not y i e l d any s i g n i f i c a n t amount of sulphur, t h i s f i r s t extraction was considered complete. After centrifugation, the concentration of elemental sulphur in the benzene extract was measured by cyanolysis (step (5)) according to B a r t l e t t and Skoog (1954) 50 samples extruded on board in N 2 _ filled glove_box centrifuged (I) pore water * (2) sulphide analysis sulphate analysis solid phase freeze dried (3) benzene extr. (4) 0-5N NaOH extr. (6) I humic extract S* analysis (5) benzene extr. (7) D.O.C. anal + HCI (8) (cont. N2bubbling) I benzene extr. (9) S° analysis (10) centrifuged(ll) elemental HCI analysis hydrolysis (12) sulphate hydrolysed analysis(l3) H.A. I CrCI 2 reduction (14) I pyrite analysis F i g . 5 : Humic extraction procedure. 51 (Appendix I I ) . The benzene s t i l l present in the sediment after centrifugation was displaced by oxygen-free deionized water. The humic substances were extracted with NaOH 0.5N (step(6)). The D.O.C. of the humic extracts was measured by the dry-combustion method, as explained in Appendix I I . Polysulphides associated with the humic extracts were determined by measuring the elemental sulphur formed by their acid hydrolysis in the following manner (see also Appendix I I ) . The alk a l i n e humic solutions were f i r s t extracted with benzene, to check for the presence of elemental sulphur before a c i d i f i c a t i o n (step(7)). Elemental sulphur was never detected at this stage, confirming the e f f i c i e n c y of the sulphur extraction in step (4). The humic solutions were then a c i d i f i e d to pH2 with HC1 (step (8)) over 12 hours under constant nitrogen bubbling, to avoid the formation of S° by the oxidation of co-extracted a c i d - v o l a t i l e sulphides (AVS). These a c i d i f i e d extracts were then re-extracted with benzene (step (9)). The elemental sulphur measured in these extracts was assumed to come from the acid hydrolysis of organic polysulphides (step (10)). These polysulphides were then normalized to the D.O.C. of the alk a l i n e humic solution. After benzene extraction, the a c i d i f i e d humic extracts were centrifuged (step (11)) and the precipitated humic substances recovered and freeze-dried for subsequent analysis. A l l operations up to step (8) were performed s t r i c t l y under nitrogen. The C, N,and S contents of the humic material were determined as described in 52 Appendix I I . Sulphate esters, present in the humic acids were also determined, by measuring the sulphate produced by their hydrolysis in 5N HCl, at 120°C (King and Klug, 1980) (step (12)) (Appendix I I ) . Sulphate in the hydrolysate was measured t i t r i m e t r i c a l l y (Howarth, 1978) (step (13)). The hydrolyzed humic acids were f i n a l l y dried, ground and analyzed for p y r i t i c sulphur (step(l4)) (Appendix I I ) . CORE B: This core, for isotope analysis, was processed in e s s e n t i a l l y the same way, although with some modifications. The samples were not centrifuged (step (1), F i g . 5), but instead, after addition of oxygen-free deionized water, a stream of nitrogen was passed through the slurry for 48 hours and the H2S stripped off the sediment was co l l e c t e d in a 2M zinc acetate solution. This procedure quant i t a t i v e l y recovered H 2S from a pore water sample spiked with 1mM/l of dissolved sulphide. Within 4 hours, a l l traces of H2S disappeared even though the pH of the water had risen from 8.5 to 9.7, due to the stripping of C0 2 > Accordingly, a quantitative recovery from the sediment samples must have been obtained and the isotopic composition of the zinc sulphide formed must r e f l e c t the isotopic composition of the aqueous sulphides. The samples were subsequently freeze-dried (step (3), F i g . 5) and extracted with benzene (step (4), F i g . 5). In t h i s case, the elemental sulphur was not measured, but p u r i f i e d by thin layer chromatography on S i 0 9 , with 30% CH_C19 53 and 70% Hexane. This treatment separated the organic impurities from sulphur, which was then eluted with benzene and a i r - d r i e d . The humic substances were then extracted in the same manner as for core A (step 6,8 and .11, F i g . 5) but no attempts were made to recover the sulphur formed by the decomposition of polysulphides. The humic material was f i n a l l y treated with 5N HC1 for 5 hours at 120°C pr i o r to isotope analysis. The results of the stable isotope analysis are expressed in the notation, using Canon Diablo T r o i l i t e as the standard. CORE C: Bulk sediment analyses were performed on this core. Total carbon was measured by dry combustion - gas chromatography with a c o e f i c i e n t of v a r i a t i o n of 1.25%. Carbonates were analyzed on a C0 2 coulometer (Coulometrics Inc. model 5010) with a precision of 10%. Organic carbon was estimated by difference. Total sulphur and manganese were measured on an automated P h i l i p s X-ray fluorescence spectrometer u t i l i z i n g a Rh target X-ray tube (Appendix I I ) . SEDIMENT TRAP MATERIALS: Because of the small quantity of material available, a modified procedure had to be used. The interceptor trap c o l l e c t e d 2.1g of dried material, of which 2g were extracted with 100ml NaOH 0.5N under nitrogen. After centrifugation, the humic extract was dialyzed against deionized water for 4 days in order to remove NaOH and s a l t . The s l i g h t l y a c i d i c c o l l o i d a l solution obtained was evaporated in vacuo, at room . temperature and the dried residue redissolved in exactly 54 10ml NaOH 0.5N. The D.O.C. of thi s solution was measured. The remaining solution was added to 0.5g of microcrystalline c e l l u l o s e and dried under an infra-red lamp. The dried mixture was weighted and homogenized and i t s sulphur content measured on the Fischer sulphur analyzer (detection l i m i t : 20ppm) as before. Duplicate analyses were made and agreed to within 2.5%. 2.3.3 RESULTS AND DISCUSSION. The results from the bulk analysis of core C are shown in Table 11 and F i g . 6. The surface of the sediment analyzed consisted of a well-defined oxide layer (1 to 2 cm in thickness), indicative of intensive Fe and Mn remobi1ization within the underlying anoxic zone. This i s in agreement with the Mn p r o f i l e showing a s i g n i f i c a n t enrichment in the surface sample. Organic carbon decreased gradually from 4.28% to 3.41% within the top 25cm of the core and stayed e s s e n t i a l l y constant in the deeper parts. Total sulphur increased rapidly within the top 15cm, i . e . in the oxic and suboxic zones and increased more gradually deeper, within the sulphidic part of the core. This p r o f i l e i s consistent with the presence of anoxic microniches within the upper part of the sediment. Such microenvironments have been suggested to explain the occurrence of authigenic FeS 2 (Emery and Rittenberg, 1952) and to account for b a c t e r i a l reduction of 55 Table 11. Bulk sediment analys i s (% dry weight). Depth (cm) £C% r 9-c a r b ° C % org S% Mn% 0- 1 4.43 0.15 4.28 0.24 3.02 3- 6 4.23 0.09 4.14 0.40 0.83 7-10 4.15 0.08 4.07 0.59 0.49 11-14 4.15 0.15 4.00 0.73 0.84 1 5-18 3.95 0.09 3.86 0.73 0.76 23-26 3.46 0.05 3.41 0.69 0.53 27-30 3.63 0.11 3.52 0.83 1.18 35-38 3.80 0.20 3.60 0.85 1.10 39-42 3.71 0.14 3.57 0.92 0.88 43-46 3.88 0.16 3.72 0.93 0.41 47-50 3.68 0.08 3.60 0.80 0.74 51-54 3.85 0.23 3.62 0.89 1 .32 55-58 3.79 0.30 3.49 0.82 1 .04 56 Fig 6.: Bulk sediment analysis (data from core C ) . 57 r a d i o - l a b e l l e d sulphate (Jorgensen, 1977) in the oxidized surface layers of marine sediments. Pore water H2S was below detection l i m i t (1juM) in the surface 20cm and increased rapidly between 30 and 45 cm to a maximum value of ~550 J J M (Fig. 7). The dissolved sulphides recovered from core B in the zinc acetate traps showed a decreasing o~34S °/oo to a depth of ~40cm, followed by an increase deeper in the core (Fig. 12). It has been shown that sulphur isotope fractionation i s generally inversely proportional to the rate of sulphate reduction (Harrison and Thode, 1958). The l i g h t e r H 2S formed deeper in the upper part of the core may, therefore, r e f l e c t a decrease in sulphate reduction rate, due to the depletion of readily metabolizable organic matter with depth. The increase in cT 3 4S°/oo deeper in the core i s a pattern often reported (e.g. Goldhaber and Kaplan, 1980) and r e f l e c t s an increase in the /oo of the pore water sulphate, due to 32 = p r e f e r e n t i a l reduction of SO^ , under semi-closed system conditions. The elemental sulphur p r o f i l e showed a broad peak, just above the sulphidic zone (Fig. 8). This is probably due to the 3 + upward d i f f u s i o n of H2S and i t s subsequent oxidation by Fe in the sub-oxic zone, according to: 2 FeOOH + 3 HS~ > 2 FeS + S° + 3 OH~ + H 20 (Berner, 1964) A s i g n i f i c a n t amount of elemental sulphur was also found in the top layers of the sediment column, even within the oxide 58 E o UJ O H 9 S ( M M L T 1 ) 100 200 300 400 500 600 19 21 23 25 27 SOI (mML"') F i g . 7: D i s t r i b u t i o n of pore water sulphide and sulphate concentrations (data from core A). 59 F i g . 8: Concentration p r o f i l e (data from core A) and isotope composition (data from core B) of elemental sulphur. 60 surface layer, far from the zone of influence of the H 2S pore water gradient. This is probably due to the presence of anoxic microenvironments within the oxic and sub-oxic zones, in which diss i m i l a t o r y sulphate reduction occurs and from which H2S d i f f u s e s . A l t e r n a t i v e l y , this could have also been produced by mixing due to bioturbation. Within the sulphidic zones, the elemental sulphur concentration tended to decrease, either because of i t s reduction, chemically and/or micr o b i o l o g i c a l l y , or i t s incorporation into p y r i t e . The stable isotope composition of S° extracted from the second core (core B) showed a very s t r i k i n g pattern. In general, the very negative c) 3 4S 0/oo values obtained are consistent with i t s postulated o r i g i n ( i . e . oxidation of H2S produced by the sulphate reducers). However, elemental sulphur becomes much heavier at the suboxic/sulphidic boundary, where i t i s most abundant, and becomes li g h t e r again in the deeper part of the sediment column (Fig. 8). It i s very d i f f i c u l t at t h i s stage to interpret the minimum in the p r o f i l e . Chemosynthetic oxidation of o 32 sulphide by a Thiobacillus produces a S enriched in S by about 2.5°/oo (Kaplan and Rittenberg,. 1964). In the upper part of the 32 core B, elemental sulphur would seem'slightly enriched in S compared to H2S (Table 16). It i s therefore possible that the S° found in the top 15 cm of the core i s the result of the metabolic a c t i v i t y of chemoautotrophs. These bacteria require oxygen or n i t r a t e as electron acceptors. It i s therefore expected that 61 their influence would be r e s t r i c t e d to the upper part of the sediment column. This explanation may seem somewhat problematic when considering the large pool of FeOOH available which w i l l compete with the b a c t e r i a l oxidation. However, H 2S produced 3 + within microenvironments l o c a l l y depletes the Fe . If some suitable electron acceptor diffuses toward the boundary of these microniches, chemoautotrophic oxidation of H 2S would be possible. Deeper in the sediment, t h i s type of oxidation i s impossible because of the lack of suitable electron acceptors {unless they are being brought in by bioturbation) and chemical oxidation by 3 + Fe (e.g. Rickard, 1974) i s probably the main mechanism producing S°. It i s interesting to note that Kaplan and Rafter (1958) reported a 3 4 S enrichment in elemental sulphur produced during a b i o t i c oxidation of H2S by 0 2 < This i s in accordance with the heavier S° recovered at the suboxic/sulphidic boundary where large amounts of H 2 S ' d i f f u s i n g up along the pore water concentration gradient, i s being oxidized by iron oxides. The fractionation reported by Kaplan and Rafter (3°/oo) i s much smaller than that reported here (~15°/OO); however, the 3 + conditions of oxidation (0 2 vs Fe ) were very d i f f e r e n t . The decrease in /oo of the elemental sulphur found in the deeper part of the sulphidic zone could r e f l e c t a gradual e q u i l i b r a t i o n between S° and dissolved sulphides. Isotopic equilibrium between these species would produce elemental sulphur s l i g h t l y enriched 62 in S (Ohmoto and Rye, 1979) such as observed in the 60-66 cm horizon of core B. E q u i l i b r i a in the l^S-Sg-H^O system have been reported to be rapid and reversible (e.g. Boulegue et a l . , 1982). Since isotopic equilibrium seems to be achieved only 30cm below the elemental sulphur peak formed at the suboxic/sulphidic boundary, that would seem to indicate that elemental sulphur found in the sulphidic zone was not residual but rather was continuously being produced and consumed at a rate which was higher than the rate of isotopic e q u i l i b r a t i o n . S° reacts with FeS to produce pyrite (e.g. Berner, 1972). Since no isotopic discrimination has been reported during t h i s reaction (Sweeney and Kaplan, 1973) the heavy isotopic composition of S° must be a result of discrimination occurring during i t s formation. The reduction of Fe(lII) held in clay l a t t i c e s i s a possible mechanism which could account for the formation of S° within the sulphidic zone (Drever, 1971; van Breemen, 1980). This would be consistent with the formation of i s o t o p i c a l l y heavy S° upon 3 + chemical oxidation of H2S by Fe . The gradual decrease of 03 4S°/oo toward values at equilibrium with dissolved sulphides could r e f l e c t a decrease in turnover rate of S° with depth. Explanations for the isotope p r o f i l e of S° can only be speculative at this stage. The general features of t h i s p r o f i l e need to be confirmed. If so, laboratory experiments could be designed to shed l i g h t on the various processes involved. The humic acids extracted from t h i s sediment showed a 63 continuous increase in their S/C ratios with depth (Fig. 9, Table 14). The ratios obtained from the s e t t l i n g particulates (Table 12) and from the upper 2cm of the core (Table 14) seemed higher but were s t i l l very close to the values reported for planktonic materials (Table 2). They increased rapidly within the top 20cm of the sediment column, i . e . in the sub-oxic zone, before H2S started to accumulate in the pore waters, and reached values which were s i g n i f i c a n t l y higher than any planktonic values reported. Some macrophyte species ( p a r t i c u l a r l y red algae) have been reported to contain more sulphur than plankton (Kaplan et a l . , 1963); however, the sediment studied here was far from the influence of any extensive i n t e r t i d a l zone. Also, b a c t e r i a l biomass which w i l l be in part incorporated in the humic fraction i s not p a r t i c u l a r l y high in sulphur even in isol a t e s from anoxic mud (Table 13). The S/C p r o f i l e reported must therefore r e f l e c t a diagenetically-induced increase in S r e l a t i v e to C in the sedimentary humic materials. Such an increase could be the result of several processes, possibly occurring simultaneously. An increase in the S/C r a t i o of organic matter can occur by p r e f e r e n t i a l mineralization of C over S. Since we are dealing here with only a fracti o n of the organic matter, i t may also r e f l e c t a variation in the rate of incorporation of these elements into the humic f r a c t i o n , during the humification process. A l t e r n a t i v e l y , sulphur addition to the humic substances 64 S/C 0-02 0 03 0-04 005 F i g . 9: S/C ratios by weight of humic acids extracted from core A: S/C = t o t a l sulphur content of HA normalized to C; S /C = C-bonded sulphur of HA normalized to C. 65 Table 12. Amount of C and S extracted by NaOH 0.5N from s e t t l i n g p a r t i c u l a t e materials (org C% = 5.14%) coll e c t e d from an interceptor trap deployed in Jervis Inlet (Station JV 11.5). % dry weight particulates C 1.17+ 0.025 S 0.032 + 0.0015 S/C 0.027 + 0.001 66 Table 13. Microbial S/C r a t i o s . Organism g S/C ng S/10 c e l l s References Bacteria Bacter ia 0.013 0.010 1 Fresh water isolates 0.004-0.010 .2 Sea water isolates' 0.007-0.012 74-421 Desulfovibrio salexigens <0.019 Fermentive bacteria . <0.017 from anoxic sediments 1 25 Spector (1956) Bowen (1979) Jordan and Peterson (1978) Cuhel et a l . (1981) Cuhel et a l . (1982) Cuhel et a l . (1982) 1 - Chromobacterium 1ividum, Pseudomonas fluorescens and unidentified i s o l a t e s 2 - Pseudomonas halodurans and Alteromonas luteo-violaceous 3 - S wt% in b a c t e r i a l proteins = 1.00%. This corresponds to a S/C in average proteins = 0.019. Since more than 90% of b a c t e r i a l sulphur were reported to be associated with proteins, the S/C r a t i o of the whole organism must be considerably less than 0.019. 4 - Same reasoning as above with a S wt% in b a c t e r i a l protein = 0.92%. 67 Table 14. C and S content of humic a c i d s e x t r a c t e d from core A. Sfc = t o t a l sulphur, Spy = p y r i t i c sulphur, S = organic sulphur ( i . e . S t -S ), S c = C-bonded s u l p h u r 1 ( i . e . S - S + 6 ) , S + 6 = sulphate e s t e r s . % wt humic a c i d s Depth C S. S„ S S + 6 S C S/C S + 6/C S C/C (cm) 1 p y S u r f . 49. 9 1 .52 0. 03 1 .49 0. 35 1 .14 0. 030+0. 0008 0. 007 0. 023 0- 2 49. 7 1 .55 0. 03 1 .52 0. 38 1 .14 0. 031+0. 0009 0. 008 0. 023 2- 6 43. 6 1 .43 0. 04 1 .39 0. 36 1 .03 0. 032+0. 0009 0. 008 0. 024 18-22 46. 0 2 .19 0. 27 1 .92 0. 46 1 .46 0. 042+0. 0014 0. 010 0. 032 22-26 35. 4 1 .62 0. 18 1 .44 0. 46 0 .98 0. 041+0. 0012 0. 013 0. 028 28-32 39. 9 2 .02 0. 18 1 .84 0. 48 1 .36 0. 046+0. 0014 0. 012 0. 034 32-36 41 . 0 2 .05 0. 20 1 .85 0. 48 1 .37 0. 045+0. 001 4 0. 012 0. 033 44-48 31 . 5 1 .57 0. 13 1 .44 0. 32 1 .12 0. 046+0. 0014 0. 010 0. 036 56-60 35. 3 2 .00 0. 15 1 .85 0. 46 1 .39 0. 052+0. 0016 0. 013 0. 039 68-72 38. 2 2 .02 0. 24 1 .77 0. 36 1 .41 0. 046+0. 001 5 0. 009 0. 037 1 - S r e f e r s to o r g a n i c sulphur which does not produce sulphate d u r i n g HC1 h y d r o l y s i s ( i . e . a l l o r g a n i c sulphur but the sulphate e s t e r s ) . 2 - Not c o r r e c t e d f o r ash. 68 could also be brought about by chemical reactions between organic matter and inorganic reduced sulphur species during early diagenesis. The r e l a t i v e importance of these various processes was investigated further by studying the chemical form of organic sulphur and by stable isotope analysis. Incorporation of sulphur into the humic matrix by reaction with H2^' and/or polysulphides would l i k e l y produce a C-bonded reduced organic sulphur with a l i g h t isotopic composition. Organic polysulphides were found associated with the extracted humics. A well-defined peak occurs just above the depth where I^S starts to accumulate in the pore water (Fig. 11), i . e . in the region where inorganic polysulphides are more l i k e l y to be formed in abundance as an intermediate of H 2S oxidation (Chen and Gupta, 1973). These polysulphides could then react with organic matter, v i a free r a d i c a l reactions, and produce organic polysulphides and t h i o l groups. Organic polysulphides could also be formed by reaction between nucleophilic groups of humic acids (e.g. t h i o l s , amines...) and S° (see reactions (5) and (6)). Once in the sulphidic zone, the amount of organic polysulphides decreases substantially, probably due to their reduction, as they are known to be unstable under strongly reducing conditions (Boulegue, 1982). The r a t i o of sulphate esters to carbon (S +^/C) in the humic fr a c t i o n seemed to increase with depth within the suboxic zone and then stayed roughly constant (Table 14). From the S/C and 69 70 S S n / C F i g . 11: Polysulphides (SSn) associated with the humic extracts obtained from core A. The results are expressed in weight r a t i o of elemental sulphur produced by t h e i r acid hydrolysis to carbon. 71 S /C r a t i o s , the r a t i o of C-bonded organic sulphur to carbon (S c/C) can be estimated (Fig. 9; Table 14). This r a t i o also shows a continuous increase with depth. This i s further confirmed by the S/C r a t i o of the humic residue l e f t after hydrolysis of the sulphate esters and amino-acids (S/C n ^) (Fig. 10, Table 15). Therefore, there i s an addition of non-hydrolyzable, C-bonded sulphur to the organic matrix during early diagenesis. In an attempt to di s t i n g u i s h between " d i f f e r e n t i a l humification rate" ( i . e . difference in rate of incorporation of organic sulphur and carbon into the humic fraction) or d i f f e r e n t i a l mineralization rate and S addition to the humic matrix by chemical reaction with inorganic reduced species, the stable isotopic composition of hydrolyzed humic acids was determined (Fig. 12; Table 16). This organic sulphur was of very l i g h t isotopic composition, which would support the importance of the chemical addition of sulphur to the organic matrix. However, a number of considerations must be taken into account before reaching such a conclusion. An isotope mass balance can be estimated, using the SA-ftyd r a t i o s (Fig. 10, Table 15) and c T 3 4 s°/oo of HA (Fig. 12, Table 16). If we assume that the sulphur system in the sediment has reached steady-state, that most of the chemical sulphur addition i s due to nucleophilic addition of HS and that there is no isotopic fractionation during t h i s reaction, then: 72 Table 15. C and S content of humic acids extracted from core A after hydrolysis in 5N HCl, 120°C, 5 hrs. % wt humic acids Depth (cm) C s2 S / C h y d Surf. 56 .8 1 .29 0 .023+0.0006 0- 2 59 .4 1 .60 0 .027+0.0008 2- 6 51 .7 1 .43 0 .028+0.0008 18-22 54 .5 1 .99 0 .037+0.0012 22-26 39 .8 1 .40 0 .035+0.0010 28-32 47 .3 1 .96 0 .041+0.0012 32-36 47 .4 1 .95 0 .041+0.0013 44-48 34 .0 1 .48 0 .043+0.0013 56-60 39 .5 1 .98 0 .050+0.0015 68-72 43 .2 2. 18 0 .050+0.0016 1 - Not corrected for ash. 2 - Corrected for p y r i t i c sulphur. 73 F i g . 1 2 : I so tope c o m p o s i t i o n o f f r e e s u l p h i d e s (H2S) and h y d r o l y z e d humic a c i d s (HA) (data from core B). 74 Table 16. Sulphur isotope composition of free sulphides, elemental sulphur and hydrolyzed humic acids. S> 3 4 s ° / Depth H.S S° Hydrolyzed (cm) humic acids 0- 6 - -22.3 -17.4 6-12 - -27.6 -26.2 12-18 -27.3 -29.6 -25.6 18-24 - -24.8 -26. 1 24-30 -32.4 -17.7 -29.7 30-36 -33. 1 -15.0 -28.7 36-42 -33.8 -15.8 -30.6 42-48 -31.6 -17.7 -29. 1 48-54 -32.3 -26.4 -29.4 54-60 -27.9 -23.8 -28.9 60-66 -27. 1 -31.5 -27.9 75 5 [ S / C h y d ] i S i + [ H S / C ] i + 1 § H S i + 1 ( ^ 1 + 1 l s / C h y d J i + L H S / C j i + 1 [ s / c , , ] . (X. - S. ) [HS/C]. + 1 = h y d 1 1 1 + 1 (2) $ i + 1 - J H S i + 1 where ^ / C ^ i s the S /C r a t i o of hydrolyzed humic aci< :ds at depth i ; (!) ^  i s the stable isotope r a t i o of hydrolyzed humic acids at depth i ; 0 ^ + 1 i s the stable isotope r a t i o of hydrolyzed humic acids at depth i+1; ^ HS^ + 1 i s the stable isotope ratio of free H 2S at depth i+1; [HS/C] i + 1 i s the amount of HS~ added to the hydrolyzed humic , normalized to C, at depth i+1. If the HS addition accounts for the sulphur enrichment observed then: [HS/C] i + 1 = [ S / C h y d ] i + 1 - [ S / C h y d ] . = A [ S / C h y d ] i + 1 (3) If [HS/C]^ + 1 < A [ S/C^yjj] i +! t part of the sulphur enrichment observed must be due to a " d i f f e r e n t i a l humification rate" or d i f f e r e n t i a l mineralization rate of sulphur and carbon. If [HS/C] i + 1 > A t s/ chyd-'i + 1 ' s o m e s u l P h u r r i n i t i a l l y present in the organic matter or incorporated higher in the sediment column, must have been replaced by HS from depth i+1, i. e . some isotopic exchange must have occurred.' In order to apply t h i s scheme to the present s i t u a t i o n , the data were clustered into three groups (Fig. 12, Table 17). The results show that the amount of HS added to the humic matrix to account for i t s isotopic composition is s i g n i f i c a n t l y larger than the increase in sulphur actually recorded. These re s u l t s can be 76 interpreted in two ways: either the c T 3 4 S /oo of the sulphur added to the organic matrix is quite d i f f e r e n t from that of HS , or some isotopic exchange occurs at each depth. Besides HS , the two other inorganic sulphur species susceptible to reacting with organic matter are elemental sulphur and polysulphides (e.g. Casagrande and Ng, 1979). Elemental sulphur i s much heavier at mid-depth in the core, and t h i s i s not re f l e c t e d in the hydrolyzed humic acids. It seems therefore that elemental sulphur has very l i t t l e e f f e c t in enriching the humic materials, at least in functional groups which can r e s i s t acid hydrolysis. This i s in agreement with the work of Mango (1983) who showed that H2S was very e f f i c i e n t at reductively dehydrating carbohydrates, producing a variety of organosulphur compounds, while elemental sulphur was t o t a l l y inactive under the same conditions. The stable isotope composition of inorganic polysulphides has not been measured, but i t i s l i k e l y to be close to HS or of an intermediate value between S° and HS . The isotopic composition of the added sulphur necessary to account for the A f s/ Chyd-'i + i and cT^ + 1 observed can be computed by rearranging Eq. (2). $ . - T j , , [ s / c l - i t [ S / c h Y d ] i 1 ' [HS/C] i + , where [HS/C] i + 1 i s taken as equal to A [ S / C h y d ] i + 1 . This gives <^~34S°/oo of -50 + 8 °/oo for the sulphur to be added at mid- depth (24-54 cm) and -24 + 7°/oo for the deeper part of the 77 Table 17. Isotope mass balance (see text for explanations). Depth <f. *HS. S/C h y d . HS/ C i A S/C h y d . 6-24 -26 ? 3.5X10" 2 24-54 -29.5 -33 4.1X10~ 2 (3.5+0.8)10"2 » 0.6xl0 _ 2 54-66 -28.5 -27.5 5.0X10~ 2 (4.1+3.0)10 _ 2 » 0.9xl0~ 2 78 core (54-66 cm). Neither S nor polysulphides seem an adequate sulphur source. It appears l i k e l y therefore that some isotopic exchange between H2S and organic sulphur occurred at each depth in the core. This isotopic exchange could possibly have been mediated by b a c t e r i a l a c t i v i t y . Most microorganisms can meet their anabolic sulphur requirement via assimilatory sulphate reduction (e.g. Roy and Trudinger, 1970). The organic sulphur produced has an isotopic composition very close to the sulphate being reduced (Kaplan et a l . , 1963; Kaplan and Rittenberg, 1964). However, some bacteria (e.g. methanogens) are unable to reduce sulphate and w i l l instead assimilate sulphide for their protein synthesis (Truper, 1982). Also, sulphide can t o t a l l y suppress sulphate uptake while allowing optimal growth (e.g. Roberts et a l . , 1955). Since sulphate assimilation requires more energy, i t seems that many bacteria w i l l p r e f e r e n t i a l l y assimilate sulphide when av a i l a b l e . This w i l l produce a ba c t e r i a l biomass with an isotopic composition similar to the sulphide u t i l i z e d . More than 90% of the sulphur present in bacteria can be accounted for by proteins and low molecular weight molecules (Roberts et a l . , 1955; Cuhel et a l . , 1981, 1982). Since both classes of compounds are very l a b i l e , i t can be argued that a pool of b a c t e r i a l sulphur which has been synthetized at depth i w i l l l i k e l y be p r e f e r e n t i a l l y mineralized and replaced at depth i+1 by a newly-formed biomass with an isotopic signature similar to that of the H2S of the corresponding depth , producing an apparent isotopic 79 exchange between organic sulphur and sulphide. However, in the present context, t h i s explanation seems unl i k e l y . The organic matter analyzed (hydrolyzed humic acids) must have been of a very refractory nature and i t would be d i f f i c u l t to validate a rapid turnover rate of microbially-derived materials in this f r a c t i o n . 2.3.4 CONCLUSIONS. Accumulation of organic sulphur into sedimentary humic acids does occur during early diagenesis. This i s shown by the increase in their S/C ratios with depth, even though a l l precautions to avoid S contamination during sample handling and extraction have been taken. The l i g h t isotopic composition of t h i s humic sulphur indicates that reduced inorganic sulphur, species, produced by di s s i m i l a t o r y sulphate reduction are involved. However, because of isotopic exchange, these data cannot be used to reveal the nature of the i n i t i a l source of sulphur. The actual mechanism of t h i s sulphur enrichment i s , therefore, s t i l l speculative and chemical data must be used to constrain the p o s s i b i l i t i e s . Humic substances constitute the bulk of the organic matter found in marine sediments (e.g. Vandenbroucke et a l . , 1985). If we assume that the S/C ratios measured in humic acids ( i . e . that part of the humic substances which is extractable and which pre c i p i t a t e s at low pH) r e f l e c t the S/C ra t i o s of humic materials 80 as a whole, i t would seem d i f f i c u l t to argue that the increase in S/C r a t i o i s due to the accumulation of non-biodegradable organic sulphur residue in the organic matrix. A doubling of the S/C r a t i o would require the mineralization -of at least 50% of the organic carbon found in the upper cm of the core, within the top 50cm of the sediment column. This i s not r e f l e c t e d in the organic carbon p r o f i l e (Fig. 6, Table 11). Moreover, sulphur found in organisms i s generally associated with the most l a b i l e classes of compounds, mainly proteins and low molecular weight soluble metabolites (e.g. aminoacids, coenzymes, vitamins). Sulpholipids are also found in phototrophic organisms (e.g. Busby and Benson, 1973; Cuhel and Waterbury, 1984). Labile proteins and l i p i d s are the most readily metabolized fractions of the organic matter deposited under oxygenated conditions (Khripounoff and Rowe, 1985). Therefore, the accumulation of their sulphur-containing components is very u n l i k e l y . The only other class of organic sulphur which i s found in s i g n i f i c a n t amount are the sulphate-esters. They occur mainly as sulphate polysaccharides and can serve important structural functions (e.g. Siegel, 1975). They seem to accumulate in the humic materials within the upper 20cm of the sediment column (Table 14). However, th i s accumulation alone cannot explain the S/C p r o f i l e observed, since the major part of the sulphur increment seems to be in the form of more reduced, carbon-bonded groups which also r e s i s t acid hydolysis. The accumulation of b a c t e r i a l l y - d e r i v e d organic sulphur i s also 81 unlikely, since i t mainly consists of proteins. The increase in humic sulphur during early diagenesis must therefore be the result of an addition of sulphur to the humic matrix during .humification. Considering the r e a c t i v i t y of reduced inorganic sulphur species and their abundance in sediments, chemical addition seems the more l i k e l y mechanism. The s i g n i f i c a n t sulphur enrichment which occurs above the sulphidic zone points to the r e l a t i v e importance of redox boundaries in the process of sulphur enrichment. Such boundaries are found just above the sulphidic zone of the sediment column or at the interface of microniches in oxic and suboxic layers. Bioturbation, by increasing the contact between sedimentary zones of d i f f e r e n t redox regime w i l l l i k e l y enhance the importance of such processes. H2S d i f f u s e s along i t s pore water concentration gradient, from the sulphidic to the suboxic zone where i t i s oxidized. It has also been shown that sulphate i s being reduced at a measurable rate in suboxic sediments (Jorgensen, 1977) presumably by sulphate reducers, l i v i n g in anoxic microenvironments. The residence time of F^S within these microniches i s very short. It very quickly diffuses out and i s oxidized to produce elemental sulphur, probably v i a polysulphides, since they are well-known intermediates in the process of H„S oxidation (Chen and Gupta, 1973). One can 82 therefore speculate on three possible mechanisms by which sulphur can be chemically added to the humic matrix in marine sediments (Fig. 13): Within the microaggregates or the sulphidic zones, HS could react with organic matter through nucleophilic substitution and/or addition. Experiments done with S l a b e l l e d sulphate in salt-marsh sediments show that the rate of formation of organic 35 S is much lower than the rate of formation of a c i d - v o l a t i l e sulphides and p y r i t e (Howarth and Merkel, 1984). One could therefore argue that sulphur enrichment of organic matter by reaction with H2S should not occur within the oxic and sub-oxic zones, since H2S would be readily oxidized and/or precipitated before i t could react with the organic matrix. However, the microniches sustain a high rate of sulphate reduction so that the 3+ Fe readily available within the aggregates is quickly depleted 2+ and H2S must diffuse out to be oxidized, while Fe diffuses in to produce FeS and FeS 2 (Berner, 1969). This w i l l provide a continuous pool of free H2S within the microenvironments, which w i l l be available for reaction with humic materials, even i f such reactions are comparatively slow. Alternative mechanisms for S addition into sedimentary humic substances are provided by the products of H 2S oxidation. Polysulphides are formed as intermediates of the oxidation of H2S or by reaction between sulphide and elemental sulphur. They can e a s i l y be cleaved h o m o l i t i c a l l y and produce free 83 a n o x i c e n v i r o n m e n t s HS" reactions with HS" nucleophilic addition ; H S : + C=A Y ' A " A S H nucleophilic substitution: HSf+ - C - ^ Z -- C - S H + Z*. o x i c / s u b o x i c H S r e n v i r o n m e n t s reactions with polysulphides: nucleophilic attack on S 8 H S : < S g — H S - S ~ R - S H + S 8 — - R - S - S g + H" HS-S:-~HSg+Sf R-NH + S « — R - N - S * + H + R - N - S ^ H H H + HS: F i g . 13: Possible mechanims of sulphur addition to the organic matrix in the oxic, sub-oxic, and sulphidic zones of nearshore marine sediments (see text for explanation). 84 r a d i c a l s which can then react with organic matter to form organic polysulphides and eventually t h i o l groups (Fig. 13). Such reactions could occur either at a redox boundary or within the sulphidic zone of the sediment column where a pool of elemental sulphur, small but possibly with a high turnover rate, was found. Also, nucleophilic groups present in the humic fraction (such as amines and t h i o l s ) could cleave the Sg rings of elemental sulphur and produce organic polysulphides which could also produce free r a d i c a l s l i a b l e to further react with organic matter. The presence of organic polysulphides found to be associated with humic acids, just above the depth at which H2S st a r t s to accumulate in pore water (Fig. 11) seems to indicate that t h i s type of reaction does occur. The lack of co-variation in the isotopic composition of elemental sulphur and non-hydrolyzable sulphur in the humic material would seem to indicate that the elemental sulphur has l i t t l e e f fect on the addition of non-hydrolyzable sulphur-containing f u n c t i o n a l i t i e s in the organic matrix. However, such reactions would have been masked by subsequent isotopic exchange with the H2S pool. F i n a l l y , i f we assume that the S/C ratios reported for humic acids r e f l e c t the sulphur content of the humified materials and since such materials would constitute the bulk of sedimentary organic matter, an estimate of the proportion of sulphur associated with the organic matter can be made by multiplying % C Q rg by S/C and comparing i t with the t o t a l sulphur content for 85 each depth i n t e r v a l . Such a calc u l a t i o n would suggest that in some marine sediments, r e l a t i v e l y r i c h in organic matter, organic sulphur could represent a s i g n i f i c a n t proportion of the t o t a l sedimentary sulphur, ranging from ~50% at the sediment interface to 15-20% in the sulphidic zone. This contention i s supported by the work of Zhabina and Volkov (1978) who found that, as a rule, organic sulphur represents the second largest pool of reduced sulphur in marine sediments. 2.4 REACTIONS BETWEEN REDUCED SULPHUR SPECIES AND HUMIC SUBSTANCES AT SEAWATER pH, UNDER LABORATORY CONDITIONS. 2.4.1 INTRODUCTION. Reactions between humic materials and sulphides, elemental sulphur or polysulphides were shown to proceed rapidly at high pH (see section 2.2). In the previous section, i t was also argued that such reactions could possibly explain the high sulphur content often reported in humic substances extracted from marine sediments. In an attempt to evaluate further the p l a u s i b i l i t y of these mechanisms, the r e a c t i v i t y of various inorganic reduced sulphur species was tested at seawater pH. 86 2.4.2 METHODS. Humic acids, previously extracted from an oxic marine sediment, were dispersed in d i s t i l l e d water and neutralized to pH 8.2 with Na 2C0 3 u n t i l the pH s t a b i l i z e d for at least 12 hrs. The c o l l o i d a l solution was then divided into four portions. One portion was kept as a control while 0.63mmol/l S g, 1.6mmol/l HS (pH 8.2) and 0.63mmol/l S g + 1.6mmol/l HS~ (pH8.2) respectively, were added to the three others. After having been kept under nitrogen for I8hrs, the humic acids were reprecipitated at pH2, under a stream of nitrogen. The samples were then freeze-dried and the elemental sulphur exhaustively extracted with benzene before proceeding with their elemental analysis. 2.4.3 RESULTS AND DISCUSSION. The elemental composition of the humic materials obtained after these treatments i s shown in Table 18. As expected, at seawater pH, the reactions proceed at lower rates. . However, an appreciable S enrichment was s t i l l observed in the presence of H2S and polysulphides, even within the r e l a t i v e l y short period of I8hrs. In contrast, elemental sulphur did not react to any s i g n i f i c a n t extent within the short time span studied. This experiment further supports the view that HS~, formed in marine sediments by sulphate-reducing bacteria, or 87 Table 18. Sulphur enrichment of humic acids by various sulphur species after 18 hours of contact at seawater pH (8.2). Wt% HA C S S/C HA control 39 .6 + 0. 5 1 .15+0 .03 0 .029+0. 001 HA + elemental sulphur 41 .0 + 0. 5 1 .15 + 0 .03 0 .028+0. 001 HA + sulphides 41 .8 + 0. 5 1 .53 + 0 .04 0 .037+0. 001 HA + polysulphides 42 .3 + 0. 5 1 .46 + 0 .04 0 .035+0. 001 1.Not ash corrected. 88 polysulphides produced as an intermediate in oxidation of HS , are the main sulphur species responsible for the sulphur enrichment of humic substances during early diagenesis. On the other hand, elemental sulphur i s r e l a t i v e l y inert under these conditions. These conclusions are in agreement with the work of Mango (1983). 2.5 INFLUENCE OF S ENRICHMENT ON THE COMPLEXING CAPACITY OF HUMIC MATERIALS. 2.5.1 INTRODUCTION. Humic substances can be viewed as a system of competing ligands, each of which w i l l have d i f f e r e n t a f f i n i t i e s for d i f f e r e n t metals. Ligands (or Lewis bases) are molecules or anions containing at least one free pair of electrons. On the other hand, metal ions (or Lewis acids) contain at least one vacant o r b i t a l which can accommodate an electron pair and thus can form coordination compounds or complexes with ligands. These bonds can be mainly e l e c t r o s t a t i c , mainly covalent or intermediate in character. When one me.tal ion combines with one ligand, they form a unidentate complex. However, most metal ions are able to coordinate several ligands simultaneously. Therefore, i f a ligand molecule contains several electron-donor atoms, multidentate complexes, also c a l l e d 89 Table 19. Unidentate ligands l i k e l y to be found in humic mater i a l s . Oxygen f u n c t i o n a l i t i e s alcohols,phenols, ethers "0- alkoxide, phenoxide ions "o2c- carboxylate ions :0=C^ aldehydes, ketones, esters Nitrogen f u n c t i o n a l i t i e s •N- amines ~< amide ions :N=CV Imines, oximes, unsat. heterocycles Sulphur f u n c t i o n a l i t i e s *s- t h i o l a t e , thiophenolate ions :s=c\ thiocarbonyls Halogen f u n c t i o n a l i t i e s :X- a l k y l , a r y l halides 90 chelates, can be formed. As a rule, chelates have a higher s t a b i l i t y constant than monodentate complexes, and they have been often invoked to explain the high a f f i n i t y of humic substances for certain metals. A l i s t of unidentate ligands l i k e l y to be found in humic materials i s shown in Table 19. Some examples of possible bidentate ligands are also shown in Table 20. Each ligand has a d i f f e r e n t a f f i n i t y for di f f e r e n t metals. Summing up the experimental information available on complex s t a b i l i t y , Pearson (1968) concluded that hard acids prefer to bind to hard bases and soft acids prefer to bind to soft bases. Hard acids are those electron-acceptors with a high ionic charge. They have the electron configuration of an inert gas and their valence s h e l l is of low p o l a r i z a b i 1 i t y . They correspond to the "class-a" metals of Ahrland et a l . (1958), and w i l l react mainly with O-containing groups (known as hard bases) and to a lesser extent with N-containing groups. The bonds so produced w i l l be mainly electrovalent in character, which means that the s t a b i l i t y of these complexes w i l l increase with the ionic charge of these metals. Metals of t h i s type w i l l include the a l k a l i s , the alka l i n e earths, the lanthanides, the actinides and Al (Fig. 14). On the other hand, soft acids (or "class-b" metals) are electron-acceptors of r e l a t i v e l y large atomic size, i . e . with a low ionic charge. They also possess unshared electron pairs in p or d o r b i t a l s or their hybrids in their valence s h e l l s . These valence sh e l l s w i l l be highly polarizable and w i l l form bonds with a 91 Table 20. Some examples of bidentate ligands possibly present in humic materials (after Houghton, 1979). 92 '/./.- De Na M g Cs^'Ba ^ La •Fr - Ra ^ A c Ji V \ Cr^-Mri^ Fe 'Co ^Ni >CuA;Zn Zr Nb M o Tc Ru Hf Ta W Re Os : Rh~P6-Ag [Cdy In\Srt<S6" _ | r — Pt -A'u -'Hg =J\-^Pb±:Q\= Po At Rn Te / Xe Lanthanides C Z J Class A I ~ i Qorderhne f==^ Class B . C e -/ / Nd ' ' / ^ ' P m - S m T b ^ D y - ' H o ' " E r " W L u " r . x / Pa "u • ^ N p ^ P u ' ' A m " C m ' B k ^ C f ' Es F m ' M d ' Li'. Act in ides F i g . 14: The periodic table of the elements showing the d i s t r i b u t i o n of the "class-a", "borderline" and "class-b" metal and metalloid ions (after Nieboer and Richardson, 1980). 93 highly covalent character. "Class-b" metals w i l l form p a r t i c u l a r l y stable complexes with donor-atoms from the t h i r d period ( i . e . P, S, and C l ) , primarily because of the p o s s i b i l i t y of forming T|-bonds with the unshared electron pair of the metals and empty d-orbitals of the donors (Ahrland, 1966). Such bonds are not possible with the elements of the second period ( i . e . N, 0, and F) because their valence o r b i t a l s are at a much higher energy l e v e l than the 3d o r b i t a l s . "Class-b" w i l l be t r a n s i t i o n metal ions with t y p i c a l l y 8 to 10 electrons in their valence s h e l l s . In the periodic table, they occupy a triangular zone to the right of the t r a n s i t i o n series (Fig. 14). In sea water, their speciation may be dominated by chloro-complexes (Martin and Whitfield, 1983). The change from "class-a" to "class-b" character is gradual, since i t is controlled by the electron configuration of the elements and there i s no well- defined boundary between the two types of metals. It i s convenient, therefore, to distinguish in the periodic table a borderline zone (Fig. 14) which w i l l encompass many of the t r a n s i t i o n elements of interest in environmental chemistry. These elements w i l l have properties intermediate between "class-a" and "class-b". Their "class-b" character w i l l increase as their d-orbitals f i l l up ( i . e . their "class-b" character w i l l increase upon reduction). Their s e l e c t i v i t y for soft bases w i l l not be as marked so that they w i l l also strongly interact with hard bases, and p a r t i c u l a r l y with N-containing groups (Nieboer and Richardson, 94 1980). Also, in sea water, their chloro-complexes w i l l be less dominant than for the s t r i c t l y "class-b" metals. Humic substances are p o t e n t i a l l y important metal complexers and such associations have often been implied to explain discrepancies between observed and predicted metal behaviour in natural systems. As shown in Table 19, humic polymers contain a variety of complexing f u n c t i o n a l i t i e s (soft and hard bases) which w i l l readily form unidentate coordination compounds with metal ions in aqueous solutions. If these ligand groups are positioned in an appropriate s t e r i c configuration, multidentate complexes could also be formed. Extensive studies of the structure of t e r r e s t r i a l humic substances by a variety of independent techniques have shown that many of their properties are determined by the presence of carboxyl and phenolic functional groups. Schnitzer and Skinner (1965) noted a sharp decrease in the complexing capacity of p u r i f i e d s o i l humic acids after chemically blocking these f u n c t i o n a l i t i e s . Oxidative degradation studies also suggest that many of the "building blocks" of t e r r e s t r i a l humic substances consist of carboxylic and phenolic groups in the ortho position on a benzene ring (e.g. Schnitzer, 1978). It has therefore been generally accepted that the complexing capacity of t e r r e s t i a l humic substances is the result of interactions between such groups and metal ions (Fig. 15). Recently, an ESR study (Boyd et 95 \ .-oo J-0H + M 2+ ; » — \ 9 -c-o N M H -0 , Q \-c-o-'-C-0H + M 2+ ^ ^ : , 0 Vc-G\ J-c-o" 0 M H F i g . 15: Chelate formation between o-hydroxycarboxylic a c i d s , o - d i c a r b o x y l i c acids and d i v a l e n t metal i o n s . 96 a ++ a l . , 1981 ) supported th i s conclusion by showing that Cu forms two equatorial bonds in c i s - p o s i t i o n with oxygen atoms of humic acids. This model is also consistent with the I.R. spectra of C u + + and F e + + + humates (Boyd et a l . , 1981^) and with the release of one, otherwise untitratable, H + from f u l v i c acids upon addition of C u + + (Beckwith, 1959; Gamble et a l . , 1970; Van Dijk, 1971). Therefore, when saturated with a given metal, humic substances w i l l form coordination compounds with carboxylic and phenolic groups. Other O-containing functional groups, such as conjugated ketonic structures and quinone groups could also play a s i g n i f i c a n t role in metal complexation (Piccolo and Stevenson, 1981; Stevenson, 1985). On the other hand, the influence of N and S-containing functional groups is generally believed to be minor, although their potential as complexing s i t e s i s recognized (e.g. Malcolm, 1985). Whether or not humic polymers w i l l form chelates with metal ions w i l l depend on the occurrence of o-hydroxycarboxylic acids or similar s t e r i c a l l y appropriate moieties. That such groups are a main component of s o i l organic matter seems well established. On the other hand, humic materials from marine environments display a much more a l i p h a t i c character (Stuermer and Payne, 1976; Stuermer et a l . , 1978; Hatcher et a l . , 1980), have a lower t o t a l a c i d i t y ( p a r t i c u l a r l y phenolic a c i d i t y ) (Vandenbroucke et a l . , 1985) and also are enriched in N and S r e l a t i v e to their t e r r e s t r i a l counterparts (Nissenbaum and Kaplan, 1972; Stuermer et a l . , 1978). Considering these factors, 97 and also in the l i g h t of Ahrland's c l a s s i f i c a t i o n of metals, i t may not be true that in marine environments, O-containing f u n c t i o n a l i t i e s w i l l have the overriding importance which has been attributed to them for the complexing of t r a n s i t i o n metals in t e r r e s t i a l environments. In sea water, and p a r t i c u l a r l y when the DOC is low, the t r a n s i t i o n metals must compete with Mg + + and C a + + at concentrations orders of magnitude higher than their own. Therefore, in order to be complexed, these metals w i l l have to react with ligands having a very high degree of s p e c i f i c i t y for them. The degree of s p e c i f i c i t y w i l l be more important than the degree of s t a b i l i t y of the complexes so formed, i . e . even less stable unidentate complexes, highly s p e c i f i c to t r a n s i t i o n metals, w i l l be much more important for trace metal speciation in sea water than more stable but less s p e c i f i c chelates. C a + + and Mg + + are t y p i c a l "class-a" metal's and therefore w i l l react p r e f e r e n t i a l l y with O-containing groups. Transition elements, as borderline metals, w i l l also have strong a f f i n i t i e s for 0-containing groups and the s t a b i l i t y constant of their complexes are in many cases higher than for C a + + and Mg + +. However, the difference in the s t a b i l i t y constants of these two classes of metals for O-containing groups may not be large enough to override the concentration e f f e c t . Thermodynamic calculations tend to support t h i s view (e.g. Mantoura et a l . , 1978). Nevertheless, many independent experimental studies have 98 i n d i r e c t l y demonstrated the existence of organo-metallic compounds in sea water (e.g. Mantoura, 1981). This contradiction may be understood by considering the complexing a b i l i t i e s of N-and S-containing groups present in marine humic polymers. Ca ++ and Mg + + w i l l only form r e l a t i v e l y l a b i l e complexes with such functional groups which w i l l have a much higher s e l e c t i v i t y for tr a n s i t i o n and "class-b" metals. This phenomenon i s well i l l u s t r a t e d in F i g . 16 where the s t a b i l i t y constants of a series of bivalent metals with various 0, N, and S-containing groups of similar s t e r i c configuration are shown (Sigel and McCormick, 1970). B a + + , S r + + , C a + + , and Mg + + are t y p i c a l "class-a" metals, but of decreasing "class-a" character (in the order given), while the series from Mn to Zn (also known as the Irving-Williams series) corresponds to the second half of the f i r s t t r a n s i t i o n period, with increasing "class-b" character (although s t i l l "borderline") from Mn + + to C u + + and a decrease in "class-b" character for Z n + + . The much higher s p e c i f i c i t y of amine and t h i o l groups for t r a n s i t i o n metals i s c l e a r l y shown. Si m i l a r l y , one could speculate that most complexed bivalent t r a n s i t i o n metals with a predominant "class-b" character w i l l be found in sea water associated with S- and N-contaming groups, while Ca , Mg + + and A l + + + w i l l saturate O-containing groups. Trace metals with a predominant "class-a" character, such as Mn and Fe, w i l l not be organically-bound to a s i g n i f i c a n t extent, while the speciation of "class-b" metals (e.g. Hg + +, Pb + +, Cu +) w i l l be the 99 I F i g . 16: Logarithms of the s t a b i l i t y c o n s t a n t | f o r the 1:l +complexes between Ba through Zn and the bidentate l i g a n d s o x a l i c a c i d , g l y c i n e , ethylenediamine, mercaptoacetic a c i d , and mercaptoethylamine ( a f t e r S i g e l and Mccormick, 1970). 100 result of competition between Cl and organic sulphur or s i m i l a r l y soft organic bases. From the above discussion, i t can be concluded that sulphur enrichment in humic materials could have a s i g n i f i c a n t influence on their complexing capacities with respect to t r a n s i t i o n and "class-b" metals. As a preliminary experiment to test t h i s hypothesis, the influence of sulphur-enrichment on the formation of non a c i d - l a b i l e Cu + +-humic complexes was investigated. 2.5.2 METHODS. An outline of the procedure followed is presented in F i g . 17. One hundred mg of a humic acid extracted from a podzolic s o i l was dispersed in 0.1N HC1/0.3N HF for I8hrs to decrease i t s ash content. After centrifugation and thorough rinsing, i t was re-dispersed in deionized water and brought to pH 7.8 with NaOH and l e f t overnight to e q u i l i b r a t e . The dissolved materials were recovered by f i l t r a t i o n (on 0.45>um Nucleopore f i l t e r s ) , 0.5N NaOH was added to the solution under nitrogen and then i t was divided into two portions. 25-30 mmol/1 Na 2S was added to one of the portions, while the other was kept as a control. After standing for 40hrs, the solutions were a c i d i f i e d to pH~2, with HC1 and the excess H 2S driven off with nitrogen. The preci p i t a t e d humic materials were centrifuged and rinsed with de-aerated deionized water and re-dissolved at pH 7.5-8. Ten mg C u + + (as 10ml of a 101 Humic a c i d s e x t r a c t e d from p o d z o l i c s o i l I d i s p e r s e d i n 0.3N HF/0.1N HC1 (18hrs) I c e n t r . & r i n s e d I brought t o pH7.8 (with c h e l e x - c l e a n e d NaOH) l e f t o v e r n i g h t f i l t e r e d through 0.45um I f i l t r a t e + NaOH (0.5N) I i n s o l . d i s c a r d e d +25-30mmol/l S~ 40hrs, under N_ I c e n t r . & r i n s e (with de-aerated d e i o n i z e d water) I 40hrs, under N 2 • J * I c e n t r . & r i n s e r e - d i s s o l v e d a t pH 7.5-8 +10ml lOOOppm Cu i n 0.3N HNO, e q u i l i b r a t e f o r 18hrs • J * I c e n t r . & decant I wash with 0.1N HCl, ~2hrs, 2X I r e - d i s s o l v e d i n "Chelex"cleaned 0.5N NaOH I r e - p r e c i p i t a t e d w i t h HC1 I r i n s e w i t h 0.1N HCl (2X) I r e - d i s s o l v e d i n 10ml 0.5N NaOH (Chelex-cleaned) I d e t e r m i n a t i o n of C & Cu c o n c e n t r a t i o n s I r e - p r e c i p i t a t e d w i t h HCl c e n t r . I f r e e z e - d r i e d I C & S a n a l y s i s 17: Procedure f o l l o w e d i n the experiment on the i n f l u e n c e of S-enrichment on the Cu r e t e n t i o n of humic substances. 102 1000ppm solution in 0.3N HNO^) were added and l e f t to equilibrate for 18 hrs. After measuring the pH of e q u i l i b r a t i o n (pH 6 and pH 6.3 for the S-enriched material and the control, respectively), a few. drops of HC1 were added and the precipitated material was centrifuged and washed thoroughly with 0.1N HC1. The recovered material was then f i n a l l y dissolved in 0.5N NaOH and the DOC and Cu concentration of this solution was measured. DOC was determined following the procedure explained in Appendix II. The Cu concentration was measured by d i r e c t injection on a graphite furnace atomic absorption spectrometer, after appropriate d i l u t i o n in d i s t i l l e d and deionized water, (precision: +4%). Subsequently, the humic acids were re-precipitated, freeze-dried, and t h e i r sulphur and carbon contents measured (see appendix I I ) . 2.5.3 RESULTS AND DISCUSSION. It can be seen that upon sulphur enrichment, much more Cu was retained by the humic material after thorough washing in acid (Table 21). This i s consistent with the hypothesis that S f u n c t i o n a l i t i e s can provide binding sites for t r a n s i t i o n metals with a predominantly "class-b" character from which they w i l l be d i f f i c u l t to displace. An increment of 7.6 x 10 gr-at.S/gr-at.C produced an increase in retained Cu of 0.61 x 10 gr-at.Cu/gr-at.C. This corresponds to the binding of 0.08 gr-at.Cu/gr-at.S or 0.16 1 03 Table 21. Influence of S enrichment on the Cu retention of acid-washed t e r r e s t r i a l humic materials. Wt% HA atomic r a t i o s (10~ 3) Samples %C %S %Cu S/C Cu/C humic acids 51.4 0.33 0.25 2.37+0.08 0.93+0.05 S enriched 48.0 1.28 0.39 9.99+0.35 1.53+0.08 humic acids 104 gCu/gC. If we assume that the same Cu/S r e l a t i o n s h i p holds for the i n i t i a l humic material used in t h i s experiment ( i . e . containing 0.325% S), i t can be calculated that 0.052% ( i . e . 0.325% X 0.16) of the Cu bound to the non S-enriched humic material after acid washing was bound to S f u n c t i o n a l i t i e s . This amounts to ~20% of the t o t a l Cu which was retained under these conditions, assuming that the sulphur added by reaction with HS is of the same chemical nature as the sulphur i n i t i a l l y present. This shows the p o t e n t i a l of S as a binding s i t e for Cu, even in the case of t e r r e s t r i a l humic materials which are t y p i c a l l y low in t h i s type of ligand. One would expect the influence of S f u n c t i o n a l i t i e s to be much more pronounced for marine organic matter and p a r t i c u l a r l y for sedimentary humic materials which can become enriched in sulphur during early diagenesis. In many instances, various trace metals have been found in sulphidic pore waters at concentrations which greatly exceed the values expected from the s o l u b i l i t y of their sulphides (Brooks et a l . , 1968; Presley et a l . , 1972; E l d e r f i e l d and Hepworth, 1985). Here also, thermodynamic calculations would indicate that amino-acids and hydroxycarboxylic acids ( i . e . hard bases) would not be able to maintain the concentrations of metals in sulphidic waters which are generally observed (Gardner, 1974). Instead, such calculations strongly suggest that bisulphide and polysulphide anions ( i . e . soft bases) w i l l be the main agent for trace metal s o l u b i l i t y . Nevertheless, a d i r e c t association between organic 105 polymers and various t r a n s i t i o n metals in sulphide-bearing i n t e r s t i t i a l waters has been reported (Nissenbaum and Swaine, 1976; E l d e r f i e l d , 1981). Organic sulphur f u n c t i o n a l i t i e s may be involved in thi s association and further study of their role may help solve t h i s apparent contradiction. Copper is often the t r a n s i t i o n metal found most closely associated with organic matter. Although t h i s i s consistent with i t s greater "class-b" character, there are also indications that i t s redox properties may be d i r e c t l y involved in i t s behaviour. It has been demonstrated that Cu(II) can be rapidly reduced by a h e a t - k i l l e d suspension of E^ c o l i , and solutions of cystein or alcohol dehydrogenase, under anaerobic conditions (McBrien, 1980). Since such reduction does not occur when the c e l l extract or the protein solutions are pre-treated with a reagent blocking t h i o l groups (N-ethylmaleimide), i t has been concluded that C u + + could be reduced by sulphydryl groups, v iz 2 C u + + + 2 R-SH > R-S-S-R + 2 Cu + + 2 H + Cu + i s very unstable under oxic conditions and oxidizes readily according to , viz „ + „ ++ „ -Cu + CU > Cu + 0„ 106 thus producing superoxide r a d i c a l s (Moffet and Zika, 1983; Wong et a l . , 1984). However, in the absence of or F e + + + , Cu + i s stable and can react with organic matter. Upon reduction, the "class-b" character of Cu, and therefore i t s a b i l i t y to -form coordination compounds with soft bases, increases. Consequently, the l i k e l i h o o d of finding Cu in close association with t h i o l groups i s also increased. The a b i l i t y of C u + + to displace other metals (such as C d + + and Zn + +) from S-containing proteins (metallothioneins) i s well documented (e.g. Suzuki and Maitani, 1981). Such displacement i s also accompanied by a disappearance of the ESR signal of ++ . . . + paramagnetic Cu ions, presumably due to their reduction to Cu , which i s diamagnetic and therefore ESR-inactive (McBrien, 1980). It has therefore been argued that, under anoxic conditions, C u + + i s able to oxidize t h i o l groups and the Cu + so produced readily forms complexes with the remaining sulphydryl f u n c t i o n a l i t i e s , d i s p l a c i n g other metals (with a lesser "class-b" character) which could have been previously complexed by them (Fig. 18). Considering the . high sulphur content of sedimentary organic matter, such a mechanism could conceivably be very important for the speciation of Cu in suboxic and anoxic pore waters. 107 -S-Zn(II) -SH -SH + CU ++ > -S-Cu(I) -S I - s Zn ++ P i g , 18: Reaction between Cu and S-containing p r o t e i n s under anoxic c o n d i t i o n s . 1 nfl 3. THE INFLUENCE OF HUMIC SUBSTANCES ON THE GEOCHEMISTRY OF IODINE IN NEARSHORE AND HEMIPELAGIC MARINE SEDIMENTS. 3.1 INTRODUCTION. The work of Vinogradov (1939), Shishkina and Pavlova (1965), Price et a l . (1970), Bojanowski and Paslawska (1970), Pedersen and Price (1980), Wakefield and E l d e r f i e l d (1985), and Kennedy and E l d e r f i e l d (1987) appears to demonstrate that the geochemistry of iodine in marine sediments is controlled almost e n t i r e l y by i t s association with organic matter. This association i s quite complex because the 1 / c o r g r a t i o s of dif f e r e n t deposits vary with the redox conditions p r e v a i l i n g during deposition, and with the source and therefore the nature of the organic matter present. Thus, Price and Calvert (1973, 1977) showed that oxic s u r f i c i a l sediments had higher concentrations of iodine and higher I/C Q rg ratios than anoxic sediments from the same area, and Malcolm and Price (1984) showed that in nearshore environments where input of t e r r e s t r i a l organic matter can be substantial, the I content was higher where the organic matter was predominantly of planktonic o r i g i n . In oxygenated nearshore environments, both the iodine content and l/C„„„ r a t i o often decrease with depth from variable org 1 09 surface values to those t y p i c a l l y found in sediments that are ent i r e l y anoxic, where no I or I/C gradients are found (Price et a l . , 1970; Price and Calvert, 1973). This has been explained by the p r e f e r e n t i a l diagenetic release of iodine from the buried organic matter. Observations of the d i s t r i b u t i o n of dissolved iodine in the pore waters of marine sediments (Pedersen and Price, 1980; E l d e r f i e l d et a l . , 1981) and the experimental results of Ullman and A l l e r (1983), which showed that more iodine r e l a t i v e to carbon was released from sediments, e s p e c i a l l y when s u r f i c i a l oxic sediments were incubated under anoxic conditions, are consistent with t h i s general scheme. Hence, iodine i s evidently enriched by some mechanism in s u r f i c i a l oxic sediments and/or s e t t l i n g particulate materials, and p a r t i a l l y l o s t when these same sediments are buried under anoxic conditions. Price and Calvert (1973, 1977) proposed that the surface enrichment of I in oxic sediments was due to the adsorption of iodide by planktonic tripton at the sediment/water interface via reactions similar to the uptake of iodide by marine algae. This uptake i s mediated by an enzyme (iodide-oxidase) which i s active only in oxygenated conditions (Shaw, 1962). This p o s s i b i l i t y has recently been supported by Malcolm and Price (1984) who showed that plankton scavenge iodine from seawater under oxygenated conditions but not under oxygen-free conditions. Furthermore, because decaying plankton adsorbed more iodine than fresh plankton, these authors suggested that t h i s scavenging could be 110 the result of b a c t e r i a l uptake rather than dire c t adsorption by plankton debris. An alternative explanation for the surface enrichment of I in terrigenous, nearshore marine sediments has recently been proposed by Ullman and A l l e r (1985). They argued that i t was mainly due to the adsorption of iodate by Fe oxyhydroxides precipitated at the surface of oxic sediments as a result of diagenetic remobilization. They reached their conclusion from the observation that there was no s u r f i c i a l iodine enrichment in the upper horizon of a Fe-poor, calcareous sediment. This mechanism was consistent with laboratory experiments demonstrating the well-known scavenging a b i l i t i e s of Fe oxides for iodate (Sugawara et a l . , 1958; Whitehead, 1974; Music et a l . , 1980; Ullman and A l l e r , 1985). The decrease in I/C r a t i o with depth would then org r r e f l e c t the reductive d i s s o l u t i o n of Fe oxyhydroxides upon b u r i a l with simultaneous release of the adsorbed iodine to the pore waters. In the present study, a t h i r d mechanism is proposed to account both for the s u r f i c i a l iodine enrichment in oxic sediments and i t s release from the sediment during b u r i a l , based on observations of the p a r t i t i o n i n g of iodine in marine sediments and on laboratory experiments on the uptake and release of iodine by and from sedimentary organic matter. 1 1 1 3.2 MATERIALS A variety of sediments, showing variable iodine enrichments, was selected for study. A bulk hemipelagic sediment sample (HUD 22) was coll e c t e d from the top ~8cm of a box-core raised from the Eastern Subtropical P a c i f i c at 20°53.6' N, 109°12.8' W in 2768m water depth. Nearshore organic-rich, fine-grained muds were recovered by gravity coring and by grab sampling from two well-flushed B.C. fjords (Hastings Arm, Je r v i s Inlet) in water depths ranging from 200m to 600m. Pore waters were extracted by centrifugation following sediment extrusion under a nitrogen atmosphere, and the solid-phase samples were preserved frozen. 3.3 METHODS. 3.3.1 ANALYTICAL METHODS. The d e t a i l s of the a n a l y t i c a l methods used are given in Appendix I I . 3.3.2 EXPERIMENTAL METHODS. 3.3.2.1 PARTITIONING OF IODINE IN SEDIMENTS. 3.3.2.1.1 OXYHYDROXIDE PHASE. Duplicate subsamples of dried sediment (8g) were treated with 250 ml of hydroxylamine hydrochloride/acetic acid for 4 h at room temperature, following the method described by Chester and 112 Hughes (1967). Total iodine was measured in the sediment residue, and that fracti o n of the I associated with the oxyhydroxide phases was estimated from the difference between the untreated and treated sediment values. Allowance was made for the loss of weight during treatment. The possible re-adsorption of iodine released during the reduction step was checked by duplicating the hydroxylamine treatment in the presence of resorcinol (see text for explanations). The amounts of oxyhydroxides s o l u b i l i z e d were estimated from the Fe and Mn concentrations in the leachate as measured by atomic absorption spectrophotometry. Precisions were + 3% (10", n = 1 1 ) and +4.5% (10", n=l3) for Fe and Mn respectively. 3.3.2.1.2 HUMIC MATERIALS Humic substances were extracted from the sediments by 0.5N NaOH under nitrogen (Appendix I I ) . Iodine and carbon were measured in the humic extracts (Appendix II) and on the sediment residue by the same techniques as those used for bulk sediments, making allowance for the change in weight due to the extraction. 3.3.2.2 UPTAKE OF IODINE BY HUMIC SUBSTANCES. 3.3.2.2.1 PRELIMINARY EXPERIMENT: Freeze-dried humic substances with a known I/C r a t i o were dispersed in 100 ml of f i l t e r e d seawater spiked with either 1 mmol/1 KI or 1 mmol/1 KJOg for 4 days under oxygenated conditions. After f i l t r a t i o n and thorough rinsing with deionized water, they were freeze-dried and their I/C r a t i o re-measured. 1 13 3.3.2.2.2 REACTION BETWEEN HUMIC SUBSTANCES AND IODATE: Two samples of f i n e l y ground humic material (0.2g dry weight) were dispersed in 10 ml d i s t i l l e d water (pH 2.5-3) spiked with 2.5 mmol/1 K I 0 3 and kept in suspension by continuous s t i r r i n g . To one sample, 2.5 mmol/1 of resorcinol was added. The two samples were shaken in the dark for I8h. The humic material was then recovered by centrifugation and rinsed with d i s t i l l e d water. A control, comprising 2.5 mmol/1 KIO^ and resorcinol, brought to pH 2.5-3 but without humic materials, was treated in a similar way. The samples containing resorcinol were extracted with ethyl acetate and the extracts were checked for the presence of iodinated resorcinol compounds by thin layer chromatography on Si02. A developing solvent mixture containing 80% chloroform and 20% ethyl acetate was found to give the best separation between resorcinol and i t s iodinated derivatives. The i d e n t i f i c a t i o n of the resorcinol derivatives was confirmed by mass spectrometry. A similar experiment was performed at pH 7.5-8. In this case, 0.3 g of humic material was dispersed in 100 ml of d i s t i l l e d water and brought to pH 8 with Na^O^ before adding the potassium iodate (2.5 mmol/1). The humic solution was l e f t to stand for 5 days and then dialysed against deionized water u n t i l the dialyzate was free of iodate. Iodate was detected by adding iodide and H + to an aliquot of the dialyzate and scanning for the presence of 1^ on a spectrophotometer. The dissolved organic carbon and iodine were then determined as explained above. 1 14 3.3.2.2.3 RELEASE OF IODINE FROM HUMIC SUBSTANCES. Humic substances, previously enriched in iodine by reaction with iodate at pH 3.4, were re-dispersed in f i l t e r e d , oxygen-free seawater spiked with either 12-15 mmol/1 sulphide (pH 8.0) or 5 mmol/1 Na 2S 202 (pH 7.0), and kept for 56 h in a tight container before re-measuring their iodine content. The humic substances extracted from HUD 22 were brought to pH 8.5 with HC1, and the c o l l o i d a l extract was divided in two portions. 15-20mmol/l sulphide (as Na 2S neutralized to pH8) was added to one half only, and both portions were kept for 4 days, under nitrogen, in tight containers. Subsequently, they were dialysed against deionized water and their I/C r a t i o re-determined as before. 3.4 RESULTS AND DISCUSSION. 3.4.1 THE PARTITIONING OF IODINE IN MARINE SEDIMENTS. The d i s t r i b u t i o n of I between the oxyhydroxide and organic phases of a marine sediment was evaluated by carrying out a simple leaching experiment on the hemipelagic sediment HUD 22. This sediment shows the common s u r f i c i a l I enrichment, a decrease in the I/C r a t i o with depth, and contains a moderate amount org of free oxyhydroxide (Fig. 19; Pedersen et a l . , 1986). This 1 15 l/CorgOO"4) Mn wt% 0 100 200 300 0 0.3 0.6 0.9 1.2 0.7 08 0.9 Fe/Al F i g . 19: I / C 0 r g ' F e / A 1 a n d M n p r o f i l e s of the hemipelagic sediment core (HUD 22) r a i s e d from a depth of 2768 m at 20°53.6' N, l O ^ l ^ . B 1 W ( a l l data from Pedersen et a l . f 1986). 116 experiment was done on a bulk surface sample. Its relevant chemical c h a r a c t e r i s t i c s are shown in Table 22. 3.4.1.1 OXYHYDROXIDES. During the reaction of the sediment with hydroxylamine, any IO^ released from the oxyhydroxide phase would be readily reduced to I , possibly via I 2 or HOI intermediates, which could react with sedimentary organic compounds. It was therefore necessary to check the possible re-adsorption of iodine released during the reduction step. This was done by adding resorcinol to the hydroxylamine solution. This compound has a very strong a f f i n i t y for e l e c t r o p h i l i c iodine (e.g. Fawcett and Kirkwood, 1953a) and should compete successfully with an e l e c t r o p h i l i c addition of iodine on sedimentary organic matter. If such a reaction was occurring to any s i g n i f i c a n t extent, the presence of a large excess of resorcinol should largely i n h i b i t i t and comparatively more iodine should be extracted. The presence of e l e c t r o p h i l i c iodine species could also be confirmed by the formation of soluble iodinated resorcinol compounds in the hydroxylamine extract. The s t a b i l i t y of these compounds in the acidic/reducing solution was checked over a period of 6 h by thin layer chromatography. No sign of decomposition was observed over this period. When the sediment sample was treated with hydroxylamine in the presence of 80 ;umol/l of re s o r c i n o l , centrifuged, and the supernatant extracted with ethyl acetate, thin layer chromatography of the ethyl acetate extract f a i l e d to 1 17 Table 22: Chemical composition of HUD 22 (bulk surface sample). C o r g ( % ) 1 .61+0.02 I (ppm) 470+18 ^ o r g ( 1 0 " 4 ) 292+12 Fe (%) 6.87+0.06 Mn (%) 0.62+0.01 118 show the presence of iodinated resorcinol thereby indicating that the reduction of iodate into an e l e c t r o p h i l i c species was minimal. Moreover, there were no differences between the amount of iodine extracted either in the presence of a large excess (0.5 mole/1) or without resorcinol (Table 23), thus confirming that reduction/re-adsorption of released iodate was not important. Table 23 also shows that only 13 + 5% of the t o t a l sedimentary iodine i s released by the combined acid-reducing treatment. If we assume that a l l the iodine released during t h i s treatment comes from the s o l u b i l i z e d oxyhydroxide phase, i t can be shown that the iodine concentration in t h i s phase should have been ~3500 ppm. However, i t i s not known i f t h i s iodine comes only from the oxyhydroxide phase or i f some was released from l a b i l e organic matter. Therefore, although the iodine concentration in the oxyhydroxides could be r e l a t i v e l y high, in accordance with their scavenging a b i l i t i e s for iodate (e.g. Sugawara et a l . , 1958), t h i s phase seems to be only of secondary importance for the s u r f i c i a l iodine enrichment found in hemipelagic sediments in the eastern Subtropical P a c i f i c . Since these sediments have a well-developed s u r f i c i a l oxide layer (Fig. 19) and do not contain very high concentrations of organic matter, th i s conclusion may be applicable to a wide range of sediments. 119 Table 23: Influence of resorcinol on the extraction of iodine from HUD 22 by hydroxylamine hydrochloride. Sediment Residue Extracted I (ppm) I (ppm)* Fe (%) Mn(%) Without resorcinol 410+16 60+24 0.53 0.53 In the presence of resorcinol (0.5 mol/1) 409+16 61+24 0.59 0.49 * Estimated by difference. 120 3.4.1.2 HUMIC SUBSTANCES. The importance of the organic fractio n was investigated by examining the humic substances from the same sediment. The extraction of the humic substances could not be done on the sediment sample from which the oxyhydroxides had been removed because the presence of hydroxylamine and acetic acid rendered d i f f i c u l t the estimation of the amount of carbon extracted. Therefore, this extraction was performed on a second untreated sediment sub-sample. The results are shown in Table 24. The I/C r a t i o of humic substances was very similar to that of the sediment residue after hydroxylamine treatment (255 x 10 4 ) . Although some of the iodate adsorbed on the oxyhydroxide phase could also have been desorbed by the alkaline treatment, these results would seem to indicate that in the s u r f i c i a l hemipelagic sediment studied here, iodine i s mainly associated with organic matter which could contain as much as 1.25% by weight of iodine. Moreover, this iodine seems to be roughly evenly d i s t r i b u t e d throughout the humified materials (soluble or not in NaOH). These findings are consistent with the data presented by Harvey (1980) who showed that 80% to 90% of the iodine present in marine sediment samples could be released by a 5% NaOCl treatment. The results of the two studies diverge, however, in that Harvey did not find any release of iodine upon NaOH treatment. This discrepancy may be due to the short extraction time (ih) used by t h i s author. 121 Table 24: Extraction of iodine from HUD 22 by 0.5N NaOH (duplicates) Sediment Residue Amount Extracted ^org (%) I(ppm) i/C (10~ 4) org C org (%) I(ppm) 1.10 + .02 314+12 285+12 0.56 + .01 1 40 + 6 250+10 1.10 + .02 309+12 281+12 0.63 + .01 1 54 + 6 244+10 122 3.4.2 ASSOCIATION BETWEEN HUMIC SUBSTANCES AND IODINE DURING EARLY DIAGENESIS. Further d e t a i l s of the association of iodine with humic substances and, in p a r t i c u l a r , the mechanism of the release of iodine from this organic fraction during early diagenesis were obtained by studying a nearshore sediment core (HA-2) recovered from a depth of 190m in Hastings Arm, a f j o r d on the coast of northern B r i t i s h Columbia. Details of the geochemistry of t h i s core are given by Losher (1985), some of which are included in F i g . 20 and 21. The pore water da.ta show that manganese was dissolving within the top 3 cm, and a s u r f i c i a l enrichment of Mn was seen in the s o l i d phase (Fig. 21). This core was therefore oxic only at the sea water/sediment interface and became very rapidly reducing below. Also, the sulphur p r o f i l e in the bulk sediment (Fig. 21) indicates that this element was accumulating within the top 10 cm even though H 2S started to accumulate in pore waters only below 30 cm (Fig. 21). This probably r e f l e c t s the presence of anoxic microenvironments within the suboxic zone (Jorgensen, 1977) and mixing due to bioturbation. Both organic carbon and t o t a l iodine gradually decreased with depth within the upper 25 cm (Fig. 20); the peak at 40-45 cm was probably due to an e r r a t i c input of t e r r e s t r i a l debris, as indicated by substantially higher C o rg/N and lower I/C r a t i o s . The I/C rati o s of humic materials 123 20: Sediment core HA-2: (a) Iodine carbon and C Q r g/N ra t i o p r o f i l e s (C and N data from Losher, 1985). (b) I / c o r g ratios in sediment and extracted humic substances. 124 Mn (ppm) Mn (u.mol/1) S(%) H 2 S (Mmol/1) F i g . 21: Sediment core HA-2: (a) Solid phase - Mn (ppm) and S 2+ (%) p r o f i l e s . (b) pore waters - Mn and H 2S (umol/1) p r o f i l e s ( a l l data from Losher, 1985) . 125 c l o s e l y p a r a l l e l the I/C ratios of the bulk sediment (Fig. 20), thus confirming the involvement of humic substances in the s u r f i c i a l iodine enrichment. A notable difference here, compared to the HUD 22 samples, i s that the humic substances soluble in NaOH under the chosen experimental conditions have a consistently higher I/C ratio than the bulk sediment. This may r e f l e c t the higher s o l u b i l i t y of plankton-derived materials while the t e r r e s t r i a l fraction, mainly composed of woody tissues, would be p r e f e r e n t i a l l y l e f t in the insoluble f r a c t i o n . 3.4.3. EXPERIMENTAL STUDY OF THE UPTAKE AND RELEASE OF IODINE BY SEDIMENTARY HUMIC MATERIALS. The observations made in the f i r s t part of t h i s chapter show that iodine i s indeed associated with the organic f r a c t i o n in two d i f f e r e n t types of marine sediments, and that humic substances possibly play an important role in f i x i n g iodine in s u r f i c i a l sediments. In addition, sulphide anions are thought to react with the organic matter during early diagenesis (Nissenbaum and Kaplan, 1972; Mango, 1983; Chap. 2). Therefore, i f iodinated a l i p h a t i c molecules or other forms of organic iodine susceptible to nucleophilic displacement are present, the p r e f e r e n t i a l release of iodine from the humic matrix at depth could be the result of a reaction similar to: 126 A / 1 + :Nu" —> A / -Nu + I (5) Displacement of iodine by HS , however, i s somewhat sulphidic zone of the sediment i s reached. Therefore, other nucleophiles may play an important role. Sulphate reduction i s known to occur in suboxic and even oxic zones within anoxic microenvironments (e.g. Jorgensen, 1977), so that p a r t i a l l y - o x i d i z e d soluble sulphur compounds could be present as transient species in near-surface sediment horizons. Moreover, i t has been argued that 80 to 95% of the H2S produced in the anoxic zone of nearshore sediments cannot be accounted for by the sulphide precipitated therein (Jorgensen, 1982) and must have been oxidized after transfer to the more oxidized layers by d i f f u s i o n or bioturbation. This should also produce a s i g n i f i c a n t amount of intermediate sulphur compounds. The importance of these processes i s c l e a r l y shown by the presence of r e l a t i v e l y large concentrations of reduced sulphur (elemental sulphur and sulphides) generally found in the suboxic zone of sediments (e.g. F i g . 21), where a s i g n i f i c a n t sulphur-enrichment in the humic materials also occurs (see Chap. 2). Thiosulphate i s such a transient species which can be formed by the oxidation of H 2S (Chen and Morris, 1972; Jorgensen et a l . , 1979; Boulegue et a l . , 1982). It is a strong nucleophile whose a b i l i t y to displace iodine from i t s a l k y l derivatives i s well problematic since the I/C org r a t i o usually decreases before the 127 known (Milligan and Swan, 1962), viz 0 R-I + Na 9SS0, > R-S-SJ-ONa + Na +1 (6) 6 which slowly hydrolyzes to form a t h i o l , v i z R-S-I-ONa + H„0 > R-S-H + HSO ~ + Na + (7) Reaction (6) is known to be quite rapid even at room temperature (Slator, 1905) and to proceed at concentrations in the 100 uM range (Trudinger, 1965; Roy and Trudinger, 1970). Such concentrations have already been measured in the pore waters of anoxic subtidal and s a l t marsh sediments (Boulegue et a l . , 1982; Luther et a l . , 1985). Consequently, some experiments on the adsorption of I by humic substances and on i t s subsequent release were c a r r i e d out to investigate these reactions. For thi s purpose, humic acids extracted from bulk sediment samples coll e c t e d from J e r v i s Inlet were used for a l l experiments. 3.4.3.1 UPTAKE OF IODINE BY HUMIC MATERIALS. Sedimentary humic acids were dispersed in f i l t e r e d sea water spiked with either iodate or iodide. The dispersions were not neutralized and were therefore s l i g h t l y a c i d i c . The results obtained, presented in Table 25, show that, under these conditions, iodate can react to a substantial extent with humic acids while iodide does not produce any measurable enrichment. 128 Table 25: Uptake of iodine by marine sedimentary humic substances. I n i t i a l composition + 1 mmol/1 KI* + 1 mmol/1 KIO * C(%) I(%) I/C(10 4) 49. 3 0 .29 60 + 3 47. 3 0 .26 55 + 3 46. 3 1 .06 229 + 7 * Humic substances were dispersed in 100 ml of spiked, f i l t e r e d seawater for 4 days, under oxygenated conditions. 1 29 The reaction between iodate and humic materials was then tested under environmental pH conditions. A solution of sedimentary humic substances , brought to pH 8, was spiked with iodate and l e f t for 5 days (during t h i s period the pH dropped to 7.4). As shown in Table 26, t h i s treatment also s i g n i f i c a n t l y increased the iodine content of the humic material, thus suggesting that these materials could be involved in the iodine-enrichment observed in s u r f i c i a l oxic marine sediments. 3.4.3.2 INVESTIGATION OF THE MECHANISM OF IODINE UPTAKE BY HUMIC MATERIALS. The reducing properties of humic substances are well established (e.g. Szil&gyi, 1967; 1971; 1973; Szalay and S z i l a g y i , 1967; Alberts et a l . , 1974; Schnidler et a l . , 1976; Wilson and Weber, 1979; Templeton and Chasteen, 1980; Miles and Brezonic, 1981; Sunda et a l . , 1983); consequently ,they could possibly reduce iodate. One possible product of t h i s reduction i s elemental iodine which i s unstable in seawater. It either reacts d i r e c t l y with organic matter (Truesdale, 1974; 1982) or hydrolyzes and produces hypoiodite (Wong, 1980; 1982). At sea water pH, hypoiodite is e s s e n t i a l l y protonated (HOI . H + + 10 K=10 1 1 ) . Hypoiodous acid has a strong e l e c t r o p h i l i c character and would also readily react with organic molecules possessing electron-donor groups. In order to v e r i f y t h i s hypothesis, resorcinol was added 130 Table 26: Uptake of iodine by marine sedimentary humic substances at pH 7.4 - 8 I/COO" 4) I n i t i a l composition 63+4 + 2.5 mmol/1 KIC>3* 142 + 6 * Humic substances (0.3g) were dispersed in 100 ml of spiked, d i s t i l l e d water and brought to pH 8 for 5 days. 131 with iodate to dispersions of f i n e l y ground humic materials. Resorcinol i s a substituted aromatic compound containing two hydroxyl groups in meta-position. The presence of these two electron-donor groups increases the tendency of the aromatic ring to undergo e l e c t r o p h i l i c substitution in para- and ortho-positions, and in the presence of HOI or i t readily forms iodinated resorcinol compounds (e.g. Fawcett and Kirkwood, 1953a) which can be i d e n t i f i e d by thin-layer chromatography (Table 27). Therefore, i f the iodine enrichment of humic substances by iodate is mediated by the reduction/electrophilic attack mechanism postulated above, the presence of resorcinol should compete with the e l e c t r o p h i l i c addition on humics, and two important pieces of information could be obtained. The presence of iodinated resorcinol in the reaction medium would demonstrate that an e l e c t r o p h i l i c iodine species has been produced, and a decrease of the iodine enrichment of humic materials, due to resorcinol competition, would indicate that such e l e c t r o p h i l i c attack i s responsible for the enrichment. Since the reduction of one iodate ion consumes 6 protons, viz I 0 3 ~ + 5e~ + 6H + ? = ^  1/2 1 2 + 3H20 E Q = 1.23V IO,~ + 6e~ + 6H + ^ = a I~ + 3H„0 = 1.08V 3 2 O t h i s ion w i l l be more strongly oxidizing at low pH. Therefore, 132 T a b l e 27: v a l u e s of r e s o r c i n o l and i t s i o d i n a t e d d e r i v a t i v e s d u r i n g T h i n Layer Chromatography on S i 0 2 w i th 80% C H C l 3 / 2 0 % C H 3 C O O C H 2 C H 3 . Compounds 1 R f 2 M o l . w t . 3 Rf ( r e s o r . ) 4 r e s o r c i n o l - 0 . 1 8 1 10 - 0 . 1 8 m o n o - i o d i n a t e d - 0 . 2 5 236 - 0 . 2 5 r e s o r c i n o l d i - i o d i n a t e d - 0 . 4 8 362 - 0 . 4 8 r e s o r c i n o l t r i - i o d i n a t e d - 0 . 5 6 488 - 0 . 5 6 r e s o r c i n o l t r i - i o d i n a t e d -0 .61 488 r e s o r c i n o l 1 - P r e p a r e d by r e a c t i o n between i o d i n e and r e s o r c i n o l in aqueous s o l u t i o n . 2 - Rj = ( d i s t a n c e of t r a v e l of the c o m p o u n d ) / ( d i s t a n c e of t r a v e l of the s o l v e n t f r o n t ) . 3 - M o l e c u l a r weight of the i s o l a t e d compounds determined by mass s p e c t r o m e t r y . 4 - Rf of the compounds produced d u r i n g the r e d u c t i o n of i o d a t e by humic m a t e r i a l s i n the presence of r e s o r c i n o l . 133 the reduction of iodate was f i r s t tested with humic acids dispersed in d i s t i l l e d water at pH 2.5-3.0. The results of t h i s experiment are shown in Tables 27 and 28. Iodinated resorcinol compounds (mainly mono-iodinated, but also some d i - and t r i - i o d i n a t e d forms) were found in the ethyl acetate extract of the humic/iodate/resorcinol dispersion, thus indicating that iodate was reduced to an e l e c t r o p h i l i c iodine species. Also, the s i g n i f i c a n t decrease of iodine addition to the humic matrix when resorcinol was present (Table 28) confirmed that e l e c t r o p h i l i c addition of t h i s reduced species was responsible for the iodine enrichment. The same experiment was also performed at a lower iodate concentration (10 >umol/l 10^ with 2.5 mmol/1 r e s o r c i n o l ) . Although much more d i f f i c u l t to see on the chromatographic plate, traces of mono-iodinated resorcinol were also evident a f t e r 24 h shaking in the dark. In order to i s o l a t e iodinated resorcinol occurring at a few jjmol/1 from 2.5 mmol/1 res o r c i n o l , i t was necessary to do the separation on a preparative plate. I-resorcinol was not separated but was concentrated in the upper part of the resorcinol band. This part of the plate was c a r e f u l l y c o l l e c t e d and eluted with ethyl acetate. This eluate was then re-chromatographed and a f a i n t but unambiguous trace of mono-iodinated resorcinol appeared on top of the s t i l l prominent resorcinol spot. Polyhydroxyphenols are thought to be, at least in part, responsible for the reducing properties of humic materials (e.g. 134 T a b l e 2 8 : I n f l u e n c e o f t h e p r e s e n c e o f r e s o r c i n o l on t h e i o d i n e u p t a k e by h u m i c s u b s t a n c e s a t pH 2 . 5 - 3 . C(%) K%) I / C O O 4 ) I n i t i a l c o m p o s i t i o n 4 0 . 6 0 . 5 4 132+7 + 2 . 5 m m o l / 1 K IC> 3 * 3 8 . 8 1.51 389+13 + 2 . 5 m m o l / 1 K I O * 4 0 . 9 0 . 9 7 294+9 a n d 2 . 5 m m o l / 1 r e s o r c i n o l * H u m i c s u b s t a n c e s ( 0 . 2 g ) w e r e d i s p e r s e d i n 10 m l o f s p i k e d , d i s t i l l e d w a t e r f o r 24 h r s . 135 Templeton and Chasteen, 1980). Thus, resorcinol i t s e l f could bring about the reduction of iodate with subsequent formation of iodinated r e s o r c i n o l . However, when iodate i s reduced in the presence of both humic material and resorcinol at low pH, mono-iodinated resorcinol i s detectable within one hour of reaction, whereas in the absence of humic substances, i t took 24 h to observe the f i r s t appearance of iodinated resorcinol compounds. Clearly, humic materials are responsible for most of the iodate reduction which occurred in the previous experiment. This was confirmed by an independent test in which a humic dispersion spiked with iodate was vigorously mixed with benzene. Within two hours, a pink coloration could be seen in the benzene phase which was i d e n t i f i e d as iodine by i t s absorption spectrum (A m a x = 500 mn; Benesi and Hildebrand, 1949). For the above mechanism to be of any consequence for environmental geochemistry, i t must also occur at higher pH. The reducing power of humic substances increases with pH ( S z i l a g y i , 1973; Wilson and Weber, 1979). This i s thought to be due to the involvement of semiquinone r a d i c a l s . However, because of the consumption of protons during iodate reduction, i t becomes increasingly d i f f i c u l t to reduce iodate as the-pH increases. The redox potential of an equimolar solution .of iodate and iodine drops from 1.23V to 0.75V between pH 0 and 8. Likewise, the redox potential of an equimolar solution of iodate and iodide f a l l s from 1.08V to 0.6V. The Eh at pH 0 of humic materials in water 136 has been estimated to be 0.5V (for a dispersion of peat-derived humic acids; S z i l a g y i , 1973) and 0.7V (for a solution of s o i l -derived f u l v i c acids; Wilson and Weber, 1979). If we take these values as being t y p i c a l of humified materials, i t follows that as their Eh decreases with increasing pH to reach values lower than 0.5V at pH8, the reduction of iodate would s t i l l be thermodynamically possible under environmental conditions. Consequently, resorcinol was again used as a means of showing that the reduction of iodate occurred at pH 7.5 - 8. However, in th i s case a l l attempts to show the formation of iodinated resorcinol compounds f a i l e d . This may be due to the lack of s e n s i t i v i t y of the technique used. The e l e c t r o p h i l i c iodine produced by the reduction of iodate i s a transient species whose concentration i s determined by i t s rate of formation and consumption. As the pH increases, the rate of iodate reduction, and therefore i t s steady-state concentration, decreases. Consequently, much less iodinated resorcinol compounds can be formed, and i t becomes increasingly d i f f i c u l t to separate them from a much more abundant resorcinol pool. In conclusion, although the reduction of iodate by humic substances at neutral pH has not been unambiguously demonstrated, i t has been shown that iodate i s able to enrich sedimentary humic materials at pH values close to those of sea water. A mechanism whereby iodine i s added to humic materials under ac i d i c 1 37 conditions has been demonstrated. Thermodynamic considerations suggest that t h i s mechanism s t i l l occurs under natural conditions; however, confirmation i s s t i l l required. 3.4.3.3 RELEASE OF IODINE FROM HUMIC MATERIALS. The displacement experiments were performed by dispersing I-enriched humic materials in oxygen-free seawater spiked with sulphide and thiosulphate. I/C rati o s in the humics before and after treatment are shown in F i g . 22. It can be seen that a large fractio n of the iodine added during the iodate treatment was lo s t during the S treatments. Hence, iodine is evidently displaced by these species and such reactions could occur in sediments. The results presented in F i g . 22 also show that a s i g n i f i c a n t proportion of the iodine added by iodate reduction at pH 3.4 can be displaced by sea water alone (pH 7.6), which suggests that some of the organic iodine compounds formed in aci d i c solutions are very pH-sensitive and decompose at neutral pH. Subsequently, the displacement of iodine from a naturally-enriched humic material was also tested. If excess iodine can be ea s i l y displaced by nucleophiles, one would expect OH , a nucleophile i t s e l f , to be able to contribute to the I-displacement from the humic materials s o l u b i l i z e d during the alka l i n e extraction. This was confirmed by the results presented in Table 29 which show that a large proportion of the iodine found in the NaOH extract of HUD 22 sediments was not associated 138 300. i o o 200 _ 100 0 J (a) (b) (c) (1) (2) F i g . (3) (1) (4) (5) of i o d i n e from I-enriched humic 22: Displacement substances: (1) I n i t i a l I/C r a t i o . (2) Humic substances (0.2 g) were dispersed i n 50 ml iodate s o l u t i o n (2.5 mmol/1; pH 3.4) f o r 18 h. (3) I-enriched humic m a t e r i a l s from (2) were dispersed i n : (a) Seawater (pH 7.6; 52 h ) . (b) Seawater + 5 mmol/1 t h i o s u l p h a t e (pH 6.9; 52 h ) . (c) Seawater + 15 mmol/1 sulp h i d e (pH 8.0; 52 h ) . (4) Humic substances (0.3 g) were dispersed i n 100 ml iodate s o l u t i o n (2.5 mmol/1; pH 8.0) f o r 5 days. (5) I-enriched humic m a t e r i a l s from (4) were d i a l y s e d i n 4 1 t h i o s u l p h a t e s o l u t i o n (5 mmol/1; pH 8.4) f o r 6 days. 139 Table 29: Displacement of iodine from humic materials, extracted from HUD 22,by 0H~ and HS~. I/COO 4) * Humic extract 242+10 * Humic extract 1 03+11 after d i a l y s i s * Humic extract 89+7 after sulphide treatment and d i a l y s i s * See method section for de t a i l s on the experimental procedure. 1 40 with the humic molecules. This i s presumably due to the displacement of thi s iodine f r a c t i o n from the organic matrix during the NaOH extraction. This shows the readiness with which nucleophilic attack on the excess iodine found in s u r f i c i a l marine sediment occurs. It i s also noteworthy that the I/C r a t i o obtained aft e r d i a l y s i s and H 2S treatment is very similar to the I/C r a t i o measured in the deeper part of the sediment column in the core studied e a r l i e r (Fig. 19). 3.5 CONCLUSION. The results obtained from the chemical leaching experiments indicate that, in the s u r f i c i a l hemipelagic sediment analyzed, iodine i s mainly associated with organic matter, while oxyhydroxides are only of secondary importance. From the experimental data presented here, i t can be concluded that the s u r f i c i a l I-enrichment of sediments deposited under oxygenated conditions could be the re s u l t , at least in part, of the reduction of iodate to . e l e c t r o p h i l i c iodine species by humic materials, followed by e l e c t r o p h i l i c substitution (e.g. Olcott and Fraenkel-Conrat, 1947; Roche and Michel, 1951; Fawcett and Kirkwood, 1953a; 1953b) on organic molecules containing electron-donor groups. Such a mechanism would also explain the absence of iodine enrichment in anoxic sediments, since iodide, which i s the main iodine species found 141 in anoxic environments (Wong and Brewer, 1977; Emerson et a l . , 1979), does not react with humic substances. However, the environmental significance of t h i s mechanism s t i l l needs to be assessed, and alternative explanations cannot be ruled out. I 2 and HOI can also be produced by other mechanisms. It has been suggested that the iodine enrichment in s u r f i c i a l sediments could be mediated by an enzyme (iodide oxidase) thought to be associated with the i n i t i a l degradation products of planktonic c e l l s (Price and Calvert, 1973). This enzyme oxidizes iodide to I 2 which hydrolyses and forms hypoiodous acid (Shaw, 1959, 1962). Since t h i s reaction occurs only in the presence of oxygen, i t could also explain the contrasting behaviour of iodine in oxic and anoxic environments (Price and Calvert, 1977). Also, cer t a i n marine aerobes isolated from a sea water aquarium were shown to be able to oxidize a s i g n i f i c a n t amount of iodide to iodine (Gozlan, 1968; 1973). Although such organisms have not been isolated from marine sediments, the p o s s i b i l i t y that iodide oxidation could be b a c t e r i a l l y mediated should also be considered. Moreover, Tsunogai and Sase (1969) demonstrated that I 2 could also be produced by the reduction of iodate by n i t r a t e reductase, an enzyme present in aerobic organisms for n i t r a t e assimilation and in dissimilatory n i t r a t e reducers. Nitrate reducers are present in many marine sediments and therefore may have a s i g n i f i c a n t impact on iodine geochemistry. F i n a l l y , i t was 1 42 also shown that molecular iodine could be produced by chemical reduction of iodate by HS (Jia-Zhong and Whitfield, 1986). Such reaction could possibly occur at the interface of anoxic microenvironments, such as freshly egested fecal p e l l e t s , within the oxic surface layer. The occurrence of elemental sulphur in oxide-rich surface sediments (e.g. Chap. 2) supports this p o s s i b i l i t y . A l l these processes ( i . e . chemical or enzymatic reduction of iodate and enzymatic oxidation of iodide) have in common the production of an e l e c t r o p h i l i c iodine species ( I 2 or HOI) able to react with organic matter. However, distinguishing between their r e l a t i v e importance for iodine enrichment in s u r f i c i a l oxic sediments requires further investigation. The decreasing I/C r a t i o with b u r i a l , c h a r a c t e r i s t i c of marine sediments deposited under aerobic conditions, requires a p r e f e r e n t i a l release of iodine at depth. The association of iodine with a major but l a b i l e fraction of the sedimentary organic matter has been suggested (Price and Calvert, 1977). The experiments on the release of iodine from I-enriched humic substances described here demonstrate however that direct b a c t e r i a l decomposition of the I-bearing f r a c t i o n i s not necessary to decrease s i g n i f i c a n t l y the I/C r a t i o of buried sediments. These results suggest that nucleophile species, such as HS and ^O^ - e a s i l y displace excess iodine from humic substances. Such sulphur species, i f present in the suboxic zone, could possibly explain the p r o f i l e s observed. 143 Iodine can also form weakly-bound molecular complexes (T) -complexes) with many organic molecules (e.g. Fairbrother, 1947; Benesi and Hildebrand, 1949; Hildebrand et a l . , 1950; Mulliken, 1950). The iodine from these complexes i s readily reduced to iodide (e.g. Fawcett and Kirkwood, 1953a), and could conceivably be released from the organic matrix as soon as the dropped below ~500 mV (assuming: I 2 + 2e~ =^  2I~, E° = 540 mV), without requiring the need for a nucleophilic displacement. However, the re l a t i v e i n e f f i c i e n c y of hydroxylamine hydrochloride in removing iodine from HUD 22 surface sediment argues against the presence of such compounds in any large amount. The 10-15% of iodine which was s o l u b i l i z e d by thi s reducing treatment could have come partly from such a source and not only from the oxyhydroxide phase. The above figure must therefore represent the maximum amount of iodine associated with that part of the oxyhydroxide phase which was s o l u b i l i z e d . 144 4. A STUDY OF THE REGULATION OF METAL CONCENTRATION IN SAANICH INLET SEDIMENTS. 4.1 INTRODUCTION An enrichment in various trace elements in fine-grained sediments deposited under anoxic conditions has often been observed (Krauskopf, 1955; Manheim, 1961; Calvert and Price, 1970; 1983; Calvert, 1976; Jacobs et a l . , 1985). These sediments also tend to be have high concentrations of organic matter (Richards, 1970), and a s t a t i s t i c a l c o r r e l a t i o n between organic carbon and various trace metals has often been reported (Curtis, 1966; Calvert and Price, 1970; 1983; Volkov and Fomina, 1972; 1974; Calvert, 1976; Rosental et al.,1986). While such correlations do not necessarily indicate a d i r e c t association between organic matter and metals (Volkov and Fomina, 1974; Brumsack, 1980), further support for the occurrence of such associations has been obtained from the analysis of various organic fractions extracted from anoxic sediments which showed r e l a t i v e l y high metal concentrations, • p a r t i c u l a r l y in the humic fractions (Volkov and Fomina, . 1972; Nissenbaum and Swaine, 1976; Calvert and Morris, 1977; Calvert et a l . , 1985). The mechanism for these enrichments is s t i l l obscure. An adequate supply of metals and diagenetic processes leading to 1 45 their accumulation in the enriched sediments are required. Marine plankton i s the most often c i t e d source of metals . However, i t has been argued that the metal concentration in planktonic materials i s not high enough to account for the metal enrichments observed in sediments (e.g. Brumsack, 1980). Scavenging from the water column (Volkov and Fomina, 1972; 1974) or post-depositional metal enrichment in the deposited organic matter v i a leaching of the mineralogical components of the sediment by humic materials (Nissenbaum and Swaine, 1976; Calvert and Morris, 1977; Calvert et a l . , 1985) has been suggested. Direct p r e c i p i t a t i o n or co-p r e c i p i t a t i o n of metal sulphides from sulphidic water columns has also been proposed (Krauskopf, 1956; Brongersma-Sanders, 1965; Piper, 1971; Bertine, 1972; Volkov and Fomina, 1974; Brewer and Spencer, 1974; Jacobs and Emerson, 1982; Jacobs et a l . , 1985). It i s generally accepted that within the enriched sediments the excess metal i s associated either with the organic phase or with the sulphide phase. Since both organic materials and sulphide minerals are reduced constituents of the sediments, i t is d i f f i c u l t to distinguish t h e i r r e l a t i v e importance by oxidative leaching (Nissenbaum and Swaine, 1976). Instead, various workers have attempted to separate ph y s i c a l l y these two phases, using bromoform for p y r i t e separation (Volkov and Fomina, 1974), and di s s o l u t i o n of the humic polymers in NaOH for organic 1 46 matter (Volkov and Fomina, 1972; 1974; Nissenbaum and Swaine, 1976; Calvert and Morris, 1977; Calvert et a l . , 1985). Although there are uncertainties with the interpretation of these data, p a r t i c u l a r l y from the humic extraction experiments, the results obtained suggest that both phases are s i g n i f i c a n t in the geochemical balance of various metals in d i f f e r e n t anoxic sediments. Moreover, since sediments accumulating in anoxic basins tend to be fine-grained, and since such texture i s invariably associated with higher organic matter content (Trask, 1953; Van Andel, 1964) and metal concentrations (Krauskopf, 1979; Ackerman, 1980; Salomons and Forstner, 1983), organic carbon and metal enrichments in anoxic sediments could also, at least in part, be controlled by textural and hydrodynamic factors (Volkov and Fomina, 1974). Further investigations of the control mechanisms regulating the d i s t r i b u t i o n of metals in anoxic basins were undertaken by studying the metal and organic carbon d i s t r i b u t i o n s in the sediments of Saanich Inle t , an intermittently anoxic f j o r d on the coast of B r i t i s h Columbia. Two complementary approaches were taken. The f i r s t approach consisted of a comprehensive areal survey of the metal content of the sediments of the I n l e t . The results obtained were processed s t a t i s t i c a l l y in an attempt to i d e n t i f y co-varying groups of elements. The second approach consisted of analyzing 147 the s e t t l i n g particulates recovered from sediment traps deployed in the water column over an 18 month period. Seasonal variations in p articulate fluxes and comparison of these data with the metal and organic carbon accumulation rates in the sediment at the trap s i t e s was used to evaluate the di f f e r e n t factors regulating the metal concentrations in these sediments. A better appreciation of the mechanisms whereby t r a n s i t i o n metals are trapped in anoxic environments would have a s i g n i f i c a n t bearing not only on our understanding of the geochemical cycles of these elements (e.g. Calvert, 1976) and on the formation of important ore deposits (e.g. Brongersma-Sanders, 1965), but also could provide us with a tool to examine the possible expansion of anoxic environments in the geological past. An increase in the importance of these environments may have a dramatic ef f e c t on the seawater concentration of certain elements (e.g. molybdenum) which could possibly be recognizable in the sedimentary record (Emerson, pers. comm.). 4.2 GENERAL FEATURES OF SAANICH INLET AND SAMPLING LOCATIONS 4.2.1 GENERAL DESCRIPTION Saanich Inlet i s an intermittently anoxic f j o r d on the south-east coast of Vancouver Island (Fig. 23). It i s 25 km in length, 7.2 km at i t s widest part, and i s connected to Haro 148 149 S t r a i t in the east and Georgia S t r a i t in the north-east by S a t e l l i t e Channel. Water exchange through th i s channel i s r e s t r i c t e d by a well-defined, r e l a t i v e l y deep s i l l (~75 m) at the mouth of the i n l e t , between Moses Point and Hatch Point. Beyond th i s shallower entrance, the floor deepens to a maximum of 232 m off Shepard Point. It shoals gradually toward Squally Reach (~180 m) and f i n a l l y r i s e s rapidly toward the Goldstream River. The drainage basin of the i n l e t i s small and situated in a "rain-shadow", so that i t contributes l i t t l e water run-off (Herlinveaux, 1962). The Goldstream River, situated at the head of the f j o r d , i s the largest stream entering the i n l e t d i r e c t l y ; however, i t s discharge i s small (0.85 m /sec; Herlinveaux, 1962). Most of the fresh-water run-off reaching' Saanich Inlet comes from the Cowichan River, flowing into Cowichan Bay, situated about 6 km north-west of the s i l l (Fig. 23). Its discharge follows the seasonal p r e c i p i t a t i o n pattern, with a maximum in December (~90 3 " 3 m /sec) and a minimum in August (5-10 m /sec). However, large variations have been observed over short periods, producing e r r a t i c fluctuations in the surface s a l i n i t y at the entrance of the i n l e t . This fresh water input generally influences only the top 10 m of the water column, producing a sharp sub-surface pycnocline, p a r t i c u l a r l y in winter. The surface waters of Saanich Inlet are also influenced by the fresh water discharge from the Fraser River, which is at i t s maximum in June. Each summer, a low-salinity, s i l t - l a d e n water 150 mass moves towards the Gulf Islands and enters Saanich Inlet through S a t e l l i t e Channel, producing a surface d i l u t i o n which i s generally evident down to 50 m depth (Waldichuk, 1957; Herlinveaux, 1962). This pattern of fresh water input i s unusual since in many fjords the major source of water run-off enters at the head of the i n l e t , thus producing a strong estuarine-type c i r c u l a t i o n (Tully, 1958). In Saanich Inlet, t h i s type of c i r c u l a t i o n seems very weak and sporadic (Herlinveaux, 1962; 1966; 1972) and i s driven mainly by the Cowichan water inflow which intrudes into the i n l e t at ebbing tides producing water of lower density than in nearby Haro S t r a i t , thus establishing a weak estuarine flushing mechanism. Therefore, estuarine and t i d a l flushing produce an e f f e c t i v e exchange of surface water with nearby channels, although the t i d a l currents diminish rapidly toward the head of the i n l e t where the surface water i s p a r t i a l l y isolated and only slowly exchanged. The estuarine c i r c u l a t i o n i s , however, not s u f f i c i e n t l y developed to flush the deep basin of the i n l e t below s i l l - l e v e l . Consequently, anoxia gradually develops and eventually H2S appears in the water column, generally in spring, after the vernal plankton bloom. In late summer or early f a l l , a dense, well-aerated body of water i s produced in Haro S t r a i t by intensive t i d a l mixing of 151 warm, low-salinity surface water from the S t r a i t of Georgia with cold , saline, oceanic upwelled water derived from the C a l i f o r n i a Undercurrent system that moves inward along Juan de Fuca S t r a i t (Waldichuk, 1957; Thomson, 1981). This leads to a complete replacement of the bottom water in the deeper basins of Georgia S t r a i t and nearby i n l e t s . This dense oxygenated water reaches S a t e l l i t e Channel almost undiluted, since at t h i s time the fresh water input from the Cowichan estuary i s at i t s minimum. It is then able to displace the bottom water of Saanich Inlet whose s a l i n i t y has been s l i g h t l y decreased by s a l t entrainment. Flushing seems to occur in boluses of dense water which s p i l l s over the s i l l mainly during flooding tide (Anderson and Devol, 1973). This water renewal takes place during most years; however, the extent of flushing varies widely from year to year. When l i t t l e flushing occurs, stronger anoxic conditions develop during the following spring. 4.2.2 PHYTOPLANKTON Phytoplankton biomass in Saanich Inlet shows the bimodal pattern usually reported in temperate nearshore waters ( i . e . a major spring bloom and a smaller f a l l bloom). Between these two peaks, induced by general seasonal climatic variations, are a series of e r r a t i c summer blooms produced by occasional mixing events (due to winds, tides, r i v e r run-off etc.) which l o c a l l y supply the euphotic zone with n u t r i e n t - r i c h intermediate waters 1 52 (Takahashi et a l . , 1977). The spring and f a l l blooms are dominated by centric diatoms while in winter, nanoflagellates, occasionally accompanied by d i n o f l a g e l l a t e s , are the most numerous species (Takahashi et a l . , 1978). In summer, the primary production in the inner f j o r d i s r e l a t i v e l y low, because of nutrient depletion by the spring bloom and thermal s t r a t i f i c a t i o n of the water column. The phytoplankton population is then dominated by various diatoms, d i n o f l a g e l l a t e s and nanoflagellates (Sancetta and Calvert, 1987). The presence of a b i o l o g i c a l f r o n t a l zone, associated with turbulent t i d a l mixing in the S a t e l l i t e Channel, has also been demonstrated (Parsons et a l . , 1983). This zone was characterized by high primary productivity and high surface chlorophyll. 4.2.3 GENERAL GEOLOGY OF THE SAANICH REGION The general geology of the southern part of Vancouver Island was f i r s t described in d e t a i l by Clapp (1913), and the following summary (Fig. 24) is taken from th i s work (see also Muller, 1980). The oldest rocks (Paleozoic age) are members of the Vancouver Group, c h i e f l y the Vancouver Volcanics and the Sicker Series. The Vancouver Volcanics consist mainly of metamorphosed andesites and basalts with numerous quartz and epidote veins and minor p y r i t e . They also contain numerous pockets of limestone 1 53 Fig. 24: General geology of southern Vancouver Island (known as the Sutton Formation). The andesite consists mainly of andesine and hornblende, the l a t e r being largely altered to c h l o r i t e . The basalt i s mainly composed of labradorite and hornblende, with c h l o r i t e , epidote and quartz as the most common secondary minerals. The Sicker Series i s very similar to the Vancouver volcanics, and is mainly composed of andesite with hornblende phenocrysts. These rocks are, however, more highly metamorphosed and interbedded with schists of both volcanic and sedimentary o r i g i n . The sedimentary schists contain c h i e f l y quartz, plagioclase, and argillaceous materials, with some b i o t i t e , c h l o r i t e , and epidote, while the volcanic schists consist mainly of c h l o r i t e and altered feldspars. These rocks were extensively deformed during the Late Jurassic and intruded by plutonic rocks which formed the Wark gneiss (with a composition intermediate beween gabbro and d i o r i t e ) , the Colquitz gneiss (quartz d i o r i t e ) and the Saanich granodiorite. The Wark and Colquitz gneisses consist mainly of plagioclases (varying from labradorite to andesine in composition) and hornblende, plus varying amounts of quartz, b i o t i t e , magnetite and t i t a n i t e . The presence of quartz veinlets impregnated with p y r i t e has also been reported in the Wark gneiss. The Saanich granodiorite consists c h i e f l y of feldspar (mainly andesine, with some orthoclase), and quartz, with some hornblende and b i o t i t e . Pyrite, magnetite, t i t a n i t e and apatite are also found as accessory minerals. 1 55 The chemical composition of these rocks, reported by Clapp (1913), i s given in Table 30. In the northern part of the area, a series of sedimentary rocks (the Cowichan Group) i s found. They consist mainly of unmetamorphosed conglomerates, sandstones, and minor shales. In addition to quartz, they also contain, in order of r e l a t i v e abundance, feldspars (mainly plagioclases), muscovite, b i o t i t e , c h l o r i t e and epidotes. The shales are frequently carbonaceous, contain large amounts of argillaceous materials, and are often impregnated with p y r i t e . These rocks have been greatly deformed in post-Eocene time and now form a s y n c l i n a l basin which i s drained by the Cowichan ri v e r (Fig. 24). Saanich Inlet occupies a glaciated v a l l e y . Its central part was cut into the Saanich granodiorite batholith, while i t s head i s situated in Vancouver volcanics and Wark gneiss (Fig. 24). Consequently, run-off from the central part of the basin w i l l contribute mainly f e l s i c - t y p e minerals to the sediment, while run-off originating from the southern part of the drainage basin w i l l transport materials with a more mafic ( i . e . Fe- and Mg-rich) signature. The Cowichan River drains a t e r r a i n dominated by the Cowichan Group and the Sicker Series and i s expected to supply a wide range of materials. 1 56 Table 30: Major element composition (wt %) of the gneiss and granodiorite found in the Saanich area (Clapp, 1913). Saanich Wark Colquitz granodiorite gneiss gneiss Si 29.28 22.75 29.93 Al 9.39 9.55 8.38 Fe 3.82 7.40 3.38 Mg 1 .53 1 .70 1 .64 Ca 3.17 7.15 2.57 Na 2.62 2.36 2.61 K 1 .78 1 .33 1.19 Ti 0.36 0.48 0.18 P 0.14 1.13 0.88 Mn 0.11 0.15 0.12 157 4.2.4 SAMPLING The sampling locations are shown in F i g . 25. F i f t y f i v e sediment samples (SAG1 to SAG60) were co l l e c t e d on A p r i l 18 and 19, 1983 with a Shipek grab sampler, and three cores were obtained' with a gravity corer (Pedersen et. a l , 1985) from the 2 stations where moored sediment traps were also deployed. The periods of deployment of the sediment traps at each of these stations are indicated in F i g . 26, and the depth of c o l l e c t i o n of the s e t t l i n g particulates is indicated in F i g . 27. Further d e t a i l s on sampling procedures are given in Appendix I. 4.3 BULK COMPOSITION OF SAANICH INLET SEDIMENTS The sediments of Saanich Inlet were f i r s t described in d e t a i l by Gross et a l . (1963), Gucluer and Gross (1964), and Gross (1967). Three broad types can be recognized. They are distinguished by th e i r chemical and physical c h a r a c t e r i s t i c s which partly r e f l e c t t h e i r environment of deposition. The deep central basin of the i n l e t i s covered with organic-r i c h , diatomaceous, clayey s i l t s . The combination of high primary production and r e s t r i c t e d c i r c u l a t i o n produces an oxygen deficiency in the deep water which leads to anoxic conditions in the entire sediment column, the production of hydrogen sulphide, 158 F i g . 25: Sampling locations. 159 11 comple te a n a l y s i s • C&N ana lys is only SN 0.8 SI-9 i—i 1 1 1 1 1 1 1 1 1 1 1—i 1 A S O N D J F M A M J J A S O 1 983 1984 F i g . 26: Period of deployment of the sediment-trap moorings. 160 0 SN 0.8 SI-9 10 2 0 L e n g t h ( k m ) F i g . 27: Longitudinal transect of Saanich Inlet showing the positioning of the sediment traps. 161 and the preservation of a varves (Gross et a l . , 1963). On the s i l l , the sediments consist of a l i g h t olive-grey s i l t containing s i g n i f i c a n t l y lower amount of opal and organic matter. This deposit i s coarser-grained and better sorted, which r e f l e c t s more turbulent conditions of deposition. The s i l l i s a r e l a t i v e l y shallow topographic feature which also coincides with a region of stronger t i d a l currents (Thomson, 1981). Re-suspended materials from the s i l l (mainly clays, opal, and organic matter) may eventually be deposited in the central basin which acts as a trap for fine p a r t i c l e s . The coarsest sediments are found at shallow depth, near the shores of the i n l e t . They generally consist of f a i r l y poorly sorted sands, with a low organic carbon content, and occasional gravels. 4.3.1 MINERALOGY OF SAANICH INLET SEDIMENTS Unorientated pressed powders from 16 stations were analyzed by X-ray diffractometry in order to ident i f y t h e i r major mineral components. The mineralogical composition of coastal sediments r e f l e c t s the mineralogy of the nearby parent rocks. The main source of lithogenous material in Saanich Inlet i s the Cowichan River which drains an area dominated by the Cowichan Group (also c a l l e d the Nanaimo Series) and the Sicker Series (section 4.2.3; Fig 24). Quartz, feldspars, hornblende, c h l o r i t e and/or k a o l i n i t e , and micas were readily i d e n t i f i e d in a l l the sediments analyzed. 162 Occasionally, pyrite and c a l c i t e could also be found. The rat i o s of the peak i n t e n s i t i e s of quartz (at 2.46 A) or 0 o plagioclase (at 4.04 A) to c h l o r i t e and/or ka o l i n i t e (at 7 A) were much higher in the s i l l and nearshore sediments than in the basin and Cowichan Bay samples (Table 31 and 32). Therefore, quartz and feldspars are more abundant in r e l a t i v e l y shallow and more turbulent environments while clays predominate in deeper waters. A similar approach showed that hornblende, while often only barely detectable in the deep basin diatomaceous oozes, occurs in larger quantities, r e l a t i v e to clays, in some nearshore and s i l l samples (Table 33). It i s also r e l a t i v e l y more abundant in the Cowichan Bay. I l l i t e was also i d e n t i f i e d in these sediments by peaks at 10 A which did not expand on glycolation, while peaks at 7 A indicated the presence of c h l o r i t e and/or k a o l i n i t e . The presence of a s i g n i f i c a n t amount of ka o l i n i t e was revealed by a more detailed study of the clay mineralogy in the central basin where ka o l i n i t e , c h l o r i t e and i l l i t e were found to be the main clay minerals (Powys, pers. comm.). The l o c a l i z e d influence from the gneiss formations and the Saanich granodiorite batholith should also be expected and more apparent in adjacent nearshore sediments. 163 Table 31: Peak intensity r a t i o s . Quartz (2.46 h) / c h l o r i t e and ka o l i n i t e (7 A) Central basin sediments SAG1 0.80/0.90 = 0.9 SAG7 0.80/0.65 =1.2 SAG 1 3 0.85/0.65 = 1.3 SAG 1 5 1.20/1.05 = 1.1 SAG26 1.00/1.10 = 0.9 SAG33 1.10/1.10 = 1.0 SAG36 1.30/1.30 = 1.0 SAG43 1.80/1.05 = 1.7 S i l l sediments SAG 4 7 2.60/0.70 = 3.7 SAG50 3.05/0.60 = 5.1 SAG51 1.75/0.80 = 2.2 SAG53 2.75/0.75 = 3.7 SAG56 1.85/1.50 = 1.2* SAG60 2.25/1.60 = 1.4 Nearshore sediments SAG22 2.90/0.70 =4.1 SAG 3 2 5.30/0.30 = 18 * Cowichan Bay 1 64 Table 32: Peak intensity r a t i o s . o o Plagioclase (4.04 A) / c h l o r i t e and kaolinite (7 A) Central basin sediments SAG 1 0.95/0.90 = = 1.1 SAG7 1.60/0.65 = = 2.0 SAG 1 3 1.40/0.65 = = 2.2 SAG 1 5 1.85/1.05 = = 1.8 SAG26 1.10/1.10 = = 1.0 SAG33 1.20/1.10= = 1.1 SAG36 1.00/1.30 = = 0.8 SAG43 1.70/1.05 = = 1.6 S i l l sediments SAG47 2.05/0.70 = = 2.9 SAG 50 2.80/0.60 = = 4.7 SAG51 1.90/0.80 = = 2.4 SAG53 2.35/0.75 = = 3.1 SAG 5 6 1.80/1.50 = * = 1 .2* SAG 60 1.60/1.60 = = 1.0 Nearshore sediments SAG22 2.70/0.70 = = 3.9 SAG 3 2 3.20/0.30 = = 10.7 * Cowichan Bay 165 Table 33: Peak intensity r a t i o s . Hornblende (8.40 A) / c h l o r i t e and kaolin i t e (7 A) Central basin sediments SAG 1 0.2/0.90 = 0.2 SAG7 < 0.2/0.65 < 0.3 SAG 1 3 < 0.2/0.65 < 0.3 SAG 1 5 < 0.2/1.05 < 0.2 SAG26 0.2/1.10 = 0.2 SAG 3 3 0.3/1.10 = 0.3 SAG 3 6 0.2/1.30 = 0.2 SAG43 < 0.2/1.05 < 0.2 S i l l sediments SAG47 0.2/0.70 = 0.3 SAG 50 0.3/0.60 = 0.5 SAG 51 < 0.2/0.80 < 0.3 SAG 5 3 0.8/0.75 = 1.1 SAG 5 6 0.45/1.50 = 0.3* SAG 60 0.65/1.60 = 0.4 Nearshore sediments SAG 2 2 1.7/0.70 = 2.4 SAG32 0.7/0.30 = 2.3 * Cowichan. Bay 166 4.3.2 GEOCHEMISTRY OF SAANICH INLET SEDIMENTS 4.3.2.1 ORGANIC MATTER The sediments deposited in the central basin contain s i g n i f i c a n t l y more organic carbon than the shallow-water sediments although substantial concentrations are also observed in Cowichan Bay (Fig. 28; Appendix IV-1). There i s also a tendency for a gradual increase in the concentration of organic carbon towards the head of the i n l e t . In order to explain such a d i s t r i b u t i o n , one must consider the source(s) of the organic matter, the potential d i l u t i o n by lithogenous d e t r i t a l materials and the hydrodynamic factors which regulate the accumulation of low-density p a r t i c l e s in low-energy depositional basins. Plankton is usually the p r i n c i p a l source of organic materials in marine sediments (e.g. Nissenbaum and Kaplan, 1972; Morris and Calvert, 1977; Primuzic et a l . , 1982; Jorgensen, 1983). However, in a land-locked area such as Saanich Inlet, a s i g n i f i c a n t t e r r e s t r i a l component can also be present (e.g. Hunt, 1966; Hedges and Parker, 1976; Gadel, 1979; Walsh et a l . , 1981; Malcolm and Price, 1984; Naik and Poutanen, 1984). The carbon to nitrogen r a t i o (C Q rg/N) can be used to assess the r e l a t i v e importance of these two sources. T e r r e s t r i a l plant debris contains much less nitrogen than planktonic materials (Table 34). Accordingly, a high C /N r a t i o in the sediment w i l l , suggest a 167 Fig. 28: Distribution of organic carbon. 168 Table 34: C/N ra t i o (% dry wt.) of organic materials of marine and t e r r e s t r i a l o r i g i n . C/N References Marine plankton 4.9 Vinogradov (1953) 1 5.7 Redfield et a l . (1963) 5.2 Malcolm and Price (1984) Seed plants 13.8 Rankama and Sahama (1950) 1 River particulates 8.5-15 Williams (1968) (Amazon) River sediments 21 DeGroot (1973) (Rhine) Forest s o i l 13.5 Stuermer et a l . (1978) River particulates 17.3 Malcolm and Price (1984) (Loch Etive) 1 - Cited in Bowen (1979). 169 s i g n i f i c a n t t e r r e s t r i a l input. It i s d i f f i c u l t , however, to use th i s r a t i o to quantify the r e l a t i v e proportion of the two types of materials. The C/N r a t i o of phytoplankton may vary with their n u t r i t i o n a l status (e.g. Banse, 1974; Slawik et a l . , 1978; Sharp et a l . , 1980). Moreover, N-containing organic compounds (mainly proteins) tend to be p r e f e r e n t i a l l y mineralized, thus producing a gradual increase in the C/N r a t i o of the marine component of the organic matter during i t s transport to the sediment and the early stages of diagenesis (e.g. Degens, 1970; Ulen, 1978; Rosenfeld, 1979; Landing and Feely, 1981; Honjo et a l . , 1982; Cronin and Morris, 1983; Gardner et a l . , 1983; Wassman, 1983). In contrast, an decrease in the C/N r a t i o of aging organic detritus (Newel, 1965;•Harrisson and Mann, 1975; Roman, 1977; Rice, 1983; Nedwell, 1984) and s u r f i c i a l sediments (Suess and Muller, 1979) has often been observed and attributed to the synthesis of pr o t e i n - r i c h microbial or benthic biomass. Also, the determination of the C/N r a t i o of organic matter in fine-grained sediments may be complicated by the presence of ammonium fixed in the interlayer positions of i l l i t e s and vermiculites (Muller, 1977), although t h i s problem arises mainly at low organic carbon concentrations. Consequently, an estimate of the r e l a t i v e input of marine and t e r r e s t r i a l organic materials based on C/N rati o s alone would be very tentative, even when the end-members are well characterized. However, because of the large difference in nitrogen content between the two types of materials, q u a l i t a t i v e conclusions can 170 Fig. 29: Distribution of the C / N ratio. 171 s t i l l be drawn. The d i s t r i b u t i o n of the C /N ra t i o s in Saanich Inlet org sediments i s shown in F i g . 29. The s i l l sediment samples, recovered from the eastern branch of the S a t e l l i t e Channel, display r e l a t i v e l y low C / N ratios (8.3 + 0.5). The presence of KJ L y a b i o l o g i c a l front in thi s area, characterized by high productivity, was demonstrated by Parsons et a l . (1983) and i s consistent with the presence of organic matter with a predominantly planktonic o r i g i n in the underlying sediment. On average, the C Q rg/N rati o s of the fine-grained sediment from the central basin are s l i g h t l y higher (9.8 + 1.3), thus suggesting the presence of some t e r r e s t r i a l material. This material could have been brought into the i n l e t by the Cowichan River as a fine suspension which became trapped in the stagnant water column of the central basin. A higher proportion of t e r r e s t r i a l debris i s observed in several nearshore samples and p a r t i c u l a r l y in Cowichan Bay, which suggests that the Cowichan River could be a si g n i f i c a n t source of t e r r e s t r i a l organic matter. A higher C o rg/N r a t i o in the two southernmost samples in the anoxic basin also indicates the presence of some t e r r e s t r i a l debris from the Goldstream River. There i s no well-defined primary production pattern in Saanich Inlet which could readily explain the increase in organic carbon in the sediment towards the head of the f j o r d . In fact, monthly measurements over a two-year period at stations SI9 and 1 72 SN0.8 (Calvert, unpublished) indicate that primary production i s generally higher at the mouth of the i n l e t , in accord with the general pattern of productivity reported for other fjords (Lebrasseur, 1954) and the proximity of a b i o l o g i c a l front in S a t e l l i t e Channel (Parsons et a l . , 1983). Therefore, the d i s t r i b u t i o n pattern of organic matter must r e f l e c t variations in the degree of d i l u t i o n by other sediment components. D e t r i t a l input i s expected to be higher near the s i l l , due to the r e l a t i v e proximity of the Cowichan estuary, and to decrease gradually southward. This would produce an increase in the C % in the c org sediment away from the s i l l . This i s supported by the sedimentation rates measured by various authors (Table 35), and by the inverse relationship found between %C Q rg in s u r f i c i a l sediments and sedimentation rates in four d i f f e r e n t cores (Fig. 30). However, t h i s d i l u t i o n by lithogenous materials i s not the only factor c o n t r o l l i n g the organic carbon concentration of these sediments. Simple d i l u t i o n would produce a hyperbolic relationship between %C and sedimentation rates ( i . e . %C = c org org 100 x [C /(C + L ) ] , where C i s a constant accumulation ar ar ar ar rate of organic carbon and L a r i s a variable accumulation rate of inorganic materials; F i g . 30). The linear r e l a t i o n s h i p obtained must therefore be fortuitous and, in part, produced by the decrease in carbon accumulation rates towards the head of the i n l e t , as shown in Table 36. This decrease r e f l e c t s primarily 1 73 Table 35: Sediment accumulation rates (w) in Saanich In l e t . Station w (mg/cm2.yr) %c org References SI-9 257 3.00 This work SI-7 270 - Matsumoto and Wong (1977) G 144 4. 1 0 Carpenter and Beasley (1981) 1 90 - Carpenter and Beasley (1981) SI-3 93 - Matsumoto and Wong (1977) SN0.8 95 4.54 This work CP4 42 5.35 Powys (pers. comm.) 174 W ( m g / c m .yr) F i g . 30: Relationship between organic carbon content and sediment accumulation rate in Saanich Inlet sediments. 175 Table 36: Carbon accumulation rates in the deep basin of Saanich Inlet. Stat ion Sediment accumulation rate (mg/cm . y) %C surface sediment C accumulation rate (mg/cm .y) CP4 42 5.35 2.25 SN0.8 95 4.54 4.31 G 144 4.10 5.90 SI-9 257 3.00 7.71 176 differences in the carbon fluxes to the sediment (see section 4.4.1). Although the C Q rg/N r a t i o of the sediment underlying the highly productive b i o l o g i c a l front in the S a t e l l i t e Channel indicates an organic input of predominantly marine o r i g i n , i t s organic carbon content is very low. This can be explained by considering the nature of the environment of deposition and the hydrodynamic properties of organic matter. As mentioned e a r l i e r , the s i l l represents a topographic high in a zone of r e l a t i v e l y intense t i d a l mixing (which i s responsible for the occurrence of the b i o l o g i c a l f r o n t ) . Organic-rich p a r t i c l e s of r e l a t i v e l y low density w i l l not accumulate in such an environment and w i l l , in part, be deposited under the quieter conditions pre v a i l i n g in the central basin. This i s consistent with the mineral composition of these sediments (section 4.3.1). This hypothesis is further supported by geochemical data obtained from the analysis of the s i l l sediments which also suggest that they consist of a lag deposit enriched in feldspar and quartz (section 4.3.2.3). In summary, i t appears that the d i s t r i b u t i o n of organic matter in Saanich Inlet sediments i s controlled mainly by hydrodynamic factors which hinder i t s accumulation on the s i l l but concentrate i t in the central basin where quieter conditions p r e v a i l , and by d i l u t i o n due to a larger input of mineral d e t r i t u s at the mouth of the i n l e t which produces a gradual increase in organic carbon concentration towards the head. 177 4.3.2.2 CARBONATE The carbonate content of most of the i n l e t sediments is generally low (less than 3.5%) except near Bamberton, where a lens of metamorphosed limestone (belonging to the Sutton Formation) has been commercially exploited (Fig 31). The carbonate d i s t r i b u t i o n obtained from the present work cl o s e l y resembles that reported by Gucluer and Gross (1964). The limestone quarry c l e a r l y acts as a point source for most of the carbonate present in the i n l e t . 4.3.2.3 MAJOR ELEMENTS The major element concentrations of Saanich Inlet sediments are shown in Appendix IV-1. 4.3.2.3.1 ALUMINIUM Aluminium r e f l e c t s p r i n c i p a l l y the d i s t r i b u t i o n of feldspars and clay minerals. Its concentration shows a gradual decrease from the s i l l to the head of the i n l e t (Fig. 32) which r e f l e c t s d i l u t i o n by opal and organic matter. It i s believed that in the central basin clay minerals w i l l be r e l a t i v e l y more important than on the s i l l where feldspars w i l l be predominant. This i s supported by the mineralogy of these sediments, (section 4.3.1) and by the data presented in the following sections. 4.3.2.3.2 SILICON The d i s t r i b u t i o n of s i l i c o n i s mainly controlled by diatom 178 Fig. 31: Distribution of C a C 0 3 . 179 Fig . 32: Distribution of Al . 180 opal and quartz. The source of the opal is the same as that of a major part of the marine component of organic matter, and since these two phases are expected to have quite similar hydrodynamic properties, a good co r r e l a t i o n between Si and %C Q rg should be found in sediments which are not strongly affected by t e r r e s t r i a l input. In contrast, quartz i s a very resistant component of many dif f e r e n t rocks and remains v i r t u a l l y unaltered during weathering and transport. As such, i t tends to be found in the coarser fractions of sediments and to accumulate in turbulent depositional environments where finer-grained sediment constituents such as clay minerals, opal, and organic matter are re-suspended. Hence, one would expect an antipathetic relationship between quartz and organic carbon. A plot of S i / A l vs %C o rg i s shown in F i g . 33. A reasonably good cor r e l a t i o n (r=0.68).is found in the diatomaceous ooze, thus indicating a co-variation between opal and organic matter. On the other hand, in the s i l l and nearshore samples, the S i / A l r a t i o s are always higher than expected from their organic carbon contents, except in the Cowichan Bay where a higher C/N r a t i o indicates a higher proportion of t e r r e s t r i a l organic matter. Moreover, th i s discrepency tends to increase as the ^ ^ o r g decreases. This indicates that the sediments from the s i l l and nearshore areas are comparatively enriched in non-biogenic S i , most probably in the form of d e t r i t a l quartz, although s i g n i f i c a n t amounts of feldspars must also be present, as 181 0 2 4 6 % C o r g F i g . 33: Relationship between S i / A l and %CQrg 182 indicated by the r e l a t i v e l y high Al concentrations found in these samples (Fig. 32, Appendix IV-1). These observations are consistent with the presence on the s i l l of a coarser-grained lag phase r e l a t i v e l y enriched in quartz and feldspar which was also indicated by the mineralogical composition of these sediments (section 4.3.1). 4.3.2.3.3 POTASSIUM The main minerals found in Saanich sediments which host potassium are K-feldspar (K/Al ~ 1.4), b i o t i t e (K/Al ~ 0.58 -1.4) and m u s c o v i t e / i l l i t e (K/Al ~ 0.1 - 0.3). The K/Al ra t i o s tend to be s l i g h t l y higher in the central basin (Fig. 34) and have values which would be expected from i l l i t e or a mixture of b i o t i t e and K-poor aluminosilicates such as c h l o r i t e and plagioclase. In the s i l l and nearshore sediments, the K/Al r a t i o i s much too low to indicate the presence of large quantities of K-feldspar, although i t does not rule out the presence of this phase (and b i o t i t e ) as a minor component. 4.3.2.3.4 CALCIUM AND SODIUM Calcium and sodium are mainly associated with plagioclase feldpars, while the calcium d i s t r i b u t i o n i s also strongly influenced by CaCOg. The Na/Al rat i o s are s i g n i f i c a n t l y higher in the eastern branch of the S a t e l l i t e Channel (av.~0.35) and in nearshore sediments than in the central basin (av.~0.25; F i g . 35 and 37), suggesting the presence of larger quantities of plagioclase in 183 Fig. 3 5 : Distribution of the Na/AI ratio. 185 Fig. 36: Distribution of the C a / A l ratio. 186 Na/Al C e n t r a l B a s i n 0 S i l l .10 .20 .30 .40 .50 J _ L n i i n 0 .10 S a n d 20 .30 .40 5 0 H r"1 0 .10 . 2 0 .30 .40 . 5 0 Ca/Al ( c o r r e c t e d f o r C a C 0 o ) C e n t r a l B a s i n i r 0 .10 .20 .30 .40 .50 S i l l Eq C=L 0 S a n d .10 .20 .30 4 0 . 50 n .10 .20 .30 .40 . 50 F i g . 37: Histogram of d i s t r i b u t i o n of the Na/Al and Ca/Al ratios in Saanich Inlet sediments. 1 8 7 these samples. When corrected for the presence of CaCO^, the Ca/Al r a t i o s show a similar trend (Fig. 36 and 37). If we assume that the Na and Ca present in clays are negl i g i b l e and that most of the Na and non-carbonate Ca are found in plagioclase, the maximum proportion of Al which would be contributed by these feldspars can be computed, v i z Na-feldspar: Na/Al = 0.85 Ca-feldspar: Ca/Al = 0.74 Central basin: av. Na/Al ~ 0.22 i . e . a max. of ~25% of the Al is present as Na-feldspar. av. Ca/Al ~ 0.18 i . e . a max. of ~25% of the Al is present as Ca-feldspar. i . e . a max. of ~50% of the Al present in these sediments can be associated with plagioclase. S i l l sediments: av. Na/Al ~ 0.35 i . e . a max. of ~40% of the Al (eastern side) i s present as Na-feldspar. av. Ca/Al ~ 0.25 i . e . a max. of ~35% of the Al is present as Ca-feldspar. i.e. a max. of ~75% of the Al present in these sediments can be associated with plagioclase. Similar calculations for the nearshore sediment samples suggest that most of the Al can be accounted for by plagioclase. These calculations confirm the presence of a lag deposit on the eastern part of the s i l l which contains, besides d e t r i t a l quartz, a r e l a t i v e l y large proportion of plagioclase (with a composition close to andesine as would be expected from the weathering of rocks from the Sicker Series (Section 4.2.3)). 188 This phase could account for as much as 75% of the Al present in these sediments; the remainder must be present in seme other aluminosilicates (K-feldspar, clay minerals, amphiboles). The Na/Al and Ca/Al ratios in the s i l l sediments in Cowichan Bay are s i g n i f i c a n t l y lower, suggesting a higher concentration of clay minerals. This is consistent with the data presented in Tables 31 and 32. In the central basin, plagioclase could account, at most, for 50% of the Al present, thus confirming the higher clay content in these sediments. These figures must be taken as maxima, since some Ca and Na can also be present in clay minerals. This i s p a r t i c u l a r l y true for the central basin sediments which are thought to contain more clays. Other evidence, based on the d i s t r i b u t i o n of Ti and Fe (Sections 4.3.2.2.5. and 4.3.2.2.6), suggest that plagioclase-Al accounts for s i g n i f i c a n t l y less than 50% of the t o t a l Al in the central basin sediments. 4.3.2.3.5 IRON AND MAGNESIUM A plot of %Fe vs %Mg shows that both elements co-vary very clos e l y (Fig. 38; r=0.92). Moreover, the intercept i s close to the o r i g i n and the three sediment types (basin, s i l l , and nearshore) are v i r t u a l l y indistinguishable. This suggests that the two elements are e s s e n t i a l l y controlled by one single mineral or several minerals with i d e n t i c a l Fe/Mg r a t i o s . In these sediments, c h l o r i t e and/or b i o t i t e are the most l i k e l y phases. 189 190 The Fe/Al ratios are s i g n i f i c a n t l y higher in the central basin and in Cowichan Bay than in the s i l l sediments (Fig. 41). The lowest values are obtained from some nearshore sediments, and p a r t i c u l a r l y from the shores adjacent to the Saanich granodiorite batholith. In the diatomaceous ooze, Fe (and therefore Mg) correlates quite cl o s e l y with Al (Fig. 39, r=0.94), suggesting that their d i s t r i b u t i o n s are mainly controlled by an aluminosi1icate (presumably c h l o r i t e ) . There i s also an intercept on the %Fe axis corresponding to ~0.5% Fe, i . e . there must be an additional Fe-bearing phase to these sediments not associated with aluminosilicates. This probably r e f l e c t s an input of iron oxides which have been s o l u b i l i z e d and precipitated as iron sulphides in the anoxic sediments. Since some of the Al must also be present in plagioclase, which i s very low in Fe, even more iron must have been added as oxides. The titanium d i s t r i b u t i o n (section 4.3.2.6, F i g . 44) suggests that a minimum of 1-1.5 wt % Al i s present as plagioclase in the central basin sediments. Therefore, according to F i g . 39, at least 1-1.5 wt % Fe must have been added to these sediments as oxides. Incidentally, a much larger proportion of Al in plagioclase would require u n r e a l i s t i c amounts of Fe to be added as oxides. This can be taken as circumstantial evidence to indicate the presence of plagioclase-Al in a quantity not surpassing ~25% of the t o t a l Al in the central basin sediments, hence suggesting the presence of Ca and Na in central basin clay 191 0 2 4 %AI F i g . 39: Correlation between %Fe and %A1 in Saanich Inlet sediments. 192 Fig. 40: Distribution of the F e / A l ratio. 193 minerals (see section 4.3.2.4). The Fe/Al ratios are much lower in eastern s i l l and nearshore sediments (Fig. 40), r e f l e c t i n g the p r e f e r e n t i a l accumulation of plagioclase over c h l o r i t e in these environments. As for the Na/Al and Ca/Al r a t i o s , the Fe/Al ratios of the Cowichan Bay samples have intermediate values between the eastern s i l l and the central basin. Fe and K correlate well in the deep basin (Fig. 42; r=0.87), suggesting either that these elements are cont r o l l e d by the same phase (such as an i l l i t e or b i o t i t e ) or, more l i k e l y , by two phases which would have i d e n t i c a l hydrodynamic properties (such as m u s c o v i t e / i l l i t e for R and c h l o r i t e for Fe and Mg), and therefore would be present in the same proportion throughout the diatomaceous ooze. The intercept of the regression l i n e also indicates that at least ~1 wt % of the iron cannot be accounted for by K-bearing minerals, thus confirming the conclusions drawn from the Fe-Al c o r r e l a t i o n concerning the addition of Fe oxides to these sediments. This Fe-K relat i o n s h i p breaks down in s i l l and nearshore sediments which are comparatively higher in K (Fig 42 and 43). This may be due to the presence of small quantities of K-feldspar in the lag deposits (with a K/Al~1.4, only 0.2-0.4 wt % A l -feldspar i s required to add the 0.3-0.6 wt % of K required),or b i o t i t e , or a l t e r n a t i v e l y due to the presence of r e l a t i v e l y more i l l i t e compared to c h l o r i t e in these sediments. 1 94 Fe/Al C e n t r a l B a s i n i r 0 0 .20 .40 .60 .80 1.00 S i l l i r T r 00 .20 .40 .60 .80 1.00 S a n d . 00 .20 .40 .60 .80 1.00 F i g . 41: H i s t o g r a m of d i s t r i b u t i o n of the F e / A l r a t i o s i n S a a n i c h I n l e t s e d i m e n t s . 195 O S i I I A S a n d 1 1 1 1 • i " i i i i I I I I 0 0.5 1.0 1.5 %K F i g . 42: Correlation" between %Fe and %K in Saanich Inlet sediments. 196 Fig. 4 3 : Distribution of the F e / K ratio. 1 9 7 The presence of a s i g n i f i c a n t amount of hornblende in the s i l l ( p a r t i c u l a r l y toward the Cowichan estuary) and some nearshore sediments could also be deduced from the XRD data (Table 33). The accumulation of t h i s r e l a t i v e l y heavy mineral in these samples i s consistent with the formation of a lag deposit in these shallower environments. Because of i t s highly variable composition, the impact of the presence of hornblende on the elemental composition of the s i l l sediment i s d i f f i c u l t to assess. It should, however, be minor, although i t could contain some of the Fe and Mg present in these samples. This mineral was present only as traces in the central basin sediments. 4.3.2.3.6 TITANIUM There i s a strong c o r r e l a t i o n between T i and Al in the diatomaceous ooze (Fig. 44, r=0.97). In contrast, the T i content of s i l l and nearshore samples i s s i g n i f i c a n t l y lower and does not correlate with A l . Titanium occurs as titanium oxides (ilmenite, anatase, r u t i l e ) , which are stable during weathering, and substitutes for Al in clay minerals (e.g. Deer et a l . , 1966). An increase in T i / A l r a t i o with quartz content and grain size has often been reported (e.g. H i r s t , 1962; Spears and Kanaris-Sotiriou, 1976) and has been attributed to the r e l a t i v e accumulation of T i oxides in lag deposits as a result of current.sorting. Such a trend i s not apparent in Saanich Inlet since the s i l l and nearshore sediments have a lower T i / A l r a t i o . This suggests either that Ti 198 199 does not occur primarily as a discrete heavy mineral or that i f such mineral does accumulate in high energy depositional environments, i t s eff e c t on the T i / A l r a t i o i s masked by the simultaneous accumulation of feldspars. A further indication of the pa r t i t i o n i n g of T i can be obtained by studying i t s relationship with Fe (Fig. 45). A very good correlation i s obtained between these two elements in the central basin (r=0.93). Moreover, unlike A l , Fe strongly correlates with Ti in the s i l l sediments (r=0.94). The slopes of the regression lines are i d e n t i c a l in both environments, suggesting control by the same mineral; however, the s i l l sediments have invariably an excess of~0.1% Ti when compared to the central basin sediments with the same iron content. This implies that Ti does accumulate in the s i l l sediments but i t s eff e c t on the T i / A l r a t i o i s concealed by the simultaneous increase in Al due to the accumulation of plagioclases (which contain only traces of T i (Deer et a l . , 1966)) and the winnowing of opal and organic matter. This i s consistent with the conclusions drawn e a r l i e r from the analysis of the other major elements. The excellent c o r r e l a t i o n between Ti and Al or Fe in the central basin would suggest that, in this environment, Ti i s almost exclusively controlled by clay minerals, although i t s presence as clay-size TiC^ Phases i s also possible (see Goldschmidt, 1954). 200 201 Some of the Ti present in the s i l l sediment could also come from the amphiboles which were i d e n t i f i e d in these samples (section 4.3.1). These minerals tend to have a r e l a t i v e l y high T i / A l r a t i o (e.g. Rankama and Sahama, 1950). The slope of the regression l i n e in F i g . 44 suggests that the mineral phases which control the Ti d i s t r i b u t i o n in the deep basin have a T i / A l ~ 0.083 which i s high compared with f e l s i c materials (Rankana and Sahama, 1950; Spears and Kanaris-Sotiriou, 1976). This may r e f l e c t the volcanic o r i g i n of the rocks which dominate the Saanich area (Spears and Kanaris-Sotiriou, 1976). From the intercept on the Al axis (Fig. 44), i t can be concluded that at least .1.2 wt % Al (or more i f some TiC^ i s equally d i s t r i b u t e d throughout the anoxic sediments) must be contributed by an aluminosilicate which does not contain Ti (e.g. plagioclase), thus suggesting an upper l i m i t for the amount of feldspar-Al present in these sediments. The intercept of the Fe-Ti regression l i n e also indicates that at least 1-1.5 wt % Fe must have been introduced in the anoxic sediments as oxides, which is in accord with the conclusions previously drawn (section 4.3.2.5). 4.3.2.3.7 CONCLUSIONS Due to the large uncertainties and s i m p l i f i c a t i o n s made in the discussion of the major elements, each of the individual conclusions drawn are tentative. However, the consistency obtained from a l l the major element data suggests that some 202 confidence can be given to the general picture inferred from their d i s t r i b u t i o n . The s i l l sediments, p a r t i c u l a r l y in the eastern branch of the S a t e l l i t e Channel, are characterized by a lag deposit dominated by quartz and plagioclase which accumulates due to winnowing by r e l a t i v e l y strong t i d a l currents. Up to 75% of the Al present in these sediments can be accounted for by a plagioclase with a composition close to andesine, which i s the main feldspar present in the rocks of the Vancouver Volcanics and the Sicker Series that dominate the region (section 4.2.3). The remaining Al i s present in clay minerals (mainly i l l i t e and c h l o r i t e ) and amphiboles which control the Fe, Mg, K, and Ti d i s t r i b u t i o n s . The presence of small quantities of K-feldspar and traces of T i oxides i s also l i k e l y . The sediments from the Cowichan Bay area have a composition d i s t i n c t from the rest of the s i l l sediments. They seem to contain more clay minerals, p a r t i c u l a r l y c h l o r i t e , since they have s i g n i f i c a n t l y higher Fe/K and Fe/Al r a t i o s . This i s consistent with the presence of metamorphosed volcanic rocks, composed mainly of c h l o r i t e , in the Sicker Series (see section 4.2.3). In the central basin, the d i s t r i b u t i o n of Si i s mainly controlled by opal, although X-ray d i f f r a c t i o n also reveals the presence of some quartz and plagioclase. On the basis of their Ca 203 and Na contents, up to 50% of the Al present in these sediments could be present in feldspars. However, the T i d i s t r i b u t i o n suggests that t h i s mineral cannot account for more than 25% of the t o t a l A l . The Fe d i s t r i b u t i o n confirms t h i s l a s t estimate and further indicates that a much higher proportion i s unlikely, since i t would require an u n r e a l i s t i c a l l y high input of iron oxides to the sediments. This implies that some of the Ca and Na in the central basin must occur in clay minerals. Consequently, i t can be concluded that the lithogenous fractio n of the central basin sediments consists in part of plagioclase, which accounts for ~25% of the Al present, the remainder being d i s t r i b u t e d between clay minerals ( c h l o r i t e , i l l i t e and probably k a o l i n i t e ) . The good cor r e l a t i o n found between Fe and Mg over the entire i n l e t suggests that these elements are e s s e n t i a l l y controlled by the same phase, most probably c h l o r i t e , although an addition of 1-1.5% Fe as oxides i s also l i k e l y . Fe correlates also with K in the sediments of the central basin. The main K-bearing mineral in these sediments i s probably i l l i t e which has hydrodynamic properties similar to c h l o r i t e , and therefore accumulates in the same environments. The nearshore sediment composition tends to r e f l e c t the mineralogy of the adjacent . rock l i t h o l o g i e s . For instance, samples SAG11, SAG14, SAG29, SAG33, and SAG41, on the eastern shores of the i n l e t have d i s t i n c t i v e l y low Fe/K and Fe/Al ra t i o s , which would be expected from the weathering residue of the 204 adjacent granodiorite batholith and . Colquitz gneiss (quartz d i o r i t e ) . In contrast, the nearshore sediments found at the mouth of Tod Inlet show a d i s t i n c t i v e l y more mafic character ( i . e . high Fe/K and Fe/Al) r e f l e c t i n g the composition of the Vancouver Volcanics which are the main source rocks for these sediments. A l l nearshore sediment samples have r e l a t i v e l y high Na/Al and Ca/Al, r e f l e c t i n g the accumulation of plagioclase. They are also characterized by high S i / A l ratios which indicate the accumulation of d e t r i t a l quartz (section 4.3.2.3.2, F i g . 33). 4.3.2.4 PHOSPHORUS The concentration of phosphorus in Saanich Inlet sediments i s very low (Appendix IV-1) and does not show any well-defined d i s t r i b u t i o n pattern. Phosphorus probably occurs in d e t r i t a l apatite which i s present as a secondary mineral in the surrounding rocks (Clapp, 1913), and in organic matter (correlation between %P and %C : r = 0.65). org 4.3.2.5 SULPHUR The accumulation of sulphur in marine sediments i s primarily due to the p r e c i p i t a t i o n of iron sulphide formed by the reaction between d e t r i t a l iron and H2S produced by the metabolic a c t i v i t y of sulphate-reducing bacteria. Organic sulphur, which i s , in part, also produced by diagenetic reactions with reduced sulphur species (see chap. 2), also accounts for a s i g n i f i c a n t , 205 although generally smaller, proportion of the sulphur present. As expected, the sulphur concentration in Saanich Inlet sediments is higher in the central basin deposits where free F^S i s generally found throughout the sediment column (Fig. 46). There i s a cor r e l a t i o n between C and S (r=0.78; F i g . 47) in org 3 the s i l l and nearshore sediments which were deposited under oxic conditions. Such a relationship has often been observed (e.g. Berner, 1984) and i s explained by the fact that the amount of l a b i l e organic matter used by sulphate reducers, and therefore the amount of H2S produced, i s proportional to the t o t a l carbon deposited. This covariation i s not expected to be p a r t i c u l a r l y strong since the proportion of l a b i l e materials present in organic detritus i s highly variable, depending mainly on the o r i g i n of the organic matter (Lyons and Gaudette, 1979) and on the extent of prior oxic degradation (Westrich and Berner, 1984). The lower S/C r a t i o obtained in these sediments (ca. 0.16; Fig 47) compared to the average values for "normal marine sediments" (0.33, Berner and Raiswell, 1983) may r e f l e c t a s i g n i f i c a n t t e r r e s t r i a l component in the organic fraction of these samples. In the sediments from the central basin, the %C Q rg vs %S c o r r e l a t i o n breaks down and comparatively more sulphur i s present (Fig 47). This is a sulphur d i s t r i b u t i o n pattern commonly found in anoxic environments (e.g. Berner and Raiswell, 1983; Berner, 1984) in which S accumulation depends more on Fe rather than C a v a i l a b i l i t y . The tendency for a lower S/C r a t i o in the sediments 206 Fig. 46: Distribution of sulphur. 207 1 -5H 1 .cH CO 0 . 5 t • •• • C e n t r a l B a s i n O S i I I A S a n d 2 3 % C o r g F i g . 47: Correlation between %S and %Crt„ in Saanich Inlet sediments. org 208 towards the head of the i n l e t suggests the presence of a lower amount of reactive iron in these samples. 4.3.2.6. MINOR ELEMENTS The d i s t r i b u t i o n of minor elements in sediment i s affected by a wide range of environmental variables. As discussed in section 4.1, i t has been argued that various factors can lead to their p r e f e r e n t i a l accumulation, p a r t i c u l a r l y in organic-rich anoxic sediments. However, most of these elements are also found in s i g n i f i c a n t concentration in the l a t t i c e s of the p r i n c i p a l rock-forming minerals which constitute the bulk of the lithogenous fraction of the sediments. Different minerals have di f f e r e n t minor constituents, and therefore one must expect that the minor element d i s t r i b u t i o n w i l l be s i g n i f i c a n t l y affected by the mineralogy of the sediments concerned. The d i s t r i b u t i o n of the minor elements amongst the di f f e r e n t rock-forming minerals i s primarily determined by their a b i l i t y to replace a major cation in a host c r y s t a l l a t t i c e . Such a b i l i t y results mainly from the s i m i l a r i t y in size and electronegativity of the two ions involved. Thus i t i s possible to discern a general pattern in the p a r t i t i o n i n g of trace elements' in igneous rocks (e.g. Krauskopf, 1979). Some ions w i l l primarily substitute for K + (e.g. Rb +, Cs +, B a + + , and P b + + ) , and therefore w i l l occur c h i e f l y in minerals produced during the late, stage of magmatic c r y s t a l l i z a t i o n (K-feldspars, micas). Others w i l l substitute more readily for Mg (Cr, Co, Ni) or Fe (Mn, V, Ti) and w i l l tend to be 209 higher in the mafic end of the c r y s t a l l i z a t i o n sequence ( i . e . in o l i v i n e , pyroxene, hornblende). They w i l l occur at higher concentrations in ultramafic rocks, basalts and gabbros. Also, some minor elements (e.g. Cu, Pb, Zn, Hg, Cd) w i l l not substitute readily for any of the major elements and w i l l occur in igneous rocks primarily as sulphide phases, which can separate from the melt at any stage of the c r y s t a l l i z a t i o n , depending on the sulphur concentration in the magma. Consequently, i f one wishes to investigate the environmentally-controlled enrichment mechanisms for trace metals, i t i s imperative f i r s t to determine the extent of mineralogical control on the observed d i s t r i b u t i o n pattern. This is p a r t i c u l a r l y true in the present study since both mineralogy and the d i s t r i b u t i o n of major cations suggest a clear d i s t i n c t i o n between the mineralogy of the anoxic sediments in the central basin (higher clay content with a more mafic signature) and their oxic counterparts from shallower environments. The minor element concentrations in Saanich Inlet sediments are reported in Appendix IV-1. 4.3.2.6.1 RUBIDIUM AND BARIUM The ionic radius of Rb (1.57 A) and i t s ele c t r o p o s i t i v e character make i t a p a r t i c u l a r l y suitable cation for substitution + ° for K (ionic radius: 1.46 A). Therefore, t h i s element w i l l be found mainly in the K-feldspars and micas, and w i l l occur at 210 higher concentration in f e l s i c rocks. A good co r r e l a t i o n between K and Rb i s found in the sediments from the central basin (Fig. 48, r=0.96) with an intercept close to zero. This indicates that, as expected, K and Rb are confined to the same mineral phase(s). On the s i l l , two groups of samples can be distinguished (Fig. 49). On the western s i l l , towards Cowichan Bay, most of the Rb/K ra t i o s are found within the 2 (T range of values obtained for the central basin sediments (Fig. 48), although they tend to be s l i g h t l y higher in potassium. On the other hand, the values obtained for the eastern s i l l sediments l i e outside the 2 0" boundaries, thus strongly suggesting that the lower Rb/K values recorded in thi s environment are s i g n i f i c a n t . This can be interpreted as r e f l e c t i n g a change in the predominant K-bearing mineral from both environments. It has been reported that the Rb concentration is generally higher in micas than in K-feldspars (Rankama and Sahama, 1950). The lower Rb/K ratios obtained on the eastern s i l l (Fig. 48) could therefore be due to the presence of r e l a t i v e l y more K-feldspars r e l a t i v e to micas in this lag deposit. This i s consistent with the occurrence of the lowest Rb/K rati o s in the nearshore sediments, p a r t i c u l a r l y those adjacent to the granodiorite batholith where the influence of K-feldspars would be expected to be the strongest. The much higher Rb/K found in deep-sea clays (60-70 ppm/%, Calvert and Price, 1977) further supports the occurrence of a higher Rb/K r a t i o in clay minerals 211 / / / 1 1 — 1 1 ' ' ' I I I I I I I I I 0 0.5 1.0 1.5 %K F i g . 48: Correlation between K and Rb in Saanich Inlet sediments. 212 Fig. 49: Distribution of the R b / K ratio. 213 compared to feldspars. A Rb enrichment in the clays of the Gulf of Paria was also reported and attributed to the p r e f e r e n t i a l absorption of Rb + over K + prior to deposition (Hirst, 1962b). However, the low Rb/K r a t i o of seawater (120 Xiq/l Rb +, 416 mg/1 K +, Riley and Chester, 1971) would argue against such a p o s s i b i l i t y . Barium also substitutes for potassium in rock-forming minerals; however their co-variation i s not as well-marked as that between K and Rb. Because of i t s higher ionic p o t e n t i a l , B a + + tends to p r e f e r e n t i a l l y enter e a r l y - c r y s t a l l i z i n g K minerals, thus producing a higher Ba/K r a t i o in mafic rocks (Krauskopf, 1979). The barium concentration in the sediments of Saanich Inlet shows a gradual decrease towards the head of the fjo r d (Fig. 50). This indicates that i t i s mainly present in aluminosilicates. However, a more detailed analysis of i t s d i s t r i b u t i o n reveals that, although not enriched in the organic-rich sediments, some biogenic form of barium must also be present. This i s c l e a r l y shown when considering the d i s t r i b u t i o n of Ba/K r a t i o s . Since Ba proxies for K in aluminosilicates, an increase in thi s r a t i o in the sediments w i l l r e f l e c t an additional source of barium. Not only has thi s r a t i o higher values in the nearshore sediments in which XRD and major elements analysis suggested a higher feldspar concentration (presumably because of a higher Ba/K r a t i o in these feldspars), but i t has also d i s t i n c t l y higher values towards the 214 Fig. 50: Distribution of Ba . 215 Fig. 51: Distribution of the B a / K ratio. 216 2 0 0-.' i i i i i i i 2 4 6 8 S i / A l F i g . 52: Correlation between Ba/K and S i / A l ratios in Saanich Inlet sediments. 217 head of the i n l e t (Fig. 51). Moreover, a good correlation can be found between the Ba/K and the Si / A l r a t i o s of the sediment samples col l e c t e d from the s i l l and central basin (r = 0.92; Fig. 52). This indicates that besides lithogenous Ba, present in aluminosilicates, there i s an additional source of barium d i r e c t l y or i n d i r e c t l y linked to opaline s i l i c a , although this input does not produce an increase in the absolute Ba concentration in these sediments. This i s because the concentration of Ba in t h i s biogenic phase i s not higher than in the lithogenous phase. If we assume that the biogenic barium i s present in opal, i t is possible to estimate the Ba concentration in t h i s phase. For t h i s purpose, the data from SAG3, which is a t y p i c a l sample with a high opal content (Fig. 52) can be used. The winter samples, c o l l e c t e d from s e t t l i n g particulates c o l l e c t o r s which contain very l i t t l e opal (Sancetta and Calvert, 1987), provide an estimate of the S i / A l and Ba/K ratios of the aluminosilicate phase ^ S ^ / A l ^ n t h = c a " 3 « 5 ' (Fig. 87); ( B a / K ) ^ t ^ = ca. 366, (Fig. 98)). Hence, the opal and biogenic Ba concentrations in sediments can be estimated by, viz %opal = [%Si - (%A1 x ( S i / A l ) l i t h ) ] x 2.14 Ba b i Q(ppm) = [Ba(ppm) - (%K x ( B a / K ) l i t h ) ] The data from SAG3 give, v i z %opal = [30.3 - (3.51 x 3.5)] x 2.14 = 38.5 Ba b i o(ppm) = [311 - (0.60 x 366)] = 95 218 which correspond to a barium concentration of ca. 250 ppm in the opaline s i l i c a . This value i s of the same order than the estimate given by Dehairs et a l . (1980). There i s however another possible explanation to the d i s t r i b u t i o n of Ba in Saanich Inlet sediments. Some species of microflagellate algae (e.g. Pavlova sp.) are known to contain barite micro-crystals in their cytoplasm (Fresnel et a l . , 1979), and i t has been suggested that such algae, rather than diatoms, could be the main conveyor of Ba to marine sediments (Calvert and Price, 1983). These micro-algae are able to compete with diatoms in nutrient-depleted waters only. Such conditions are more frequently met towards the head of the i n l e t , where a lower rate of primary production has been measured (Calvert, unpublished), due to higher s t r a t i f i c a t i o n of the water column. Therefore, the higher Ba/K rati o s found in the inner f j o r d sediments could r e f l e c t an input of barite from such algae, rather than an association of Ba with opaline s i l i c a (see also section 4.4.3.1). 4.3.2.6.2 STRONTIUM Strontium can replace both K and Ca in mineral l a t t i c e s . The analysis of Saanich Inlet sediments reveals a rather strong c o r r e l a t i o n between Ca (corrected for carbonates) and Sr in most of the sediment samples (Fig. 53). However, th i s relationship breaks down in some nearshore sands, p a r t i c u l a r l y those adjacent to the granodiorite batholith, which are r e l a t i v e l y poor in Sr 219 • C e n t r a l B a s i n O S i I I A S a n d 0 1.0 2.0 3.0 % C a ( non - c a r b o n a t e ) F i g . 53: Correlation between Sr and Ca in Saanich Inlet sediments. 100 2 2 0 compared to lithogenous Ca. Strontium seems therefore to be primarily held in the plagioclase feldspars, and as such is r e l a t i v e l y enriched in the nearshore sands (Table 37) with the exception of those co l l e c t e d in the proximity of the granodiorite. The constant Sr/Ca r a t i o obtained over most of the i n l e t (in the central basin, s i l l , and many nearshore areas) suggests that their plagioclase component (and possibly other Ca-bearing phases) originated from similar rock types, presumably the Vancouver Volcanics and the Sicker Series which contain andesine as one of the p r i n c i p a l mineral phases (Clapp, 1913). The nearshore samples, with d i s t i n c t l y lower Sr/Ca values, probably r e f l e c t the influence of the plagioclase present in the granodiorite which probably has a d i f f e r e n t r a t i o . Strontium is also present in CaCO^. As discussed in section 4.3.2.2, the main source of carbonate in Saanich Inlet i s a limestone quarry situated at Bamberton. This limestone is characterized by a r e l a t i v e l y low Sr/Ca r a t i o which can be estimated in the following manner. A linear regression of Sr/Al vs c c a r j 3 % in the sediments c o l l e c t e d in the zone of influence of the quarry y i e l d s the equation, viz Sr/Al (ppm/%) =5.6 C c a r b % + 35 (r=0.93) Since the Al concentration in these sediments is approximately 4.5%, i t can be concluded that an addition of 1% C c a r b P r°duce an increment of ~25ppm Sr. Thus the limestone 221 Table 37: Average Sr/Al ratios in the d i f f e r e n t types of sediment present in Saanich Inlet. Sr/Al 56+7 42+1 33 + 7 Nearshore sediments Eastern s i l l Central basin 222 has a Sr/Ca ~0.3X10 . In contrast, the s h e l l fragments which were present in the SAG 51 sample produced an increment of ~255ppm Sr per % C c a r b , corresponding to a Sr/Ca r a t i o in the carbonate - 3 phase of approximately 3x10 which i s t y p i c a l of aragonite (Goldschmidt, 1954). 4.3.2.6.3 NICKEL AND CHROMIUM The d i s t r i b u t i o n of nick e l and chromium in igneous rocks is generally closely related to the d i s t r i b u t i o n of Mg and Fe 2+ ° (Krauskopf, 1979). Ni ions have an ionic radius (0.77 A) close 2+ o to that of Mg (0.80 A), thus allowing a diadochic substitution in the l a t t i c e of Mg-bearing minerals (Rankama and Sahama, 1950). Sim i l a r l y , Cr can substitute for Mg and Fe . However, the d i s t r i b u t i o n of thi s element i s further complicated by i t s a b i l i t y to undergo oxido-reduction reactions. When oxidized, i t can readily form independent chromium minerals, mainly chromian members of the spinel group which often occur in basic rocks (Rankama and Sahama, 1950). In Saanich Inlet, nickel shows a d i s t i n c t enrichment in the diatomaceous ooze of the central basin and in Cowichan Bay (Fig 54). However, since these sediments are also characterized by a higher content of mafic minerals (section 4.3.2.3), i t i s necessary to further investigate this d i s t r i b u t i o n before concluding that an environmentally-controlled Ni enrichment i s occurring. The co r r e l a t i o n between Ni and Mg over the entire i n l e t , 223 Fig. 5 4 : Distribution of Ni. 224 which would be expected i f the Ni d i s t r i b u t i o n was primarily controlled by the mineralogy of the sediment, is very poor (Fig. 55, r=0.24). However, the three sediment types (nearshore, s i l l , and central basin) can be c l e a r l y distinguished on t h i s figure. The highest Ni/Mg ratios are found in the anoxic sediments and the lowest in the nearshore sands, while the s i l l sediments display intermediate values. Moreover, the regression c o e f f i c i e n t within each of these "provinces" i s much more s i g n i f i c a n t , p a r t i c u l a r l y for the s i l l and nearshore sediments which contain less organic matter. Also, the regression l i n e for the anoxic sediments has a very large intercept. A l l t h i s suggests that, superimposed on a mineralogically-controlled d i s t r i b u t i o n , there is a nickel enrichment associated with the conditions of deposition in the central basin. This i s more c l e a r l y shown in Fig . 56 where Ni/Mg rat i o s are plotted against % c o r g « There i s a very clear increasing trend of Ni/Mg in organic-rich sediments. Such a relationship indicates that either the "excess Ni" i s d i r e c t l y associated with organic matter, or that the environment of deposition i s conducive to the simultaneous accumulation of Ni and organic matter. Moreover, Fig 56 shows that the Ni/Mg increase i s more accentuated in the anoxic sediments than in their oxic counterparts. This suggests either that another enrichment mechanism s p e c i f i c a l l y linked with anoxic conditions i s involved, or that Ni i s s l i g h t l y enriched in a heavy mineral fra c t i o n which accumulates in low-carbon, coarser-grained 225 0 0 . 5 1.0 1.5 2 . 0 % M g F i g . 55: Correlation between Ni and Mg in Saanich Inlet sediments. 226 ioj • C e n t r a l O S i I I A S a n d B a s i n I I I I I I I 1 2 3 % C o r g F i g . 56: Relationship between Ni/Mg and %C in Saanich Inlet sediments. g 227 sediments. It seems well-established however, that Ni i s enriched in organic-rich sediments. The chromium d i s t r i b u t i o n in Saanich Inlet sediments does not show any clear evidence for a chromium enrichment in the central basin (Fig. 57). Moreover, i t s r e l a t i v e l y poor c o r r e l a t i o n with Mg (r=0.63), when a l l the sediment samples are considered, implies that i t s presence in the l a t t i c e of Mg and Fe-bearing minerals i s not the only factor c o n t r o l l i n g i t s d i s t r i b u t i o n . When considering only the anoxic sediment samples from the southern and eastern part of the central basin, an excellent c o r r e l a t i o n i s obtained between Cr/Mg and %C (Fig. 3 org 3 58, r=0.94), indicating a control mechanism similar to that suggested for Ni whereby Cr would be enriched in organic-rich sediments. In contrast to the nickel d i s t r i b u t i o n , chromium concentrations are r e l a t i v e l y high in nearshore and s i l l sediments. This i s c l e a r l y shown in F i g . 59 where the d i s t r i b u t i o n of "excess Cr" (calculated by substracting the Cr/Mg ra t i o expected from the organic carbon content, using the regression data from F i g . 58, from the Cr/Mg act u a l l y measured) is mapped. The largest excess is found in the eastern part of the S a t e l l i t e Channel where r e l a t i v e l y high turbulence favors the accumulation of heavy minerals (Section 4.3.2.3). This d i s t r i b u t i o n strongly suggests the presence of chromite or a similar mineral in these sediments and in most of the nearshore environments. The presence of t h i s mineral would not be t o t a l l y 228 Fig. 5 7 : Distribution of Cr. 229 %c o r g F i g . 58: Correlation between Cr/Mg and %C in Saanich Inlet sediments. g 230 F ig . 59: D is t r ibu t ion of " e x c e s s " C r . 231 unexpected, since i t i s known to be r e l a t i v e l y common in the o l i v i n e - r i c h inclusions found in basaltic rocks (Deer et a l . , 1 966) . In conclusion, while both nickel and chromium are present in Fe and Mg-bearing minerals which accumulate p r e f e r e n t i a l l y in the central basin, there i s evidence for a further enrichment in these two metals in the anoxic organic-rich sediments. The d i s t r i b u t i o n of the two elements d i f f e r s however in that Cr i s also enriched in lag deposits, presumably because of the accumulation of chromite or si m i l a r minerals derived from the nearby b a s a l t i c rocks. 4.3.2.6.4 VANADIUM AND MANGANESE Vanadium (V +^, V + 4 , and V +^) and Mn (Mn + 2) are strongly enriched in basic rocks, and are often found to correlate closely with Fe and Mg (Krauskopf, 1979). Vanadium shows a d i s t i n c t enrichment in the central basin of Saanich Inlet and in Cowichan Bay (Fig. 60). Furthermore, i t s good c o r r e l a t i o n with Ni in the central basin and s i l l sediments (Fig. 61, r=0.89) suggests that a similar mechanism may be c o n t r o l l i n g the d i s t r i b u t i o n of these two elements in these environments. This i s again c l e a r l y shown on a plot of V/Fe vs %C (Fig. 62) which indicates a vanadium enrichment in the org 3 organic-rich central basin sediments. Moreover, the nearshore sands seem to be the s i t e for the accumulation of a V-rich heavy mineral. F i g . 61 also shows a good correlation between Ni and V 232 Fig. 60: Distribution of V. 233 2 501 2004 £ a. Q. 15 0-1 1 00-i 50-1 • C e n t r a l B a s i n O S i 1 1 A S a n d 0 1 0 2 0 p p m N i I I I 30 40 F i g . 61: Correlation between V and Ni in Saanich Inlet sediments. 234 235 in the nearshore samples (r=0.90), suggesting that the same phase is c o n t r o l l i n g both elements in these samples. The d i s t r i b u t i o n of manganese also shows an enrichment in the central basin sediments. Some high Mn values (>900 ppm) seem e r r a t i c a l l y d i s t r i b u t e d , mainly in the central part of the i n l e t (Fig. 63). The three sediment types (nearshore, s i l l and anoxic ooze) can be readily distinguished on a Mn/Fe vs % c o r g plot (Fig. 64). The anoxic oozes tend to have high Mn/Fe r a t i o s . The increase however varies e r r a t i c a l l y (there are no correlations with organic carbon, carbonate carbon, or sulphur) and seems to be confined to the southern half of the i n l e t (Fig. 65). The s i l l sediments are characterized by a r e l a t i v e l y low Mn/Fe which stays f a i r l y constant throughout the range of organic carbon content observed, thus confirming that organic matter is not involved in the enrichment process. F i n a l l y , the nearshore sands are distinguished by a r e l a t i v e l y higher Mn/Fe r a t i o . Since Mn and V (and therefore Ni) covary to a large extent in these sediments (Fig. 66, r=0.91), i t may be concluded that t h i s i s due to the accumulation of a heavy mineral f r a c t i o n r e l a t i v e l y enriched in these three elements. The complete lack of covariation with chromium (r=-0.20), which i s p r i n c i p a l l y enriched in the lag deposit present in the eastern part of the s i l l , implies that a d i f f e r e n t mineral i s contributing to i t s d i s t r i b u t i o n . Carbonate p r e c i p i t a t i o n i s a mechanism whereby Mn could be 236 Fig. 63: Distribution of Mn. 237 4 0 0 -i . 3 0 0 0 L L 2 0 0 1 0 0 • • C e n t r a l B a s i n O S i 1 1 A S a n d • • \* * / • • • • • • • • • • • • • • ( o o 0 ^ o oo • • • • 1 ) 1 2 3 4 5 % C o r g F i g . 64: Relationship Saanich Inlet between Mn/Fe and %C in sediments. g 238 Fig. 65: Distribution of the Mn/Fe ratio. 239 A A I 0 200 4 0 0 6 0 0 p p m Mn F i g . 6 6 : Correlation between Mn and V in nearshore sands. 240 concentrated in anoxic sediments (Li et a l . , 1969; Klinkhammer, 1980; Pedersen and Price, 1982). It requires, however, the 2+ presence of enough Mn in the pore waters to exceed the s o l u b i l i t y product of rhodochrosite (Johnson, 1982).Such a concentration could only be attained i f enough Mn oxides reach the sediment surface. In Saanich Inlet, such an input is possible only after aeration of the water column. There are indications that during the flushing of the i n l e t very large quantities of Mn 2 + oxides are produced by the oxidation of Mn ( G r i l l , 1982). If these oxides sink into the anoxic sediment (see also section 2+ 4.4.3.6), they w i l l be reduced, thus increasing l o c a l l y the Mn concentration to values which could possibly exceed Mn carbonate s o l u b i l i t y . 4.3.2.6.5 ZINC AND LEAD Zinc i s p r i n c i p a l l y a chalcophile element (Krauskopf, 1979). However, i t s a f f i n i t y with sulphur i s less prominent than that of other t r a n s i t i o n metals, and the amount of Zn found in early magmatic sulphides i s r e l a t i v e l y low. Because of their s i m i l a r i t y 2 2 ^* 2 in ionic size, Zn can substitute for Fe and Mg . Therefore, amphiboles, pyroxene, and b i o t i t e are the main zinc c a r r i e r s in igneous rocks (Rankama and Sahama, 1950). In Saanich Inlet, zinc shows a higher concentration in the central basin (Fig. 67) which f a l l s again to lower values in the southernmost part of the i n l e t (Finlayson Arm). A plot of Zn/Fe vs %C shows a clear increase in Zn with organic matter without org 3 241 Fig. 67: Distr ibut ion of Zn. 242 an indication of a p r e f e r e n t i a l accumulation under anoxic conditions as the linear r e l a t i o n holds for the three sediment provinces (Fig. 68). However, the sediments from Finlayson Arm are r e l a t i v e l y depleted in Zn. In contrast, high Zn values are obtained for the sediments c o l l e c t e d near the Bamberton Quarry, presumably due to a s i g n i f i c a n t concentration of t h i s element in the limestone. Although lead i s also considered a chalcophile metal, since i t readily forms sulphide minerals, i t occurs in igneous rocks c h i e f l y in K-bearing minerals such as K-feldspars and micas and is r e l a t i v e l y enriched in a c i d i c rocks. Notwithstanding the marked d i s s i m i l a r i t y between the chemical properties of lead and ++ ° potassium, Pb (ionic radius: 1.26 A) seems able to substitute + ° for K (ionic radius: 1.46 A) in rock-forming minerals (Rankama and Sahama, 1950; Krauskopf, 1979). As for zinc, the lead d i s t r i b u t i o n shows the presence of a s i g n i f i c a n t l y higher concentration in the central basin, with an apparent depletion in Finlayson Arm sediments (Fig. 69). A plot of Pb/K vs % c o r g (Fig. 70) c l e a r l y shows the importance of K-bearing minerals and organic matter (or an associated factor) in explaining the Pb d i s t r i b u t i o n in Saanich sediment. Unlike zinc, however, Fi g . 70 suggests a p r e f e r e n t i a l Pb enrichment in. the anoxic sediments. In t h i s case, the negative Pb/K intercept obtained by extrapolating the regression l i n e drawn through the ooze samples (not considering Finlayson Arm sediments) supports 243 501 10 s v v Bamberton Quarry Fnlayson Arm • C e n t r a l B a s i n 0 S i l l A S a n d 0 2 i i 3 % C o r g F i g . 68: Relationship between Zn/Fe and %C in Saanich Inlet sediments. org 244 Fig. 69: Distribution of Pb. 245 F i g . 70: Relationship between Pb/K and %C in Saanich Inlet sediments. g 246 the view that at least some of the Pb has been added independently of the organic matter. There i s also a very s i g n i f i c a n t Pb contamination associated with the a c t i v i t i e s of the Bamberton Quarry (Fig. 70). It can therefore be concluded that Zn and Pb are enriched in the organic-rich sediments from the central basin. Furthermore, the data suggest that Pb is add i t i o n a l l y concentrated through a process d i r e c t l y linked to anoxic conditions (possibly sulphide p r e c i p i t a t i o n ) . It i s however more d i f f i c u l t to present a rationale for the behaviour of these two elements in Finlayson Arm. These samples represent the most reducing sediments found in the i n l e t (Gucluer and Gross, 1964). They have the highest organic carbon content and the lowest sedimentation rates (Table 35). Moreover, the water column in t h i s part of the i n l e t i s r e l a t i v e l y more isolated, and during years of weak flushing i t may not be renewed (e.g. 1965: U.B.C. Oceanography Data Report, 1966). If the enrichment process were due to sulphide p r e c i p i t a t i o n from the water column, a stronger metal enrichment in such an environment would be expected. On the contrary, a very s i g n i f i c a n t Zn and Pb depletion i s observed. Such a discrepency cannot be readily explained by a variation in the mineralogy of these sediments. The K/Al (Fig. 34) and Fe/K (Fig. 43) di s t r i b u t i o n s show a r e l a t i v e potassium depletion in these same sediments. This i s thought to r e f l e c t an input of mafic minerals from the Goldstream River catchment area. Such a source would 247 contain K-bearing minerals formed early in the c r y s t a l l i z a t i o n 2+ sequence. Such phases would be expected to contain more Pb r e l a t i v e to K + (Krauskopf, 1979) and therefore cannot explain the observed Pb d i s t r i b u t i o n . Moreover, zinc is the only element predominantly present in Fe- and Mg-bearing minerals which shows this depletion anomaly. If a mineralogical control were to explain such a d i s t r i b u t i o n , one would expect similar patterns with other elements, such as V, Cr, Mn, and Ni. Consequently, although a possible effect due to the presence of a d i f f e r e n t lithogenous component in these sediments cannot be completely ruled out, i t seems more l i k e l y that the depletion of Pb and Zn in Finlayson Arm r e f l e c t s their geochemical behaviour in t h i s environment. Further study i s necessary to c l a r i f y these processes. 4.3.2.6.6 COPPER 2+ 2 + Although Cu may replace Fe in mineral structures, the copper present in igneous rocks c h i e f l y occurs in sulphide minerals (Rankana and Sahama, 1950; Krauskopf, 1979). These sulphides are oxidized during weathering and C u + + i s released into solution. Therefore, very l i t t l e Cu i s expected to be present in lithogenous d e t r i t a l materials. Copper is strongly enriched in the central basin sediments and in Cowichan Bay (Fig. 71). A very good co r r e l a t i o n (r=0.96, Fi g . 72) i s obtained between Cu/Mg and %C in s i l l and 248 Fig. 71: Distribution of Cu. 249 I I I I I I I I I I 2 3 4 5 % C o r g F i g . 72: Relationship between Cu/Mg and %C Q in Saanich Inlet sediments. g 250 nearshore samples and anoxic oozes deposited towards the s i l l of the i n l e t . Southward, and p a r t i c u l a r l y in Finlayson Arm, the Cu content of the anoxic sediments i s in large excess to that expected from their organic carbon contents. This i s c l e a r l y indicated on F i g . 73 where the d i s t r i b u t i o n of "excess Cu/Mg" ( i . e . Cu/Mg measured - Cu/Mg deduced from the organic carbon content) i s shown. This d i s t r i b u t i o n suggests a p r e f e r e n t i a l accumulation of Cu under the conditions pr e v a i l i n g in this environment, i.e lower sedimentation rates and predominantly intensely anoxic conditions, possibly by sulphide p r e c i p i t a t i o n (Jacobs and Emerson, 1982). F i g . 72 also suggests that only ca. 25% of the Cu present in Finlayson Arm sediments i s held within mineral l a t t i c e s . 4.3.2.6.7 MOLYBDENUM On average, a concentration of ca. 1.5 ppm Mo i s found in the earth's crust (Krauskopf, 1979). Because of i t s r e l a t i v e l y high charge and large ionic radius, molybdenum cannot readily substitute for any of the major cations present in the l a t t i c e s of aluminosilicates. It accumulates, along with other s i m i l a r l y incompatible elements, in the l a s t d i f f e r e n t i a t e s produced during magmatic c r y s t a l l i z a t i o n , and consequently i s found in r e l a t i v e l y higher concentration in ac i d i c rocks, and p a r t i c u l a r l y granite where i t occurs mainly as MoS2 (Rankama and Sahama, 1950; Krauskopf, 1979). The molybdenum content of Saanich Inlet sediments deposited 251 Fig. 73: Distribution of "excess" Cu. 252 on the s i l l and in nearshore environments i s below detection l i m i t (3 ppm). In contrast, in the anoxic oozes, the Mo concentration gradually increases towards the head of the i n l e t and reaches values of up to 128 ppm in Finlayson Arm (Fig. 74). This very strong Mo enrichment has also been reported by Gross (1967), and is invariably associated with anoxic environments (Bertine and Turekian, 1974; Jones, 1974; Pilipchuk and Volkov, 1974; Calvert, 1976). Among the minor elements, molybdenum shows the largest enrichment in the anoxic sediments compared with lithogenous debris. 4.3.2.6.8 ZIRCONIUM Like molybdenum, zirconium i s an incompatible element which does not readily substitute for any major element present in aluminosilicates (Krauskopf, 1979). Consequently, i t becomes enriched in the la s t c r y s t a l l i z a t i o n products of igneous processes where i t i s mainly r e s t r i c t e d to the accessory mineral zircon (ZrSiO^). This mineral i s very stable during weathering (Rankama and Sahama, 1950), and thus tends to accumulate in d e t r i t a l deposits, although i t can be found in a l l size grades, and therefore also be present with clay minerals (Hirst, 1962b). The zirconium d i s t r i b u t i o n in Saanich Inlet sediments shows a d i s t i n c t i v e l y higher concentration in the s i l l sediments (Fig. 75). This probably r e f l e c t s d i l u t i o n by biogenic and authigenic materials in the central basin. Since Zr/Al r a t i o s of the s i l l sediments (av. 22.7 +2.3, n=12, 10") are s l i g h t l y higher 253 Fig. 74: Distribution of Mo. 254 Fig. 75: Distribution of Zr. 255 than in the central basin (av. 18.0 +1.1, n=26, 10"), thi s may indicate a p r e f e r e n t i a l accumulation of zircon in the s i l l sediment. 4.3.2.6.9 CONCLUSIONS While the d i s t r i b u t i o n of Ba, Rb, Sr, and Zr i s e s s e n t i a l l y c o n t r o l l e d by the mineralogy of the sediments, the behaviour of most t r a n s i t i o n metals r e f l e c t s t h e i r b i o p h i l i c and/or ch a l c o p h i l i c nature and displays a much more complex picture. A l l the t r a n s i t i o n elements analyzed (except Mn and Mo) show a strong co r r e l a t i o n with organic matter after correction for their l a t t i c e - h e l d f r a c t i o n . In some instances (Ni, V, Cr, and Zn), thi s association seems to explain the enrichment observed in the central basin, while in other cases (Pb, Cu, and Mo) an additional source, d i r e c t l y linked to the anoxic conditions which often develop in the i n l e t , i s c l e a r l y needed. The association of these elements with organic matter can be either d i r e c t ( i . e . within the organic matrix, or adsorbed) or indirec t (e.g. adsorbed on fine-grained sediments associated with higher organic carbon concentration). Additional enrichment under anoxic conditions can be due to sulphide p r e c i p i t a t i o n either from the water column or at the sediment/water interface. Lower sedimentation rates occurring towards the head of Saanich Inlet w i l l enhance the importance of t h i s second p o s s i b i l i t y , and may help explain the s i g n i f i c a n t l y higher Cu and Mo concentrations 256 found in th i s part of the i n l e t . 4.3.2.7 IODINE AND BROMINE The contrasting geochemical behaviour of these two elements in marine sediments i s well documented (Price and Calvert, 1977). The re l a t i o n s h i p between bromine and organic carbon i s invariably linear and i s not affected by the redox regime of the environment of deposition, while iodine i s comparatively enriched at the surfaces of sediments deposited under oxic conditions (see Chap. 3). Analyses obtained from Saanich Inlet confirm these observations. There i s an excellent linear c o r r e l a t i o n between Br and % c o r g throughout the i n l e t (r=0.97, F i g . 76), with an intercept close to the o r i g i n , thus confirming that bromine i s not affected by redox chemistry and i s e n t i r e l y associated with the organic matter. On the other hand, the r e l a t i o n s h i p between iodine and organic carbon is much more complex and r e f l e c t s the impact of the redox potential on iodine geochemistry. The black oozes from the central basin have a s i g n i f i c a n t l y lower I/C ratios than the nearshore sands, while the s i l l sediments y i e l d intermediate values (Fig. 77 and 78). This i s consistent with the presence of a mechanism whereby iodine i s added to the s u r f i c i a l sediments under oxic conditions. This phenomenon i s discussed in d e t a i l in chapter 3. 257 258 Fig. 77: Distribution of the I/C ratio. 259 o r g F i g . 78: Correlation between I and %C in Saanich Inlet sediments. ° ^ 260 4.4 ELEMENTAL FLUXES IN SAANICH INLET FROM AUGUST 1983 TO SEPTEMBER 1984 The elemental fluxes measured at the stations SI-9 and SN0.8 are shown in Appendix IV-3. Some seasonal events, such as freshwater discharge peaks and flushing of the i n l e t , are l i k e l y to influence the par t i c u l a t e fluxes in the i n l e t . An evaluation of the timing of these events would therefore help to interpret the flux data. The run-off from the Cowichan River during the period of interest i s shown in F i g . 79. The fresh-water input into the i n l e t was very small during late summer and early f a l l 1983, and rose abruptly to a maximum in mid-November. There was a second lesser peak in early January, followed by a general downward trend throughout spring. By mid-June and through summer, very low values were again observed. Such a pattern i s t y p i c a l of thi s region (e.g. Herlinveaux, 1962), c l o s e l y following the p r e c i p i t a t i o n . Another important source of fresh water into Saanich Inlet comes from the Fraser River. The discharge variations of t h i s r i v e r are not associated with the p r e c i p i t a t i o n pattern, but are linked to the snow-melt in the Coast Ranges. Discharge i s therefore at i t s maximum in June and July (Fig. 79). This water c a r r i e s large quantities of fine sediment. It eventually reaches the i n l e t (Waldichuk, 1957) and thus may be another s i g n i f i c a n t 261 in 1 1 1 A S O N D J F M A M J J 1 1 A S 300 J F i g . 79: Fraser and Cowichan River discharge from August 1983 to September 1984 (data from Environment Canada, 1984; 1985). 262 source of d e t r i t a l materials. The s a l i n i t y , oxygen and hydrogen sulphide p r o f i l e s in the water column, measured at three stations during the sampling period, are reported in F i g . 80. From the H2S and 0 2 p r o f i l e s , i t is readily apparent that very l i t t l e water renewal occurred in 1983. H2S was detectable at depth throughout the year of sampling u n t i l June 1984. There was no noticable increase in the H 2S concentration in the deep basin during spring, suggesting that i t had reached steady-state. The shallowest traps were permanently situated in oxygenated water. On the other hand, the deepest traps were c o l l e c t i n g materials in the anoxic water column, while those at mid-depth were positioned near the oxic/anoxic boundary (Fig. 80). Between June 18^ "^  and August 24^, dramatic changes occurred in the water column, as the deep water of the entire i n l e t was renewed. This i s shown c l e a r l y on the 0 2/H 2S p r o f i l e s (Fig. 80). In August, oxygen was present throughout the water column at station SI-9 and H 2S had completely disappeared, while at station SN0.8, some traces of H 2S were s t i l l apparent at mid-depth (between 100 m and 160 m), probably the remnants of upwelled anoxic bottom water. Several weeks l a t e r , a l l traces of H 2S had disappeared from the entire water column. Deep-water renewal i s also shown in F i g . 81, where s a l i n i t y and 0 2/H 2S p r o f i l e s for June 18 and August 24 are compared. These p r o f i l e s show c l e a r l y the aeration of the deepest part of the water column by a water mass of higher s a l i n i t y . There is also a 263 Aug.8, '83 Nov .28 , '83 Jan .12 , '84 June 18, '84 Aug.24, '84 Nov.8, '84 S (%o) 28 30 3228 30 3228 30 3228 30 32 H 0 S Cumol/I) 0 40 80 0 40 80 0 40 80 0 40 80 P i g . 80: 3°/oo and 0 2/H 2S p r o f i l e s i n the water column over t h e time of sa m p l i n g o f t h e s e t t l i n g p a r t i c u l a t e s . 264 1 5 0 1 0 0 Og (ml/l) 2 0 4 0 6 0 8 0 HgS (umol/l) O 0 2 ( m l / l ) • S (%o) A H 2 S Cumol/I) A u g . 2 4 , 1 9 8 4 J u n e 1 8 , 1 9 8 4 B 1 0 0 1 5 0 2 0 0 S (%o) 0 2 0 4 0 6 0 8 0 H 2 S Cumol/I) F i g . 81: Comparison between the S°/oo and 0^ p r o f i l e s measured in the water column on June 18 and August 24, 1984. 265 s i g n i f i c a n t decrease in oxygen concentration at mid-depth, presumably due to i t s consumption by H^S from the displaced bottom water. The upper 30 m were found to be less saline in August. This could be due to the a r r i v a l of the Fraser River water discharge, whose eff e c t i s generally l i m i t e d to the upper 50 m of the water column (Herlinveaux, 1972). 4.4.1 FLUXES OF ORGANIC MATTER The fluxes of organic carbon and nitrogen at station SI-9 and SN0.8 are reported in Appendix IV-3. 4.4.1.1 STATION SI-9 4.4.1.1.1 45 M A well-defined seasonal v a r i a t i o n in the flux of organic carbon can be observed at thi s depth (Fig. 82) with a maximum in 2 July and August (500-600 mgC/m .day), and a minimum in December 2 and January (100-200 mgC/m .day). There i s also a clear d i s t i n c t i o n in the nature of the s e t t l i n g organic matter. In winter, a r e l a t i v e l y high C/N r a t i o (9-10) indicates a larger proportion of t e r r e s t r i a l organic matter compared with the material c o l l e c t e d in spring and summer whose C/N rati o s (6.5-7.5) suggest a predominantly planktonic o r i g i n . The C/N rat i o of the material c o l l e c t e d in the presence of NaN^ decreases abruptly during February and March. On the other hand, in the traps without preservative, the C/N r a t i o of the co l l e c t e d material 266 A S O N D J F M A M J J A S 1 0 9 O 8 5 7 8 0 0 n 6 0 0 - E Jr " 4 0 0 -\ 2 0 0 S I - 9 ( 1 1 0 m) • • • N a N «• - - » n o N a N 1 2 0 0 1 0 0 0 >• 8 0 0 x ^ = E CT o 6 0 0 o CT O E 4 0 0 2 0 0 H 1 0 9 O 7 S I - 9 ( 1 5 0 m) • • N a N * • - - > • n o N a N A S O N D J F M A M J J A S F i g . 82: Seasonal f l u x e s of organic carbon at s t a t i o n SI-9 (45 m, 110 m, and 150 m). 267 decreased e a r l i e r (December and January) and was consistently lower than that of the preserved material throughout summer (Fig. 82) . 4.4.1.1.2 110 M The flux of organic carbon at 110 m i s invariably larger than the flux recorded at 45 m (Fig. 83), although i t shows the same seasonal fluctuations (Fig. 82). This probably r e f l e c t s the l a t e r a l advection of resuspended materials from the nearby s i l l . This input i s p a r t i c u l a r l y important during the flushing period (June-August; F i g . 82). The C/N r a t i o drops sharply in March (Fig. 82), suggesting the presence of r e l a t i v e l y fresh planktonic material in the par t i c u l a t e s c o l l e c t e d in spring and summer. The C/N r a t i o of non-preserved trap materials was always lower than that of preserved materials from A p r i l to September. 4.4.1.1.3 150 M The flux of organic carbon at 150 m was intermediate between the flux at 45 m and 110m, which seems to indicate that a large part of the resuspended materials from the s i l l passes over t h i s set of traps and i s transported further towards the head of the i n l e t (Fig. 83). This s i t u a t i o n i s , however, reversed during the flushing period. Presumably, the material which was resuspended from the s i l l by the high-density water i s transported to the deeper part of the i n l e t , and co l l e c t e d in the deeper traps. The r e l a t i v e l y low C/N r a t i o observed during spring and summer (Fig. 268 1 2 0 0 1 0 0 0 8 0 0 i >> O O 5 4 0 0 2 0 0 J S I - 9 • 4 5 m 1 1 0 m o ° 1 5 0 m A S O N D J F M A M J J A S F i g . 83: Variations in the organic carbon fluxes with depth at s t a t i o n SI-9. 269 82) indicates the presence of r e l a t i v e l y fresh planktonic matter, presumably originating from the b i o l o g i c a l front present over the s i l l (Parsons et a l . , 1983). This material i s mostly resuspended and trapped in the central basin. This i s consistent with the observation made on the d i s t r i b u t i o n of organic matter in the in l e t sediments (see section 4.4.1). There was, however, no systematic difference between the C/N ratios of preserved and non-preserved trap materials at thi s depth. 4.4.1.2 STATION SN0.8 4.4.1.2.1 50 M The carbon flux at station SN0.8 i s s i g n i f i c a n t l y smaller than at station SI-9. This i s consistent with the presence of a zone of higher primary production at the mouth of the i n l e t . As for station SI-9, a seasonal fluctuation in the organic carbon flux i s also observed, with a maximum in summer (250-300 2 2 mgC/m .dy; F i g . 84) and a minimum in winter (~50 mgC/m .dy). The summer maximum i s however reached e a r l i e r (April) than at station SI-9 (July; F i g . 82). The C/N ra t i o also decreases sharply in February and March from winter values of ca. 8-9 to 5.5-6 in March, and stays r e l a t i v e l y low (6-7.5) throughout summer (Fig. 84). As observed at station SI-9, t h i s r a t i o tends to be lower in the materials c o l l e c t e d without preservative. 4.4.1.2.2 130 M and 180 M The fluxes at these two depths are almost i d e n t i c a l , 270 0-1 , , , • i , . , . . 1 1—•— A S O N D J F M A M J J A S 0 \ i 1 1 1 1 1 1 1 1 1 1 1—1— A S O N D J F M A M J J A S O A S O N D J F M A M J J A S F i g . 84: Seasonal f l u x e s of organic carbon at s t a t i o n SN0.8 (50 m, 130 m, and 180 m). 271 0 I i 1 1 1 1 1 1 1 1 1 1 1 1— A S O N D J F M A M J J A S F i g . 85: Variations in the organic carbon fluxes with depth at s t a t i o n SN0.8. 2 7 2 suggesting a minimal amount of resuspension (Fig. 85). The seasonal variations are s t i l l present but somewhat dampened (Fig. 84). During winter, the carbon fluxes increase with depth, suggesting a certain degree of l a t e r a l advection, while in summer a decrease in the C flux with depth i s observed, thus indicating that the main source of organic carbon at th i s station i s the euphotic zone. The seasonal variations in C/N rati o s found at these depths are very similar to those observed at 50 m. Moreover, the C/N rati o s of the materials recovered without NaN, were always lower than those recovered in the presence of the preservati ve. 4.4.1.3 DISCUSSION The organic materials c o l l e c t e d from the sediment traps deployed in Saanich Inlet have several origins whose r e l a t i v e importance varies in time and space. Marine sources are predominant in spring and summer. They consist mainly of sinking planktonic c e l l s during the early part of the spring bloom, and fecal p e l l e t s in late spring and throughout summer. Unlike planktonic c e l l s , which can only originate from the euphotic zone, f e c a l material can be egested at any depth in the water column because of the d i e l v e r t i c a l migration of zooplankton (e.g. Barry, 1967). This source of organic matter i s d i r e c t l y dependent on the rate of carbon f i x a t i o n by photosynthetic organisms in the euphotic zone, thus 273 Table 38: Annual carbon and aluminium fluxes and accumulation rates in sediment at station Depth C „ Flux C/N ( 2 ) Al Flux C/Al org (gC/m2 yr) (gAl/m 2 yr) 45 m 122 ( 1 1 2 ) ( 3 ) 8.0+0.5 102 (102) 1.20 (1.10) 110 m 181 (164) 8.2+0.5 240 (230) 0.75 (0.71) 150 m 179 (140) 8.3+0.5 289 (214) 0.62 (0.65) Sediment 77 9.8+0.5 169 0.46 (1) Preserved trap materials. (2) Weighted average over the year of sampling. (3) Numbers in brackets indicate average fluxes and rati o s obtained omitting the two months of flushing (July and August, 1984). 274 explaining the higher flux of carbon found just below the 2 euphotic zone at SI-9 (122 gC/m .yr; Table 38) compared with SN0.8 (57 gC/m2.yr; Table 40). The t e r r e s t r i a l component of the organic matter found in the sediments of Saanich Inlet originates mainly from water run-off, and therefore i t s input follows the rive r discharge pattern. The Cowichan River i s the main source of t e r r e s t r i a l debris and has a maximum discharge in f a l l (Fig. 79). The r e l a t i v e proximity of SI-9 to Cowichan Bay explains the higher flux of carbon at t h i s station during the winter months (C n flux from 12/1/84 to 3 org 5/3/84: SI-9, 160 mgC/m2.dy; SN0.8, 53 mgC/m2.dy). Lateral transport of resuspended sediments from shallower environments is also a very important consideration, p a r t i c u l a r l y for station SI-9, due to i t s proximity with the s i l l of the i n l e t (Fig. 27). It has been argued that the s i l l sediment i s mainly composed of a lag deposit which i s produced by the sorting effect of r e l a t i v e l y strong t i d a l currents (section 4.3). The effect of this resuspension i s expected to be p a r t i c u l a r l y evident in the deepest traps (110 m and 150 m) deployed at SI-9, thus explaining the s i g n i f i c a n t increase in carbon fluxes with depth observed at t h i s station (Fig. 83). This increase could also be partly due to zooplankton migration. However, since such an increase i s not observed at station SN0.8, t h i s mechanism cannot be very important. The comparatively lower carbon accumulation rate in the 275 sediment at station SI-9 compared to the C flux at 150 m (Table 38) can be due to b i o l o g i c a l mineralization of organic matter at the sediment-water interface and to resuspension of the newly-deposited sediment. A comparison.between the Al accumulation rate in the sediment and the s e t t l i n g flux at 150 m allows some d i s t i n c t i o n between these two processes. Table 38 indicates that at station SI-9 the annual Al flux recorded at 150 m i s 1.7 times larger than the Al accumulation rate in the sediment, thus suggesting that resuspension occurs to a s i g n i f i c a n t extent, even though t h i s sediment i s deposited in a stagnant environment. There i s , however, an a l t e r n a t i v e and more l i k e l y explanation. 210 Sedimentation rates, as measured by Pb in sediments, represent an average over several decades, while the trap data reported here estimate the flux of material which occurred between August 1983 and September 1984. Therefore, interannual variations bring a large degree of uncertainty to the conclusions drawn from the comparison of these two sets of data. There are indications that the year of sampling was f a i r l y a t y p i c a l , in that the flushing was exceptionally intensive. This flushing i s responsible for the large increase in flux recorded in the deepest traps at station SI-9 during the months of July and August. Thus, the apparent discrepancy between the Al (and C) flux at 150 m and the sediment accumulation rate may be in part due to an abnormally high flux during the year of sampling. If the two months of flushing are 276 not taken into account in the ca l c u l a t i o n of the yearly average (Table 38; in brackets), the agreement i s much closer, as the Al flux becomes only 1.27 times larger than the accumulation rate. Some resuspension at SI-9 would however be s t i l l necessary to explain the data. It i s l i k e l y that such resuspension would mainly occur during the flushing periods. Notwithstanding such uncertainties, i t i s s t i l l possible to estimate roughly the extent of b i o l o g i c a l mineralization at the sediment interface by ca l c u l a t i n g the C/Al rati o s of s e t t l i n g p a r t i c u l a t e s and sediment. This r a t i o drops from 0.62 at 150 m to 0.46 at the sediment surface (top two cm; Table 38). If we assume that Al and C behave in a similar way during resuspension, i t can be argued that ca. 25% of the organic matter has been mineralized at the interface. However, the assumption made about the hydrodynamic behaviour of Al and C i s probably erroneous, as one would expect a p r e f e r e n t i a l resuspension of low-density organic-r i c h p a r t i c l e s compared to heavier aluminosilicates. The 25% estimate computed above must therefore be taken as a maximum value. The s i g n i f i c a n t decrease in C/Al r a t i o with depth observed in the trap materials (Table 38) c h i e f l y r e f l e c t s the l a t e r a l advection of materials with increasingly lower C/Al ratios due to d i f f e r e n t i a l s e t t l i n g between aluminosilicates and organic-rich p a r t i c u l a t e s rather than organic carbon mineralization. The continuation of such a trend towards the sediment interface would also lead to an overestimate of the extent of b i o l o g i c a l 277 mineralization, thus confirming that the above estimate must be taken as a maximum value. A comparison of the C/N r a t i o s of trap materials and sediment (Table 38) suggests, on the other hand, that most of the carbon mineralization occurs at the sediment interface. Resuspension and l a t e r a l advection at station SN0.8 are expected to occur to a lesser extent because of i t s r e l a t i v e remoteness from the s i l l or any extensive shallow area. In winter, the carbon fluxes at 130 m and 180 m are larger than at 50 m (Fig. 85), thus suggesting some l a t e r a l transport from shallower environments. In summer, the s i t u a t i o n i s reversed, and the carbon flux diminishes with depth. This could indicate that the main source of carbon i s the euphotic zone. Some l a t e r a l transport s t i l l continues through summer, however, as shown by the Al fluxes (Table 39), but the associated carbon is completely masked by the v e r t i c a l flux. This i s in contrast with station SI-9, where l a t e r a l advection i s always quantitatively more important than the flux from the euphotic zone. Since there i s some l a t e r a l transport at station SN0.8, the difference in carbon flux between 50 m and 130 m (Table 39) indicates the minimum carbon mineralized during transport between these two depths ( i . e . at least 15-20%). S i g n i f i c a n t l y less organic carbon seems to have been mineralized in the deepest part of the water column which was anoxic at the time of 278 Table 39: Seasonal C and Al fluxes at station SN0.8. Fluxes (mg/m .dy) Depth Jan.-Feb. Apr.-Aug C Al C Al 50 m 53 130 m 105 180 m 92 270 28 227 59 218 60 279 sampling. The r e l a t i v e consistency of the Al flux between 130 m and 180 m (Table 39) suggests that there i s very l i t t l e l a t e r a l advection at depth or resuspension from the deep basin. The difference between C accumulation rates in sediment and the flux at 180m (Table 40) should therefore r e f l e c t the extent of mineralization at the sediment surface. As for station SI-9, the data suggest that ca. 20% of the s e t t l i n g organic matter is mineralized at the sediment-water interface. During spring and summer, the C/N rati o s were consistently lower in the non-preserved trap materials, except at SI-9, 150 m (Fig. 82). S t a t i s t i c a l treatment of the data obtained from the shallowest traps at both station, using a non-parametric method (Kruskal-Wallis test, Sokal and Rohlf, 1981) suggest that the differences observed are s i g n i f i c a n t at the 95% confidence l e v e l (a similar test did not reveal any s i g n i f i c a n t differences between the C fluxes measured with or without biocide). This observation indicates that instead of having a p r e f e r e n t i a l mineralization of N-containing compounds as has often been noticed in sediments and s e t t l i n g p articulates (e.g. Degens, 1970; Rosenfeld, 1979; Honjo et a l . , 1982; Gardner et a l . , 1983; Wassman, 1983), the b a c t e r i a l colonization of these trap materials was associated with nitrogen enrichment. Such a phenomenon has already been observed, p a r t i c u l a r l y with freshly egested f e c a l p e l l e t s from deposit feeders (Newel, 1965) and detr i t u s derived from estuarine macrophytes (Harrison and Mann, 280 Table 40: Annual carbon fluxes and accumulation rates in sediment at station SN0.8 ( 1 * C „ Flux C/N ( 2 ) Depth o r 9 . (gC/m.y) 50 57 7.4+0.5 130 m 57 7.9+0.5 180 m 55 7.8+0.5 Sediment 43 8.9+0.5 (1) Preserved trap materials. (2) Weighted average over the year of sampling. 281 1975; Rice and Tenore, 1981). Although in some cases the N-enrichment i s due to a p r e f e r e n t i a l release of carbon, a net transfer of nitrogen from seawater to the d e t r i t a l pool has also been observed (Rice, 1982). - This r e l a t i v e accumulation of N in the detritus has been attributed to their colonization by a pr o t e i n - r i c h microbial population (Newel, 1965) or to N-incorporation into humified materials (Rice, 1982). This N-enrichment was not observed in the non-preserved materials c o l l e c t e d in the deepest traps at station SI-9, where resuspension from the s i l l i s the dominant source of carbon. This i s consistent with the observation made by Newel(l965) that only r e l a t i v e l y fresh organic material becomes quickly enriched in nitrogen. Knauer et a l . (1984) also reported a higher C/N r a t i o in materials c o l l e c t e d by sediment traps in the presence of NaN^ r e l a t i v e to those recovered without biocide. However, formaline and Hg + + did not produce such an e f f e c t , thus casting doubt on the p o s s i b i l i t y of a b a c t e r i a l mediation for the N-enrichment observed. 4.4.2 FLUXES OF MAJOR ELEMENTS The fluxes of major elements at stations SI-9 and SN0.8 are reported in Appendix IV-3. These fluxes w i l l mainly r e f l e c t the input of terrigenous materials, and therefore are expected to be linked to rive r discharge, p r i n c i p a l l y from the Cowichan and Fraser River. 282 T3 e 11 S I - 9 ( 4 5 m ) - • N a N 3 • n o N a N „ >• 0 0 3 • T3 J 0 0 2 • CT 0 0 1 • 0 . 4 0 . 3 0 . 2 i 0 . 3 0 . 2 0 . 1 0 0 8 • >* •o eg 0 0 6 • E ^- 0 0 4 • cn 0 0 2 • 0 1 0 • >> •o 0 0 8 • CM E 0 0 6 • cn 0 0 4 ->• 0 . 1 5 J o N E 0 . 1 0 CT 0 . 0 5 A S O N D J F M A M J J A S F i g . 86: Seasonal fluxes of major elements (SI-9 r 45 m). 283 4.4.2.1 STATION SI-9 4.4.2.1.1 45 M The fluxes of A l , Fe, Mg, T i , Ca, and K at t h i s depth show very similar seasonal variations (Fig. 86). A peak was recorded for a l l these elements in November 1983, corresponding to a maximum water discharge from the Cowichan River (Fig. 79). After reaching a minimum in March, a gradual increase was observed and a maximum was reached in summer. This increase may r e f l e c t the increasing abundance of sinking organic aggregates (Fig. 83) which scavenge suspended clays from the water column. This was also suggested by Honjo (1982) to explain the seasonal co-vari a t i o n of biogenic and lithogenic p a r t i c l e fluxes in the Panama Basin. The maximum flux observed in July and August could r e f l e c t the a r r i v a l of the c l a y - r i c h Fraser River plume as was also suggested by the lower s a l i n i t y observed in the upper 30 m of the water column during t h i s period of time (Fig. 81). Si displays a s l i g h t l y d i f f e r e n t seasonal pattern with a r e l a t i v e l y enhanced flux in spring and summer due to the sinking of opaline s i l i c a (Fig. 86). This i s shown more c l e a r l y in F i g . 87 where the seasonal variations of the S i / A l r a t i o are reported and in F i g . 88 where opal-Si has been estimated by substracting the aluminosilicate contribution from the t o t a l Si (the aluminosilicate contribution was estimated by multiplying the Al flux by the S i / A l r a t i o of the winter samples (Fig. 86)). Other elemental ratios show some seasonal v a r i a t i o n in the 284 F i g . 87: Seasonal variations in the S i / A l r a t i o of the s e t t l i n g particulates at station SI-9. 285 S I - 9 ( 45 m) A S O N D J F M A M J J A S F i g . 88: Seasonal fluxes of opaline s i l i c a at s t a t i o n SI-9. 286 S I - 9 ( 4 5 m) — + N a N 3 +--+ no N a N J A S O N D J F M A M J J A S F i g . 89: Seasonal variations in the K/Al and Fe/Al ra t i o s of s e t t l i n g p a r t i c u l a t e s at st a t i o n SI-9 (45 m). 287 chemical composition of the lithogenous materials introduced into the i n l e t . The contrasting behaviour of Fe and K i s shown in F i g . 89, where the seasonal variations in Fe/Al and K/Al ratios are indicated. In the case of Fe/Al, the seasonal fluctuations are very close to detection l i m i t , but there seems to be a downward trend from October 1983 to March 1984. On the other hand, a sharp drop in the K/Al r a t i o i s recorded in November 1983, followed by a gradual increase toward maximum values in summer. The Fe/K r a t i o displays a p a r t i c u l a r l y s t r i k i n g pattern (Fig. 90). A prominent maximum i s associated with the maximum in water run-off (Nov. 1983). Subsequently, i t stays r e l a t i v e l y high throughout winter, drops sharply in March and stays r e l a t i v e l y low through summer. Sim i l a r l y , variations in the mineralogy of the samples could be detected. A summer sample displayed a well-defined o i l l i t e peak (9.8 A) which was almost completely absent in the o November sample (Fig. 91). On the other hand, hornblende (8.4 A) was detected in the f a l l sample but not in the summer sample. Such chemical and mineralogical variations could r e f l e c t a change in the source of the lithogenous material. In winter, during the time of higher water run-off, most of the lithogenous materials at station SI-9 come from the Cowichan catchment area which consists in large part of volcanic rocks (see section 4.2.3) with a predominant mafic character. As the intensity of p r e c i p i t a t i o n diminishes, the importance of t h i s source, compared with that of suspended clay minerals carried by water-masses from more remote 288 S I - 9 ( 45 m) 0 l . i i i i i i i i i i i i i A S O N D J F M A M J J A S Seasonal variations in the Fe/K r a t i o of s e t t l i n g p a r t i c u l a t e s at station SI-9 (45 m). 289 o< 290 areas (such as the Fraser estuary), also decreases. This second source of lithogenous materials seems to contain a s i g n i f i c a n t l y higher proportion of i l l i t e . 4.4.2.1.2 110 M and 150 M Unlike at 45 m, the major element fluxes at 110 m at thi s station do not show any consistent seasonal pattern (Fig. 92). It is l i k e l y that periods of high fluxes correspond to periods of high turbulence on the s i l l which would produce more resuspension and l a t e r a l advection. This resuspension was p a r t i c u l a r l y intense during the month of flushing. This i s c l e a r l y shown by the much larger fluxes obtained at 150 m during July and August (Fig. 93 and 94). Such a flux pattern i s in contrast with that observed for organic carbon which showed a seasonal pattern ( p a r t i c u l a r l y at 110 m) with an increasing trend through spring, superimposed on the "saw-teeth" pattern observed for the major elements (Fig. 82). This suggests that the organic material which i s deposited on the s i l l i s very rapidly resuspended and transported to the deep basin. In spring, low-density, organic-rich particulates w i l l be p r e f e r e n t i a l l y transported upon their a r r i v a l at the sediment/water interface by t i d a l currents, thus explaining the increasing C o r g / A l r a t i o of the material c o l l e c t e d during spring and summer (Fig. 95). During flushing, a p a r t i c u l a r l y strong current has resuspended a much higher load of sediment. This was also r e f l e c t e d in a lowering of the C Q r g / A l r a t i o , p a r t i c u l a r l y 291 SI-9 (110 m) . • +NaN g • no NaNg A S O N D J F M A M J J A S F i g . 92: Seasonal fluxes of major elements (SI-9, 110 m). 292 A S O N D J F M A M J J A S F i g . 93: Seasonal fluxes of Al at station SI-9 (150 m). 293 2.4 2.0 4 S I - 9 - 4 5 m + — + 1 1 0 m » . . . . 4 > 1 5 0 m T3 CM E •— 1.2 J 0 .8 4 0 .4 4 0 i i i i i i . . . . . . • A S O N D J F M A M J J A S F i g . 94: Variations in the Al flux with depth at sta t i o n SI-9. 294 S I - 9 1.0 0 .8 0 .6 -+ _ - + 110 m »....© 1 5 0 m 0.4 i: N A S O N D J F M A M J J A S Seasonal variations in the C /Al r a t i o of the org s e t t l i n g particulates at st a t i o n SI-9 (110 m and 150 m). 295 S I - 9 +--+ 110 m o 150 m CD 4.0 4 3 .6 4 3 .2 4 2CT 4 : e 2.8 i i 1 i 1 1 i i 1 i i i i i J A S O N D J F M A M J J A S F i g . 96: Seasonal variations in the Fe/K r a t i o of the s e t t l i n g p a r t i c u l a t e s at st a t i o n SI-9 (110 m and 150 m). 296 in the 150 m trap (Fig. 95). There were no systematic seasonal variations in the Fe/K ratios (Fig. 96), which i s to be expected i f a large proportion of t h i s material consists of resuspended sediment from the s i l l . The Fe/K annual average of the sediment-trap materials c o l l e c t e d at 110 m and 150 m was 3.52+0.06 and 3.55+0.06 respectively, which i s similar to the average value of the sediments of the central basin (3.4+0.2; F i g . 43) but di f f e r e n t from the r a t i o found in the eastern s i l l sediments (2.6+0.1). S i m i l a r l y , the annual average of the Fe/Al r a t i o s of the trap materials (0.69+ 0.01 and 0.68+0.01 for the 110 m and 150 m traps respectively) i s similar to that reported for the deep basin (0.67+0.04; F i g . 40 and 41), but unlike that from the eastern s i l l (0.48+0.02). Since much of the materials c o l l e c t e d in these traps must be a result of resuspension from the s i l l (since the fluxes of materials increase with depth), these r a t i o s are compatible with t i d a l sorting of the s i l l sediment, p r e f e r e n t i a l resuspension of K-and Fe-rich clay minerals, and the formation of a lag deposit enriched in feldspars (and quartz; see section 4.3, 4.4.1, and 4.4.3) . 4.4.2.2 STATION SN0.8 Only the samples c o l l e c t e d from A p r i l to August were large enough for analysis by XRF. It i s therefore not possible to discuss the seasonal fluctuations in the fluxes of major (and minor) elements at this s t a t ion. 297 One can note however that the fluxes of major elements which were measured at station SN0.8 (50 m) are, on average, one order of magnitude lower than at station SI-9 (Appendix IV-3). Moreover, the Si / A l and C /Al rati o s of the materials c o l l e c t e d org at SN0.8 are much larger than at SI-9 (Table 41). This confirms that, although the carbon flux decreases towards the head of the i n l e t , the underlying sediment has a higher organic carbon and opal content because of a lesser d i l u t i o n by lithogenous materials (see section 4.4.1). There are s i g n i f i c a n t variations in the magnitude of the fluxes of major elements at 50 m over the 5 months analyzed. Higher fluxes of aluminium and iron were obtained during the months of A p r i l and May (Appendix IV-3) probably because of a higher run-off during t h i s period (Fig. 79), compared with late spring and summer when these fluxes decreased by approximately a factor of two. S i l i c o n shows a similar pattern, although this element i s not only controlled by aluminosilicates, but also by biogenic opal. The Al flux increases s i g n i f i c a n t l y between 50 m and 130 m, indicating some l a t e r a l transport at mid-depth (Fig. 97). The fluxes measured at 130 m and 180 m are, however, almost i d e n t i c a l over the period of analysis, thus indicating a minimal amount of l a t e r a l advection and benthic resuspension at thi s station in the deepest part of the basin, even during the month of flushing. 298 Table 41: Average C /Al and Si / A l ratios in sediment trap materials c o l l e c t e d at station SI-9 and SN0.8 from May 5 to August 24, 1984. Depth SI-9 C o r g / A l S i / A l Depth SN0.8 C o r g / A l S i / A l 45 m 1 .6 7.2 50 m 10.3 21.3 110m 0.9 5.2 130 m 3.8 11.8 150 m 0.6 5.0 180 m 3.7 11.4 Sediment 0.46 4.3 Sediment 1 .0 6.0 299 0 . 0 8 0 . 0 4 A S N 0 . 8 ( 5 0 m) ( 1 3 0 m) • • ( 1 8 0 m) 0 A S O ' N D J F M A M J J A S 97: Variations i n the Al fluxes with depth at station SN0.8. 300 4.4.3 FLUXES OF MINOR ELEMENTS The fluxes of minor elements at station SI-9 and SN0.8 are reported in Appendix IV-3. 4.4.3.1 BARIUM From the sediment analysis (section 4.4.6.1), i t has been deduced that Ba d i s t r i b u t i o n in Saanich Inlet i s e s s e n t i a l l y controlled by two phases. While a large proportion of the barium i s present in the aluminosilicates, where i t proxies for K, i t appears also to be present in a biogenic phase, p a r t i c u l a r l y in the central basin sediments where the Ba/K rat i o s correlate well with an estimate of the opal content ( i . e . S i / A l r a t i o s ; Fig. 52). The involvement of barium in biogeochemical processes is well established, p a r t i c u l a r l y in the open ocean. Dissolved Ba correlates c l o s e l y with dissolved s i l i c a and a l k a l i n i t y in the water column (Chan et a l . , 1977). Barium also often occurs in higher concentration in sediments underlying higher productivity zones (Goldberg and Arrhenius, 1958; Brongersma-Sanders, et a l . , 1980; Schmitz, 1987) and i t has been argued that i t can be transported to the sediments as barite c r y s t a l s or in association with ske l e t a l materials (Dehairs et a l . , 1980). Of par t i c u l a r relevance to the present study i s the cor r e l a t i o n found between Ba concentration and opal content in the sediments of the Bering Sea (Goldberg, 1958). However, Calvert and Price (1983) did not find any barium enrichment in the diatomaceous ooze on the 301 Namibian Shelf. Instead, they found higher Ba concentration in the upper reaches of the continental slope which they attributed to a lower sediment accumulation rate, and possibly to the influence of microflagellate algae which are known to secrete barite c r y s t a l s (Fresnel et a l . , 1979). The good co r r e l a t i o n obtained between the concentrations of Ba and K (corrected for sea-salt) at station SI-9 (r=0.92; F i g . 98) confirms the importance of the aluminosilicates. There was no apparent increase in the Ba/K ratios during the summer months (Fig. 99), even at 45 m where a well-defined opal peak was observed (Fig. 87). The Ba/K values obtained at the three depths were indistinguishable and a l l were within the 2O" values of the a n a l y t i c a l error. This suggests that, at this station, biogenic Ba does not have any noticable influence on the Ba concentration of the s e t t l i n g p a r t i c u l a t e s . This i s in sharp contrast with the behaviour of Ba at station SN0.8. In t h i s case, a well-defined Ba/K peak occurred in May-June (Fig. 100), when a similar maximum was observed in the Si / A l r a t i o . Such contrasting behaviour between the two stations could be due to the much higher proportion of opal found in the partic u l a t e s s e t t l i n g at SN0.8. The S i / A l r a t i o corresponding to the Ba/K peak was ca. 34 (Fig. 100). This r a t i o never exceeds 8 at SI-9 (Fig. 87) r e f l e c t i n g the much larger input of lithogenous materials at thi s s t a t i o n . The biogenic Ba s e t t l i n g at SN0.8 can 302 Table 42: Fluxes of biogenic barium at station SN0.8 (50 m). Time of K f l u x Lithogenic Total Biogenic deployment (g/m .dy) Ba flux Ba flux Ba flux (ug/m .dy) (ug/m .dy) (jug/m .dy) 5/3- 9/4 (NaCl) 0. 0074 271+35* 295+30 24 + 65 (NaN3) 0. 0072 263+34 301+30 38 + 64 9/4- 10/5 (NaCl) 0. 0108 395+51 499+50 96+101 (NaN3) — — 394+40 -10/5 -18/6 (NaCl) 0. 0057 209+27 351+36 142+63 (NaN3) 0. 0060 220+29 423+42 203+71 1.8/6 -16/7 (NaCl) - - 212+21 _ (NaN3) 0. 0044 161+21 227+23 66 + 44 16/7 -24/8 (NaCl) 0. 0068 249+32 267+27 18 + 59 (NaN,) 0. 0064 234+30 274+27 40 + 57 * Error bars estimated from a n a l y t i c a l precision (2<T). 303 F i g . 98: Correlation between K and Ba i n the s e t t l i n g p articulates collected at s t a t i o n SI-9 (at the three depths). 304 . 4 5 m 1 1 0 m • o 1 5 0 m A S O N D J F M A M J J A S F i g . 99: Seasonal variations in the Ba/K r a t i o of the s e t t l i n g particulates at station SI-9. 305 S N 0 . 8 (50 m) . + N a N ^ S N 0 . 8 ( 1 8 0 m) + no N a N 0 • i i i i i i i i i i . i • A S O N D J F M A M J J A S . 100: Seasonal variations in the Ba/K and S i / A l ratios of the s e t t l i n g particulates at station SN0.8. 306 SN0.8 (50 m) 3. 200 100 -0 • A S O N D J F M A ' M ' J J A S 101: Seasonal fluxes of biogenic barium at sta t i o n SN0.8 (50 m). 307 be estimated by subtracting the lithogenous Ba flux from the t o t a l Ba flux (Table 42; F i g . 101).The lithogenous f r a c t i o n was° estimated from the K flux and an estimate of the Ba/K r a t i o of the l i t h i c phase ( i . e . the average Ba/K value obtained from the s e t t l i n g particulates c o l l e c t e d at SI-9). This c a l c u l a t i o n assumes that the Ba/K r a t i o of the lithogenous phase at both stations i s i d e n t i c a l , which i s supported by the good co r r e l a t i o n e x i s t i n g between the S i / A l and Ba/K ratios in the i n l e t sediments 2 (Fig. 52). A flux of ca. 150-200 ;ug/m .dy of biogenic Ba was 2 associated with a flux of ca. 0.67 g/m .dy of opaline s i l i c a . This would correspond to a Ba concentration in opal skeletons of 100 - 150 ppm which, considering the large uncertainties on these values, is- in reasonable agreement with the estimate obtained from sediment analysis (ca. 250 ppm; section 4.4.6.1). A similar 2 association at the peak of opal flux at SI-9 (ca. 1.1 g Si/m .dy) 2 would produce an additional Ba flux of ca. 285 ;ug Ba/m .dy. The t o t a l Ba flux at t h i s station, at t h i s time of the year (June 2 through August), varied from 1500 to 3000 ;ug Ba/m .dy, (Appendix IV-3). i . e . the biogenic Ba flux would represent only 10 - 20% of the t o t a l flux. With an a n a l y t i c a l precision in the measurement of the Ba/K r a t i o of ca. 12% (2<T), such a signal would be at the l i m i t of detection. As discussed in section 4.4.6.1, there i s an alternative explanation for the Ba d i s t r i b u t i o n in Saanich Inlet sediments which i s also consistent with the data c o l l e c t e d from the 308 sediment trap moorings. The peak in Ba/K observed at station SN0.8 (and the higher Ba/K values observed in the inner f j o r d sediments) could be due to the addition of barite from microflagellate algae. These algae would not be able to compete with diatoms at SI-9 because of the replenishment of the euphotic zone with nutrients by t i d a l mixing above the nearby s i l l . However, at station SN0.8 the water column is more s t r a t i f i e d , producing a nutrient-depleted surface layer during summer (Sancetta and Calvert, 1987), which would be conducive to the p r o l i f e r a t i o n of such micro-algae. At t h i s stage, i t i s d i f f i c u l t to d i s t i n g u i s h between these two p o s s i b i l i t i e s . The c o r r e l a t i o n between Ba/K and S i / A l in the s e t t l i n g p articulates peak at SN0.8 would seem to weaken the argument for barite input since microflagellates cannot thrive when diatoms are blooming. However, with sampling intervals of + 1 month, species succession within shorter time periods cannot be resolved. A more detailed sampling program, in association with taxonomic determination i s needed to c l a r i f y the nature of the c a r r i e r of biogenic barium. The addition of biogenic Ba does not lead, however, to a Ba enrichment in the central basin sediments because the Ba concentration of t h i s biogenic component i s similar to or lower than that found in the aluminosilicates. This i s also consistent with the observation made by Calvert and Price (1983) in the 309 Namibian Shelf sediments. 4.4.3.2 ZINC, CHROMIUM, LEAD, COPPER, VANADIUM, AND NICKEL The analysis of the surface sediments of Saanich Inlet showed that these elements correlate strongly with organic matter, after correction for their l a t t i c e - h e l d fraction (section 4.4.6). This could be due either to their d i r e c t association with planktonic materials, to their scavenging from the water column by s e t t l i n g p a r t i c u l a t e s , or to diagenetic reactions at the anoxic sediment-water interface. Further indications on the mode of transport of t h i s "excess metal" to the sediments could possibly be obtained by studying the seasonal variations of t h e i r r a t i o s to major elements. This approach i s , however, more ambiguous than when applied to sediment samples since the main sources of lithogenous materials into Saanich Inlet vary from season to season and t h i s i s r e f l e c t e d in their mineralogy and elemental composition (e.g. section 4.4.2). Such seasonal variations are not a concern when looking at correlations in sediments, since the samples analyzed represent an average over several years of deposition. 4.4.3.2.1 ZINC At station SI-9, there i s no evidence for a d i r e c t association between zinc and organic matter at the 45 m l e v e l (r=0.l8), probably because the flux of Zn at t h i s station i s dominated by i t s lithogenous f r a c t i o n (Fig. 102), and the seasonal variations in %C Q rg in the s e t t l i n g particulates are not 310 F i g . 102: Seasonal variations in the Zn/Fe r a t i o of the s e t t l i n g p a r t i c u l a t e s at station SI-9 (45 m) and SN0.8 (50 m). 311 F i g . 103: Seasonal variations in the C /Fe r a t i o of org' the s e t t l i n g p a r t i c u l a t e s at s t a t i o n SI-9 (45 m) and SN0.8 (50 m). 312 large enough to produce s i g n i f i c a n t variations in their Zn/Fe ratios (Fig. 103). However, when considering the results from SN0.8 (50 m), where organic matter concentrations reach much larger values, such an association becomes apparent (Fig. 102). The "excess zinc" which was found in the anoxic sediments from the deep basin may therefore have been added with planktonic debris. This i s also i l l u s t r a t e d in F i g . 104. The Zn/Fe ratios of the s e t t l i n g particulates at station SI-9 (averaged over the year of sampling) are very similar to those found in the underlying sediments. The s l i g h t l y higher r a t i o found at 45 m i s consistent with the presence of Zn associated with planktonic materials. No addition of Zn by diagenetic reactions seems necessary to explain the data. At station SN0.8, the Zn/Fe r a t i o at 50 m (averaged over May to August) i s much higher than in the underlying sediments. Moreover, since the Zn/Fe r a t i o at 130 m i s well below the mixing l i n e between the s e t t l i n g p a r t i c u l a t e s at 50 m and aluminosilicates (i.e with a Zn/Fe r a t i o corresponding to %C Q rg=0), th i s suggests that a large proportion of the zinc present in planktonic materials i s recycled in the water column within the upper 130 m. The Zn/Fe ratios at 130 m and 180 m are very s i m i l a r , indicating that zinc scavenging from the anoxic water column i s minimal. The s i m i l a r i t y between these ratios and those from the underlying sediments also suggests that there i s no s i g n i f i c a n t Zn addition at the sediment-water interface, and therefore that the the "excess zinc" i s indeed associated with 313 F i g . 104: Relationship between Zn/Fe and %C ( s a l t -*• org corrected) i n sediments and s e t t l i n g p a r t i c u l a t e s . 314 organic matter. However, since the values from the s e t t l i n g particulates at SN0.8 are summer averages, one would expect them to be somewhat higher than the annual average. Therefore, the p o s s i b i l i t y that some zinc i s added to the sediment during early diagenesis cannot be e n t i r e l y discounted, p a r t i c u l a r l y considering the large variations in Zn/Fe r a t i o found within the SN0.8 core. Such an addition , however, i s not supported by the relationship between Zn/Fe and %C Q rg in Saanich sediments (Fig. 68; section 4.4.6.5) which does not indicate any p r e f e r e n t i a l accumulation of Zn under anoxic conditions. This relationship suggests an increase of ca. 5.8x10 4 Zn/Fe per % organic carbon, i. e . ca. 1000 >ug Zn per g. of organic material added to the sediment. 4.4.3.2.2 CHROMIUM The chromium concentration in the organic fracti o n of phytoplankton seems low. In many instances, values below 1 ppm have been reported with a maximum concentration of 20 ppm (Martin and Knauer, 1973). The seasonal variations in Cr/Fe ratios (Fe was used instead of Mg because of the d i f f i c u l t y in correcting the Mg values for the presence of s a l t in the trap materials) in the trap materials at the shallowest depth (Fig. 105) suggest, however, that in Saanich Inlet some Cr i s associated with plankton. Although the variations seen at station SI-9 are close to the detection l i m i t (C vs Cr; r=0.64), much higher values org 3 were observed at SN0.8 where planktonic material concentrations 315 105: Seasonal variations i n the Cr/Fe r a t i o of the s e t t l i n g p a r t i c u l a t e s at station SI-9 (45 m) and SN0.8 (50 m). 316 are highest. Cr/Fe rat i o s vs %C Q rg for the SAG samples from the central basin, SI-9 and SN0.8 cores and average trap materials are plotted in F i g . 106. The relat i o n s h i p found in the anoxic sediments of the central basin (r=0.87) i s very similar to that obtained with the Cr/Mg ratios (Fig. 58). Values higher than expected are also found towards the s i l l , which i s also reflected in the SI-9 core. The annual average values obtained from the s e t t l i n g particulates at station SI-9 are very similar to those obtained in the underlying sediments. At station SN0.8, however, where only the summer average i s presented, s i g n i f i c a n t l y higher values are obtained at 50 m. In recent studies, various authors reported a correlation between dissolved s i l i c a and Cr in seawater (Cranston and Murray, 1978; Campbell and Yeats, 1981), suggesting an association between t h i s element and opaline s i l i c a . The coincidence between the S i / A l peak (Fig. 100) and the Cr/Fe peak (Fig. 105) at SN0.8 supports t h i s p o s s i b i l i t y . The s e t t l i n g particulates recovered at greater depth have an average r a t i o which approximately l i e s on the mixing l i n e between the 50 m trap materials and aluminosilicates (Fig. 106). Their Cr/Fe ratios can therefore be explained by l a t e r a l advection of lithogenous materials and a minimal Cr recycling in the water column. There i s no s i g n i f i c a n t difference in the ratio s of the materials c o l l e c t e d at 130 m and 180 m, thus suggesting that scavenging from the anoxic water column i s also minimal. However, due to the large uncertainties in each 317 31 29 27 ~ 25 — 23 21 19 17 15 Ji5Q m -as 1 50 m a1 80'm 130 rrtif' • SAG ("Shipek* grab)-Central basin O Surface sediment (Gravity core) * Mean value for labelled core f~) Standard deviation about mean value A Settling particulates-SI-9 (year average) A Settling particulates-SN0.8 (summer average) 10 11 12 13 org F i g . 106: Relationship between Cr/Fe and % C Q r g ( s a l t -corrected) in sediments and s e t t l i n g p a r t i c u l a t e s . 318 measurement i t i s not possible to di s t i n g u i s h between the addition of non-lithogenous Cr into the anoxic muds by i t s direct 3+ association with planktonic materials and i t s addition by Cr adsorption at the sediment-water interface. Chromate anions, the main Cr species in oxygenated seawater, are reduced to Cr(OH) 2 + in anoxic waters (Emerson et a l . , 1979). Cr(OH) 2 + i s readily adsorbed by parti c u l a t e s ( E l d e r f i e l d , 1970) and could conceivably be incorporated in the sediments. The fact that the mixing l i n e between the s e t t l i n g p a r t i c u l a t e s and aluminosilicates (Fig. 106) is below the sediment regression l i n e (SAG) implies at least that a l l the biogenic Cr reaching the sea-floor must be incorporated into the sediments. The Cr/Mg vs %C„„. c o r r e l a t i o n in the anoxic 3 org muds of the deep basin requires an increase of ca. 8x10 4 Cr/Mg per % organic carbon, i . e . ca. 400;ug Cr per g. organic matter added to the sediments. 4.4.3.2.3 COPPER Although the b i o p h i l i c nature of Cu i s well-established, there i s not any obvious c o r r e l a t i o n between seasonal primary production pattern and the Cu/Fe rat i o s of s e t t l i n g particulates c o l l e c t e d at 45 m at station SI-9 (Fig. 107). Moreover, Cu addition to the sediment during early diagenesis i s not necessary to explain the data at thi s station, since the Cu/Fe of the s e t t l i n g p articulates is similar to that of the underlying sediments (Fig. 108). Such an addition to the anoxic sediments of the deep basin i s , however, strongly suggested by the 319 S I - 9 ( 4 5 m) + N a N 3 A S O N D J F M A M J J A S F i g . 107: Seasonal v a r i a t i o n s i n the Cu/Fe r a t i o of the s e t t l i n g p a r t i c u l a t e s at s t a t i o n SI-9 (45 m) 320 32 F i g . 108: Relationship between Cu/Fe and %C_ in 3 org sediments and s e t t l i n g p a r t i c u l a t e s ( % c o r g values for s e t t l i n g p a r t i c u l a t e s were not salt - c o r r e c t e d ) . 321 r e l a t i o n s h i p between %C Q rg and Cu/Mg (Section 4.3.2.6.6; F i g . 72) or Cu/Fe (Fig. 108), as both have an intercept on the C Q r g axis. This i s supported by the data presented by Jacobs and Emerson (1982) which show a depletion of Cu within the anoxic zone of the water column in Saanich Inlet. Indications of whether th i s addition occurs within the water column or at the sediment-water interface, however, cannot be obtained from the elemental composition of the s e t t l i n g particulates at SN0.8. Some abnormally high values were found in some of the samples (Appendix IV-3) and contamination i s suspected. 4.4.3.2.4 VANADIUM As for the other t r a n s i t i o n metals, there are no indications from the seasonal variations in the V/Fe ratios that the vanadium concentrations in the s e t t l i n g particulates at station SI-9 are influenced by planktonic materials (Fig. 109). Moreover, the values found in the summer samples at SN0.8 (50 m) are not s i g n i f i c a n t l y higher, thus indicating that although a s i g n i f i c a n t enrichment (and c o r r e l a t i o n with organic carbon) was found in the anoxic sediments of Saanich Inlet (Section 4.3.2.6.4, F i g . 60), V i s not d i r e c t l y added to the sediment with planktonic materials. The V/Fe ra t i o s of the s e t t l i n g particulates at both stations are s i g n i f i c a n t l y lower than those found in the underlying sediments (Fig. 110) thus suggesting that a s i g n i f i c a n t fraction of the extra non-lithogenous V in the anoxic sediment was added during early diagenesis at the sediment-water 322 S I - 9 • N a N . o S N 0 . 8 + N a C l V J A S O N D J F M A M J J A S 109: Seasonal variations in the V/Fe r a t i o of the s e t t l i n g p a r t i c u l a t e s at st a t i o n SI-9 (45 m) and SN0.8 (50 m). 323 F i g . 110: 45 m ••.180 m 130 m • A • SAG ("Shipek" grab)-regression line Surface sediment (Gravity core) Mean value for labelled core Standard deviation about mean value Settling particulates-SI-9 (year average) Settling particulates-SN0.8 (summer average) org 6 (%) 8 50 m 10 1 1 Relationship between V/Fe and % c o r g * n sediments and s e t t l i n g p a r t i c u l a t e s ( % c o r g values for s e t t l i n g p a r t i c u l a t e s were not salt - c o r r e c t e d ) . 324 interface. A geochemical association between V and organic matter has often been reported (e.g. Goldschmidt, 1954; Brumsack and Gieskes, 1983). The reduction of vanadate ions (H2VC>4~) to 2 + vanadyl cations (VO ) by humic substances under environmental conditions, with subsequent formation of vanadyl organic complexes, has been demonstrated (e.g. Szalay and S z i l a g y i , 1967; Wilson and Weber, 1979; Templeton and Chasteen, 1980). Such reactions could conceivably occur at the sediment-water interface. Moreover, since humic substances formed under anoxic conditions have a stronger reducing capacity than th e i r counterparts formed in more oxidizing environments (Chapter 1), V uptake by organic materials could be more pronounced in anoxic sediments. A l t e r n a t i v e l y , vanadate could also be reduced to vanadyl in anoxic waters (e.g. van der Sloot et a l . , 1985), v i z HoV0 ~ + 4H + + 1e" = = V 0 2 + + 3Ho0 E =1,000 mv 2 Q 2 O -i.e with a pE = -4 [VO,-] } |-- = ca. 0.05 pH = 7.4 [VO^ ] 2 + At seawater pH, VO hydrolyzes and forms insoluble hydroxides (e.g. F r a n c a v i l l a and Chasteen, 1975), viz V 0 2 + + 20H~ ---> V0(0H) o , * 2 ( S) which could possibly accumulate in anoxic sediments. 4.4.3.2.5 NICKEL The seasonal variations of Ni/Fe at station SI-9 (45 m) suggest that r e l a t i v e l y less Ni reaches the sediment during 325spring and summer (Fig. 111) compared with the winter months, while Ni was barely detectable in the summer samples c o l l e c t e d at SN0.8, thus suggesting that t h i s element i s not d i r e c t l y associated with planktonic materials. Moreover, there was no indication that nickel was scavenged from the water column (Fig. 112). A l l t h i s , therefore, strongly suggests that the increase in Ni concentration found in the anoxic sediments of Saanich Inlet (section 4.4.6.3; F i g . 54) i s the result of an addition of Ni via reactions occurring at the sediment-water interface, and not due to i t s d i r e c t association with planktonic organic matter. F i g . 112 suggests that ca. 2-5 ppm of non-lithogenous Ni per %Fe ( i . e . ca. 6-15 ppm) are added to the sediment at SN0.8, with a sediment accumulation rate of 95 mg/cm .yr (Table 35). This corresponds to a non-lithogenous accumulation rate of ca. 0.6 2 1.5 jjg/cm .yr. The nickel concentration in seawater i s ca. 0.35 3 ng/cm (Jacobs and Emerson, 1982). The Ni added to the sediment should therefore decrease the Ni concentration in the isolated body of water in the deep basin of Saanich Inlet by 30-40%. Such a decrease was not, however, observed in the water column p r o f i l e of Jacobs and Emerson (1982). This could possibly be due to the addition of Ni into the anoxic water by scavenging from the oxic zone by manganese oxides, v i a a mechanism similar to that suggested for Mo (Berrang and G r i l l , 1974). The lower Ni/Fe r a t i o s found in the s e t t l i n g materials at 326 S I - 9 . + NaN 3 S N 0 . 8 • no N a N 3 A S O N D J F M A M J J A S F i g . I l l : Seasonal variations in the Ni/Fe r a t i o of the s e t t l i n g p a r t i c u l a t e s at station SI-9 (45 m) and SN0.8 (50 m). 327 •o 1 8 16 14 1 2 10 • SAG ("Shipek" grab)-Central basin O Surface sediment (Gravity core) * Mean value for labelled core l~l Standard deviation about mean value A Settling particulates-SI-9 (year average) • Settling particulates-SN0.8 (summer average) 130 m 180 m ik50 m org 6 (%) 10 1 1 F i g . 112: Relationship between Ni/Fe and % c o r g * n sediments and s e t t l i n g particulates ( % c o r g values for s e t t l i n g p a r t i c u l a t e s were not salt- c o r r e c t e d ) . 328 station SI-9 during summer compared to the winter samples (Fig. 111) suggest that the lithogenous materials c o l l e c t e d in summer are r e l a t i v e l y poor in Ni compared to the materials brought into the i n l e t from the nearby catchment area by winter run-off. A similar decrease in the Cu/Fe, Cr/Fe, and Zn/Fe ratios of t h i s l i t h i c f r a c t i o n could explain the lack of indications of an association between planktonic materials and various metals (e.g. Cu, Cr, Zn) at SI-9, where an increase in the Cu/Fe, Cr/Fe, and Zn/Fe rat i o s due to addition of organically-held metals could have been masked by a simultaneous decrease in the ratios of the lithogenous f r a c t i o n . 4.4.3.3 MOLYBDENUM Of a l l the elements analyzed, Mo showed the strongest enrichment in the anoxic sediments of Saanich Inlet (section 4.4.6.7). The Mo concentration in the s e t t l i n g particulates at both stations were a l l found to be below detection l i m i t (5 ppm) even in the material c o l l e c t e d in the deepest trap at SN0.8 (180 m) (Appendix IV-3). This observation indicates that molybdenum is added to the anoxic sediments by reactions occurring below 180m, presumably at the sediment-wa-ter interface. At SN0.8, the .rate of accumulation of Mo can be calculated, v i z 2 S M q = 0.1 g/cm .yr x 100 ug/g 2 = 10 jug/cm .yr 329 The Mo concetration in seawater i s ca. 10 ng/l; therefore, such an accumulation would represent the removal over one year of 10-20% of the Mo present in the bottom water of the i n l e t . A decrease of the Mo concentration in the anoxic water, however, may not be apparent since there are indications that i t i s also added to t h i s zone by scavenging from the oxic water by manganese oxides (Berrang and G r i l l , 1974). Various mechanisms have been proposed to explain the accumulation of Mo in anoxic sediments. It could be co-precip i t a t e d as MoSg with the FeS formed at the sediment-water interface (Korolev, 1958; Bertine, 1972). It was also suggested that MoO^~ could be reduced to MoC>2+ in anoxic waters (Bertine, 1972). This cationic species could then be subsequently scavenged by negatively-charged p a r t i c u l a t e s . The presence of organically-bound molybdenum in the pore waters of anoxic sediments (Contreras et a l . , 1978; Brumsack and Gieskes, 1983; Malcolm, 1985), the large Mo concentration found in the humic fraction of anoxic sediments (Nissenbaum and Swaine, 1976; Calvert and Morris, 1977; Calvert et a l . , 1985) and the known a b i l i t y of these organic molecules to reduce MoO^ ( S z i l a g y i , 1967) would support t h i s second hypothesis; however, since NaOH solutions used to extract humic materials, also dissolve MoS^ (Korolev, 1958, Volkov and Fomina, 1972b), the d i s t i n c t i o n between these two p o s s i b i l i t i e s awaits further investigation. It i s interesting 330 to note the large difference in Mo concentration found between the cores c o l l e c t e d at SI-9 and SN0.8 (which i s also r e f l e c t e d in the SAG samples (Fig. 74)). Even though the sediment deposited at SI-9 i s r i c h in sulphide minerals, very l i t t l e Mo accumulates at th i s station (Appendix IV-2.2). The difference cannot be only due to d i l u t i o n by a higher input of lithogenous materials; the sedimentation rate at SI-9 i s less than 3 times that at SN0.8 (Table 35), so that i f Mo were accumulating at a similar rate, at least 30 ppm Mo should be found at SI-9. The difference in Mo accumulation rate must therefore r e f l e c t the chemical environment in which the sediments are deposited. Due to i t s higher degree of i s o l a t i o n , the water column i s more often, and for longer periods of time, anoxic towards the head of the i n l e t . Near the s i l l , although the sediments are e n t i r e l y anoxic, they are often deposited under more oxidizing conditions. Therefore, more permanent anoxic conditions in the water column seem necessary to occasion the accumulation of Mo in anoxic sediments; or a l t e r n a t i v e l y , Mo i s released from anoxic sediments in contact with oxygenated water. The presence of lower Mo concentration in upper section of a core c o l l e c t e d after the intensive 1984 flushing which completely renewed the bottom water (Powys, pers. comm.), compared to SN0.8 (Appendix IV-2.4) which was c o l l e c t e d before the flushing, supports t h i s p o s s i b i l i t y . The molybdenum accumulation rate calculated for station SN0.8 suggests that t h i s type of anoxic environment can be very 331 important for the geochemical balance of Mo in seawater. The 9 river input of dissolved Mo has been estimated at ca. 18x10 g/yr (Martin and Whitfield, 1983). Such an input could be matched by a removal of the type found in Saanich Inlet at station SN0.8 4 2 over an area of ca. 18x10 km ( i . e . less than the area of the Persian G u l f ) . Therefore, i f the history of the Mo concentration in seawater could be deduced from the sedimentary record, i t could be a very sensitive indicator of the extent of anoxic environments in the past, and the absence of any signal should rule out the p o s s i b i l i t y of the occurrence of anoxia in the water column over extensive areas. A better understanding of the mechanism of accumulation of Mo in anoxic sediments i s required, however, before the usefulness of t h i s potential indicator can be assessed. The high Mn concentrations (1.3 - 1.4% Mn)which were found in the deepest traps at station SI-9 in September 1984 ought to have been associated with a measurable amount of Mo (ca. 10 -15 ppm; Berrang and G r i l l , 1974) since scavenging of Mo from seawater by Mn oxides was c l e a r l y indicated in a previous study (Berrang and G r i l l , 1974). However, no molybdenum could be detected in these samples (detection l i m i t : 5 ppm). 4.4.3.4 RUBIDIUM The Rb/K ratios obtained from the analysis of the s e t t l i n g p a r t i c u l a t e s at SI-9 and SN0.8 are very similar (Fig. 113), thus 332 S I - 9 . + N a N 3 S N 0 . 8 + no N a N r — i — i 1 1 i 1 1 1 i i i i A S O N D J F M A M J J A S F i g . 113: Seasonal variations i n the Rb/K r a t i o of the s e t t l i n g p a r t i c u l a t e s at station SI-9 (45 m) and SN0.8 (50 m). 333 confirming that aluminosilicates are the main rubidium c a r r i e r . There seems to be a minimum in the Rb/K r a t i o in spring which may indicate a di f f e r e n t source of lithogenous materials. 4.4.3.5 ZIRCONIUM The Zr/Al r a t i o s of the materials c o l l e c t e d in summer at station SN0.8 at 50 m are s i g n i f i c a n t l y higher than those of the materials c o l l e c t e d at SI-9 (Fig. 114), thus suggesting a possible association of some Zr with planktonic materials. This result requires further investigation. 4.4.3.6 MANGANESE The fluxes of Mn associated with the s e t t l i n g p articulates at both stations show c l e a r l y the influence of the well-established redox chemistry of t h i s element. Throughout most of the year of sampling, the highest Mn flux was intercepted by the traps deployed at mid-depth, i . e . close to the oxic/anoxic boundary (Fig. 115). This, very probably, r e f l e c t s the formation 2 + of manganese oxides from Mn d i f f u s i n g up from the anoxic zone into the oxic water. In August and September, just after the renewal of the bottom water, very large amounts of Mn were col l e c t e d throughout the water column at SI-9 ( p a r t i c u l a r l y at 2+ 150 m) resu l t i n g from the oxidation and p r e c i p i t a t i o n of Mn present in the upwelled anoxic water. The Mn/Fe rat i o s of the s e t t l i n g p a r t i c u l a t e s c o l l e c t e d at 150 m at SI-9 were invariably higher than the r a t i o of the underlying sediment (Fig. 115), suggesting that, although a large 334 F i g . 114: Seasonal variations in the Zr/Al r a t i o of the s e t t l i n g p a r t i c u l a t e s at station SI-9 (45 ra) and SN0.8 (50 m). 335 4000 2000 1000 800 600 400 200 SI-9 . . 45 m • - -+ 110 m • • 150 m - i sed. A S O N D J F M A M J J A S 3 . 115: Seasonal v a r i a t i o n s i n the Mn/Fe r a t i o of the s e t t l i n g p a r t i c u l a t e s at s t a t i o n SI-9 and SN0.8 (recovered i n the presence of NaN^). 336 f r a c t i o n of ' the manganese oxides formed at the redoxcline i s s o l u b i l i z e d in the anoxic water column, some reaches the sediment before being dissolved and recycled to the water column. This i s in contrast with the data c o l l e c t e d from SN0.8, where the Mn/Fe ratios in the deepest traps were very similar to the r a t i o of the underlying sediment, suggesting that , in t h i s part of the i n l e t , most of the oxide d i s s o l u t i o n occured in the water column. Very often, s i g n i f i c a n t l y more Mn was c o l l e c t e d in the traps poisoned with NaN^ (Appendix IV-3, F i g . 116) indicating that Mn was remobilized from the materials c o l l e c t e d without preservatives. 4.4.4 FLUXES OF IODINE The monthly fluxes of iodine at station SI-9 and SN0.8 are reported in Appendix IV-3. A seasonal pattern can be observed in the I/C r a t i o of org the s e t t l i n g p articulates c o l l e c t e d at SI-9 (Fig. 117). This r a t i o i s s i g n i f i c a n t l y higher in winter and drops sharply at the beginning of the spring bloom to values t y p i c a l for planktonic materials (e.g. Bowen, 1979; E l d e r f i e l d et a l . , 1981). The occurrence of a high !/C o rg in winter i s puzzling. A higher C/N r a t i o was also measured in these samples (Fig. 82) which was interpreted as r e f l e c t i n g the larger proportion of t e r r e s t r i a l organic matter brought into the i n l e t by winter run-off. Such 337 3 0 0 0 -> 2 0 0 0 T3 CM X 3 1 0 0 0 -0 S N 0 . 8 ( 1 3 0 m) . . + N a N o +—+ no N a N _ / \ / \ / \ A S O N D J F M A M J J A S F i g . 116: Comparison between the Mn f l u x e s measured at s t a t i o n SN0.8 (130 m) w i t h and without NaN^ poison i n g . 338 F i g . 117: Seasonal variations in the I/CJ r a t i o of the org s e t t l i n g p a r t i c u l a t e s at s t a t i o n SI-9 and SN0.8. 339 materials would, however, be expected to have a very low l / C o r g r a t i o (ca. 0.1x10 4 ; Bowen, 1979). It has been argued (see section 4.5.1.1) that a s i g n i f i c a n t f r a c t i o n of the organic materials c o l l e c t e d in the sediment traps at station SI-9 consists of re-suspended materials from the s i l l sediments. Since these oxic sediments have a much higher I/C r a t i o than org planktonic materials (section 4.3.2.7), their re-suspension could explain the seasonal variations I/C r a t i o observed at SI-9. In org spring and summer, the laterally-advected organic material seems to consist primarily of r e l a t i v e l y fresh plankton, and thus would be expected to have a r e l a t i v e l y low J / C Q r a t i o . F i g . 117 also indicates that, at station SI-9, the I/C of org the s e t t l i n g p a r t i c u l a t e s invariably increases between 45 m and 110 m. This could either r e f l e c t the uptake of iodine by s e t t l i n g p a r t i c u l a t e s as suggested by Malcolm and Price (1984) or re-suspension and l a t e r a l advection of I-enriched s i l l sediments. The I / / C o r g °^ t h e underlying sediment also suggests the displacement of some of t h i s iodine during early diagenesis. S i m i l a r l y , at station SN0.8, there i s a s i g n i f i c a n t increase in the J / C Q J . r a t i o between 50 m and 130 m, apparently followed by a decrease in the anoxic zone ( i . e . between 130 m and 180 m, from March to June, 1984). Since l a t e r a l advection i s much less important at t h i s station (section 4.5.1.2), th i s observation lends support to the p o s s i b i l i t y of iodine uptake by particulates in oxic seawater, with subsequent release in the anoxic zone, 340 possibly via the mechanism suggested in Chap. 3. Al t e r n a t i v e l y , iodine uptake could also occur at the oxic/anoxic boundary in the water column, where iodate could be reduced by l^S to 1^ which could then react with organic matter (Jia-Zhong and Whitfield, 1986). More work i s necessary to dis t i n g u i s h between these p o s s i b i l i t i e s . 4.5 CONCLUSIONS The chemical composition of Saanich Inlet has indicated that many trace metals are enriched in the anoxic ooze found of the central basin of the i n l e t over the possible contributions from lithogenous sources (section 4.3.2.6.9). Spatial and seasonal variations in the chemical composition of the s e t t l i n g p a r t i c u l a t e s c o l l e c t e d with interceptor traps gave further indications of the mode of incorporation of these metals in these anoxic sediments. Biogenic Ba and Cr seem to be mainly associated with opaline s i l i c a , although al t e r n a t i v e explanations are also possible, p a r t i c u l a r l y for Ba. These two metals, however, are not enriched in the anoxic sediments because their concentration in the biogenic phase is lower than in the l i t h i c materials. Zinc seems to be added to the sediment in association with organic matter. There i s no indication that i t i s precipitated or adsorbed from the anoxic water column or at the sediment-water 341 interface. On the other hand, the association of Cu with organic matter alone cannot explain i t s d i s t r i b u t i o n in the sediments of Saanich In l e t . This element must also be added via a mechanism d i r e c t l y linked to the anoxic conditions present in this environment. S i m i l a r l y , Ni, V, and Mo are added to these sediments by reactions occurring at the sediment-water interface. In the nearshore environment studied here, these metals are not associated to any s i g n i f i c a n t extent with planktonic materials, p a r t i c u l a r l y Ni and Mo. Of a l l the elements analyzed, Mo showed the largest enrichment in the anoxic sediments of the central ba s i n. Nearshore sediments deposited under anoxic conditions constitute a very important sink for various trace metals when compared with their accumulation rates in pelagic sediments (Calvert, 1976). Therefore, variations in the areal extent of anoxic basins over geological times could have had a s i g n i f i c a n t impact on the seawater concentrations of these metals. If these concentrations could be deduced from the sedimentary record (possibly from the metal content of mi c r o f o s s i l s in a way similar to that used to deduce the Cd concentrations in the North A t l a n t i c Deep Water over the past 200,000 years (Boyle and Keigwin, 1982); Emerson pers. comm.), the results could be used to estimate the occurrence of anoxic basins in the past. More 342 information on the mode of incorporation of trace metals in sediments (both oxic and anoxic) i s required, however, before the potential of t h i s approach can be adequately assessed. 343 5 . CONCLUDING REMARKS. Although the three problems which were addressed in thi s thesis are c l e a r l y d i s t i n c t , t h i s work confirms the already well-established importance of humic substances in many environmental processes. It was demonstrated that these complex polymers can play a s i g n i f i c a n t role in the sulphur geochemistry of nearshore sediments. The uptake of sulphur by humic materials has a bearing not only on the geochemical cycle of sulphur by providing an additional mechanism whereby sulphur can be removed to the sediments, but also, possibly, on the geochemical cycles of other elements. It was shown that S-addition could increase the complexing capacity of humic substances with respect to Cu. Similar e f f e c t s are l i k e l y to be found for other metals and could influence their accumulation in anoxic sediments. The displacement of iodine from the humic matrix by nucleophilic sulphur species may explain the behaviour of iodine during early diagenesis. The high concentration of thi s element found in s u r f i c i a l oxic sediments could also be due to the reducing a b i l i t y of these ubiquitous organic molecules. This property may also be implicated in the removal of certain metals such as vanadium and molybdenum to the sediments. The role of humic materials in the incorporation of trace 344 metals in marine sediments was not d i r e c t l y addressed in t h i s study. However, the removal of some t r a n s i t i o n metals into nearshore anoxic sediments and the importance of t h i s process for the geochemical cycle of these elements have been examined. It was shown that Ba, Cr, Zn, Pb, Cu, Ni, V, and Mo were enriched in the anoxic ooze found in the central basin of Saanich Inlet, an intermittently anoxic f j o r d situated on the coast of B r i t i s h Columbia. It was also discovered that for some of these metals ( p a r t i c u l a r l y Ni, V, and Mo), the enrichment occurs p r i n c i p a l l y at the sediment-water interface during the very early phase of diagenesis. It i s not known at t h i s stage i f humic substances are d i r e c t l y implicated in the enrichment processes. However, their potential as metal complexers, p a r t i c u l a r l y when enriched in sulphur by reactions with reduced inorganic sulphur species, suggests that they could have an important bearing on the behaviour of these metals in such environments. Humic materials may have two c o n f l i c t i n g roles in the process of metal incorporation in marine sediments. They may, in part, prevent metal accumulation by forming soluble metal complexes which could be released to the water column at the sediment-water interface. This process could be es p e c i a l l y important in anoxic sediments, where metal complexation has been invoked to explain the occurrence of metals in pore waters at concentrations higher than predicted from their sulphide s o l u b i l i t i e s . In t h i s context, the sulphur enrichment of humic 345 polymers, demonstrated in t h i s work, may be of p a r t i c u l a r s i g n i f i c a n c e . On the other hand, they may also enhance the metal accumulation process both in oxic and anoxic environments by increasing the number of binding s i t e s available for metal addition onto the s o l i d phase. The actual role of humic substances in any p a r t i c u l a r environment w i l l depend upon competition between their soluble and insoluble components and also on competition with various mineral phases present in the sediments, such as oxyhydroxides, sulphides or clay minerals. Their significance w i l l depend upon the metal considered and the r e l a t i v e abundance of the various phases involved. The environmental conditions in which the humic materials were formed may also be a very important consideration for their complexing properties. Humification processes under oxic conditions y i e l d a substance r e l a t i v e l y r i c h in O-containing functional groups which are produced by the oxidative cleavage of the organic macromolecules. These functional groups may not be very e f f i c i e n t at complexing trace metals in the presence of much 2+ 2 + larger concentrations of Ca and Mg . On the other hand, under anoxic conditions, the addition of such groups w i l l be prevented and instead a substantial S-addition is l i k e l y to occur. As discussed already, the presence of sulphur functional groups in the humic structure can increase substantially the complexing capacity of these materials by providing complexing s i t e s for 346 which competition by the major cations i s expected to be minimal. Further work i s needed on these very complex problems. There i s l i t t l e doubt that humic materials w i l l be important in many geochemical processes, especially in moderately organic-rich nearshore sediments. This thesis provides a star t i n g point for some of these investigations. 347 6. BIBLIOGRAPHY Ackermann, F. 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(1977) Metal binding organic macromolecules in s o i l 1- Hypothesis interpreting the role of S.O.M. in the translocation of metal ions from rocks to bi o l o g i c a l systems. S o i l S c i . 123, 65-76. 389 APPENDIX I: SAMPLE COLLECTION AND INITIAL SAMPLE PREPARATION. 1-1 BOTTOM SEDIMENTS AND PORE WATERS. Sediment cores were co l l e c t e d from two fjords on the coast of B r i t i s h Columbia (Saanich and Je r v i s Inlets) with a s t a i n l e s s -steel gravity corer (Pedersen et a l . , 1985) using a 8cm inner diameter butyrate core b a r r e l . This coring device has been s p e c i a l l y designed for soft sediments and allows a r e l a t i v e l y undisturbed sampling of the sediment/water interface. Upon recovery of the cores, the sediments were extruded immediately from the core barrel into a n i t r o g e n - f i l l e d glove-box to minimize oxidation of the samples. The butyrate cylinders were removed from the corer weight-stand and clamped d i r e c t l y beneath the plexiglass glove-box. The sediments were extruded into the glove-box through an O-ring sealed port in the base by slowly jacking up a piston into the core b a r r e l . The sediment cores were subsampled at 2 cm depth in t e r v a l and loaded either into 250 ml nitrogen-flushed , acid-washed, linear polypropylene (LPE) bottles, i f the pore waters were to be recovered by centrifugation, or into screw-cap p l a s t i c containers and stored frozen, i f only the s o l i d phase was to be analyzed. The supernatant of the centrifuged samples were c a r e f u l l y decanted and 2 ml were immediately placed into a test-tube with 50 jul of a 2 M zinc acetate solution to pr e c i p i t a t e H 2S which was 390 subsequently measured on board following the method described by Cline (1969). The remaining pore water samples were placed into pre-weighed 30 ml LPE bottles and a c i d i f i e d with 500 >ul cone. HCl. The H 2S was removed by a stream of nitrogen before storage for subsequent sulphate analysis. The sediment samples were immediately frozen or freeze-dried on board (see Chap. 2). Bulk surface sediment samples were c o l l e c t e d from Saanich Inlet at 64 stations with a "Shipek" grab. These samples were stored frozen in screw-cap p l a s t i c containers p r i o r to analysis. After returning to the laboratory, the frozen sediment samples were thawed and dried at 55-60°C and f i n a l l y ground in a tungsten carbide m i l l for 2 minutes. 1-2 SETTLING PARTICULATES. Materials f a l l i n g through the water column were c o l l e c t e d in Saanich Inlet over a 18 month period using sediment interceptor traps designed by K. Iseki, F. Whitney and C.S. Wong -IOS (unpublished). The traps consisted of pairs of PVC cylinders with an internal diameter of 12.5 cm and a height of 48 cm. Baffle grids were placed at the opening of the cylinders and in the sampling chambers to decrease the size of turbulent eddies and mixing within the traps (Gardner, 1980), p a r t i c u l a r l y during deployment and recovery. In order to further l i m i t resuspension of the c o l l e c t e d materials, a saturated NaCl solution (500 ml) 391 was c a r e f u l l y poured at the bottom of each cylinder. Sodium azide (5 g/1) was added to the brine of one of each pair of sediment trap in order to l i m i t b a c t e r i a l a c t i v i t y and investigate the influence of microbial metabolism on the composition of the recovered materials by comparison with the second trap which did not contain any bactericide. N a N 3 i n h i b i t s only aerobic respiration by blocking i t s electron-transport system (cytochrome oxidase) (e.g. Honjo et a l . , 1982; Lee et a l . , 1983; Knauer et a l . , 1984). The prevention of aerobic respiration should likewise i n h i b i t the a c t i v i t y of obligate anaerobic bacteria. However, fa c u l t a t i v e fermentive microbes could possibly s t i l l be growing in the presence of th i s poison (e.g. Lee et a l . , 1983). Each pair of cylinders was mounted on a PVC frame and attached to a 6 mm diameter plastic-impregnated wire (Spacelay) at 3 d i f f e r e n t depths. The l i n e s were positioned on station by a chain-anchor (ca. 150 kg) resting on the sea-floor, and were supported by a sub-surface buoy made of 4 v i n y l f l o a t s (80 kg fl o t a t i o n ) positioned at a depth of 20 m to dampen v e r t i c a l motion due to wave action. A 40 m recovery l i n e was shackled from the main l i n e to a surface marker. In order to recover the sediment trap samples, the surface marker was hauled on board ship and the l i n e wound onto a hydraulic winch via an A-frame at 'one stern of the vessel. Sub-surface f l o a t s and c o l l e c t o r traps were removed from the l i n e 392 succesively as they reached the l e v e l of the deck. The sediment traps were l e f t standing for ca. 30 minutes to allow p a r t i c l e s to s e t t l e after their possible resuspension during the recovery procedure. Seawater was removed from the cylinders through a draining hole placed just above the sampling chamber, and the particulate material was recovered as a suspension in the brine solution. These samples were kept at 4°C in covered p l a s t i c p a i l s . The sediment traps were redeployed by f i r s t lowering the anchor, and then attaching each pair of cylinders on the wire at their pre-marked positions. The traps were f i r s t f i l l e d with seawater by lowering them to approximately 1 m below surface and re-hoisting them to deck l e v e l where the saturated NaCl solutions (with and without NaN^) were added by displacement to the bottom of each trap. The sediment trap samples were sieved through a "Nitex" monofilament bolting c l o t h (0.47 mm mesh opening) in order to remove the larger zooplankton. After being washed through the net with a known volume of deionized water, the samples were centrifuged at 3000 rpm for 30 minutes in pre-weighed centrifuged tubes. The volume of the supernatant was recorded and the s o l i d phase was freeze-dried , weighed and ground to a fine powder in an agate mortar and pestle. The extent of flushing ( i . e . the displacement of the brine solution by seawater through molecular and eddy dif f u s i o n ) at the end of each deployment was estimated in the following manner: The 393 chloride concentration in the supernatant obtained after centrifugation of the sieved trap materials ([Cl ]) was measured by a conventional t i t r i m e t r i c method ( i . e . an aliquot of the solution, spiked with r^CrO^, was t i t r a t e d with an AgNO^ solution of known concentration u n t i l a red p r e c i p i t a t e of Ag 2Cr0 4 appeared). The volume of supernatant (Vfc) and deionized water added for the sieving (V^^) were also measured, in order to take into account the d i l u t i o n produced by the deionized water. The chloride concentration of the recovered brine ([Cl ]tfc) could then be calculated: [C1-] . = [C1-] x £  Vt - Vdiw Knowing the volume and chloride concentration of the brine solution added to the traps (500 ml and [Cl J^), and knowing the c h l o r i n i t y of seawater at the depth of deployment ([Cl J s w)» the chloride concentration which should be obtained in the recovered brine, i f there were no flushing ([Cl l ^ 1 1 1 3 * ) . can be calculated: (V. x [Cl"],) + ((V.. - 0.5) x [ C l " ] e ) r _ , i _ D D t D SW [Cl-L.max = V t b Where V ^ = Vfc - ( i . e . the volume of recovered trap brine). The chloride concentration of the recovered brine, i f complete flushing had occurred ([Cl J ^ 1 1 1 1 1 1 ) * would be equal to 394 the c h l o r i d e c o n c e n t r a t i o n of the seawater a t the depth of deployment ( [ C l ] ): O W [ c r ] t b m i n - [c i - ] s w By comparing [ C l " ] t b w i t h [ C l " ] t b m i n and [ C l " ] t b m a x , and assuming t h a t the d i f f u s i o n r a t e of C l i s r e p r e s e n t a t i v e of s e a s a l t i n g e n e r a l , one can e s t i m a t e the p r o p o r t i o n of the b r i n e i n i t i a l l y added which was r e c o v e r e d a f t e r the p e r i o d of deployment ( V ) : [cl_] = l ! ^ i ^ J b L : . l l ! t b _ : _ ! ! _ L [ ^ J s w ! t b v t b <[cr] b - [cr ] s w ) Hence: % f l u s h i n g = ( l - ( V / 0 . 5 ) } x 100 (Ta b l e 43) 395 Table 43: Evaluation of the extent of flushing which occurred during the deployments of the sediments traps (cone, in mole/1; v o l . in 1). STATION SI-9 Dates Depth/Brine [Cl ] ,f [Cl ],, V., max min J V % f l u s h i n g 5/3/84- 45m NaCl 0. 50 2. 31 1. 16 1. 13 2. 53 0. 47 0. 17 66% 9/4/84 HaH3 0. 29 2. 98 0. 86 0. 99 2. 82 0. 47 0. 08 33% 115m NaCl 0. 86 1. 81 1. 56 1. 14 2. 53 0. 49 0. 26 48% NaN3 0. 52 2. 19 1. 14 1. 14 2. 53 0. 49 0. 16 68% 150m NaCl 0. 66 1. 69 1. 11 1. 25 2. 35 0. 50 0. 17 67% NaN3 0. 57 1. ,65 0. 94 1. ,18 2. ,46 0. ,50 0. 11 77% 9/4/84- 45m NaCl - - -10/5/84 NaN3 0. 42 1. ,95 0. 83 1. ,22 2. ,38 0. ,48 0. ,09 81% 115m NaCl 0. 89 2. ,03 1. 81 1. ,01 2. ,79 0. ,49 0. ,29 43% NaN3 0. 47 1. ,64 0. 77 1. ,71 1. ,85 0. ,49 0. ,10 79% 150m NaCl 0. 87 1. ,79 1. 55 1. ,15 2. ,51 0. ,50 0. ,26 48% NaN 0. 33 1. .68 0. 55 1. ,42 2. .13 0. ,50 0. ,02 97% 10/5/84- 45m NaCl 0. 71 2. .11 1. 50 1. .02 2. .76 0. .47 0. ,22 55% 18/6/84 NaN3 0. 53 1. .52 0. 80 1. .81 1. .76 0. .47 0. ,13 75% 115m NaCl 0. 75 1. .88 1. 41 1. ,05 2. .70 0. .49 0. .21 58% NaN3 0. 48 1. .46 0. 70 1. .83 1. .76 0. .49 0. ,08 83% 150m NaCl -NaN3 -18/6/84- 45m NaCl 0. 81 1, .57 1. 26 1. .31 2. .25 0. .47 0. .22 56% 16/7/84 NaM3 0. 56 1. .66 0. 93 1. .24 2. .35 0, .47 0. .12 76% 115ra NaCl 0. 96 1, .55 1. 49 1, .29 2, .29 d, .49 0. .28 45% NaN3 0. 73 1, .42 1. 03 1. .27 2. .32 0. .49 0. .15 71% 150m NaCl 0. 75 1, .56 1. 17 1, .13 2, .55 0, .49 0, .16 67% NaN3 0. 39 1, .79 0. 70 1. .12 2, .57 0. .49 0. .05 90% 16/7/84- 45m NaCl 0. 36 1, .48 0. 53 1, .46 2 .07 0, .48 0, .02 97% 24/8/84 NaN3 0. 27 1, .85 0. 51 1, .33 2, .23 0 .48 0, .01 98% 115m NaCl 0. 48 1 .72 0. 82 1 .50 2 .04 0 .50 0, .10 79% NaN3 0. 87 1 .62 1. 40 1 .26 2 .73 0 .50 0, .20 60% 396 15 0m NaCl 0. 34 1. 45 0. 49 1. 29 2. 68 0. 50 0. 00 100* Nan ^  0. 36 1. 55 0. 55 1. 44 2. 45 0. 50 0. 01 97% 24/8/84- 45m NaCl 0. 47 1. 57 0. 74 2. 28 1. 52 0. 48 0. 13 75% 19/9/84 NaN ^  0. 37 1. 89 0. 70 1. 42 2. 12 0. 48 0. 07 87% 115m NaCl 0. 88 1. 85 1. 63 1. 48 2. 09 0. 50 0. 36 30% NaN3 0. 60 1. 86 1. 12 1. 34 2. 23 0. 50 0. 15 70% 150m MaCl 0. 94 1. 71 1. 61 1. 42 2. 16 0. 50 0. 33 33% NaN ^  0. 63 1. 77 1. 11 1. 25 2. 35 0. 50 0. 16 67% STATION SN 0. 8 Dates Depth/Brine [ C l - ] f 1 [Cl ~>tb V tb max^ min^ V %f l u s h i n g 5/3/84- 50m NaCl 0. 58 1. .64 0. 95 1. 95 1. 67 0. 48 0. 20 60% 9/4/84 NaN3 0. 42 1. ,65 0. 69 2. 43 1. 44 0. 48 0. 11 78% 135m NaCl 0. 84 1, ,46 1. 23 1. 88 1. 73 0. 50 0. 30 41% NaN3 0. 45 1. ,40 0. 63 2. 54 1. 41 0. 50 0. 07 85% 180m NaCl 0. 88 1. ,76 1. 55 1. 14 2. 53 0. 50 0. 26 48% NaN3 -9/4/84- 5 0m NaCl 0. 86 i . ,63 1. 39 1. 32 2. 15 0. 47 0. 25 50% 10/5/84 NaN3 — 135m NaCl 0. 99 l . .52 1. 51 1. 07 2. 67 0. 50 0. 23 53% NaN3 0. 61 l , .59 0. 97 1. 13 2. 55 0. 50 0. 12 77% 180m NaCl 0. 85 l . .34 1. 14 1. 45 2. 10 0. 50 0. 20 60% N a N 3 0. 58 l . .50 0. 87 1. 10 2. 61 0. 50 0. 09 82% 10/5/84- 50m NaCl 0. 53 l , .55 0. 82 1. 28 2. 29 0. 47 0. 10 81% 18/6/84 NaN3 0. 35 I, .50 0. 53 1. 33 2. 23 0. 47 0. 02 97% 135m NaCl 0. 47 l . .25 0. 59 1. 12 2. 57 0. 50 0. 02 95% NaN3 0. 45 I. .29 0. 58 2. 21 1. 55 0. 50 0. 04 92% 180m NaCl 0. 72 I, .65 1. 18 1. 21 2. 42 0. 50 0. 18 64% NaN3 0. 50 I, .67 0. 84 1. 05 2. 71 0. ,50 0. 08 85% 18/6/84- 5 0m NaCl -16/7/84 NaN3 0. 57 I, .38 0. 79 1. 27 2. 31 0. ,47 0. 09 83% 135m NaCl 1. .06 I .38 1. 46 1. 31 2. ,27 0. ,49 0. 27 46% NaM3 0. ,61 I .41 0. 85 1. ,25 2. ,35 0. ,49 0. 10 81% 397 180ra Had 0. 64 1. 26 0. 80 1. 19 2. 45 0. 50 0. 08 84% NaN3 0. 63 1. 27 0. 80 1. 80 1. 79 0. 50 0. 12 76% 16/7/84- 45m NaCl 0. 40 1. 39 0. 56 1. 28 2. 30 0. 47 0. 02 95% 24/8/84 NaM3 0. 42 1. 19 0. 50 2. 99 1. 25 0. 47 0. 02 97% 135m NaCl 0. 66 1. 45 0. 96 1. 27 2. 32 0. 50 0. 13 75% NaN3 0. 79 1. 39 1. 10 1. 39 2. 17 0. 50 0. 18 64% 180m NaCl 0. 52 1. 29 0. 66 1. 43 2. 12 0. 50 0. 05 90% NaM3 0. 51 1. 16 0. 59 1. 76 1. 82 0. 50 0. 04 93% 24/8/84- 45m NaCl 0. 60 1. 28 0. 77 2. 88 1. 29 0. 48 0. 18 64% 6/10/84 NaN3 0. 49 1. 29 0. 64 2. 86 1. 30 0. 48 0. 10 81% 135m NaCl 0. 89 1. 41 1. 25 1. 42 2. 13 0. 50 0. 23 54% NaN3 -180m NaCl 0. 75 1. 52 1. 14 1. 24 2. 37 0. 50 0. 17 66% NaN3 0. 53 1. 37 0. 72 1. 27 2. 33 0. 50 0. 06 88% l : f - — ^ V t - Vdiw 2: Max = [ C l ~ ] t b m a X 3: Min = [ C l - ] t b m i n 398 APPENDIX II: ANALYTICAL METHODS. 1 1-1 SOLID PHASE. 1 1 -1.1 ELEMENTAL ANALYSIS BY X-RAY FLUORESCENCE. Determinations of major and minor elements were made by XRF using an automated P h i l i p s PW1400 X-ray fluorescence spectrometer with a Rh target X-ray tube. The instrumental conditions are shown in Table 44. 1 1-1 .1 .1 SAMPLE PREPARATION. II-1.1.1.1 MAJOR ELEMENTS. The determinations of t o t a l iron, manganese, titanium,, calcium, potassium, s i l i c o n , aluminium, magnesium, phosphorus, and sulphur were made on fused d i s c s . They were prepared by fusing 0.4 g sediment with 3.6 g Spectroflux 105 (47.03% L i 2 B 4 0 7 , 36.63% LiC 0 3 , 16.34% L a 2 0 3 ; Johnson-Matthey Chemicals Ltd.) at 1100°C for 20 minutes in platinum/gold c r u c i b l e s . After cooling, the fused samples were made up to their i n i t i a l weight with Spectroflux 100 (100% L i 2 B ^ 0 7 ) to keep the r a t i o sample/La constant. La i s used as a heavy absorber to increase the t o t a l mass absorption of the samples and standards thereby minimizing the matrix absorption contrasts between d i f f e r e n t samples. Subsequently, the glasses were refused on a burner and poured onto an aluminium mould on a hot pist e set at 400°C. The molten 399 Table 44: Instrumental c o n d i t i o n s for elemental a n a l y s i s of sediment samples by X-ray fluorescence. Element (Peak) Tube kV mA C r y s t a l Counter Peak 26(°) Collimator Fe ( K o O 60 40 LiF(200) F 57 .67 -1 .60 C Mn (Kw ) 50 20 LiF(200) F 63 . 1 4 -0.86 C T i ( K o O 60 40 LiF(200) F 86 .35 +3.0/-1. 0 C Ca (K<*) 50 10 LiF(200) F 1 1 3 .34 + 1 .40 C K (Kcx) 60 40 LiF(200) F 136 .76 + 2.00 F Si (Roe) 60 40 TLAP F 32 .23 +2.3/-1. 2 C A l ( K o O 60 40 TLAP F 37 .88 ' +1.00 C Mg (Kc* ) 30 60 TLAP F 45 .21 -1 .20 c P (K«) 30 60 Ge F 1 4 1 . 1 2 -1 .50 c S (K<*) 60 40 Ge F 1 10 .82 + 1 .00 c Ba Up) 60 40 LiF(200) F 87 .19 + 1 .20 F Co (Kcx ) 60 40 LiF(220) F 77. 90 +.54/-.54 F . Cr (K«c) 60 40 LiF(200) F 69 .52 + 1 . 00 c Cu (Kc*) 60 40 LiF(200) F/S 45 .00 -0.62 F Ni (Kc(.) 60 40 LiF(200) F/S 48 .66 +1.2/-0. 6 F Pb (L|S) 60 40 LiF(200) F/S 28 .29 +0.5/-0. 5 F Rb ( K o O 60 40 LiF(200) S 26 .66 +0.4/-0. 9 F Sr (K°0 60 40 LiF(200) s 25 .20 +0.6/-0. 6 F V ( K o O 60 40 LiF(200) F 77 . 1 4 +4.0/-2. 6 c Y ( K d O 60 40 LiF(200) S 23 .83 +0.6/-0. 6 F Zn ( K w ) 60 40 LiF(200) F/S 41 .78 + 0.72 F Zr ( K o ) 60 40 LiF(200) S 22 .56 +.74/-.74 F Mo ( K e O 60 40 LiF(220) s 28 .91 +0.7/-0. 7 F U (K«0 70 30 LiF(220) s 39 .23 +1.3/-0. 4 F Na (K<x) 30 60 TLAP F 55 .25 +3.4/-1. 7 c I (K=() 60 40 LiF(200) F 12 .38 +0.6/-0. 6 F Br ( K « ) 60 40 LiF(200) F/S 29 .94 +1.1/-1. 1 F Cl ( K o O 50 40 PET F 65 .62 + 2.00 C 400 samples were flattened with a brass plunger, and the resulting glass discs stored for subsequent analysis. This method is based on the work of Norrish and Hutton (1969). International rock standards were used for the c a l i b r a t i o n of the spectrometer. The precisions obtained (1 <T) are shown in Table 45. II-1.1.1.2 MINOR ELEMENTS AND SODIUM. -Sediment samples: The determination of the minor elements (barium, chromium, copper, manganese, n i c k e l , lead, rubidium, strontium, vanadium, zinc, zirconium, molybdenum) and sodium in sediment samples was carr i e d out on borax-backed, 27 mm-diameter p e l l e t s made of 4 g of finely-ground sediment thoroughly mixed with 0.5 g of Hoechst wax C. The sample powder was placed in a stain l e s s steel die and formed into a r i g i d disc on a hydraulic press. International rock standards, prepared in the same way, were used for the c a l i b r a t i o n of the spectrometer. A correction for the differences in mass absorption between d i f f e r e n t samples and standards was applied to the elements whose a n a l y t i c a l l i n e was of shorter wave-length than the absorption edge of Fe ( i . e . for elements with an atomic number > 27) following Reynolds' method (1963, 1967). This method i s based on the observation that the amplitudes of the Compton-scattered parts of the c h a r a c t e r i s t i c tube l i n e s are inversely proportional to the mass absorption c o e f f i c i e n t s (ju) of the materials 401 Table 45: XRF a n a l y t i c a l precision for major elements (1 r e l a t i v e standard deviat ion). Elements Estimated prec i sion % Si T i . Al Fe Mg Ca K 0.3 1 .4 0.8 0.5 2.3 1 .0 1 .3 402 i r r a d i a t e d (see also Nesbitt et a l . , 1976; Sumartojo and Paris, 1980). In the present study, the Rh KoCCompton peak was used, and the i n t e n s i t i e s of the emission lines of each element were ratioed to the in t e n s i t y of the Compton peak of the same sample. For the trace elements of atomic number lower than 27 ( i . e . V, Cr, Mn), this technique cannot be used. The a n a l y t i c a l l i n e s of these elements are strongly absorbed by Fe, and the Compton peak does not r e f l e c t the mass absorption c o e f f i c i e n t . A similar problem i s presented by Ba which i s measured by means of i t s L emission l i n e . For these metals, s a t i s f a c t o r y matrix corrections were obtained by d i v i d i n g their peak amplitude by the intensity of an adjacent background wavelength. Appropriate corrections were also needed for various element interferences (Sr on Zr, Rb on Y, Ni, Ti on V and Ba, V on Cr). No matrix corrections were found necessary for Na. The precisions obtained for the analyses (1 cr) are shown in Table 46. - S e t t l i n g p a r t i c u l a t e samples: In view of the small sample sizes available for analysis, a s l i g h t l y modified procedure had to be used to measure the minor element concentrations in s e t t l i n g p a r t i c u l a t e samples. 0.5 g of ground sample (without Hoechst wax C) were pressed into a 10 mm diameter, bcrax-backed d i s c . The XRF instrumental conditions were i d e n t i c a l to those used for the sediment samples, except for longer counting times and the use of a smaller size collimator mask. 403 Table 46 : XRF an a l y t i c a l p r e c i s i o n 1 for minor elements and sodium (1 CT re l a t i v e standard deviat ion). Element 4g - p e l l e t 1g-p e l l e t Cone. Estimated Conc. Est imated range prec ision % range prec i sion % Ba 3 5 Cr 3.5 5 Cu <20ppm 10 <2 5ppm 1 0 >50ppm 4 >50ppm 4.5. Mn 3.5 4 Ni <20ppm 10 <20ppm 1 5 >40ppm 4.5 >3 0ppm 8 Pb 6 18 Rb 4.5 6 Sr 0.5 2 V 3 3 Y 4 1 0 Zn 3 6 Zr 2 2 Na 1 1 • I 3 6 (1) When cone, range is not given, the standard deviation was similar over the whole range of cone, measured. 404 In most cases, the precisions were very similar to the precisions obtained using 4 g samples (Table 46). The c a l i b r a t i o n of the instrument was done by using the same international rock standards as before, but made up in 1 g, 10 mm-diameter pressed p e l l e t s (without wax). Since the thickness of the 0.5 g discs is greater than the c r i t i c a l depth of the elements measured, 0.5 g and 1 g p e l l e t s could be measured on the same program (see Table 47). II-1.1.1.3 IODINE. Iodine was measured on the pressed-powder discs prepared for minor analyses. Since iodine i s a heavy element, i t s c r i t i c a l depth ( i . e . the depth of penetration into the p e l l e t of the short wave-length radiation necessary to excite the iodine atoms) i s deeper than the thickness of the 4 g and the 0.5 g p e l l e t s . It i s important, therefore, to use standards with the same thickness and mass absorption c o e f f i c i e n t as the samples being measured. Accordingly, three series of synthetic standards (4 g, 1 g, and 0.5 g) were prepared by spiking a finely-ground granite with various amount of Ba (I0 3) 2 .H^O. The precisions (1<r) were 3% and 6% for the 4 g and 1 g (or 0.5 g) samples respectively. II-1.1.1.4 CHLORINE AND SALT-CORRECTION PROCEDURE. The elemental concentrations obtained from the analyses of the sediment samples were corrected for the presence of salt occluded during drying by determining their chlorine contents. This measurement was made on pressed discs consisting of a 405 T a b l e 4 7 : C o m p a r i s o n o f t h e r e s u l t s o b t a i n e d f r o m t h e a n a l y s e s o f 1 g a n d 0 . 5 g s e d i m e n t p e l l e t s , u s i n g t h e same c a l i b r a t i o n c u r v e (made w i t h 1 g p e l l e t s o f i n t e r n a t i o n a l , s t a n d a r d r o c k s ) . E l e m e n t s 1.0 g d i s c s 0 . 5 g d i s c s Ba 438+19 440+17 C r 85+ 5 83+ 3 Cu 29+ 5 29+ 5 Mn 565+19 557+12 N i 25+ 3 26+ 3 Pb 1 9 + 5 20+ 5 Rb 51+ 5 51+ 4 S r . 196+13 194+12 V 105+ 4 105+ 3 Y 20+ 2 21+ 2 Zn 1 1 4 + 9 1 1 5 + 8 Na 2 . 2 2 + 0 . 0 5 2 . 2 2 + 0 . 0 4 (1 ) F i v e 1 g - p e l l e t s a n d f i v e 0 . 5 g - p e l l e t s w e r e made f r o m a h o m o g e n i z e d b u l k s e d i m e n t s a m p l e . E a c h s a m p l e was m e a s u r e d 6 t i m e s ( e r r o r s a r e r e p o r t e d a s one s t a n d a r d d e v i a t i o n on t h e 30 m e a s u r e m e n t s ) . 406 mixture of the samples and Spectroflux 105 (47.03% L i 2 B 4 0 7 , 36.63% LiCO-j, 16.34% I^O^) in a 1:4 r a t i o . Lanthanum was used to minimize the matrix differences between d i f f e r e n t samples and standards. The procedure for s a l t - c o r r e c t i o n consisted of two parts. F i r s t , some elements (sodium, magnesium, calcium, potassium, sulphur, and strontium) have seawater concentrations which are high enough to affect d i r e c t l y their concentrations in the dried sediments. Their corrected values were calculated by using the general formula, viz ( E l . ) (Wt% E l . ) s e d = (Wt% E l . ) s e d + s a U - * (Wt% C l ) s e d + s a l t ] SW where: (Wt% E l ' ) s e a = corrected element concentration. (Wt% E l • ) s e d + s a i t = e l e m e n t concentration in the dried sediment samples. (El.) = element concentration in seawater. sw (Cl ) = chlorine concentration in seawater. (Wt% Cl) , + ,. = chlorine concentration in the e dried sediment samples. The s p e c i f i c equations for each of the elements which are affected by this correction are given in Table 48. Second, the concentrations of a l l the elements have to be corrected for the d i l u t i o n e f f e c t produced by the presence of sea-salt in the dried samples, according to, v i z 407 Table 48: Correction for sea s a l t . (Wt% Na) sed (Wt% Na) sed+salt • [0. 556 X (wt% Cl) sed+salt (Wt% Mg) sed (Wt% Mg) sed+salt - [0. 067 X (Wt% Cl) sed+salt (Wt% Ca) sed (Wt% Ca) sed+salt • [0. 021 X (wt% CD sed+salt (Wt% K ) sed (Wt% K ) sed+salt - [0. 020 X (wt% Cl) sed+salt (ppm S ) sed (ppm S ) sed+salt - [16 .6 X (wt% Cl) sed+salt (ppm Sr) sed (ppm Sr.) sed+salt - [4. 1 3 X (wt% Cl) sed+salt (1) For oxic sediments only. 408 100 (Wt.% E l . ) , , r = (Wt% El.) , x S a l t - f r e e S 6 d 100 - 1.82 (Wt% C l ) s e d + s a U The elemental concentrations of the s e t t l i n g p a r t i c u l a t e materials, as measured by XRF, did not require a correction for sa l t d i l u t i o n because the values reported are expressed in flux units, viz (dry Wt) , . E l . flux = (Wt% E l . ) s e d + s a l t x - - - - - - - - § e d S(m2) x t(days) where: (dry Wt) , , , = weight of particulates and s a l t sea salt o b t a i n e d after drying. 2 S(m ) = surface area of the opening of the c o l l e c t o r traps. t(days) = period of deployment of the c o l l e c t o r traps. and concentration r a t i o s , viz (Wt% El.) sed+salt { W t % A l ) s e d + s a l t They did, however, require a correction to take into account the major elements present in seasalt. In t h i s case, the equations given in Table 48 had to be modified, by using the data on the extent of flushing given in Table 43, to take into account the presence of NaCl from the brine solutions. When these data were not available, a range of values were reported (Appendix IV-3) . 409 II-1.2 CARBON AND NITROGEN ANALYSIS. II-1.2.1 TOTAL CARBON (C t) AND NITROGEN. Total carbon and nitrogen were determined by gas-chromatography on a Carlo-Erba CHN analyzer (model 1106). Five to ten mg of sediment or s e t t l i n g p articulate samples were precisely weighed into small t i n cups with a microbalance (Mettler, model M3) and then loaded into the sample changer of the instrument. Each sample was combusted at ca. 1800°C in a stream of helium and oxygen. The combustion gases were quanti t a t i v e l y oxidized by passing through a column of C^O-j. The excess oxygen was removed by passing over heated copper (650°C). This treatment also reduced the nitrogen oxides produced during the sample combustion. F i n a l l y , CO2, H 2 0 ' a n < ^ N2 w e r e separated on a chromatographic column (Porapak QS) and measured by thermal conductivity. Acetanalide (CH^CONHCgHg) was used to c a l i b r a t e the instrument. The a n a l y t i c a l precision (10") was estimated at +1.25% for C and +2% for N. II-1.2.2 CARBONATE (C , ) AND ORGANIC (C ) CARBON. carp org Three d i f f e r e n t techniques were used for the determination of carbonate and organic carbon depending on the quantity of material and the equipment available at the time of the analysis. 11-1 .2.2.1 GRAVIMETRIC DETERMINATION OF THE CARBONATES. This technique was used where sample sizes were large. 0.5 -410 1 g of sediment were weighed precisely into a small glass reaction f l a s k s . 5 ml of 10% HC1 were added, and the flask was brought to b o i l i n g under a stream of nitrogen. The C0 2, produced by the acid decomposition of the carbonates present in the samples, was carried by the nitrogen stream through a condenser tube and two water traps (cone. sulphuric acid and magnesium perchlorate), and f i n a l l y into an A s c a r i t e - f i l l e d absorption bulb. The water produced by the neutralization of C0 2 by Ascarite was also absorbed inside the trap by magnesium perchlorate. The C0 2 produced was estimated gravimetrically by the difference in weight of the Ascarite trap before and after the sample run. The precision (1 (T) was estimated at +2.5% but was much poorer when only a very small amount of carbonate was present in the sample analyzed (e.g. standard deviation of the result of analyses made in the concentration range 0.10% < C c a r b < 0.40% = +15%). Organic carbon was estimated by substracting C c a r b from the t o t a l carbon measured on the CHN analyzer (section II—1.2.1). I1-1.2.2.2 ELEMENTAL ANALYZER This technique was developed for small sample sizes, and was used to measure the carbonate and organic C content of the s e t t l i n g p a r t i c u l a t e samples. Six subsamples of 5-10 mg of trap material were precisely weighed into t i n cups designed to hold l i q u i d samples. 10 Ail aliquots of a phosphate buffer (55 ml 85% H 3P0 4 d i l u t e d to 250 41 1 ml, brought to pH 2.1 with NaOH and f i n a l l y made up to 500ml) were added to three of the weighed subsamples u n t i l no frothing was apparent. After each addition, the samples were placed in an oven at 60°C. Subsequently, they were analyzed on the Carlo Erba CHN analyzer. Total C and organic C were determined from the untreated and acid-treated samples respectively. Carbonate C was estimated by difference. The precision of the procedure compared favorably with the Leco technique. Its accuracy was tested by measuring well-characterized samples (SAP8 and SAG12) by both methods (Table 49). 11- 1 . 2.2.3 COULOMETRY This technique allows the d i r e c t determination of carbonate C on small size samples. Carbonates are decomposed with 10% HCl in a heated reaction vessel and the C0 2 produced i s swept by a C02~free a i r stream into an ethanolamine solution containing a colorimetric indicator. C O 2 reacts with ethanolamine to form a strong, t i t r a t a b l e acid, v i z . which causes the % Transmittance (monitored by a photo-detector) to increase. The t i t r a t i o n current i s then automatically turned on, and OH ions are e l e c t r i c a l l y generated by reducing ^ 0 at a s i l v e r electrode, v i z . HO-CH2-CH2-NH2 o + Ag > Ag + e -> 1/2 H 2 + OH 412 Table 49: Comparison of C analyses by Leco and Carlo Erba CHN analyzer (precision reported as one standard deviat ion). Samples Leco CHN SAP8 carb 'org_ 9.27+0.45 5.93+0.30 3.38+0.75 9.25+0.12 5.67+0.20 3.58+0.09 5.89+0.07 3.53+0.10 2.36+0.03 3.18+0.04 0.22+0.08 2.96+0.04 SAG 12 Cfc% 'carb" org 3.56+0.18 SAA 'carb° org 413 u n t i l the solution returns to i t s o r i g i n a l colour. The t o t a l amount of current required i s integrated, and the result displayed as jjg C. The accuracy of the procedure was found to be within 1%. The precision was estimated at +3.5% (1CT) in the 0.1%-0.25% C^j-fc concentration range. II-1.3 ELEMENTAL SULPHUR ANALYSIS. After extrusion under nitrogen, the sediment samples were quickly frozen into a mixture of dry-ice and acetone and freeze-dried immediately. When dried, the samples were extracted with a known volume of benzene (approx. 200 ml benzene/50 g sediment; 2 days shaking; under nitrogen), centrifuged and c a r e f u l l y decanted. The s o l i d residue was dried and weighed, and the benzene extract was analyzed for elemental sulphur. The f i r s t extraction was considered to be quantitative because a second extraction did not y i e l d any s i g n i f i c a n t amount of sulphur. The elemental sulphur concentration in the benzene extract was measured by cyanolysis, according to the method developped by B a r t l e t t and Skoog (1954). 15 ml of NaCN (1 g/1; in a 95:5 acetone/water mixture) were added to 5 ml of the benzene extract. Cyanide ions are strong nucleophiles which readily cleave the Sg rings and produce sulphocyanide ions. The solution was gently mixed and the reaction allowed to proceed for a few minutes before bringing the volume to 25 ml with the acetone/water solvent. Subsequently, 3 ml aliquots were withdrawn and added to 414 3 ml of a F e C l 3 solution (4 g/1; in a 95:5 acetone/water mixture). SCN ions produced by the reaction between CN and Sg 3 + present in the benzene extract react with Fe to produce a red complex (Fe(SCN)g ) which can be measured c o l o r i m e t r i c a l l y by determining the absorbance at 465 nm. A c a l i b r a t i o n curve was prepared by treating a series of standard sulphur solutions in benzene in the same way. The elemental sulphur concentration in the sediment (in % dry weight) could be calculated from the S concentration and volume of the benzene extracts, and from the dry weight of the sediment extracted. The precision was estimated at +2.5% (10") . II-2 PORE WATERS. II-2.1 SULPHATE ANALYSIS. The sulphate concentration in pore waters was measured by gravimetry, following the method given by Pedersen (1979). 1.0 ml of 1 N HC1 was added to 10 ml aliquots of pore waters. The samples were brought to near b o i l i n g and 2 ml of warm 10% w/v BaCl2 were added under slow a g i t a t i o n . They were l e f t covered overnight to cool before f i l t r a t i o n onto pre-weighed 0.45 xim Nucleopore f i l t e r s . The f i l t e r s were dried to constant weight in a dessicator, and the sulphate concentration estimated from the weight of BaSO^ recovered. The precision was estimated at ±4% (itr). 415 11-2. 2 SULPHIDE ANALYSIS. Hydrogen sulphide concentration in pore waters was determined by colorimetry following the method given by Cline (1969). H2S present in 2 ml aliquots of pore water was immediately precipitated by zinc acetate. Subsequently, 250 ul of a mixed diamine reagent (N,N-dimethyl-p-phenilenediamine sulphate and f e r r i c chloride) were added to the samples. A blue coloration developped immediately and was measured spectrophotometrically, after standing 20', at 670 nm. If necessary, the samples were di l u t e d after colour development to•stay below 0.4 absorbance. Standard curves were made with solutions of known sulphide concentration prepared by dis s o l v i n g Na 2S.9H 20 in oxygen-free water. The precision was estimated at +3% (10~). II-3 HUMIC EXTRACTS. II-3.1 EXTRACTION OF HUMIC MATERIALS. Humic materials were extracted by shaking the sediment samples in 0.5 N NaOH (1:5 w/v) for 18 hours under nitrogen. The dispersions were then centrifuged and the supernatants c a r e f u l l y decanted. II-3.2 DISSOLVED ORGANIC CARBON (D.O.C.) IN HUMIC EXTRACTS. The D.O.C. of the humic extracts was measured by a dry 416 combustion method, using a Carlo Erba 1106 elemental analyzer. Three to f i v e 25 ul aliquots of the humic solution, interspersed with 25 ul aliquots of a concentrated H 3P0 4/H 2P0 4 buffer (pH 2.1; section 11 -1 .2.2.2) to remove the adsorbed C0 2, were dried in c y l i n d r i c a l t i n containers. These containers were combusted at 1800°C and the C0 2 produced measured by gas-chromatography as described previously. The precision was + 1.4% (10"). II-3.3 POLYSULPHIDE CONCENTRATION (SS n) IN HUMIC EXTRACTS. Polysulphides associated with the humic extracts were determined by measuring the elemental sulphur formed by their acid hydrolysis in the following manner. The alkaline humic solutions were f i r s t extracted with benzene, to check for the presence of elemental sulphur before a c i d i f i c a t i o n . The humic solutions were then a c i d i f i e d to pH 2 with HC1, and l e f t under constant nitrogen bubbling for 12 hours to avoid the formation of S° by the oxidation of co-extracted acid v o l a t i l e sulphides. These a c i d i f i e d extracts were then re-extracted with a known volume of benzene. The elemental sulphur present in these extracts which was measured by cyanolysis (section 11 — 1 .3) was assumed to come from the acid hydrolysis of organic polysulphides. These polysuphides were then normalized to the D.O.C. of the a l k a l i n e humic solutions, measured before a c i d i f i c a t i o n as explained in section II-3.2. 417 1 1 - 3 . 4 IODINE IN HUMIC EXTRACTS (D.O.I.). The iodine content of the humic extracts was determined by X-ray fluorescence using the same conditions outlined in Table 4 4 . Forty ml of the humic solutions were gradually added to 3 . 0 0 0 g of microcrystalline c e l l u l o s e and dried under an infrared lamp in a laminar-flow fume-hood. The dried mixture was then weighed and homogenized in a carbide m i l l . 3 . 5 g of the dried powder were pressed into a 31 mm diameter disc and analyzed. Standards were made by following the same procedure with- 0 . 5 N NaOH solutions spiked with various amounts of iodate. Allowance was made for the difference in weight of the dried residues from d i f f e r e n t humic extracts (the difference was always less than 4 % ) . Slight variations in mass absorption between d i f f e r e n t samples due to varying amounts of ash co-extracted with the humic materials were corrected by normalizing the iodine peak intensity to the Compton scattered Rh K o c p e a k (section I I — 1 . 1 . 1 . 2 ) . The counts obtained at the Compton peak were always within 2%, and therefore t h i s correction was minimal. The precision varied from 2% to 6% (10") according to the concentration measured ( 1 - 2 0 mg 1/1). I I - 4 HUMIC MATERIALS. I I - 4 . 1 ISOLATION OF HUMIC MATERIALS. 418 After their extraction by 0.5 N NaOH (section 11 — 3 .1) a frac t i o n of the humic materials (conventionally c a l l e d humic acids) was precipitated by a c i d i f i c a t i o n to pH 1.5 - 2.0 with HC1. The pr e c i p i t a t e was recovered by centrifugation after ~12 hrs standing and rinsed several times with d i s t i l l e d water before being freeze-dried and ground with an agate mortar and pestle for subsequent experiments and analyses. 11-4. 2 CARBON AND NITROGEN CONTENT. The carbon and nitrogen content of humic materials was measured on a Carlo Erba CHN analyzer as previously described for the sediment samples (section II—1.2.1). 11-4.3 IODINE CONTENT. The iodine content of humic materials was measured by re-dissolving a known amount of dried polymer ( 20 to 40 mg) in 40 ml 0.5 N NaOH. The iodine content of thi s solution was measured as described for the humic extracts (section II-3.4). II-4.4 SULPHUR CONTENT. 11-4.4.1 TOTAL SULPHUR (S f c). The t o t a l sulphur content of humic materials was measured on an automatic amperometric t i t r a t o r (Fisher model 475 sulphur analyzer) (Guthrie and Lowe, 1984). Known weights of sample were 419 combusted at 1350 C in a tube furnace, under a low oxygen pressure, in the presence of vanadium pentoxide. The S0 2 thus produced was driven into the reaction vessel of the analyzer where i t was t i t r a t e d amperometrically with an automatic burette coupled to a microprocessor. The precision was evaluated at +2.5% (1CT). II-4.4.2 PYRITIC SULPHUR (S ). Acid-resistant sulphur minerals, presumably in the form of fine-grained, highly-dispersed pyrite and g r e i g i t e which were co-extracted with the humic materials, were estimated by treating a 2 + few mg of the dried humic polymer with Cr (Zhabina and Volkov, 1978; Howarth and Jorgensen, 1984). Two to five mg of dried, ground humic substances were weighed accurately and placed into small glass reaction bulbs. 250 ul of ethanol were added, and a stream of nitrogen was driven through the dispersion. After purging 3 to 5 minutes, 1 ml of a freshly prepared C r C l 2 solution (CrCl^ was reduced by amalgamated zinc in 0.5 N HCl) and 0.5 ml of concentrated HCl were introduced into the reaction flasks which were maintained at room temperature for ~15 min and subsequently brought to b o i l i n g for 45 min. During t h i s treatment, the nitrogen stream was continuously passed through the reaction vessel followed by two successive zinc acetate solutions to recover the H2S produced by the decomposition of pyrite and g r e i g i t e . After the evolution of H 2S had stopped, the two zinc acetate traps were retrieved and 420 analyzed for H 2S using the method of Cline (1969). The precision was +8% (1<T). The recoveries obtained when using t h i s method on pyrite of known stoichiometry (ground and mixed with granite) was estimated at 107+9%. A similar treatment performed on freeze-dried planktonic material did not produce any detectable H 2S (Table 50), thus confirming the claim of Zhabina and Volkov 2 + (1978) that organic sulphur i s not affected by the Cr treatment. II-4.4.3 ORGANIC SULPHUR (S) The organic sulphur content of the humic materials recovered from sediments was determined by substracting their p y r i t i c sulphur content (S ) measured as described in section II-4.4.2 py from their t o t a l sulphur content (S f c; section II-4.4.1). II-4.4.4 ESTER SULPHATES ( S + 6 ) Sulphate esters present in the humic materials were determined by measuring the sulphate produced by their acid hydrolysis. This was conducted by suspending ~100 mg of samples in 5 ml of 5 N HC1 in an autoclave, for 5 hrs, at 121°C (King and Klug, 1982). Subsequently, the sulphate concentration in the hydrolyzate was measured t i t r i m e t r i c a l l y (Howarth, 1978). The suspensions were partly neutralized with 4 ml of 0.5 N NaOH and l e f t standing overnight before f i l t r a t i o n on 0.45 Aim Nuclepore f i l t e r s . The f i l t r a t e s were placed in 50 ml Erlemeyer flask with 0.045 mmole EDTA for the removal of i n t e r f e r i n g metal ions, and 421 Table 50: Sulphur recovery by CrCl 2/HCl'treatment (BDL = Below detection l i m i t ) . Sample S present S recovered %recovery Pyrite/Granite 1 .37 xxmol 1 . 46+0. 1 4 jumol 107+9% Plankton ~0 .5 Aimol BDL 0% .422 boiled gently for two minutes. Ten ml of 0.05 N HCl were then added and the solutions allowed to cool for a few minutes before adding 5 ml 10% BaCl 2. After 20 min, the pre c i p i t a t e s of BaS0 4 were f i l t e r e d onto 0.45 jjm Nuclepore f i l t e r s , washed with 0.05 N HCl and deionized water, and transferred (with the f i l t e r s ) into 50 ml Erlemeyers to which a known excess of EDTA (10 ml of a 0.01 mol/1 EDTA and 4 ml cone. NH^OH) was added. EDTA dissolves BaS0 4 by complexing B a + + . The excess EDTA present in the solutions was t i t r a t e d by a MgC^ solution ( 10 mmol/1) with Eriochrome Black-T as an indicator. The sulphate concentrations derived from the excess EDTA were converted into weight percent sulphur in the humic materials analyzed. II-4.4.5 C-BONDED SULPHUR (S C) S c refers to organic sulphur which does not produce sulphate during HCl hydrolysis ( i . e . a l l organic sulphur, excluding sulphate es t e r s ) . This sulphur pool was estimated by substracting the sulphate esters (S ; section II-4.4.4) from the organic sulphur (S; section II-4.4.3). 423 APPENDIX III: SEDIMENTATION RATE MEASUREMENTS. 111-1 PRINCIPLES OF THE METHOD. The rates of sediment accumulation in Saanich Inlet have 21 0 been obtained from the measurement of the decrease in Pb excess a c t i v i t y as a function of depth in the sediment column. The p r i n c i p l e s of the method have been described by Krishnaswami et a l . (1971), Koide et a l . (1972, 1973), Robbins and Edgington 2 1 0 (1975). The applications of Pb techniques to geochemistry were reviewed by Robbins (1978). III-2 MEASUREMENT OF 2 1 ° P b ACTIVITY IN SEDIMENT SAMPLES. 2 1 0 The measurement of Pb a c t i v i t y in sediments i s based on 2 1 0 the measurement of i t s daughter Po ( oL emitter; h a l f - l i f e : 138.4 days) which i s assumed to be in secular equilibrium with . . . 210 210 i t s parent. Since equilibrium between Pb and Po should be reached within a year, this assumption holds true, except maybe for the upper few mm of the sedimentary column where a disequilibrium could be observed due to the short residence time 210 of Pb in the water column. 21 0 The measurement of Po was based on the method proposed by Flynn (1968) and Smith and Hamilton (1984). 1 g of dry sediment was digested in a Teflon bomb with 6 ml cone. HNO^ and 6 ml cone. HF for 6 hrs at 95°C. A spike of 9.3 dpm of 2 0 8 P o was also added 424 to estimate the 2 1 ^ Po recovery and counting e f f i c i e n c y . After cooling overnight, the bomb contents were transferred to a Teflon beaker and the bomb rinsed with 0.5 N HCl and f i n a l l y with cone. HC1. The HCl was then boiled off in a fume-hood. When almost dry, 20 ml cone. HCl were added and boiled to near dryness. This procedure was repeated three times. Subsequently, the residue was centrifuged to remove the organic materials which had not been digested by the HF/HNO^ treatment. This residue was rinsed several times with 0.5 N HCl and the clear supernatants were combined into a glass beaker for subsequent p l a t i n g . 0.2 g ascorbic acid and 0.5 g hydroxylamine hydrochloride were added to 3+ the solution to reduce Fe which interferes with the pl a t i n g . 210 Po was plated on a Ni disc (cleaned in methanol and d i s t i l l e d water) at 85 °C under constant s t i r r i n g for 6 h. The disc was f i n a l l y rinsed with methanol and d i s t i l l e d water, and a i r - d r i e d in a Petri dish before being counted for 24 h in a ORTEC alpha counter (model 576A) using a semi-conductor surface barrier 208 210 detector. The Po and Po peaks were integrated over the same number of channels (250) and expressed in dpm/g (after 21 0 appropriate s a l t - c o r r e c t i o n ) . The supported Pb, in secular 2 2 6 equilibrium with Ra, was estimate:: from the asymptotic value 210 approached by the Pb p r o f i l e s a t depth (ca. 1 dpm/g) and 210 . substracted in order to determine the excess Po present in the sample. 425 II1-3 SEDIMENTATION RATE CALCULATIONS. 111-3.1 STATION SN0.8 Depth Corrected 2 Plating/Counting 210„ 3 Excess Po (cm) Depth Ef f ic iency (dpm/g) (cm) 5 8.7 0.208 (4.83) 7 13.7 0.205 (5.41) 9 19.4 0.215 (8.95) 1 1 25.6 0.262 1 1 .52 13 32.3 0.246 10.14 1 7 46.5 0.265 8.67 21 61 .7 0.230 7.97 23 69.5 0.236 7.01 28 89.4 0.219 5.75 36 1 22. 1 0.219 3.88 1 - Corrected for compaction according to, viz £ = (ft - *') e " a z + $>' z 0 1 ft - ft z' = — — [z (1 - fc') + - 5  1 - d> a o where: z i s the sediment depth. z' i s the sediment depth corrected for compact ion. S> i s the porosity at depth z. o i s the porosity at the sediment-water interface (0.984; Matsumoto and Wong, 1977). <&' i s the porosity at f i n a l compaction (0.933; Matsumoto and Wong, 1977). a i s a constant (0.109; Matsumoto and Wong, 1977). 426 2 - Estimated from the recovery of Po. 3 - Salt-corrected. When discarding the data from the top 3 samples which gave anomalously low values (Fig. 127) the following relation i s obtained. In (Excess 2 1 0 P O ) = -0.0108 z' + 2.70 (r = 0.997) corresponding to the accumulation rate S = 2.87 cm/y 2 The sedimentation rate (w; mg/cm .y) was estimated by using the porosity and density values reported by Matsumoto and Wong (1977), v i z w = S d p (1 - ft ) s o 3 where d g i s the density of the s o l i d phase (2.06 g/cm ). i.e . w = 2.87 x 2.06 x (1 - 0.984) = 0.095 g/cm2.y II-3. 1 STATION SI-9 Depth Corrected Plating/Counting Excess Po (cm) Depth E f f i c i e n c y (dpm/g) (cm) 1 1 .2 0.202 14.55 3 4.3 0.203 15.07 7 13.4 0. 196 14.94 9 19.1 0. 193 12.92 1 1 25.5 0.203 1 1 .73 1 3 32.4 0.203 11.51 1 5 39.8 0.210 10.19 21 64.2 0. 184 (4.76) 427 29 37 100.2 1 38.6 0. 189 0. 183 9.58 7.29 1 - Corrected for compaction. 208 2 - Estimated from the recovery of Po. 3 - Salt-corrected. In (Excess 2 1°Po) = -4.83 x 10 _ 3 z' + 2.66 (r = 0.938) corresponding to the accumulation rate S = 6.45 cm/y and the sedimentation rate (Fig. 127) w = S d e (1 - ft ) s o = 6.45 cm/y x 2.21 g/cm3 x (1 - 0.982) = 0.257 g/cm2.y 428 1 ° P 0 (dpm/g) collected from station SI-9 and SN0.8. The points in parentheses were not used in the ca l c u l a t i o n s . 4 2 9 APPENDIX IV: CHEMICAL DATA. IV-1 CHEMICAL COMPOSITION OF SAANICH INLET SEDIMENTS ("SHIPEK" GRAB SAMPLES). 430 IV-1 .1 CHEMICAL COMPOSITION (SALT-CORRECTED) AND DEPTH OF COLLECTION OF FINE-GRAINED SEDIMENT SAMPLES FROM THE CENTRAL BASIN OF SAANICH INLET. Sample SAG1 SAG2 SAG3 SAG4 SAG6 SAG7 SAG8 SAG1 0 SAG 12 Depth(m) 195 1 38 205 2 1 4 1 84 222 .162 230 118 C o r a ( % ) 5.33 3.58 5.06 4.42 4.01 4.13 3.11 3.54 2.46 c S 6 8 , ( % ) 2.8 2.7 2.2 2. 1 2.1 2.4 0.8 4.9 31.2 N(%r 0.557 0.351 0.552 0.479 0.467 0.467 0.326 0.395 0.227 Major Elements (wt %) S i 28. 1 26.7 30.3 27.9 30.6 28.3 28. 3 25.8 18.3 T i 0.28 0.37 0.23 0.25 0.18 0.30 0.33 0.33 0.23 A l 4.58.. 4.77 3.51 4.21 3.27 4.77 4.98 5.11 4.08 Fe 2.95 4.02 2.55 2.84 2.03 3.30 3.48 3.64 2.74 Mg 1 .00 1 .90 0.83 1 .00 0.74 1 .09 1 .24 1 .25 1.21 Ca 2.18 3.82 1 .63 1 .61 1 .40 1 .98 1 .43 3.21 14.9 Na 0.91 0.96 1 .26 0.83 0.23 1 .08 1 .09 1.13 0.88 K 0.72 0.61 0.60 0. 75 0.49 0.89 0.93 1 .08 0.73 P 0.11 0.13 0.09 0.09 0.07 0.09 0.08 0.09 0.07 S 1.10 1 .04 1 .32 1.51 1.07 1 .37 1 .43 1 .35 0.49 Minor Elements (ppm) Ba 375 255 31 1 335 264 384 334 386 213 Cr 86 100 ' 74 81 58 87 90 94 75 Cu 68 53 57 58 44 64 46 65 50 Mn 596 900 493 805 329 697 856 976 .470 Ni 40 47 38 39 28 40 45 41 32 Pb 20 1 0 13 1 5 10 21 1 3 35 40 Rb 36 29 33 35 31 42 45 50 29 Sr 1 78 207 1 42 1 54 1 29 1 69 1 72 203 1 97 V 238 280 193 203 1 33 •217 216 201 1 38 Zn 136 109 91 . 1 04 72 1 28 93 1 49 1 34 Zr 77 79 68 73 63 81 • 89 93 72 Mo 1 1 7 33 . 126 1 20 77 98. 69 58 3 I 1 53 81 1 1 7 1 1 7 98 1 03 82 108 101 Br . 301 175 276 269 255 241 1 76 213 1 19 431 Sample SAG 1 3 SAG1 5 SAG 1 6 SAG 1 7 SAG1 8 SAG24 SAG26 SAG27 SAG30 Depth(m) 234 203 224 228 216 235 228 1 1 3 106 c S 6 8 - ( % j N(%) J . 3.38 3 .7 o! .306 1 .30 50.3 0.115 2.33 21.2 0.244 3.25 3.2 0.327 3. 56 2.3 0. 385 .3.07 2.7 0.347 3.11 2.2 0.358 3.95 2.6 0.433 3.59 0.3 0.401 Major Elements (wt %) S i 27.5 14.6 22. 1 27.3 27 .0 25.9 28. 1 26.7 28.0 T i 0.32 0.14 0.30 0.33 0.33 0. 36 0.41 0.36 0.39 A l 5.29 2.87 4.72 5.18 5. 18 5.50 6.25 6.03 5.97 Fe 3.54 2.30 3.41 3.60 3.53 3.80 4.15 3.79 3.83 Mg 1 .23 1.12 1 .29 1 .24 1.23 • 1.34 1 .24 1 .36 1 .32 Ca 2.13 22.7 9.87 2.16 1 .91 2.07 1 .74 1 .77 1 .48 Na 1 .20 0.51 1.13 1.16 1 . 26 1.21 1 .00 1 .34 1 .23 K 0.99 0 .42 0.87 1 .03 1 .02 1 .08 1 .22 1.14 1.19 P 0.08 0.06 0.07 0.08 0.09 0.09 0.09 0.09 0.09 S 1 .35 0.61 1 .07 1 .48 1 . 56 1 .40 1 •. 48 1.17 1 .06 Minor Elements (ppm) Ba 381 1 1 7 323 374. 358 375 382 395 385 Cr 90 61 88 90 89 97 101 104 106 Cu 61 55 51 55 55 50 52 64 53 Mn 1 458 582 788 715 654 1 1 45 1086 543 550 Ni 46 25 36 39 39 39 38 43 41 Pb 28 39 35 26 28 32 30 43 28 Rb 46 1 9 43 53 52 57 54 55 53 Sr 1 78 216 222 185 1 74 1 87 1 87 173 1 77 V 202 92 1 62 1 75 1 76 1 80 1 76 1 99 189 Zn 1 22 1 42 1 49 1 1 7 1 25 1 35 1 38 1 52 1 28 Zr 91 52 83 93 89 101 1 00 98 1 05 Mo 67 7 19 51 67 34 37 1 7 1 4 I 1 04 32 74 93 94 85 100 1 32 123 Br 203 42 1 27 229 220 1 98 204 219 187 432 Sample SAG31 SAG33 SAG35 SAG36 SAG 3 7 SAG39 SAG 40 SAG43 Depth(m) 220 209 1 36 1 94 96 1 46 99 1 44 c o c a ( %) 2.90 2.83 2.91 2.61. 2.63 2.47 3.33 2.19 c S $ L (%) 1.7 1.2 0.9 1 .2 0.2 1.1 - 0.4 0.8 N(%r . 0.328 0.293 0.296 0.249 0.280 0.254 0.385 0.244 Major Elements • (wt % ) S i 27 .3 27.2 27. 1 28. 1 26.7 27.2 26.2 28. 1 T i 0.40 0.40 0.30 0.41 0.51 0.45 0.49 0.47 A l 6.08 6.36 6.06 6.24 7.20 6.'55 7.12 6.66 Fe 4.12 4.24 4.08 4. 30 4.17 4.19 4.03 4.04 Mg 1 .43 1 .36 1 .39 1 .43 1 .53 1 .43 1 .59 1 .38 Ca 1 .73 1.61 1 .53 1 .56 1 .57 1.61 1 .46 1 .77 Na 1.31 1 .44 1 .43 1 .29 1 .72 1 .58 1 .65 1 .87 K 1 .20 •1.17 1 .23 1 .29 1 .48 1 .28 1 .39 1 .37 P 0.08 0.09 0.08 0.08 0.09 0.08 0.10 0.08 S 1 .26 1.27 1 .34 • 1 .24 0.30 1 .06 0.51 0.59 Minor Elements (ppm) Ba - 41 1 397 400 452 469 404 454 437 Cr 1 09 99 101 1 1 5 1 22 1 02 1 22 1 04 Cu 47 47 44 42 49 42 54 37 Mn 888 680 530 577 527 529 . 530 512 Ni 41 40 42 39 41 37 45 35 Pb 28 28 25 29 31 28 39 23 Rb 56 59 57 55 63 54 64 57 Sr •183 186 185 1 90 2 1 7 201 200 230 V 189 1 77 200 182 . 1 93 1 58 1 94 161 Zn 1 36 1 35 1 27 1 29 1 40 1 28 1 47 1 1 0 Zr 1 08 113 1 07 1 1 2 141 1 25 1 30 141 Mo 24 20 18 1 3 BDL BDL . BDL BDL I 91 90 85 81 1 38 76 186 85 Br 1 80 1 69 1 69 1 64 1 50 141 202 1 1 9 433 I V - 1 . 2 ' CHEMICAL COMPOSITION (SALT-CORRECTED) AND DEPTH OF COLLECTION OF THE SILL AND COWICHAN ESTUARY SEDIMENTS. Sample SAG 4 5 SAG 4 6 SAG47 SAG48 SAG49 SAG 50 SAG51 Depth(m) 27 72 43 68 79 87 • 43 C o r a ( % ) 0.66 1 .90 0.98 0.59 0. 62 0.78 1 .02 c S 6 8 , ( % ) 0.3 0.3 0.3 0.2 0.3 0.3 21.1 N(%) J 0.070 0.200 0,113 0.068 0. 071 0.089 0.130 Major Elements (wt %) S i 31.5 28.6 29.7 30.9 31.5 31.3 24.4 T i 0.49 0.50 0.47 0.42 0. 42 0.43 0.33 A l 5.95 6.92 7.27 7.49 7.41 7.41 5.89 Fe 3.89 4.01 ,3.61 3.48 3.37 3.45 2.82 Mg 1 .42 1 .34 1.19 1 .06 1.11 1 .07 0.96 Ca 3.04 1 .82 2.00 1 .96 2.01 1 .98 10.2 Na . 2.25 2.08 2.53 2.70 2.61 2.50 1 .69 K 0.79 1 . 45 1 .36 1 .35 1 . 34 1 .37 1 .07 P 0.07 0.08 0.08 0.07 0.06 0.07 0.07 S BDL 0.35 0.08 0.05 0.08 0.06 0.23 Minor Elements (ppm) Ba 440 447 455 449 . 450 465 342 Cr 68 1 07 95 91 89 95 . 79 Cu 32 39 25 20 17 22 32 Mn 653 482 465 427 . 416 417 386 Ni 27 34 28 24 25 25 23 Pb 1 0 25 18 1 7 1 3 18 1 6 Rb 27 56 54 51 49 51 41 Sr 262 255 300 315 310 307 750 V 173 1 48 121 99 1 03 1 1 2 1 03 Zn 69 1 20 86 77 74 79 7 4 Zr 108 1 66 1 75 158 . 183 1 60 1 36 Mo' BDL BDL BDL BDL BDL BDL BDL I 93 94 55 43 28 47 80 . Br 76 . 85 34 22 19 24 78 434 Sample SAG52 SAG53 SAG55 SAG56 SAG57 SAG 5 8 SAG59 SAG60 Depth(m) 86 80 68 123 72 67 60 51 c o c o ( %) 1.00 0.88 1 . 57 1 .29 1 .72 2.09 2.40 2.20 (%) 1.2 0.3 0.4 0.7: 0.7 0.5 0.3 0.2 N(%) J 0.119 0.086 0. 147 0.127 0. 186 0.225 0.217 0. 176 Major Elements (wt %) S i 31.3 30.9 30.0 29.3 29.2 29.4 27.7 27.6 T i 0.45 0.45 0.51 . 0.49 0.48 0.49 0.50 0.54 A l 7.34 7.43 7.75 7.52 7.24 7.35 7.46 7.59 Fe 3.51 3.56 3.93 4.20 3.92 4.12 4.27 4.59 Mg 1.11 1.16 1 .29 1 . 39 1 .28 1.41. 1 .53 1 .68 Ca 2.38 2.08 1 .91 1 .83 1 .95 1 .79 1 .72 2.17 Na 2.49 2.65 3.02 2.00 1 .99 1 .65 1 .92 2.06 K '• • 1 .34 1 .33 1 .35 1 . 37 ' 1 .37 1.31 1 .32 1.18 P 0.07 0.08 0.09 0.10 0.08 0.10 0.09 0.09 S 0.22 0.07 0.12 0.48 0.37 0.30 0.31 0.26 Minor Elements (ppm) Ba 442 449 444 419 438 421 403 396 Cr 97- 98 1 00 97 101 1 07 1 1 3 119 Cu 2 4 24 32 32 34 41 45 50 Mn 458 454 488 522 487 521 530 644 Ni 27 24 30 33 33 34 38 36 Pb 1 7 16 21 16 20 20 21 19 Rb 50 53 56 59 57 . 59 56 47 Sr 310 306 . 268 261 268 247 238 285 V 1 28 1 18 1 53 1 57 1 49 1 56 1 74 206 Zn 82 80 104 94 1 06 113 1 1 9 113. Zr 195 1 79 1 70 1 53 1 62 1 49 1 38 1 28 Mo BDL BDL BDL BDL BDL BDL BDL BDL I 45 49 80 71 86 111 110 67 Br 19 23 39 54 86 109 1 07 73 435 I V - 1 . 3 CHEMICAL COMPOSITION (SALT-CORRECTED) AND DEPTH OF COLLECTION OF THE COARSE-GRAINED NEARSHORE SEDIMENTS. Sample SAG1 1 SAG1 4 SAG21 SAG22 SAG23 SAG25 SAG28 SAG2 9 SAG32 Depth(m) 90 85 40 28 85 66 68 1 4 52 C o r a ( % ) 0.99 0.51 0.95 0.98 1 .37 0.19 0.43 0.17 0.14 c 8 £ 8 , ( % ) 0.2 0.2 0.2 0.1 0.1 0.2 0.1 BDL 0.1 N(%r 0.101 0.059 0.082 0.086 0. 1 52 0.022 0.034 0.017 0.016 Major Elements (wt %) S i 31.3 29.3 28.9 30.5 32. 1 33. 1 32.9 34.0 33.3 T i 0.34 0.38 0.44 0.38 0.30 0.31 0.33 0.26 0.33 A l 6.60 7.91 7.80 7.07 6.72 6.45 6.94 6.25 6.78 Fe 2.77 3.95 3.94 3.29 2.19 2.23 2.77 1 .86 2.38 Mg • 1 .07 1.17 1 .56 1 .23 0.79 0.86 1 .04 0.68 0.91 Ca 2.57 2.63 3.12 3.45 2.52 2.87 3.14 2.47 2.92 Na 2.78 2.46 2.74 2.71 2.92 2.87 2.78 3.12 2.88 . K 1.10 1 .57 1 .08 0.98 1 .06 0.92 1 .08 1 .08 0.94 P 0.07 0.10 0.08 0.10 0.06 0.04 0.06 0.04 0.04 S 0.20 0.13 0.29 0.12 0.12 BDL 0.07 BDL BDL Minor Elements (ppm) Ba 434 608 479 452 507 500 519 543 486 Cr 67 . 40 57 . 74 77 68 69 48 64 Cu 34 20 33 28 26 1 6 23 1 1 1 3 Mn 61 1 874 774 653 470 491 598 422 514 Ni 21 18 27 24 23 1 7 2 1 1 3 1 7 Pb 20 13 1 6 20 • 1 2 1 0 9 8 9 Rb 34 47 33 31 33 26 29 27 26 Sr 368 384 371 346 359 389 330 306 376 V 1 47 1 65 1 96 161 1 24 1 1 7 . 137 1 08 1 08 Zn 90 85 81 70 54 35 44 24 33 Zr 1 03 1 09 1 06 99 1 00 96 .1 09 101 121 Mo BDL .- BDL BDL BDL BDL BDL. BDL BDL BDL I 1 45 66 65 75 1 23 1 2 49 1 1 1 3 Br 56 32 58 44 54 1 4 32 1 9 1 3 436 Sample SAG38 SAG41 SAG42 SAG44 SAG54 Depth(m) 23 24 53 35 20 c n r , ( %) 1.14 0.26 0.38 0.25 0.27 (%) 1.3 0.1 0.2 0.1 0.1 N(%r 0. 1 04 0.031 0.036 0.033 0.037 Major Elements (wt % ) Si 30.7 35.0 33.5 33.5 34.2 Ti ; 0.38 0.24 0.29 0.30 0.30 Al 6.70 6.78 6.57 6.55 7.32 Fe 3.33 1 .49 2.28 1 .97 2.63 Mg 1 .27 0.64 0.84 0.78 0.78 Ca 3.14 2.66 2.84 2.76 2.65 Na 2.65 3.07 2.95 2.81 1 .45 K 1.13 0.97 1.01 0.95 1 .02 P 0.07 0.05 0.04 0.04 0.06 S 0.06 0.07 BDL. BDL BDL Minor Elements (ppm) Ba 473 473 436 465 469 Cr 96 51 61 68 1 07 Cu 28 1 2 1 5 1 2 1 7 Mn 572 362 434 420 489 Ni 28 1 1 1 6 1 5 ' • 18 Pb 1 5 10 1 1 1 0 9 Rb 37 25 29 26 32 Sr 305 407 382 387 397 V 139 74 99 91 1 27 Zn 72 24 38 36 43 Zr 1 1 6 94 95 111 85 Mo BDL BDL BDL BDL BDL I 1 05 27 24 20 1 4 Br 53 1 8 BDL 1 0 BDL 437 IV-2 CHEMICAL COMPOSITION OF SI"9 AND SN0.8 SEDIMENT CORES. IV-2.1 SALT-CORRECTED MAJOR ELEMENT CONCENTRATIONS: SI-9 Depth Si Ti Al Fe Mg Ca Na K S C C LOI o- 2 28 .3 0. 45 6. 37 .4. 1 5 1 .42 1 .53 1 .83 1 .34 0 .89 3. 00 0. 1 1 14. 7 2- 4 28 .5 0. 44 6. 57 4. 1 7 1 .45 1 .60 2 .08 1 .34 0 .91 2. 86 0. 1 1 14. 3 6- 8 28 .3 0. 44 6. 46 4. 04 1 .48 1 .52 2 .03 1 .42 0 .83 2. 81 BDL 13. 4 8-1 0 27 .8 0. 44 6. 46 4. 21 1 .40 1 .59 •1 .91 1 .34 1 .03 2. 73 0. 1 0 14. 0 10- 1 2 28 .0 0. 44 6. 05 4. 26 1 .48 1 .67 1 .92 1 . 25 1 .04 2. 50 0. 10 13. 5 1 2-1 4 28 .4 0. 44 6. 60 4. 27 1 .60 1 .74 1 .94 1 .34 0 .93 2. 51 0. 10 13. 9 1 4-1 6 28 .0 0. 44 6. 71 4. 23 1 .68 1 .66 2 .00 1 .42 0 .84 2. 49 0. 10 13. 6 20-22 27 .9 0. 44 6. 83 4. 49 1 .66 1 .82 1 .96 1 .43 0 .93 2. 41 0. 10 14. 3 22- 24 27 .6 0. 44 6. 57 4. 21 1 .59 1 .74 1 .99 1 .43 0 .92 2. 52 0. 1 0 14. 7 28- 30 28 .3 0. 44 6. 79 4. 25 1 .54 1 .66 1 .97 1 .42 0 .94 2. 40 0. 1 0 13. 7 30-32 28 .3 0. 44 6. 90 4. 32 1 .67 1 .66 2 .05 1 . 34 1 .04 2. 29 0. 10 13. 5 34- 36 29 .2 0. 44 6. 29 4. 10 1 .55 1 .59 1 .85 1 .34 1 .05 2. 39 0. 10 12. 1 36- 38 28 .7 0. 38 6. 1 4 3. 93 1 .34 . 1 .52 1 .83 1 .43 1 .03 2. 41 0. 10 12. 7 438 I V - 2 . 2 SALT-CORRECTED MINOR ELEMENT CONCENTRATIONS: SI -9 Depth Ba Cr Cu Mn Ni Pb Rb V Zn Zr Mo I Br 0- 2 418 1 04 46 477 38 30 56 186 1 26 1 30 2 1 1 6 207 2- 4 418 1 05 48 493 32 27 57 1 92 1 20 1 27 3 110 205 6- 8 437 1 08 42 494 38 30 58 203 128 131 4 1 07 184 8-10 421 1 10 41 479 37 25 57 204 121 1 28 8 95 189 10-12 436 110 45 . 509 32 30 58 207 1 26 1 27 2 84 166 1 2-14 434 104 52 502 40 29 58 203 138 134 1 87 1 64 14-16 440 1 07 50 519 37 35 60 207 1 60 1 30 0 89 171 20-22 440 1 1 3 55 584 41 29 59 213 159 131 2 84 1 56 22-24 444 1 09 53 546 39 35 .59 207 1 50 1 32 2 88 1 65 28-30 443- 1 06 49 507 42 31 60 207 1 34 1 35 5 76 1 63 30-32 438 1 09 50 535 35 27 59 207 131 1 32 2 73 1 54 3 4 - 3 6 4 1 7 1 04 49 443 38 28 58 192 1 30 1 27 1 0 7 5 1 70 36-38 417 1 00 49 445 39 24 57 1 97 1 34 1 24 1 0 72 1 62 439 IV-2.3 SALT-CORRECTED MAJOR ELEMENT CONCENTRATIONS: SN0.8 Si Ti Al Fe Mg Ca Na K S C C LOI ^ org car o- 2 28. 0 0. 27 4. 54 3 .19 1 .34 2 .41 1 .83 0. 80 1 .06 4. 54 o. 44 -2- 4 28. 6 0. 27 4. 70 3 .22 1.18 2 .26 1 .95 0. 98 0 .93 4. 58 0. 34 -4- 6 27. 6 o. 26 4. 55 3 .22 1.11 2 .24 1 .77 0. 99 1 .18 4. 37 0. 33 21 . 3 6- 8 27. 2 0. 26 4. 56 3 .23 1.17 2 .55 1 .79 0. 99. 1 .07 4. 49 0. 44 22. 1 8-10 26. 6 0. 32 4. 77 3 .40 1 .27 2 .53 1 .55 0. 99 .98 4. 97 0. 43 23. 0 10- 1 2 24. 5 0. 32 4. 79 3 .89 1 .22 3 .52 1 .56 0. 99 1 .21 5. 05 0. 75 24. 0 1 2-1 4 25. -1 0. 26 4. 52 3 .52 1 .35 5 .21 1 .40 0. 81 1 .21 4. 40 1 . 29 23. 0 1 4-1 6 24. 5 0. 32 4. 96 3 .98 1 .44 4 .64 1 .50 0. 99 1 .22 4. 25 0. 96 21 . 7 1 6-18 24. 0 0. 31 5. 29 4 .08 1 .33 4 .45 1 .62 1 . 08 1 .34 4. 31 0. 95 19. 6 1 8-20 25. 8 0. 32 4. 99 3 .93 1 .49 3 .89 1 .49 0. 90 1 .2 1 4. 59 0. 85 20. 3 20-22 25. 1 0. 32 5. 1 4 3 .94 1 .45 3 .55 1 .57 0. 99 1 .55 4. 43 0. 74 19. 3 22-24 25. 5 0. 32 5. 10 3 .67 1 .45 3 .71 1 .53 0. 90 1 .02 4. 34 0. 7 4 19. 4 24-26 25. 3 0. 32 5. 36 3 .89 1 .45 3 .79 . 1.51 1 . 2 5 1 .23 4. 22 0. 74 18. 7 26-30 26. 7. 0. 32 4. 68 3 .37 1.16 3 .06 1 .45 0. 99 1 .32 4. 29 0. 54 19. 4 30-34 27. 8 0. 26 4. 66 3 .22 1 .23 2 .67 1 .33 0. 90 1 . 1 1 4. 59 0. 43 2.0. 2 34-38 28. 3 0. 32 4. 77 3 .33 1.13 1 .98 1 .53 0. 90 1 . 1 2 ,4. 2 3 0. 21 19. 2 38-42 30. 1 0. 26 4. 42 2 .81 1 .21 1 .84 1 .36 0. 90 1 .09 4. 1 0 0. 22 19. 3 42-46 29. 1 0. 25 4. 36 2 .99 1.18 1 .37 1 .44 0. 81 1 .01 4. 15 0. 11 18. 5 46-50 29. 7 0. 25 4. 59 3 .06 1 .24 1 .52 1 .52 0. 90 1 .01 3. 72 0. 1 1 17. 3 50-54 28. 5 0. 25 4. 51 3 . 1 2 1.12 1 .52 1 .24 0. 99 0 .91 3. 92 0. 1 1 17. 7 54-58 26. 8 0. 31 4. 55 3 .35 1 .22 1 .59 1 .38 0. 99 1 ,25 4. 1 7 0. 10 17. 6 440 I V - 2 . 4 SALT-CORRECTED MINOR ELEMENT CONCENTRATIONS: SN0.8 Depth Ba Cr Cu Mn Ni . Pb Rb V Zn Zr Mo I Br 0- 2 380 83 70 715 45 34 47 200 1 68 84 96 121 262 2- 4 383 86 74 722 48 34 50 211 1 70 87 97 119 280 4- 6 382 86 68 740 41 28 46 .1 97 160 81 100 118 295 6- 8 370 84 65 718 41 33 47 1 84 157 80 94 1 28 310 8- 10 353 87 65 643 43 45 43 201 •1 57 81 75 151 328 10- 1 2 355 1 00 64 680 38 51 44 225 1 64 80 70 1 79 330 1 2- 1 4 328 94 65 664 41 54 40 189 1 77 72 71 1 56 31 1 1 4- 16 360 1 04 71 858 49 68 43 261 231. 81 48 1 49 289 1 6-18 3 94 1 10 . 69 940 48 65 47 268 286 86 64 1 48 298 18- 20 396 1 04 69 906 46 95 48 226 237 85 77 143 304 20- 22 398 1 04 67 939 48 52 47 232 179 84 86 1 33 293 22- 24 365 97 72 884 44 42 46 214 189 83 85 124 294 24- 26 399 99 73 1 043 43 63 52 220 181 88 77 1 23 279 26- 30 398 94 67 873 41 41 48 202 1 65 81 80 117 258 30- 34 407 95 69 795 38 33 47 1 98 173 78 1 08 1 28 296 34- 38 401 93 61 839 39 25 43 218 1 38 80 90 1 1 2 254 38- 42 372 81 54 724 30 29 38 1 86 1 1 4 73 101 1 09 243 42- 46 401 80 54 646 38 25 42 218 1 30 77 88 1 1 2 238 46- 50 392 7 7 52 553 38 21. 41 180 1 1 3 76 96 89 221 50- 54 388 83 53 532 37 27 41 1 82 1 04 76 1 05 84 254 54- 58 . 41 7 88 54 588 42 13 43 203 1 04 78 93 93 253 441 IV-3 FLUXES OF ELEMENTS AT SI-9 AND SN0.8 442 SI - 9 Dates 9/8/P. 3 - 12/9/83 P r e s e r v . - NaN ^  Depth(ra) 45 110 150 I 45 110 150 -2 -1 Dry wt. (g .rn .dy ) 1 9.64 16.42 17.45 c n r n (mg .m""2 .dy" 1) f ]carb „ c o r c / N I 502 I 23 I 60.7 1 8.3 723 28 82.1 8.8 684 47 78.5 8.7 MAJORS (g.m~ 2.dy" 1) S i T i A l Fe K Mg Ca I 2.73 I 0.029 I 0.411 I 0.289 I .089/.090 I .100/.103 1 .140/.141 4.55 0.058 0.835 0.580 .170/.173 .192/.202 .217/.221 4.95 0.068 0.950 0.660 .203/.204 .213/.216 0.249 MINORS ( <ug.m" 2.dy _ 1) Ba Cr Cu Mn Ni Pb Rb V Zn Zr Mo I 3075 I 704 I 386 I 9756 I 357 I 299 I 492 I 1080 I 1147 I 925 I RDL 6158 1593 591 21477 624 411 854 2447 1675 1691 BDL 6334 1640 611 12459 558 401 890 2618 1605 1937 BDL I 1620 3366 287 SI-9 Dates 12/9/33 - 30/9/83 Preserv. - NaN3 Depth(m) 45 110 150 I 45 110 150 Dry wt. (g.m" 2.dy _ 1) I 7.69 12.94 11.97 Cnrn ( m9 .m"2.dy"1) I 471 632 560 c o r g b 11 I 20 39 24 N C a r II 1 56.1 69.9 61.0 I 8.4 9.0 9.2 org' MAJORS (g.m" 2.dy - 1) Si I 2.27 3.62 3.35 Ti I 0.018 0.045 0.042 Al I 0.267 0.626 0.593 Fe I 0.187 0.448 0.428 K I .059/.060 0.122 0.117 Mg I .065/.067 .159/.160 0.142 Ca I 0.076 0.158 0.141 MINORS Oug.m 2.dy _ 1) Ba I 2253 4645 4345 Cr I 554 1242 1125 Cu I 254 453 515 Mn I 6306 24133 13335 Ni 1 177 401 287 Pb I 215 272 287 Rb I 315 660 610 V I 915 1967 1772 Zn I 784 1165 1089 Zr I 584 1190 1185 Mo I BDL BDL BDL I I 1230 2484 252 S I - 9 D a t e s 3 0 / 9 / 8 3 - 3 1 / 1 0 / 8 3 P r e s e r v . - N a N D e p t h ( m ) 4 5 1 1 0 1 5 0 I 4 5 1 1 0 1 5 0 - 2 - 1 D r y w t . ( g . m . d y ) I 5 . 2 1 9 . 8 8 1 0 . 8 3 C o r a ( m g . m " 2 . d y " 1 ) p u t y I I N c a r b C o r / N I 2 9 2 1 9 I 3 2 . 3 I 9 . 0 4 2 2 7 4 6 . 4 9 . 1 4 2 2 8 4 8 . 7 8 . 7 M A J O R S ( g . m " 2 . d y ~ 1 ) S i T i A l F e K Mg C a I 1 . 4 3 I 0 . 0 1 7 I 0 . 2 3 2 I 0 . 1 6 8 I . 0 5 1 / . 0 5 2 I . 0 5 7 / . 0 5 9 I . 0 8 3 / . 0 8 4 2 . 6 9 0 . 0 3 8 0 . 5 3 4 0 . 3 8 4 . 1 0 6 / . 1 0 5 . 1 2 2 / . 1 2 6 . 1 2 6 / . 1 2 7 3 . 0 1 0 . 0 4 5 0 . 6 2 6 0 . 4 4 1 0 . 1 1 8 0 . 1 4 6 0 . 1 5 2 M I N O R S ( u g . m ~ 2 . d y _ 1 ) B a C r C u Mn N i P b R b V Z n Z r Mo I 1 8 6 0 I 4 7 9 I 2 2 9 I 4 3 9 2 1 1 7 7 I 1 5 6 I 2 6 6 I 6 7 2 I 7 8 2 I 5 3 1 I B D L 3 4 6 8 8 7 9 4 1 5 2 3 4 4 5 3 4 6 2 0 7 5 1 4 1 5 2 2 8 7 9 9 7 8 B D L 4 5 7 0 1 2 0 2 5 5 2 9 6 9 3 4 2 2 2 6 0 6 0 6 1 8 9 5 1 2 3 5 1 2 5 6 B D L I I 943 1976 2144 S I - 9 Dates 31/10/83 - 28/11/33 Pr e s e r v . - MaN3 Depth(m) 45 110 150 I 45 110 150 -2 -1 Dry wt. (g.m .dy ) | 6.44 - 6.70 C n r . (mg.m"2.dy"1) N c a r b C o r g / N I 296 1 3 I 30.9 1 9.6 - 273 BDL 32.8 8.3 MAJORS (g.m~ 2.dy _ 1) S i T i A l Fe K Mg Ca I 1.66 I 0.029 I 0.412 I 0.293 I 0.070 I .102/.103 I 0.117 -1.74 0.031 0.426 0.306 0.079 0.099 0.104 MINORS Ug.m~ 2.dy _ 1) Ba Cr Cu Mn Ni Pb Rb V Zn Zr Mo I 2563 I 657 I 457 I 6852 I 316 I 180 1 367 I 1185 I 1082 I 689 I BDL -3142 811 436 11846 389 141 369 1380 978 811 BDL I 869 1454 SI-9 Dates 28/11/83 - 12/1/84 Preserv. Depth(m) NaN 45 4.02 110 8.76 150 8.28 45 4.11 3 110 150 8.09 -2 -1 Dry wt. (g.rn .dy ) 8.60 Cara (mg;m~2.dy_1) Ncarb C_or^_ 146 2 15.3 9.6 262 5 27.2 9.6 250 9 23.3 9.2 163 5 16.9 9.7 268 BDL 27.5 9.7 241 6 25.1 9.6 MAJORS (g.rn ^.dy Si 1.02 - 2.19 | 1.03 2.29 2.16 Ti 0.019 - 0.040 | 0.020 0.042 0.040 Al 0.274 - 0.547 | 0.271 0.581 0.550 Fe 0.189 - 0.370 | 0.192 0.402 0.368 K 0.049 - .108/.1071 0.050 0.110 0.108 Mg .070/.071 - .121/.126| .066/.067 0.130 0.121 Ca 0.075 — .142/.143| 0.081 0.154 0.145 MINORS -2 -1 (ug.m .dy ) Ba 1813 3942 3825 | 1706 3870 3738 Cr 454 990 1002 I 427 972 979 Cu 285 526 505 | 288 516 493 Mn 3907 6570 5175 | 3991 6450 5056 Ni 225 420 373 | 197 413 364 Pb 117 307 257 | 119 301 251 Rb 241 543 505 I 238 533 493 V 812 1691 1565 | 781 1660 1529 Zn 627 1104 1358 | 617 1084 1327 Zr 458 •1156 1101 | 469 1135 1076 Mo BDL BDL BDL | BDL BDL BDL I 639 1533 1300 | 559 1445 1311 S I - 9 Dates 1 2 / 1 / 8 4 - 9 / 2 / 8 4 P r e s e r v . - NaN ^  Depth(m) 4 5 1 1 0 1 5 0 | 4 5 1 1 0 . 1 5 0 - 2 - 1 Dry wt. (g.m .dy ) 4 . 1 6 5 . 6 7 5 . 5 7 | 3 . 9 9 - 5 . 7 9 C o r a (mg.m"2.dy"1) 2 1 4 1 9 9 1 9 5 | 1 7 6 - 2 0 0 C " BDL BDL BDL | 7 - BDL N c a r b 2 7 . 5 2 1 . 0 2 0 . 1 | 1 8 . 8 - 1 9 . 7 C o r 2 / N 7 . 8 9 . 5 9 . 7 | 9 . 4 8 . 9 1 0 . 1 MAJORS (g.m" 2.dy _ 1) S i 1 . 0 2 1 . 5 0 1 . 4 7 | 1 . 0 2 - 1 . 5 3 T i 0 . 0 1 9 0 . 0 2 8 0 . 0 2 7 | 0 . 0 1 9 - 0 . 0 2 8 A l 0 . 2 7 1 0 . 3 9 5 0 . 3 9 4 | 0 . 2 7 5 - 0 . 4 0 6 Fe 0 . 1 8 8 0 . 2 7 9 0 . 2 7 2 | 0 . 1 9 0 - 0 . 2 8 2 K . 0 4 7 / . 0 4 9 0 . 0 7 3 0 . 0 7 0 | 0 . 0 4 9 - 0 . 0 7 2 Mg . 0 5 4 / . 0 5 8 0 . 0 8 6 0 . 0 7 8 | 0 . 0 6 1 - 0 . 0 8 7 Ca . 0 5 6 / . 0 5 8 0 . 0 7 9 0 . 0 7 6 | 0 . 0 7 0 - 0 . 0 9 0 MINORS ( A j g.ra" 2.dy _ 1) Ba 1 7 0 6 2 7 5 0 2 5 0 1 | 1 7 4 4 - 2 4 7 8 Cr 4 6 2 7 6 5 6 1 8 | 4 5 5 - 6 3 1 Cu 2 7 9 3 5 7 3 5 1 | 2 1 5 - 2 9 0 Mn 3 5 6 1 9 8 4 3 4 5 7 3 | 3 6 4 7 - 4 2 6 1 Ni 1 8 7 2 4 9 2 1 7 | 1 8 0 - 2 3 7 Pb 1 3 7 1 7 0 1 6 7 | 1 3 6 - 1 7 4 Rb 2 3 3 3 1 8 3 0 6 | 2 1 1 - 3 1 8 V 7 6 5 1 1 3 4 1 0 0 8 | 7 1 8 - 1 0 4 8 Zn 5 9 5 9 2 4 9 3 0 | 6 6 6 - 8 9 2 Zr 4 6 2 6 6 3 6 7 4 | 4 5 1 - 7 0 1 Mo BDL BDL BDL j BDL — BDL 5 6 6 9 5 8 8 6 9 5 4 3 9 1 5 51-9 Dates 9/2/84 - 5/3/84 P r e s e r v . - NaN 3 Depth(m) 45 110 150 | 45 110 150 -2 -1 Dry wt. (g.m .dy ) 3.04 12.36 9.65 | 3.06 12.34 9.19 C o r a (mg.m" 2.dy - 1) 170 361 277 | 142 368 274 c o r gb BDL BDL BDL j BDL BDL BDL N c a r 24.9 35.8 29.0 | 16.5 39.5 28.5 C o r a / N 6.9 10.1 9.6 | 8.6 9.3 9.6 MAJORS (g.m" 2.dy - 1) S i 0.77 3.26 2.54 | 0.77 3.24 2.47 T i 0.014 0.059 0.045 | 0.014 0.059 0.045 A l 0.195 0.842 0.654 | 0.195 0.817 0.625 Fe 0.134 0.534 0.414 | 0.138 0.552 0.417 K 0.035 .144/.149 .111/.116| .035/.034 .149/.151 0.115 Mg .043/.044 .155/.170 .117/.133| .044/.046 .163/.172 .133/.135 Ca 0.047 .179/.184 .137/.143| .055/.056 .195/.198 0.152 MINORS (Jjg.m" 2.dy _ 1) Ba 1234 5191 3706 | 1187 5405 4044 Cr 334 1310 965 | 318 1444 1020 Cu 170 482 376 | 122 481 404 Mn 2578 15326 6427 | 3115 13858 5863 Ni 103 433 376 | 98 592 340 Pb 109 383 222 | 92 383 331 Rb 152 618 492 | 144 654 441 V 532 2188 1554 | 508 2197 1608 Zn 395 1458 955 | 422 1394 1149 Zr 304 1594 1187 | 297 1604 1204 HO BDL BDL BDL | BDL BDL BDL I 459 1891 1312 | 419 1839 1406 SI-9 D a t e s 5/3/84 - 9/4/84 P r e s e r v . - N a N 3 D e p t h ( m ) 45 110 150 | 45 110 150 -2 -1 D r y w t . ( g . r n . d y ) 3.80 8.61 6.72 I 3.76 8.52 6.64 C o r _ ( m g . n i " 2 . d y " 1 ) 223 265 245 I 217 332 254 C " " B D L B D L 4 j B D L B D L B D L N D 34.2 34.4 31.6 1 32.3 45.2 33.9 C o r g / N 6.5 7.7 7.8 1 6.7 7.4 7.5 M A J O R S ( g . m " 2 . d y _ 1 ) S i 1.08 2.41 1.82 I 1.07 2.38 1.86 T i 0.012 0.037 0.028 I 0.012 0.034 0.027 A l 0.173 0.516 0.388 I 0.167 0.497 0.389 F e 0.114 0.332 0.268 I 0.114 0.331 0.260 K 0.032 0.093 0.070 I 0.032 0.094 0.073 Mg 0.039 0.105 0.082 I 0.038 0.105 0.084 C a 0.036 0.116 0.075 I 0.040 0.111 0.086 M I N O R S ( i i g . m " 2 . d y - 1 ) B a 1083 3057 2177 I 1083 3076 2351 C r 274 827 585 I 290 861 584 C u 137 344 296 I 120 298 312 Mn 1676 9204 3656 I 1696 5955 3526 N i 49 207 235 I 68 273 199 P b 68 172 188 1 79 170 153 R b 122 396 316 I 117 409 312 V 445 1197 1089 I 414 1278 950 Z n 304 680 726 I 384 895 618 Z r 239 956 632 I 248 835 631 Mo B D L B D L B D L I B D L B D L B D L 247 956 820 | 305 1039 784 SI-9 Dates 9/4/84 - 10/5/84 Pr e s e r v . - NaN 3 Depth(m) 45 110 150 | 45 110 150 -2 -1 Dry wt. (g.rn .dy x) 5.48 16.33 13.10 I 5.49 17.05 13.19 C (mg.m~2.dy"1) 328 567 441 I 309 583 443 pOrg „ BDL BDL BDL j BDL 10 9 N c a r b „ 48.2 75.1 55.0 I 42.3 75.0 55.4 /N 6.8 7.5 8.0 I 7.3 7.8 8.0 org MAJORS (g.rn"2 .dy"' ) S i 1.54 4.52 3.64 I 1.52 4.71 3.67 T i 0.017 0.071 0.057 I 0.019 0.075 0.057 A l 0.241 0.978 0.773 I 0.258 1.035 0.801 Fe 0.168 0.627 0.514 I 0.172 0.658 0.516 K 0.050 0.189 0.145 I 0.049 0.197 0.153 Mg .053/.057 0.195 0.158 I 0.062 0.235 0.184 Ca .057/.058 0.227 0.170 I 0.080 0.259 0.194 MINORS (Aig.m" 2.dy _ 1) Ba 1606 6418 5332 I 1932 6684 5078 Cr 395 1535 1415 I 483 1466 1425 Cu 208 621 524 j - -Mn 2269 10549 7467 I 5073 20068 11765 Ni 126 490 419 I 148 477 448 Pb 55 294 314 I 115 358 448 Rb 175 768 603 j - -V 669 2401 2162 I 670 2472 2110 Zn 532 1404 1205 I 648 1569 1293 Zr 367 1943 1546 I 395 1756 1425 Mo BDL BDL BDL I BDL BDL BDL I 444 1878 1585 Dates 10/5/84 - 18/6/84 Pres e r v . - NaN 3 Depth(m) 45 110 150 | 45 110 150 -2 -1 Dry wt. (g.ra .dy ) 6.74 11.79 9.11 | 6.46 11.61 9.09 C n r _ (mg.m"2.dy"1) 400 569 406 | 380 593 405 P ° r g „ i - a r-W 17 38 BDL | 8 12 17 60.0 81.4 52.8 | 53.6 81.3 55.4 C o r g / N 6.7 7.0 7.7 | 7.1 7.3 7.3 MAJORS (g.m" 2.dy - 1) S i 1.95 3.15 2.53 | 1.88 3.21 2.53 T i 0.016 0.040 0.032 I 0.015 0.040 0.031 A l 0.229 0.555 0.430 | 0.214 0.562 0.424 Fe 0.148 0.376 0.304 | 0.145 0.376 0.303 K .050/.051 0.189 0.145 | 0.049 0.197 0.153 Mg 0.050 0.117 .079/.090| 0.055 0.133 .095/.102 Ca 0.054 0.125 .090/.094| 0.068 0.142 .104/.107 MINORS (Jjg.m" 2.dy _ 1) Ba 1388 3820 2861 | 1641 3506 2772 Cr 425 790 738 | 394 1010 645 Cu 195 424 364 | 187 511 255 Mn 2211 5364 4373 | 2351 6978 4118 Ni 54 354 228 | 71 186 155 Pb 61 248 164 | 129 244 191 Rb 182 460 282 | 168 441 291 V 566 1368 1193 I 543 1544 1136 Zn 512 1085 711 | 510 1022 709 Zr 357 920 756 I 355 871 664 Mo BDL BDL BDL | BDL BDL BDL I 661 1391 1157 | 691 1370 1227 SI-9 Dates 18/6/84 - 16/7/84 Pres e r v . - NaN 3 Depth(m) 45 110 150 | 45 110 150 -2 -1 Dry wt. (g.rn .dy ) 9.04 19.48 37.57 | 8.05 18.61 37.36 C n M (mg.m" 2.dy - 1) 580 880 1244 | 467 804 1162 r o r g 3 „ ^ _____ i_. BDL 35 BDL j 15 19 22 Ncarb 88.6 126.6 161.6 | 62.8 111.7 142.0 6.5 7.0 7.7 | 7.4 -7.2 8.2 org' MAJORS (g.m" 2.dy _ 1) S i 2.49 5.23 10.42 | 2.25 5.14 10.79 T i 0.025 0.075 0.164 | 0.022 0.070 0.168 A l 0.349 1.025 2.20 | 0.298 0.978 2.27 Fe 0.235 0.677 1.46 | 0.207 0.679 1.46 K 0.070 0.192 0.435 | 0.060 0.200 0.426 Mg 0.072 0.195 0.421 | 0.073 0.216 0.485 Ca 0.079 0.232 0.568 | 0.102 0.256 0.680 MINORS (Aig.m" 2.dy - 1) Ba 2703 6799 14277 | 2133 6309 16961 Cr 705 1695 3381 | 564 1749 4147 Cu 262 643 1240 | 137 949 1308 Mn 4628 10889 22504 | 3228 12822 23051 Ni 145 545 1315 | 193 465 1308 Pb 145 273 714 | 225 391 672 Rb 298 838 1691 | 250 837 1868 V 949 2610 5410 | 845 2550 5716 Zn 877 1617 3607 | 797 1898 3848 Zr 606 1831 4696 | 491 1787 4595 Mo BDL BDL BDL | BDL BDL BDL I 850 1948 4321 | 886 2438 4633 SI-9 Dates 16/7/84 - 24/8/84 Preserv. - NaN3 Depth(m) 45 110 150 | 45 110 150 -2 -1 Dry wt. (g.m .dy ) 8.29 15.36 28.89 | 8.14 15.38 28.41 C. r n (mg.m~ 2.dy _ 1) 551 846 1028 | 527 749 994 c o r g „ BDL BDL 12 | 6 6 9 N c a r b 84.6 115.2 138.7 | 70.8 95.4 125.0 Corg/ N 6.5 7.3 7.4 | 7.4 7.9 8.0 MAJORS (g.m" 2.dy _ 1) Si 2.40 4.20 8.29 | 2.32 4.23 7.93 Ti 0.021 0.052 0.119 | 0.021 0.053 0.119 Al 0.317 0.743 1.70 | 0.306 0.751 1.64 Fe 0.211 0.503 1.10 | 0.208 0.513 1.05 K 0.063 0.149 0.348 | 0.060 0.138 0.322 Mg 0.070 0.159 0.371 | 0.071 0.153 0.344 Ca 0.083 0.192 0.455 | 0.104 0.194 0.438 MINORS (Aig.m 2.dy - 1) Ba 2172 4900 10834 | 2263 5352 11108 Cr 539 1352 2600 | 529 1323 2614 Cu 274 722 1127 | 260 385 938 Mn 2868 10875 24152 | 3460 33944 45854 Ni 166 384 1127 | 187 415 795 Pb 257 384 896 | 187 246 795 Rb 298 768 1618 | 293 692 1449 V 804 2043 4449 | 895 2199 4489 Zn 904 1290 2773 I 781 1430 2642 Zr 572 1336 3582 | 611 1400 3608 Mo BDL BDL BDL | BDL BDL BDL I 937 2243 3496 | 1042 2522 4233 SI-9 Dates 24/8/84 - 19/9/84 Preserv. - NaN3 Depth(m) 45 110 150 | 45 110 150 -2 -1 Dry wt. (g.m .dy ) 7.11 9.11 9.41 | 6.91 8.86 9.89 C n r a (mg.m~2.dy_1) 563 546 489 | 464 512 496 corg „ BDL BDL 8 I 6 6 BDL N c a r b 77.5 78.3 67.8 | 62.2 66.5 64.3 Corg/ N 7.3 7.0 7.2 | 7.4 7.7 7.7 MAJORS (g.ra"2.dy_1) Si 1.84 2.38 2.44 | 1.79 2.34 2.42 Ti 0.023 0.033 0.036 | 0.023 0.033 0.036 Al 0.330 0.484 0.501 | 0.334 0.466 0.515 Fe 0.220 0.340 0.370 | 0.227 0.337 0.373 K 0.069 0.093 0.099 | 0.066 0.091 0.097 Mg 0.078 0.111 0.118 | 0.076 0.108 0.111 Ca 0.102 0.143 0.150 | 0.099 0.140 0.148 MINORS (Aig.m" 2.dy _ 1) Da 2176 2833 3190 | 2128 2924 3372 Cr 562 720 800 | 518 771 851 Cu 306 301 367 | 180 292 316 Mn 3022 56282 124278 | 10047 38825 138608 Ni 114 164 188 | 111 177 178 Pb 128 191 151 | 159 177 158 Rb 284 410 395 | 276 416 405 V 903 1348 * 1468 | 822 1426 1513 Zn 604 774 753 | 574 762 841 Zr 519 . 711 800 | 511 709 870 Mo BDL BDL BDL | BDL BDL BDL I 1152 1804 1873 | 1075 1657 1988 S N 0 . 8 D a t e s 12/1/84 - 9/2/84 P r e s e r v . - N a N D e p t h ( m ) 45 135 180 | 45 135 180 D r y w t . ( g . m " ^ . d y - i ) 0.98 2.15 1.76 I 0.99 2.08 1.85 C ( m g . r a " 2 . d y ~ 1 ) 58 104 83 I 57 101 93 C ° ^ = h " B D L B D L B D L | 2 3 B D L N c a r " 7.0 11.4 8.4 | 6.4 10.0 9.3 C r t r _ / N 8.3 9.1 9.8 | 8.8 10.1 10.0 D a t e s 9/2/84 - 5/3/84 P r e s e r v . - N a N -D e p t h ( m ) 45 135 180 | 45 135 180 D r y w t . ( g . m " 2 . d y ~ 1 ) 0.65 2.11 1.73 I 0.64 2.15 1.70 C ( m g . m " 2 . d y _ 1 ) 47 109 90 I 48 112 90 C ° ^ = h " B D L B D L B D L | 5 B D L 6 N " 6.0 13.7 10.7 | 6.0 14.2 11.1 C / N 7.8 8.0 8.4 I 7.8 7.9 7.7 Dates 5/3/84 - 9/4/84 Preserv. - NaN ^ Depth(m) 45 135 180 | 45 135 180 -? -1 Dry v/t. (g.m .dy ) 1.93 2.52 2.39 | 2.12 2.55 2.30 C n (mg.m"2.dy-1) 199 182 171 | 228 192 186 rorg •• 2 BDL BDL | 18 9 BDL Ncarb 32.8 28.5 25.8 | 37.3 28.1 27.4 C o r g / N 6.0 6.4 6.6 | 5.6 6.5 6.8 MAJORS (g.m"2.dy_1) Si 0.549 0.695 0.651 | 0.613 0.680 0.632 Ti 0.0026 0.0067 0.0057 | 0.0028 0.0058 0.0055 Al 0.035 0.091 0.081 | 0.034 0.087 0.084 Fe 0.028 0.069 0.054 | 0.027 0.067 0.056 K 0.0070 0.0167 0.0141 | 0.0068 0.0189 .0177/.0173 Mg 0.0104 0.022 0.021 | 0.0107 0.021 .020/.018 Ca 0.0099 0.019 0.016 | 0.0099 0.030 .022/.021 MINORS (/ug.m"2.dy-1) Ba 268 701 569 | 273 632 550 Cr 83 202 167 | 83 166 156 Cu 75 154 134 | 40 125 163 Mn 486 3702 832 | 473 3659 823 Ni 2 60 38 | 0 36 23 Pb 39 91 55 | 38 61 48 Rb 19 60 53 | 19 56 51 V 122 330 246 | 114 278 239 Zn 114 297 208 | 131 288 202 Zr 50 121 120 | 53 122 104 Mo BDL BDL BDL | BDL BDL BDL I 116 386 332 | 125 405 274 SN 0.8 Dates 9/4/84 - 10/5/84 Preserv. - NaN3 Depth(m) 45 135 180 | 45 135 180 -2 -1 Dry v/t. (g.m .dy ) 3.64 4.34 2.88 | 3.52 3.36 3.08 C: M (mg.m"2.dy_1) 298 247 173 | 278 200 188 v- ~ ^ BDL 9 BDL | BDL BDL BDL Ncarb 44.4 34.7 24.2 | 36.3 24.5 25.3 6.7 7.1 7.2 | 7.7 8.1 7.5 org/ MAJORS (g.m"2.dy~1) Si 0.915 1.28 0.877 | 0.936 0.979 0.937 Ti 0.0026 0.0083 0.0057 | 0.0034 0.0062 0.0063 Al 0.039 0.116 0.083 | 0.043 0.087 0.087 Fe 0.030 0.097 0.062 | 0.031 0.064 0.061 K 0.0102 0.0230 0.0165 | .0063/.0103 0.0194 0.184 Mg 0.016 0.029 0.020 | .023/.007 0.023 0.024 Ca 0.017 0.034 0.020 | .035/.029 0.035 0.034 MINORS (Aig.m" 2.dy _ 1) Ba 455 855 590 | 359 682 604 Cr 84 226 141 | 60 178 142 Cu 102 143 233 | 46 97 99 Mn 612 9943 850 | 1049 20365 1152 Ni 0 35 32 | 0 20 31 Pb 55 65 66 | 32 44 49 Rb 36 74 60 | - - -V 146 356 233 | - - -Zn 218 230 311 | 282 239 323 Zr 87 182 130 | 81 141 132 Mo BDL BDL BDL | BDL BDL BDL 255 681 3 4 3 SN 0.8 Dates 10/5/84 - 18/6/84 Preserv. — NaN3 Depth(m) 45 135 180 | 45 135 180 -2 -1 Dry wt. (g.m .dy ) 2.85 2.95 3.25 | 2.63 3.24 3.16 C n r. (mg.m"2.dy"1) 252 218 235 | 251 234 222 -°rg „ BDL 6 BDL j BDL 6 5 Ncarb „ 36.2 31.3 33.2 | 34.5 32.1 30.7 C---/N 7.0 7.0 7.1 I 7.3 7.3 7.2 org MAJORS (g.m"2.dy-1) Si 0.777 0.812 0.870 | 0.727 0.877 0.864 Ti 0.0017 0.0042 0.0043 | 0.0016 0.0045 0.0042 Al 0.022 0.055 0.055 | 0.020 0.063 0.064 Fe 0.013 0.051 0.046 | 0.015 0.058 0.048 K 0.0054 0.0130 0.0104 | 0.0057 0.0139 0.0133 Mg 0.0093 0.020 0.016 | 0.0116 0.018 0.019 Ca 0.0108 0.028 0.021 | 0.020 0.037 0.035 MINORS Ug.m"2.dy-1) Ba 319 546 452 | 387 671 528 Cr 48 103 114 | 58 159 120 Cu 51 97 367 | 897 107 98 Mn 276 720 585 | 339 2910 629 Ni 3 9 10 | 0 10 0 Pb 40 38 36 | 34 62 44 Rb 17 32 46 | 26 49 44 V 60 195 179 | 68 211 186 Zn 145 189 192 | 200 288 246 Zr 54 100 107 | 55 104 104 Mo BDL BDL BDL | BDL BDL BDL I 234 392 416 | 292 505 404 SN 0.8 D a t e s 1 8 / 6 / 8 4 - 1 6 / 7 / 8 4 P r e s e r v . — N a N 3 D e p t h ( m ) 4 5 1 3 5 1 8 0 | 4 5 1 3 5 1 8 0 - 2 - 1 D r y w t . ( g . m . d y ) 2 . 5 9 3 . 1 7 2 . 4 9 | 2 . 0 6 1 . 2 2 4 . 0 0 C . . . ( m g . m ~ 2 . d y _ 1 ) 3 0 5 2 5 9 2 4 1 | 2 6 2 9 6 3 3 2 r ° r g ,, B D L B D L B D L | 3 2 8 N c a r b 5 0 . 8 4 1 . 2 4 0 . 1 | 3 8 . 3 1 4 . 0 4 7 . 6 C o r g / N 6 . 0 6 . 3 6 . 0 | 6 . 8 6 . 8 7 . 0 M A J O R S ( g . m " 2 . d y - 1 ) S i 0 . 3 0 7 0 . 6 4 4 0 . 5 5 6 | 0 . 4 0 1 - 0 . 9 3 2 T i 0 . 0 0 3 6 0 . 0 0 3 8 0 . 0 0 3 9 | 0 . 0 0 1 6 - 0 . 0 0 5 7 A l 0 . 0 1 7 0 . 0 5 7 0 . 0 5 3 | 0 . 0 2 5 - 0 . 0 8 2 F e 0 . 0 1 4 0 . 0 5 7 0 . 0 4 2 | 0 . 0 1 5 - 0 . 0 8 0 K . 0 0 7 3 / . 0 0 0 0 . 0 1 0 1 0 . 0 1 1 4 | 0 . 0 4 2 - 0 . 0 1 7 5 Mg - 0 . 0 1 1 1 0 . 0 1 1 7 | 0 . 0 0 5 0 - 0 . 0 2 3 C a — 0 . 0 2 0 0 . 0 1 2 6 | 0 . 0 2 7 — 0 . 0 4 5 M I N O R S ( x i g . m " 2 . d y - 1 ) B a 1 9 4 3 6 1 4 5 3 | 2 0 6 - 6 8 0 C r 4 9 1 2 0 1 2 0 | 3 9 - 1 5 6 C u 1 3 7 1 6 2 1 6 9 | 5 4 - • 6 4 0 Mn 2 6 4 1 3 6 9 6 1 0 | 2 7 6 - 3 2 3 2 N i 0 1 3 1 5 | 0 - 0 P b 5 4 6 7 5 7 | 4 3 - 8 0 R b 2 3 5 1 5 0 | 1 9 - 6 4 V 47 1 8 7 1 6 2 | 5 4 - 2 2 0 Z n 2 7 2 2 5 4 2 5 6 | 2 7 6 - 3 9 6 Z r 57 1 0 5 9 0 | 4 5 - 1 4 0 Mo B D L B D L B D L | B D L — B D L 3 0 8 523 4 1 8 276 760 S N 0 . 8 D a t e s 1 6 / 7 / 8 4 - 2 4 / 8 / 8 4 P r e s e r v . — N a N ^ D e p t h ( m ) 4 5 1 3 5 1 8 0 | 4 5 1 3 5 1 8 0 - 2 - 1 D r y v / t . ( g . m . d y ) 2 . 3 2 2 . 1 0 2 . 0 9 | 2 . 1 9 2 . 1 7 2 . 0 8 C o r a ( m g . m ~ 2 . d y _ 1 ) N c a r b C o r c / N 3 1 0 2 4 5 . 5 6 . 6 2 3 9 4 3 3 . 8 7 . 1 2 3 5 | 3 I 3 4 . 1 | 6 . 9 | 2 8 9 5 4 3 . 4 6 . 7 2 1 8 6 2 8 . 4 7 . 7 2 2 2 5 2 9 . 8 7 . 4 M A J O R S ( g . m ~ 2 . d y - 1 ) S i T i A l F e K Mg C a 0 . 5 9 4 0 . 0 0 2 2 0 . 0 2 5 0 . 0 2 1 0 . 0 0 6 4 0 . 0 0 9 6 0 . 0 1 8 0 . 4 9 3 0 . 0 0 2 6 0 . 0 3 7 0 . 0 3 5 0 . 0 0 8 3 0 . 0 1 0 7 0 . 0 2 4 0 . 4 8 0 | 0 . 0 0 2 8 | 0 . 0 4 0 | 0 . 0 3 5 | 0 . 0 0 9 8 | 0 . 0 1 0 9 | 0 . 0 1 9 | 0 . 4 9 9 0 . 0 0 1 8 0 . 0 2 5 0 . 0 1 7 0 . 0 0 6 1 0 . 0 0 8 7 0 . 0 2 7 0 . 5 0 1 0 . 0 0 2 6 0 . 0 3 7 0 . 0 3 9 0 . 0 0 8 1 0 . 0 1 0 8 0 . 0 3 0 0 . 5 0 9 0 . 0 0 3 0 0 . 0 4 2 0 . 0 3 5 0 . 0 0 9 0 0 . 0 1 1 8 0 . 0 3 0 M I N O R S ( A i g . m . d y l ) B a 2 4 4 3 0 5 3 2 0 | 2 5 0 3 3 0 3 4 9 C r 6 3 8 2 8 6 | 5 9 1 1 5 1 0 9 C u 9 7 7 6 1 0 2 | 3 2 2 1 1 5 1 2 4 Mn 3 2 7 5 6 1 3 7 6 | 3 7 9 2 3 0 0 4 9 0 N i 7 8 8 I 0 2 9 P b 3 7 4 8 4 0 | 5 3 5 0 4 6 R b 2 8 3 4 3 6 | 3 1 3 3 3 3 V 97 1 2 4 1 4 8 | 7 9 1 2 6 1 2 6 Z n 3 4 6 1 4 7 1 8 6 | 4 3 8 1 7 4 2 4 1 Z r 6 0 6 9 6 5 | 5 0 6 9 7 8 Mo B D L B D L B D L j B D L B D L B D L I 2 9 5 4 6 8 4 2 0 | 3 3 5 4 9 9 4 6 0 Dates Preserv. Depth(m) 45 135 Dry wt. (g.m"2.dy_1) 0.88 0.96 c n (mg.m~2.dy_1) 122 93 C g. " BDL 1 NC " 17.9 13.4 CoEg/N 6.8 6.9_ to SN 0.8 24/8/84 - 6/10/84 NaN 180 | 45 135 180 1.05 | 0.81 - 0.64 108 | 108 - 72 BDL j 4 - 1 15.0 | 13.8 - 10.2 7.2 | 7.9 - 7.1 

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