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UBC Theses and Dissertations

The effect of manganese oxide scavenging on the distribution and sedimentation of molybdenum in saanich… Berrang, Peter Gottfired 1972

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THE EFFECT OF MANGANESE OXIDE SCAVENGING ON THE DISTRIBUTION AND SEDIMENTATION OF MOLYBDENUM IN SAANICH INLET,BRITISH COLUMBIA by P e t e r G o t t f r i e d Berrang B.Sc. U n i v e r s i t y of Waterloo, 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Chemis t r y ( I n s t i t u t e of Oceanography) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1972 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 representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver 8, Canada > ( i i ) Abstract This study investigated the process by which molybdenum was removed from sea water in Saanich Inlet, an anoxic fjord, whose basin sediments are enriched i n molybdenum. Water samples were collected in the inlet from July 1971 to Apr i l 1972 at about two month intervals and were analyzed for pH, s a l i n i t y , temperature, dissolved and suspended molybdenum, suspended manganese and iron, and dissolved oxygen and hydrogen sulphide. A new technique for the determination of dissolved and suspended molybdenum was developed. The data showed a negative correlation between dissolved molybdenum and suspended manganese, and a positive correlation between suspended molybdenum and suspended manganese. This suggested that molybdenum was being scavenged from sea water by suspended manganese oxides. The distribution of molybdenum i n the basin surface sediments was qualitatively correlated to the distribution of suspended molybdenum in the overlying basin water. During about September to December, the molybdenum profile was described by a two layer system. In the top 75 m layer the molybdenum followed the s a l i n i t y profile. Below 75 m the distribution was described by a one dimensional mathematical model. The yearly deposition of molybdenum in the basin sediments was calculated from the estimated sediment deposition rate. This value was not inconsistent with that calculated from the rate molybdenum is scavenged by manganese oxides from the basin water. ( i i i ) Table of Contents Page Introduction 1 General Description of Saanich Inlet' 4 Sampling Methods Analytical Methods • ^ Dissolved Molybdenum ^ Suspended Molybdenum Molybdenum in Sediments •— \\ Suspended Manganese — 12 Suspended Iron 12 Dissolved Oxygen 12 Sulphide-Sulphur • 12 p H : _ 12 Experimental Observations' • 13 Discussion 24 Bibliography • — 45 Appendix • 51 ( i v ) L i s t of Tables Page Table I. Data C o l l e c t e d i n Saanich In l e t 13 Table I I . Comparison of Values of A 2 and w 41 (v) L i s t of Figures Page Figure 1. Location of Saanich I n l e t 2 Figure 2 . Sampling Stations- 3 Figure 3 . C a l i b r a t i o n curve f o r suspended -^Q molybdenum • Figure 4. D i s t r i b u t i o n of d i s s o l v e d molybdenum during August, 1971 15 Figure 5 . D i s t r i b u t i o n of suspended manganese j_5 during August, 1971 Figure 6. D i s t r i b u t i o n of d i s s o l v e d molybdenum during February, 1972 L 7 Figure 7. D i s t r i b u t i o n of d i s s o l v e d molybdenum during A p r i l , 1972 • 1 7 Figure 8. D i s t r i b u t i o n of d i s s o l v e d molybdenum at Sta t i o n 2 18 Figure 9 . D i s t r i b u t i o n of suspended manganese at S t a t i o n 2 1 8 Figure 1 0 . D i s t r i b u t i o n of d i s s o l v e d oxygen at Station 2 • 2 0 Figure 1 1 . D i s t r i b u t i o n of d i s s o l v e d oxygen during August,1971 Figure 1 2 . D i s t r i b u t i o n ofsuspended mianganese „ during A p r i l , 1972 Figure 13 . D i s t r i b u t i o n of suspended molybdenum ^ during A p r i l , 1972 Figure 14 . D i s t r i b u t i o n of temperature at Station 2 • 23 Figure 1 5 . D i s t r i b u t i o n of s a l i n i t y at 23 Station 2 Figure 16 . Plot of dissol v e d molybdenum against s a l i n i t y during August, 1971 25 Cvi) Page Figure 17. V e r t i c a l p r o f i l e of dissol v e d molybdenum at S t a t i o n 2 during August, 19 71 2 6 Figure 18. V e r t i c a l p r o f i l e of dissolved manganese at S t a t i o n 2 during August, 1971 2 8 Figure 19. V e r t i c a l p r o f i l e of suspended molybdenum and suspended manganese at Station 2 i n February and A p r i l , 1972 Figure 20. V e r t i c a l p r o f i l e of suspended manganese at S t a t i o n 2 during December, 1971 35 Figure 21. P l o t of suspended molybdenum against suspended manganese during December 1971, February 1972 and A p r i l 1972 36 Figure 22. Molybdenum p r o f i l e f o r samples c o l l e c t e d at Station 2 during December, 1971 40 ( v i i ) Acknowledgment I sincerely thank Dr. E.V. G r i l l for his patience, advice and guidance at every stage in the preparation of this thesis. I would also l i k e to thank Mr. F.A. Whitney for his assistance in collecting samples at sea. -1-INTRODUCTION Enrichment of molybdenum in anoxic sediments has been observed in the Black Sea CPhilipchuk and Volkov, 1967), the Baltic Sea (Manheim, 1961) and Saanich Inlet (Gross, 1967). These authors attributed this enrichment to a process related to the reducing environments. Philipchuk and Volkov (1967) and Manheim (1961) suggested that the removal of molybdenum was due to coprecipitation with colloidal ferrous sulphide. Sugawara (1961) observed that molybdenum could be removed from sea water by precipitation of ferrous sulphide. Since soluble* thiomolybdates form at pH > 7.2, precipitation as MoS^ i s unlikely. Krauskopf (1956) concluded that the molybdenum concentration of the oceans was probably controlled by organic reactions and not by sulphide precipitation. In oxygenated sea water he found that molybdenum was most effic i e n t l y adsorbed by manganese and iron oxides. The high levels of suspended manganese oxides observed in Saanich Inlet (E.V. G r i l l , personal communication) and the fact that molybdenum can be quantitatively coprecipitated from sea water with manganese dioxide (Chan and Riley, 1966; Bachmann and Goldman, 1964) suggested that scavenging by manganese oxides may be important in controlling the molybdenum distribution. This study investigated scavenging of molybdenum by manganese oxides in the oxygenated zone in Saanich, and the possibility that this process supports the downward flux of molybdenum necessary to enrich the sediments. The actual mechanism by which molybdenum is incorporated into the sediments in the anoxic zone was not investigated. -2--3-1 2 3 ° 3 0 ' Figure 2 . Sampling Stations _4-GENERAL DESCRIPTION OF SAANICH INLET Saanich Inlet (Figure 2) i s the only fjord on the southeast coast of Vancouver Island, Bri t i s h Columbia. The inlet i s approximately 26 km long and varies in width from 0.4 to 7.6 km. The average depth i s 120 m with a maximum depth of 236 m. A s i l l located at the entrance with a maximum depth of approximately 70 m restricts exchange of the bottom water in the inlet with that in the approaches. According to Herlinveaux (1962) the inlet receives l i t t l e runoff from the various streams discharging into i t and most of the fresh water inflow i s due to runoff from the Cowichan and Fraser Rivers, which enters at the mouth. Herlinveaux (1962) noted that the deep waters of the inlet are anoxic throughout most of the year. He concluded that, due to the small amount of fresh water In the surface layer, only a weak estuarine and t i d a l flushing circulation exists and that, as a consequence, the water below s i l l depth tends to be highly oxygen deficient. However, data taken in August 1953 (Herlinveaux, 1962) indicated that the bottom waters were oxygenated and he concluded that the deep anoxic water may flush periodically. Evidence that deep water oxygenation beginning in August or September i s a normal annual phenomenon has been obtained by Richards (1965). Data for the Fraser and Cowichan River outflows (Herlinveaux, 1962) indicate that this corresponds with the period when the runoff of both rivers w i l l generally be low, suggesting that the sal i n i t y (and density) of water in the approaches of the inlet is then near i t s seasonal maximum. SAMPLING METHODS A l l sampling was done from the oceanographic vessel C.S.S. Vector at the six sampling stations indicated in Figure 2. Samples were collected using 1.2 l i t r e plastic N.I.O. bottles, except for suspended molybdenum samples which were collected in 5 l i t r e plastic Nisken bottles. Temperature observations, s a l i n i t y , pH, dissolved oxygen and sulphide samples were a l l taken from a single water bottle. The samples used for the determination of dissolved molybdenum and suspended manganese and iron were obtained from a second sample bottle (collected on a subsequent cast) whose entire content was f i l t e r e d immediately after collection through a 0.2 ym membrane f i l t e r . The suspended molybdenum samples were collected by f i l t e r i n g the contents of two 5 l i t r e Niskin bottles (positioned 2 m apart) through a 0.45ym membrane f i l t e r . The f i l t e r s containing the suspended matter were stored in plastic Petri dishes u n t i l analyzed and the dissolved molybdenum samples were preserved by adding 50 ml of HC£ to a 500 ml polyethylene bottle containing 400 ml of f i l t e r e d sea water. '• Color development in the colorimetric procedure for sulphide determination was carried out immediately after sample collection and the absorptrimetric measurements completed in the shore laboratory after the end of the cruise. Temperature, pH and dissolved oxygen measurements were completed on board ship. Surface sediment samples were collected at stations 1 through 5 (Figure 2) using a 2 m long plastic gravity corer with a stainless steel -6-nose piece. The samples were frozen immediately after collection and stored frozen in the shore laboratory u n t i l analyzed. ANALYTICAL METHODS Dissolved Molybdenum Because of i t s low concentration (ca. 10 yg/i) a l l methods for determining molybdenum in sea water invariably employ a preconcentration step, such as coprecipitation (Kim and Z e i t l i n , 1969; Bachmann and Goldman, 1964; Chan and Riley, 1966; Sugawara, et. al.,1969),co-crystalliza-tion (Weiss and L a i , 1961) or ion exchange (Riley and Taylor, 1968; Kawabushi, et. a l . , 1969). After concentration, molybdenum can then be quantitatively determined either by colorimetry, using a reagent such as d i t h i o l , or by atomic absorption spectrophotometry. Since this study required the analysis of a large number of samples, a procedure in which the concentrative and determinative steps could be combined was desirable. This was achieved by reacting molybdenum directly with d i t h i o l i n the f i l t e r e d sea water sample and measuring the color of the resulting complex spectrophotometrically after a 20 fold concentration by extraction into iso-amyl acetate. Advantages of this method aside from rapidity are: quantitative recovery using two extractions; minimum sample handling; good reproducibility, (a) Reagents. Complexing solution: Dissolve 5 g of thiourea and 7.5 g of sodium citrate in 100 ml of d i s t i l l e d water. - 7 -'Ferrous ammonium sulphate solution: Dissolve 0.7 g of ferrous ammonium sulphate hexahydrate in 100 ml of 0.2N sulphuric acid. Prepare fresh weekly. Dithiol solution: Dissolve 0.04 g of the zinc salt of toluene-3,4-d i t h i o l (Fisher Certified Reagent) in 10 ml of 0.1 N potassium hydroxide. Prepare fresh daily. (This amount i s sufficient for one 400 ml sea water sample). If an insoluble^ red-brown oxidation product is present, f i l t e r the solution through a Whatman No. 41 H f i l t e r paper. Hydrochloric acid: Use concentrated reagent grade. Iso-amyl acetate: Use r e d i s t i l l e d reagent grade (b.p. 140 - 142°C). 0>) Procedure. Fifty m i l l i l i t r e s of concentrated HC£, 10 ml of the complexing solution, 1 ml of the ferrous ammonium sulphate solution and 10 ml of the d i t h i o l solution were added to 400 mis of sea water in a 500 ml erlenmeyer flask. (The hydrochloric acid can be added as a preservative at the time of sample collection i f the analysis i s to be delayed for any period of time.) The sample was then extracted twice with, f i r s t , a 15 ml and, next, a 10 ml portion of iso-amyl acetate. The organic and aqueous phases were mixed for 30 minutes during each extraction using a magnetic s t i r r i n g bar and motor. After separation, the organic phase was removed using a pipette and rubber suction bulb and the extracts combined in a 125 ml separatory funnel where they were shaken for about 1 minute with 10 ml of concentrated HC& to remove turbidity. After transferring the organic phase to a 25 ml glass stoppered cylinder and bringing i t to volume with iso-amyl acetate, the absorbance was measured -8-with a Beckman Model DU Spectrophotometer at 670 nm i n a 5 cm c e l l , (c) Discussion. The distribution coefficient for the molybdenum-dithiol complex between sea water and iso-amyl acetate was £a. 400; thus, two extractions of 15 and 10 ml should give a recovery of about 99%. Calibration curves were prepared by extracting 400 ml sea water samples spiked with 0 to 8 ug of molybdenum. These curves were linear and had a slope of 22.0 ~ 0.3 yg molybdenum per unit absorbance, corresponding to a molar extinction coefficient (e) of 21, 800 (£ mole "'"cm *") . Values of e (in iso-amyl acetate) calculated from calibration curves of Clark (1955) and Piper (1948) were 21,100 and 21,200 respectively. Replicate determinations on f i l t e r e d sea water samples gave a coefficient of variation of 1.2%. Ferrous iron was added to speed formation of the molybdenum-di t h i o l complex (Gilbert and Sandell, 1959) and, under the conditions given, an extraction time of 30 minutes was found sufficient to achieve maximum color development. Interference by tungsten was prevented by addition of citrate (Sandell, 1965) and the interference of many elements that compete with molybdenum for the di t h i o l reagent was reduced by thiourea (Chan and Riley, 1966). No change in absorbance was noted for samples stored in the dark for several weeks. After about five weeks the samples showed a 5-10% increase in absorbance. The complex can be broken down with strong oxidizing agents. -9-The present method was compared with that used by Bachmann and Goldman (1964), who used thiocyanate spectrophotometry after coprecipitating molybdenum with manganese dioxide. The molybdenum concentration of a sea water sample analyzed by the d i t h i o l and thiocyanate methods was 9.7 and 9.3 ug /jl , respectively. These results differ by about 4%o Suspended Molybdenum Philipchuk and Volkov (1967) found no significant difference in molybdenum concentration of 7 l i t r e samples of f i l t e r e d and unfiltered Black Sea water. However, no report could be found of an attempt to determine suspended molybdenum in sea water directly by the analysis of suspended matter. After a number of t r i a l s , suspended molybdenum was f i n a l l y detected at the nanogram/litre level in some samples from Saanich by analyzing the suspended matter obtained upon f i l t e r i n g 10 l i t r e s of water through a 0.45 urn membrane f i l t e r . The suspended matter was f i r s t leached with concentrated HC£ and after treating the f i l t r a t e with ascorbic acid to overcome possible interference by iron(III) (Chan and Riley, 1966), the molybdenum was then determined by d i t h i o l colorimetry. The procedure concentrated suspended molybdenum by a factor of 3,000. (a) Procedure. The reagents used were the same as those described for the determination of dissolved molybdenum. The membrane f i l t e r containing the suspended matter was boiled for 5 minutes with 6 ml of concentrated HC£ -10-and the a c i d digest, a f t e r f i l t r a t i o n through a 0.45ym membrane f i l t e r , was t r a n s f e r r e d to a 125 ml separatory funnel using 10 ml of d i s t i l l e d water as r i n s e . Two m i l l i l i t r e s of complexing s o l u t i o n , 2 ml of a 5% (w/v) ascorbic a c i d s o l u t i o n , 0.25 ml of the ferrous ammonium sulphate s o l u t i o n and 0.005 g of z i n c d i t h i o l ( i n 0.1 N potassium hydroxide) were added to the sample. A f t e r 5 minutes, the molybdenum d i t h i o l complex was extracted by shaking f o r 2 minutes with 3.50 ml of iso-amyl acetate. A f t e r separation, the organic phase was washed with 5 ml of concentrated HC£, centrifuged u n t i l no suspended droplets were v i s i b l e and i t s absorbance measured at 670 nm i n a 1 cm c e l l . (b) Discussion. A c a l i b r a t i o n curve was constructed by adding 0.1, 0.2 and 0.4 ug molybdenum to blank membrane f i l t e r s and then proceeding as o u t l i n e d above. The r e s u l t s are i l l u s t r a t e d i n Figure 3. ;jg MOLYBDENUM Figure 3. C a l i b r a t i o n curve f o r suspended molybdenum. -11-Although the absorbances were low, the calibration curve was reasonably reproducible. Because of an apparent non-linearity in the curve, sample concentrations had to be read directly from the calibration curve. Molybdenum in Sediments Surface sediment samples were leached with concentrated HC£ and, after addition of an ammonium chloride-aluminium chloride solution to suppress matrix interferences (David, 1968), the molybdenum concentration was measured by atomic absorption spectrophotometry. (a) Procedure. One gram of a i r dried sediment sample was boiled in 10 ml of concentrated HC& for 5 minutes and the acid digest f i l t e r e d through a 0.45 Vm membrane f i l t e r into a 10 ml graduated cylinder. After dilution to 8.0 ml (ca. 3 ml of acid was lost by evaporation), 2.0 ml of a solution containing 5% (w/v) A£C£3.6H20 and 5% (w/v) NH^C£ was added and the molybdenum concentration determined with a Techtron Model IV Atomic Absorption Spectrophotometer using hollow cathode o radiation at 3133 Av a 5 cm slot burner (Techtron AB 50) and a nitrous oxide-acetylene flame. (b) Discussion. A calibration curve was constructed by adding known amounts of molybdenum in place of the dried sediment sample, and then proceeding as outlined above. The resulting curve was linear. The minimum concentration that could be measured using the above procedure was ca. 0.5 parts per million. -12-Suspended Manganese The f i l t e r s were heated with 2.5 ml of a 4:1 nitric-perchloric acid mixture to evolution of white perchloric acid fumes. The sample was then cooled and diluted to 10.0 ml with deionized water. The manganese concentration was measured by atomic absorption spectro-photometry using hollow cathode radiation at 2795 A,, a 10 cm slot burner (Techtron AB 51) and an air-acetylene flame. Suspended Iron An aliquot of the stock solution used for the determination of suspended manganese was used to determine suspended iron by o-phenanthroline colorimetry (Sandell, 1965). Dissolved Oxygen Dissolved oxygen was determined by standard Winkler t i t r a t i o n (Strickland and Parsons, 1968) using the modified reagents described by Carrit and Carpenter (1966). Sulphide-Sulphur (H2S, HS~,S~2) Sulphide-sulphur was measured by methylene blue colorimetry (Cline, 1969). pH Samples were collected in tightly stoppered 50 ml polyethylene bottles that were completely f i l l e d to exclude a i r . After reaching -13-temperature equilibrium with a pH 7.4 reference buffer (standardized against NBS buffer reagents), the pH was estimated with an Orion Model 801 pH meter using a Corning 476022 glass electrode. The pH measurement was corrected to in s i t u water temperature using the data given by Riley and Chester (1971). EXPERIMENTAL OBSERVATIONS Sampling was conducted at intervals of one or two months between July 1971 and Apri l 1972. The cruise numbers, dates of the cruises and the stations sampled are indicated in Table I. Only station 2 was sampled regularly, but more extensive surveys were carried out in August 1971 and February and Apri l 1972. In addition to temperature, sal i n i t y and dissolved oxygen observations, which were made on a l l cruises, data were collected at the various times shown in Table I for dissolved molybdenum (Mo), suspended molybdenum (Mop), suspended manganese (Mnp), suspended iron (Fe p), sulphide-sulphur (S) and pH. The results of the observations are tabulated in the Appendix. TABLE I. Data Collected in Saanich Inlet. Station Data Collected Cruise No. Date 2 Mo 71/22 July 13,1971 1 to 5 Mo,Mnp,Fep,pH 71/27 August 24,1971 2 Mo,Mnp,Fep,S 71/28 September 9,1971 2 Mo,S 71/31 October 13,1971 2 Mo,Mop,Mnp,Fep,S,pH 71/39 December 6,1971 1 to 6 Mo,Mop,Mnp,Fep,S 72/5 February 22,1972 1 to 5 Mo,Mop,Mnp,Fep,S 72/16 April 25,19 72 Geo-1 (shown in Figure 1) Mo 72/16 Ap r i l 25,1972 -14-Molybdenum concentrations in Saanich Inlet ranged between 7 and 10 ug/£,except for a few samples collected at the sediment-water interface where values as high as 69ug/£were observed (Appendix, pages 57-59) Figures 4, 6 and 7 show the molybdenum distribution in longitudinal section during August 1971 and February and Ap r i l 1972. In August, the surface and deep water had a molybdenum concentration of 9 - 9.25 Pg/&, whereas the concentration at depth levels approximat-ing that of the entrance s i l l was 9.5 - 10.0 ug/£. The distributions during February and Ap r i l were generally more complex but a layer with high concentrations just above or below s i l l depth was again evident. In August (Figure 4) the molybdenum isopleths were t i l t e d so that they were deeper near the s i l l (station 4) than at the head (station 1). Isopleths of suspended manganese (Figure 5) and dissolved oxygen (Figure 11) during August exhibit a similar t i l t i n g . A maximum in the vertical distribution of suspended manganese (Figure 5), which varies i n depth from approximately 175 m at station 4 to 125 m at station 1, coincides with a minimum i n the vertical molybdenum distribution at the same depths (Figure 4). Just below this , in the depth zone where suspended manganese concentrations sharply decrease, molybdenum concentrations increase and then decrease again in the layer adjacent to the bottom. In February, a layer with low molybdenum concentrations at 125-175m ( Figure 6) again coincides with the layer containing the highest -15-Stat ions 6 5 4 3 2 I J 1 I I L L t Figure 4. Distribution of dissolved molybdenum (ug/Jl) during August, 1971. Solid dots indicate sampling points. Stations Figure 5. Distribution of suspended manganese (ug/£) during August, 1971. Solid dots indicate sampling points. -16-concentrations of suspended manganese, although the manganese concentrations i n t h i s case never exceed 16 Ug/&. A maximum i n the v e r t i c a l molybdenum d i s t r i b u t i o n below t h i s l a y e r i s also s i m i l a r to that observed i n August. The most promiment feature i n the A p r i l molybdenum d i s t r i b u t i o n (Figure 7) i s the tongue of high concentrations at 140 - 150 m. A t h i n layer at £a.125 m i n which molybdenum concentrations are sharply reduced can be c o r r e l a t e d , as i n August and February, with a maximum i n the v e r t i c a l d i s t r i b u t i o n of suspended manganese (Figure 12). The data c o l l e c t e d at s t a t i o n 2 i l l u s t r a t e , how the concentrations changed with depth and time. Figure 8 i n d i c a t e s that there was an area of very low molybdenum concentration (<9.0 ug/Si) from l a t e August to December between ca. 100 - 200 m which developed at a time when both suspended manganese (Figure 9) and dis s o l v e d oxygen (Figure 10) were increasing at these depths. Except during August and September (when concentrations increased towards the bottom ) , there was a maximum i n the v e r t i c a l d i s t r i b u t i o n of molybdenum at about 200m with the concentration decreasing towards the bottom. Above t h i s maximum there was a minimum centred at about 150m. Also, there was a p e r s i s t e n t molybdenum maximum at about s i l l depth. Figure 9 ind i c a t e s that the amount of suspended manganese increased i n the bottom water from September to December, and -17-Stations 6 5 4 3 2 i Figure 6. Distribution of dissolved molybdenum (ug/£) during February, 1972. Solid dots indicate sampling points. Stat ions Figure 7. Distribution of dissolved molybdenum (yg/&) during A p r i l , 1972. Solid dots indicate sampling points. -18-Depth m 50 100 150 200 — v 9 .o—r " 9 .25 ' ' _ • \ \ fc75 >' - _ a p - - -- - - 9.0 - " ,~9.25- • ' 9 c l 9.75 • ^ « 9.25-'9.75 , 9.25., ^ ^: -9.75 _ _ • .9.25 - - ---' 9.75 9.5 9.0 i » ' \ | / ' _ . , 8 7 5 — \ x / ' „ . - 9 . 5 _ _ 9 . 2 5 _ - -9.25 9.25 .9.0 . a 7 S ' .85 July Aug Sept Oct Dec 1/7 i Feb 32/73 Apr 35/73 Figure 8. Distribution of dissolved molybdenum (yg/£) at Station 2. Values for Apr i l are interpolation from^data at Stations 1 and 3. Solid dots indicate sampling points. 100-Depth m 150-200-• • _ . , — _ " -^r~5~—----- . .^ ^ -• / • / / 1 • V . ' v s x 2° — 2 r ~ 4 o - " : \\ 40 \ 40 • \s / ^ 1 0 0 - ^ , \ \ ' x ,150, \\\\ * ; y"7l ^71 31/73 33/72 Figure 9. Station 2. Distribution of suspended manganese Cyg/&) at Solid dots indicate sampling points. -19-that the concentration increased continuously with depth during at least December. Subsequently, a layer of steadily increasing concentration developed at 140 - 150 m while values in the bottom water decreased sharply. Between August and December there was an abrupt upwards displacement of the oxygen isopleths and the development of a dissolved oxygen minimum at about 150 m (Figure 10). During the remainder of the year the oxygen concentration decreased continuously with increasing depth to values less than 20 yg-rat/2 below 150 m. The longitudinal profile shown in Figure 11 i s typical of the oxygen distribution during the three cruises when the inlet was completely surveyed. In August, concentrations greater than 20 yg - at/I are found near the bottom only at station 4; at a l l other stations, the oxygen concentration i s below 20 yg - at/£ below 150 m. The few samples collected within a few metres of the bottom a l l contained sulphide, but there are insufficient data to determine i f this situation persists throughout the year. Previous work (E.V. G r i l l , personal communication; Richards, 1965) suggests that sulphide i s normally present below ca. 150 m from at least May through July. I n i t i a l attempts to measure suspended molybdenum failed because of the low concentration levels present, but some usable results were f i n a l l y obtained during the February and April cruises. Figures 12 and 13 i l l u s t r a t e the distributions of suspended manganese -20-Figure 11. Distribution of dissolved oxygen (ug-at/£) during August, 1971. Solid dots indicate sample points. Stations 6 5 4 3 2 i J ' ' I I L Figure 12. Distribution of suspended manganese (yg/ji) during A p r i l , 1972. Solid dots indicate sample points. Stations 6 5 4 3 2 i Figure 13. Distribution of suspended molybdenum (ng/&) during A p r i l , 1972. B.D. means below detection l i m i t . Solid dots indicate sample points. -22-and molybdenum observed in A p r i l , In both cases, a tongue of decreasing concentrations extends from station 1 towards station 4 at about 140 - 150 m. The pattern observed in February was similar, although the concentrations were only about one third of those in A p r i l . The results of the sediment analyses (Appendix, page 74) indicate that there i s a decrease in the concentration of molybdenum in the surface layer of the basin sediment between the head and s i l l which parallels the longitudinal gradient of suspended molybdenum shown in Figure 13. In general, the pH of the water samples decreased from about 8.0 at the surface to about 7.5 at 125 - 150 m and then increased again slightly (ca. 0.05 pH units) in the deep basin water. The analyses for suspended iron indicated that there was generally a maximum in i t s vertical distribution between 75 -125 m. On a l l three cruises when the entire inlet was surveyed, the highest concentrations were always observed near the entrance s i l l and these then decreased at a l l depth levels towards the head. The temperature and sal i n i t y distributions at station 2 over the study period are shown in Figures 14 and 15. The distribution of temperature (Figure 14) indicates typical summer heating and winter cooling of the surface water. The temperature of the deep water f e l l from 9.1 - 9.2°C at the end of the summer to 9.0°C - i j -Depth m 50 100 150 200 - - - - - ; \ ^ C - -• — • \ ^ \ X 7.5 7.0„ ftfV v7.0. . a s ,9.0> . > x 7.5 s x a s \ \ \ *x 9.1 • \ 1 " 9.0 July Aug Sept 3 ^ 7 1 ^ 7 ! Oct Dec Feb 2 2 / 7 3 Apr 75/71 Figure 14. Distribution of temperature (°C) at Station 2, Solid dots indicate sampling points. Depth m son 100 150 200 •29-" ' 2 8 - - - -"x. * «'•"-„ . • . s' • ^-^ . ""30.5^ * — ^ „ • . /• -• 1—. 1 1 1 1 • 1—' July IJ /7I Aug Sept Oct y 7 i ij/71 Dec Feb 2 J / 7 2 Apr 35/72 Figure 15. Distribution of salinity (°/oo) at Station 2. Solid dots indicate sampling points. -24-between September and December, and f i n a l l y to 8.9°C in winter. Salinities (Figure 15) varied from 28.0°/oo near the surface to 31.2 /oo near the bottom. Between September and October there was an abrupt upwards shift of the salinity and temperature isopleths when the salinity of the water below 200 m increased to values greater than 31.25°/00 . DISCUSSION The results of molybdenum determinations on the sediments collected during this study (Appendix, page 74) are consistent with those reported by Gross (1967), supporting the idea that the anoxic basin sediments in Saanich Inlet are enriched with molybdenum. The dissolved molybdenum observations made during the present study provide further evidence of such enrichment. Figures 4, 6, 7, and 8 indicate that molybdenum concentrations normally decrease both above and below s i l l depth. Using the data collected in August, the decrease above s i l l depth can be linearly correlated with the decrease in salinity of the water, as illustrated in Figure 16. A sample of Pacific Ocean water collected at a depth of 250 m during July 1971 at a point approximately 150 km due west of Cape Scott, Vancouver Island, with a salinity of 33.771°/oo and a molybdenum content of 11.6 ug/Ji, would l i e on the same regression curve. -25-31 o o r— ZJ 30 < C O 29-200 '70 o 100 A ' » 0 150 A 2 2 0 9.5 10 M O L Y B D E N U M Figure 16. Plot of dissolved molybdenum (yg/£) against s a l i n i t y ( /oo) during August, 1971. Numbers adjacent to sample points indicate depth in meters. Similar c o r r e l a t i o n s have been observed elsewhere i n estuarine environments (Head and Burton, 1970) and can be a t t r i b u t e d to the d i l u t i o n of sea water by low molybdenum r i v e r water, Since the P a c i f i c Ocean water sample presumably t y p i f i e s the oceanic source of the waters from both above and below s i l l depth, the displacement of the points f o r samples below s i l l depth to the l e f t (low molybdenum side) of the regression curve suggests that they may have l o s t molybdenum as a r e s u l t of chemical processes which p r e c i p i t a t e i t from s o l u t i o n . Figure 17 compares the August v e r t i c a l p r o f i l e at s t a t i o n 2 with that computed from the equation of the regression curve, which has the form Mo(yg/£) =0.45 x salinity(°/oo) - 3.75 (1) M O L Y B D E N U M u g / l 9 9.5 10 0 100 D E P T H m 200 Figure 17. V e r t i c a l p r o f i l e of dissolved molybdenum (ug/£) at s t a t i o n 2 during August, 1971. S o l i d dots i n d i c a t e sample points. Dashed curve i s ca l c u l a t e d from equation (1) using the observed s a l i n i t y data. The difference between the calculated and observed distributions represents the apparent molybdenum loss from the-.twater:: arid, the amount presumably transferred to the sediments. The continued enrichment of the sediment in an isolated basin such as Saanich implies that the bottom water - where the anoxic processes which f i x molybdenum in the sediment occur -must at least occasionally be replenished with molybdenum, either by downward mixing , influxes of fresh bottom water or by chemical or biochemical precipitation from shallower depths. While the former two processes undoubtedly help in maintaining the necessary downward flux of molybdenum in Saanich, this study has been concerned with the third possibility and sought, in particuL to determine i f coprecipitation with hydrous manganese oxides transports molybdenum from oxygenated waters at shallower depths into the anoxic bottom waters, where reductive processes dissolve the manganese oxides and release any coprecipitated elements. Increases in the dissolved oxygen content and sal i n i t y of the bottom water (Figures 10 and 15) indicate that Saanich was intruded by water more dense than the resident bottom water between September and December. An apparent consequence of this intrusion was the appearance of large amounts of suspended manganese at a l l depth levels below approximately 150 m (Figure 9). Measurements made in August by E.V. G r i l l (shown in Figure 18) indicate that the deep water prior to the intrusion contained very high concentrations of dissolved manganese. -28-DEPTH m 0 DISSOLVED MANGANESE ug/l 2Q0 100 300 100 200 Figure 18. Vertical profile of dissolved manganese (yg/&) at station 2 during August, 1971. Solid dots are sample points. It is evident that mixing between the r e l i c t bottom water and the oxygenated water brought i n by the intrusion resulted in an intensive oxidative precipitation of manganese which continued through at least December. However, by February, the oxidation of sinking organic remains had reduced the concentration of dissolved oxygen in the deep water to such low levels that oxidative precipitation of manganese vi r t u a l l y ceased and, because of the settling of the oxide particles, the concentration of suspended manganese throughout the water column was sharply reduced. Any -29-oxide particles settling onto the anoxic basin sediments would be reduced by sulphide diffusing from the sediments and the manganese, as dissolved manganous ions, would diffuse back into the deep water. In A p r i l , high concentrations of suspended manganese were again observed, but confined to a layer at intermediate depth levels. This latter type of distribution i s similar to that observed in the Black Sea CSpencer and Brewer, 1971) where i t is caused by the oxidative precipitation of dissolved manganese as i t diffuses upward from the sulphide-bearing basin waters into the oxygenated surface waters. The sinking of the oxide particles back into the sulphide-bearing waters results in their reductive solution, confining suspended manganese to a thin layer at the interface between the oxygenated and anoxic zones. A similar mechanism was apparently controlling the suspended manganese distribution in Saanich in A p r i l , but, because no sulphide was observed in the deep water (except i n a thin layer adjacent to the bottom), solution of the sinking manganese oxide particles must have been caused either by trace reducing agents other than sulphides which were dispersed throughout the bottom water, or by mixing of the oxide particles towards the sides of the basin where they could be reduced by sulphides diffusing from the anoxic sediments. If manganese oxides are scavenging molybdenum from the basin waters, there should be a definite positive correlation between suspended molybdenum and suspended manganese. Such a correlation is clearly -30-evident from the longitudinal sections depicted in Figures 12 and 13, where the suspended molybdenum and manganese distributions observed in Apr i l are shown to have tongue shaped patterns that closely parallel each other. Figure 19, where the close correlation between the occurance of suspended molybdenum and manganese i s made particularly evident by comparing their vertical distributions at station 2, shows that a similar relationship also existed in February. Suspended Molybdenum ng/l Suspended Molybdenum ng/l Figure 19. Vertical profile of Ca) suspended molybdenum (nanograms/^) and Cb) suspended manganese Cyg/&) a t station 2 in February and A p r i l . 1972. Solid and dashed curves indicate suspended molybdenum and suspended manganese respectively. Marked negative correlations between the distributions of suspended manganese and dissolved molybdenum can be found in the 100 - 200 m depth interval from September through December CFigures 8 and 9). In fact, a l l three longitudinal sections for dissolved molybdenum CFigures 4, 6 and 7) exhibit a layer of low concentration -31-at mid depths coinciding with a layer of high suspended manganese. Given the information available, the most plausible explanation for these correlations i s scavenging by manganese oxides, although the large low molybdenum region observed at intermediate depths from September to December i n Figure 8 i s probably at least i n part caused by upwards displacement of low molybdenum bottom water by the intrusion. It should be emphasized that the dissolved molybdenum distribution in the basin at any given time i s the integrated result of both physical and chemical processes that have been operating in the past and, thus, the amount of molybdenum adsorbed on manganese oxides at any given instant cannot be equated with the total apparent molybdenum loss; i.e., area between dashed and solid curves below 75 m in Figure 17. During August, February and Apri l there was also a dissolved molybdenum maximum below the maximum in the suspended manganese profiles which appears to be due to scavenged molybdenum being released during the dissolution of sinking manganese oxides. The high dissolved molybdenum values observed near the bottom in October and December can be similarly explained, although the increase in this case must also be at least partly due to the influx of molybdenum with the newly intruded bottom water. Also noteworthy i s the fact that the suspended molybdenum gradient along the longitudinal axis of the inlet parallels that of molybdenum in the basin sediments, suggesting that scavenging by manganese oxides may ultimately control the pattern of molybdenum -32-enrichment in the sediments. Some of the suspended molybdenum might be derived from biogenous or mineral detritus; however, suspended iron, which probably i s a good indicator of suspended de t r i t a l minerals, has a distribution which runs counter to that of suspended molybdenum and Krauskopf (1956) found that plankton material does not strongly adsorb molybdenum. There i s , moreover, no particular reason for expecting mineral or biogenous detritus to accumulate into the peculiar tongue-like pattern observed in the case of suspended molybdenum. Krauskopf (1956) reported that molybdenum in oxygenated sea water was most effic i e n t l y adsorbed by manganese and iron oxides. Although no correlation appears to exist between the molybdenum and suspended iron distributions observed during this study, a relationship to hydrous iron oxides would be d i f f i c u l t or impossible to detect since much of the iron probably occurred in s i l i c a t e or other mineral phases. The above observations suggest that scavenging by manganese oxides tends to remove molybdenum from mid depths and transport i t downwards, concentrating i t at the depth at which the particles are dissolved. From September to December, the high downward flux of manganese oxides would release relatively large quantities of molybdenum in the thin layer of sulphide-bearing water adjacent to the bottom, whereas, during the remainder of the year, when the manganese oxide concentrations are lower, much smaller quantities of molybdenum would be released below the manganese oxide maximum. -33-Thus, i t appears that the downward flux of molybdenum necessary to support the enrichment found in the sediments occurs mainly during September to December. A Model for Molybdenum Scavenging The vertical dissolved molybdenum profile at station 2 between September and December can be divided into four sections consisting of: a surface layer CO - 75 m) where molybdenum concentrations parallel the sal i n i t y distribution; a middle layer C75 - 2 2 0 m) where molybdenum concentrations appear to be controlled by manganese oxide scavenging, diffusion and advection of water; a bottom layer where the intruding water spreads out ; and a zone near the sediment-water interface where molybdenum i s presumably lost by coprecipitation with ferrous sulphide. To describe the vertical profile of molybdenum i n the middle layer C75 - 2 2 0 m), a one dimensional mathematical model has been developed that w i l l be applied only to the period when the deep water i s oxygenated; no attempt has been made to describe the system during the remainder of the year, when i t is anoxic or undergoing transition between oxygenated and anoxic states. The only chemical process assumed to be acting on molybdenum in this middle layer i s scavenging by manganese oxides. The distribution equation for a non-conservative variable can be written as -34-= VCAVC) - VCUC) - R (2) where C i s the concentration of the variable (i.e., molybdenum), A i s the coefficient of eddy di f f u s i v i t y , U is the advective velocity of the water with components u, v, w in the x, y, z direction, t i s time, V i s the differential operator and R represents the net rate of decrease of C due to chemical changes. To f a c i l i t a t e the solution of equation 2, i t w i l l be assumed that: concentrations are at a steady state; that horizontal gradients of concentration are negligible; and that the vertical coefficient of eddy di f f u s i v i t y , A z, and the vertical advection velocity, w, are constant. Taking z, the ve r t i c a l co-ordinate, as directed positive downward, equation 2 becomes A * F ? - » f § - R - ° <3> To evaluate R, i t w i l l be assumed that the suspended manganese distribution is at a steady state and that mixing and advection do not affect i t s distribution. Thus, the rate of production of manganese oxides i s given by the term s ^ Mnp, where s i s the sinking oZ velocity of the particles and Mnp i s the suspended manganese concentra-tion. In December at station 2 the suspended manganese profile (Figure 20) closely followed an equation of the form -35-Mnp = Be .a (4) The values of B and a obtained from a non-linear least squares f i t of the data are 6.67 yg Mnp/£ and 0.0232/m respectively. D e p t h m Suspended Manganese o so too 150 200 Figure 20. Vertical profile of suspended manganese (yg/Jt) at station 2 during December, 1971. Solid dots represent sample points.Dashed line shows curve calculated from equation 4. If the rate at which molybdenum i s removed by scavenging i s directly proportional to the production rate of manganese oxides, then R - *s |jpp C5) or -36-R = dpsBae a (5a) where <J> is a dimensionless ratio giving the weight of molybdenum adsorbed per unit weight of adsorbant. The slope of the linear regression curve in Figure 21, where the simultaneously observed values of suspended molybdenum and suspended manganese are plotted -3 against each other, gives a value for dp of 1.1 x 10 c r r -=1, $ 1001 GJ C CO c n c n) X CD " D C OJ Q -10 ZJ C O 50-0 C r u i s e Symbol Dec. • Feb. * A p r . • • / / * • '• • 1 : ' ' ' " ' 0 50 100 Suspended Molybdenum ng / l 150 Figure 21. Plot of suspended molybdenum (nanograms/^) against suspended manganese (ug/&) during February and April 1972. During December 1971 a suspended molybdenum sample was collected at a depth of 200m. The corresponding suspended manganese concentration was calculated from equation 4. -37-It i s i n t e r e s t i n g to note that t h i s r a t i o c l o s e l y approximates -3 the molybdenum :manganese r a t i o of ca. 0.8 x 10 observed i n manganese nodules from l o c a l i n l e t waters ( G r i l l , et. al.,1968), suggesting that molybdenum i s incorporated into the nodules and suspended manganese oxide p a r t i c l e s by a s i m i l a r mechanism. An estimate of the sinkin g v e l o c i t y of the oxide p a r t i c l e s can be cal c u l a t e d from the f i r s t approximation of Stokes law 2 Pp ~ Pw df_ where s i s the s e t t l i n g v e l o c i t y i n cm/sec; g i s the a c c e l e r a t i o n due to gra v i t y (980 cm 2/sec); p p i s the p a r t i c l e density i n g/cm3; p w i s the density of sea water (ca. 1,03 g/cm 3); V i s the kinematic v i s c o s i t y (ca. 0.016 cm 2/sec at 5°C and 35°/oo s a l i n i t y ) ; and d i s the diameter of the p a r t i c l e s i n cm. This approximation i s v a l i d sd i f the Reynolds number, — , i s much smaller than one and can be V used here since d, as determined from photomicrographic observations, i s on the order of 4-6 ym. Assuming p p i s 5 g/cm3 (the approximate density of manganese di o x i d e ) , a value of 3.5 m/day i s obtained f o r s. Equation 3 now becomes A<B>- w f • *-sBa * a ( 6 ) whose s o l u t i o n i s -38-C = c 1 + c 2 e z - w / A ^ + - ^ _ e a z . . . . C7) A 2a - w The constants of integration c 2 and c 2 can be evaluated from the boundary condition. , C = C when z = 0 o and the additional condition that - r — = 0 when z = z m where z m i s the depth at which there i s a minimum in the vertical concentration profile of molybdenum. To simplify calculations, 75 m is taken as the zero depth of the model (I.e., 75 m must be added to a l l model depths to obtain the true depth). Substituting,the solution of equation 7 becomes c = c , 4>sB faA* e z m ( q - w/A z) > ( 1 _ ez.w/AZ) * a - w I w o Az + e a z - i | (8) A non-linear least squares f i t of equation 8 to the molybdenum data collected in December, 1971 at station 2 using UBC computer programme BMD:x85 gives -39 -w/Az = -1.34 x 10~2/m and ^ w = 6.59 x 10 ^  jig molybdenum/£ Using values given previously for the other constants, one obtains values of 1.12 cm2/sec and -13cm/day for A z and w respectively. Figure 22 shows the calculated and observed molybdenum profile for both the surface and middle layer. The relationship between molybdenum and sal i n i t y in the surface layer is dependent on the character of the diluting river water and, in December, the molybdenum distribution in the top 75 m closely f i t s the expression Mo0ig/&) = 0.405 x salinity(°/oo) - 2.49 (9) The curve calculated from the model (equation 8) shows a good f i t to the observed molybdenum distribution between 75 — 220 m. For purposes of this model, one year i s equivalent to 120 days (September to December); thus, w (average velocity) i s approximately -16 m/yr, where the negative sign indicates that the vertical advective velocity is directed upward. -40-Molybdenum jug/l 9 9.5 10 Of 50 Depth 1 Q 0 . m 150-200-Figure 22. Molybdenum profile for samples collected at Station 2 during De'cember ,1971. Solid dots indicate sampling points. Dashed line below 75 m is calculated using equation 8. Dashed line above 75 m i s calculated using equation 9. -41-The values of A z (ca. 1 cm2/sec) and w (ca. -16 m/yr) ca l -culated from the model l i e within the range found by other authors (Table I I ) . TABLE IT. Comparison of Values of Az. and w. Location w/Az (l/m) A z (cm2/sec) -w (m/yr) Reference Saanich Inlet .1.3 x 10~2 1.1 16 This study Black Sea 1.1 x 10~2 0.14 0.5 Spencer and Brewer, 1971 N.E. Pacific and Equatorial Atlantic 1.0 - 1.4 x 10~ 3 1.0 3.2 G r i l l , 1970 Open Ocean Water - 0.1 - 10 0.3 - 30 Craig, 1969 Spencer and Brewer (1971), using both the potential temperature and sa l i n i t y distribution in the halocline region of the .Black Sea, obtained _2 a value of 1.1 x 10 /m for w/Az. This corresponds closely with -2 the value of 1.3 x 10 /m , found for the deep water in Saanich. -3 Values of open ocean water for w/Az are ^ a. 1 x 10 /m which i s an order of magnitude lower than that found in either the Black Sea or Saanich Inlet. If one assumes, as in the present model, that a l l intrusions go straight to the bottom and none to intermediate -42-depths.then the residence time of the water below s i l l depth i s on the order of 9 years. This would indicate a f a i r l y rapid exchange of the deep water. F, the net flux of molybdenum across any horizontal plane in the middle layer of the water column,is given by the expression A z f f ~ w C ~ ^sBe 0 1 2 + F =0 (6a) Substituting from equation 8 and solving, F = c + 4>sB /aAz ezmCa - w/Az) _ ^ o A za - w I w / Using the values given previously for the other constants, the value of F obtained i s -1.0 x 10 g molybdenum/ m2/day. Thus, there i s a net flux directed upwards and the surface waters must act as a sink for excess dissolved molybdenum that is advected across the upper boundary of the layer. The third term i n equation 6a gives the downward flux of particulate molybdenum across any depth level of the middle layer. Evaluating this flux for a model depth of 145 m (220 m actual depth) and summing over the time period from September to December (120 days), the total amount of molybdenum sinking through the lower boundary of the middle layer at station 2 would be about 0.08 g/m2. -43-Since t h i s approximates the amount of molybdenum released at the sediment-water i n t e r f a c e upon d i s s o l u t i o n of the manganese oxide c a r r i e r , i t provides an estimate of the amount of molybdenum made a v a i l a b l e f o r enrichment of the sediment during t h i s period by scavenging processes. During the remainder of the study period, a p e r s i s t e n t d i s s o l v e d molybdenum gradient existed between the 175 m to 200 m depth l e v e l and the bottom (Figure 8). Assuming that the only p h y s i c a l transport process operating was eddy d i f f u s i o n , the f l u x of molybdenum i n t o the sediments and, consequently, the rate molybdenum was removed from s o l u t i o n at the sediment-water i n t e r f a c e i s given by the term Considering a time period of 8 months and using values of 9.7 m2/day and 15 Jig/m** f o r A z and the concentration gradient, the amount of molybdenum that would be tr a n s f e r r e d to the sediments i s about 0.04 g/m2. The dis s o l v e d molybdenum maximum at the 175 m to 200 m depth l e v e l appears to be maintained by molybdenum released from d i s s o l v i n g manganese oxides. Since t h i s maximum sustains the downward gradient and, hence, the f l u x , the rate at which molybdenum i s made a v a i l a b l e f o r enrichment of the sediments can be r e l a t e d to scavenging processes. -44-Gross et a l . (1963) estimated the rate of deposition of the basin sediment to be about 0,24 g/m /yr. 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Academic Press, N.Y. 30. R i l e y , J.P. and Taylor, D. , 1968. "The use of ch e l a t i n g i o n -exchange i n the determination of molybdenum and -vanadium i n sea water". Anal. Chim. Acta, 41, 175-178. 31. Sandell, E.B., 1965. C o l o r i m e t r i c Determination of Trace Metals. Interscience, N.Y. 32. Spencer, D.W. and Brewer, P.G., 1971. " V e r t i c a l adyection d i f f u s i o n and redox p o t e n t i a l s as controls on the d i s t r i b u t i o n of manganese and other trace metals diss o l v e d i n the waters of the Black Sea". J . Geophysical Research, 76_ (24), 5877-5892. -50-33. Spencer, D.W., Brewer, P.G. and Sachs, P.L., 1972. "Aspects of the distribution of trace element composition of suspended matter in the Black Sea". Geochim. cosmochim. Acta, 36, 71-86. 34. Strickland, J.D.H. and Parsons, T.R., 1968. "A Manual of sea water analysis". Bull. Fisheries Res. Board Can., No. 67, 311 p. 35. Sugawara, K., Okabe, S. and Tanaka, M., 1961. "Geochemistry of molybdenum i n natural waters (II ) " . J. Earth Sci., 9_, 114-128. 36. Weiss, H.V. and Lai, M.G., 1961. "The cocrystallization of u l t r a -micro quantities of molybdenum with a-benzoinoxime. Determination of molybdenum in sea water". Talanta, 8_, 72-76. -51-Appendix S U M M A R Y OF D A T A Cruise 71/22 Station 2 Date C o l l e c t e d July 13/71 Depth Mo Mo p Mn p Fe p 0 2 Sulphide pH Salinity Temp m ng/ l >ig/l ug/ l >jg-at/l jjg-ay'l In situ 04o °C 0 8.42 682 27.574 15.25 20 9.08 543 29.052 10.68 30 9.29 444 9.28 40 9.52 426 29.551 8.81 50 9.85 405 " 8.32 60 9.46 345 30.128 8.08 70 9.29 267 8.06 80 9.68 219 30.575 8.10 90 9.40 163 100 10.30 142 30.225(?) 8.34 110 9.29 126 8.39 120 9.35 119 30.909 140 9.29 60 31.023 8.65 150 9.08 38 . 160 9.03 33 31.096 8.85 180 8.58 14 31.189- 9.05 200 8.58 13 31.209 220 8.58 8 31.260 9.16 225 8.24 S U M M A R Y OF D A T A C r u i s e 71/27 S t a t i o n l D a t e C o l l e c t e d August 24/71 D e p t h M o M o p M n p * F e p * 0 2 S u l p h i d e p H S a l i n i t y T e m p m / j g / l n g / l ^ g / l UQ/I j j g - a t / l pg-at/\ In s i t u % o ° C 0 9.46 479 7.75 28.843 12.49 5 0.57 1.3 459 7.79 28.899 12.16 10 9.13 411 7.78 29.015 11.26 25 9.46 0.98 3.3 334 7.76 29.524 9.38 50 9.78 2.01 4.38 249 7.13 30.046 8.57 75 9.35 54 7.59 30.598 8.29 100 9.02 30.9 2.7 17 7.55 30.925 8.51 12.5 8.80 49.3 4.0 24 7.52 31.051 8.74 150 9.18 12.7 5.4 9 7.53 31.147 8.93 160 9.13 10 7.53 31.167 8.96 170 9.02 1.58 12 ~1 7.54 31.173 8.98 180 9.02 11 7.59 31.164(7) 9.03 186 8.63 1.86 7.07 2 ~1 8.04 31.191 * Analysis done by F.A. Whitney for Mnp and Fe p at stations 1 to 5. S U M M A R Y OF D A T A C r u i s e 71/27 S t a t i o n 2 D a t e C o l l e c t e d August 24/71 D e p t h m M o M o c j j g / l n g / , M n p 1 pg/\ F e p u g / l j j g - a t / l S u l p h i d e pQ-at/l p H in s i t u ' S a l i n i t y 7 '00 T e m p ° C 0 8.93 491 7.64 28.860 5 8.83(?) 430 7.69 28.928 10 9.35 393 7.72 29.009 20 9.63 370 7.70 29.313 25 0.51 1.2 30 9.63 346 7.71 29.471 9.50 50 9.68 299 7.70 29.989 8.95 75 9.89 5.63 6.48 131 7.63 30.590 8.36 100 9.41 81 7.61 30.848 8.35 125 9.41 45.5 7.9 50 7.58 31.028 8.65 150 9.07 58.8 6.5 22 7.53 31.137 8.88 170 8.91 13 7.60 31.171 8.94 175 20.9 7.5 180 9.29 13 7.60 31.176 8.97 190 9.41 (?) 13 7.60 31.191 8.96 200 8.97 41.6 , 7.6 11 7.56 31.195 8.97 210 9.02 10 7.56 31.191(7) 9.01 214 51.1 9.28 220 9.02 13 7.56 31.159(7) 9.00 221 9.73 0 3.5 7.56 31.157(7) S U M M A R Y OF D A T A C r u i s e 71/27 S t a t i o n 4 D a t e C o l l e c t e d August 24/71 D e p t h M o M o p M n p F e p 0 2 S u l p h i d e p H S a l i n i t y T e m p m / j g / l n g / l p g / \ u g / l > jg -a t / l pg-ax/i In s i t u % » ° C 0 9.13 5 9.29 10 9.41 20 9.63 25 0.75 3.6 30 9.57 50 9.46 75 9.83 1.42 35.8 100 10.05 5.86 22.9 125 9.83 13.8 20.1 150 9.41 52.2 10.5 160 9.07 170 9.18 175 159 6.2 180 9.18 190 9.13 196 9.41 622 8.05 28.741 14.82 428 7.90 29.078 376 7.88 29.212 11.40 341 7.83 29.370 10.38 339 7.82 29.712 10.33 338 7.81 30.118 10.12 204 7.70 30.753 8.95 148 7.65 30.961 8.61 129 7.63 31.045 8.71 69 7.59 31.145 8.80 34 31.165 8.89 27 7.57 31.192 8.92 7.56 31.1740?) 8.95 22 7.55 31.1730?) 8.96 24 7.55 31.1740?) 9 ~1 S U M M A R Y OF D A T A C r u i s e 71/27 S t a t i o n 5 D a t e C o l l e c t e d August 24/71 D e p t h m M o M o p n g / l M n p F e p y g / i >ig-at/i S u l p h i d e j j g - a t / l p H In s i t u S a l i n i t y OA 'oo T e m p ° C 0 5 10 20 25 30 50 70 75 9.24 9.63 10.17 0.52 0.93 1.18 14.6 20.3 49.7 612 491 393 366 351 368 252 250 7.63 7.61 7.57 28.735 28.911 29.259 29.483 29.670 30.039 30.790 30.830 14.97 12.24 11.46 11.06 10.73 10.34 9.34 S U M M A R Y OF D A T A C r u i s e 71/28 S t a t i o n 2 D a t e C o l l e c t e d September 9/71 D e p t h m M o M o p n g / l Mn p F e p u g / l u g - a t / l S u l p h i d e p H in s i t u S a l i n i t y 7 '00 T e m p ° C 0 5 10 30 50 75 100 125 150 170 175 180 190 200 210 220 8.92 9.18 9.29 9.41 8.57 9.24 8.53 8.53 8.47 8.57 8.68 9.07 9.46 ,,60 41 -60 21 11.0 7.25 8.0 8.0 15.0 642 441 372 312 283 41 36 26 13 14 21 67 70 78 85 28.400 28.905 29.077 29.520 29.963 30.696 30.979 31.086 31.171 31.180 31.210(?) 31.195 31.198 31.208 31.233 ** * None detected ** No temperatures measured C r u i s e 71/31 S U M M A R Y OF D A T A  S t a t i o n 2 D a t e C o l l e c t e d October 13/71 D e p t h M o M o p M n p F e p 0 2 S u l p h i d e p H S a l i n i t y T e m p m p<a/\ n g / l ^ g / l u g / l > jg -a t / | yg-a\/\ in s i t u °4o ° C 0 8.91 383 29.408 11.01 5 8.80 388 29.405 11.01 10 8.68 368 29,424 10.93 30 9.41 251 29.788 10. oi 50 9.63 272 30.105 9.79 75 9.35 190 30.620 9.28 90 9.07 16 31.025 8.73 100 9.02 24 31.076 8.82 110 9.02 20 31.117 8.88 120 8.58 19 •31.150 8.91 140 8.69 19 31.173 8.99 150 8.69 29 31.196 8.97 170 8.80 68 31.211 8.99 190 9.29 79. 31.229 8.97 200 9.24 81 31.248 8.97 210 9.41 90 31.260 8.96 215 10.17 31.258(?) 9.01 220 8.91 75 31.268 8.97 223 66 31.270 *223 42.0 -1400 * Mud-water slurry S U M M A R Y OF D A T A C r u i s e 71/39 S t a t i o n 2 D a t e C o l l e c t e d December 6/71 D e p t h m M o M o p n g / l Mrip F e p u g / l °2/ j j g - a t / l S u l p h i d e > j g - a t / l p H In s i t u S a l i n i t y 7 '0.0 T e m p ° C 0 8.68 1.4 536 7.84 27.527 6.89 5 9.13 0.45 15.1 10 9.41 0.6 8.82 494 28.688 7.93 25 9.63 1.01 6.4 7.76 *29.828 50 9.78 1.26 8.67 . 341 7.73 *30.129 9.18 75 9.83 2.48 9.76 254 7.66 30.240 8.93 90 9.68 5.12 12.44 30.507 8.94 100 9.52 7.65 19.24 67 7.51 30.902 8.87 120 9.24 28.8 11.53 34.4 7.51 31.097 8.91 130 9.07 140 9.02 31.4 4.52 150 8.85 41.2 4.18 25.2 7.51 31.202 8.94 160 9.07 180 9.13 77.7 3.05 26.0 7.50 31.210 9.02 200 9.46 130 2.63 20.5 7.49 31.231 8,98 210 8.80 (?) 151 3.88 18.6 220 7.58 31.247 223 **68.7 * Interpolated values Mud-water slurry S U M M A R Y OF D A T A Cruise 71/39 Station 2 Date C o l l e c t e d December 6/71 Depth m Mo / jg/ l Mo p ng/ l Mn p Fe c yt g/l >ig-at/i Sulphide pH Salinity Jjg-ay'I in situ 7 Temp °C 215 219 221 *222.5 *223 9.85 10.0 10.3 -12 49.3 158 160 101 -75 3.0 20 120 -680 2,420 ** 3.3 ,6,000 i VO I * Sample collected using 2 metre long ** None detected plastic corer S U M M A R Y OF D A T A C r u i s e 72/5 S t a t i o n 1 D a t e C o l l e c t e d February 22/72 D e p t h m M o M o p n g / l M n p F e P y g / i / j g - a t / l S u l p h i d e > j g - a t / l p H in s i t u S a l i n i t y 7 •0.0 T e m p ° C 0 7.98 0.35 654 20.448 6.17 10 * 440 ** 29.906 7.22 20 9.35 0.23 25 344 30.174 7.83 45 9.32 0.39 50 268 30.439 7.79 70 9.57 1.29 . 75 0 245 30.531 7.73 95 9.52 3.10 100 12 < 90.8 30.797 8.35 120 9.29 14.0 125 22 23 31.076 8.79 145 9.24 16.4 150 13 10 31.207 8,90 165 9.29 4.2 175 9.18 12 8 31.208 8.93 180 11.66 185 10.05 10 31.217 * Unknown interference encountered during analysis ** None detected S U M M A R Y OF D A T A C r u i s e 72/5 S t a t i o n 2 D a t e C o l l e c t e d February 22/72 D e p t h M o M o p M n p F e p 0 2 S u l p h i d e p H S a l i n i t y T e m p m / j g / l n g / l > i g / l u g / l u g - a t / i > i g - a t / l In s i t u % o ° C 0 7.59 2.2 113.2 640 $ 21.934 6.09 5 10.05 1.0 7.48 10 486 29.734 6.91 25 9.35 0.64 4.68 478 29.925 6.76 50 9.68 1.3 10.76 410 30.258 7.02 70 75 9.78 0 1.7 21.2 380 30.351 6.71 100 9.46 2 4.3 20.4 261 30.612 7.49 125 9.24 14 11.6 8.24 40 31.035 8.69 150 9.24 7 9.3 2.2 12 31.181 8.88 175 9.18 4 4.1 1.9 9 31.204 8.92 200 9.29 7 2.1 5.6 9 31.221 8.94 210 31.222 8.92 220 9.18 1.7 5.5 9 31.224 * No sulphide detected S U M M A R Y OF D A T A C r u i s e 72/5 S t a t i o n 3 D a t e C o l l e c t e d February 22/72 D e p t h m M o M o p n g / l M n p >V F e p >>g/i > jg -a t / l S u l p h i d e > i g - a t / l p H in s i t u S a l i n i t y 7 '00 T e m p ° C 0 9.24 654 19.619 5 9.41 10 486 29.745 6.99 25 9.78 6.8 19.4 469 29.947 6.89 50 9.57 1.7 21.2 425 30.195 7.00 75 9.52 0 1.1 24.8 408 30.365 6.82 100 9.68 10 1.1 14.9 352 30.500 7.07 120 9.78 0.4 9.1 125 13 56.2 30.980 8.56 140 - 8.80 0.4 24.0 150 15 9 31.113 8.90 *160 6.98 1.6 98.2 175 15 11 8.94 180 9.18 8.0 9.24 200 9.32 18 8.7 6.42 16 31.235 8.96 215 29 31.227 8.86 220 9.29 0.8 9.64 225 15.4 31.241 230 9.41 1.1 13.86 2.1 * Very dark f i l t e r paper observed S U M M A R Y OF D A T A  C r u i s e 72/5 S t a t i o n 4 D a t e C o l l e c t e d February 22/72 D e p t h M o M o p M n p F e p 0 2 S u l p h i d e p H S a l i n i t y T e m p m / j g / i n g / l > i g / l u g / l j j g - a t / l ^ g - a t / l in s i t u ° / 0 0 ° C 0 9.41 0.76 27.2 626 21.213 5.39 5 531 29.253 6.72 10 512 29.695 6.72 25 9.95 0.59 13.8 29.836 6.22 50 9.57 0.79 13.8 504 30.044 6.34 70 9.63 0.91 20.3 75 8.5 486 30.241 6.43 85 9.68 2.0 27.0 100 8.5 237 30.684 7.67 105 9.24 8.6 28.2 18.1 125 9.18 10 2.9 6.4 31.136 8.87 150 9.18 10 0.70 7.3 15.4 31.196 8.95 165 9.07 1.3 6.5 170 13.6 31.220 8.94 175 5 2.7 180 9.07 4.78 185 31.226 8.97 195 200 9.18 10 15.9 *21.8 *9.1 31.222 * Samples taken from separate casts S U M M A R Y OF D A T A C r u i s e 72/5 S t a t i o n s D a t e C o l l e c t e d February 22/72 D e p t h M o M o p M n p F e p 0 2 S u l p h i d e p H S a l i n i t y T e m p m pg/\ n g / l > jg / l / j g / l pg-ay\ ^g-ay'l in s i t u %o ° C 0 9.02 536 28.834 6.18 5 9.18 527 29.598 6.31 10 29.698 6.30 25 9.68 0 518 29.886 6.31 50 9.68 0 506 30.093 6.41 70 30.277 6.51 75 9.68 0 451 30.320 84 0 S U M M A R Y OF D A T A C r u i s e 72/5 S t a t i o n 6 D a t e C o l l e c t e d February 22/72 D e p t h M o M o p M n p F e p 0 2 S u l p h i d e p H S a l i n i t y T e m p m / j g / l n g / l > i g / l j j g / l j j g - a t / l j j g - a ^ / l in s i t u % o ° C 0 9.41 545 29.970 6.32 20 542 30 9.46 30,124 6.33 50 537 70 9.63 534 30i207 6.37 90 534 105 9.78 533 30.258 6.33 114 C r u i s e 72/16 S U M M A R Y OF D A T A  S t a t i o n GEO-I D a t e C o l l e c t e d April 25/72 D e p t h m * M o M o p n g / l M n p u g / l j j g - a t / l S u l p h i d e )iQ-at/\ p H in s i t u S a l i n i t y °/ '00 T e m p ° C 0 9.08 672 27.374 7.78 10 9.52 656 27.471 7.65 20 9.35 534 28.659 7.29 30 8.75 509 29.246 7.14 50 8.69 501 29.650 7.05 75 8.97 501 29.875 100 492 30.033 7.07 200 9.24 395 30.550 7.71 350 9.08 310 30.833 8.46 * Sea water not filtered S U M M A R Y OF D A T A C r u i s e 72/16 S t a t i o n 1 D a t e C o l l e c t e d A p r i l 25/72 D e p t h m Mo /jg/l Mop Mnp  n e / l ^ 9 / ' F e p u o / l > jg -a t / l S u l p h i d e p H in s i t u ' S a l i n i t y 7 '00 T e m p ° C 0 5 10 20 25 40 50 60 75 80 90 100 . 105 120 130 140 160 170 180 *190 9.57 9.35 9.41 9.52 9.02 10.01 8.91 9.02 7.98 12 18 36 44 24 ~2 -0.2 -0.3 -0.7 2.5 10.9 31.8 .60 27.2 5.4 1.0 5.9 4.8 5.2 7.5 5.9 6.1 6.8 4.5 * Sample had strong H2S smell 640 556 539 515 469 277 78 27 14 14 16 13 ** detected 8.05 28.607 ~1 7.93 7.89 7.85 7.80 7.64 7.50 7.46 7.49 7.52 7.52 7.53 29.150 29.210 29.277 29.426 30.152 30.650 30.886 31.136 31.191 31.204 31.213 8.46 7.27 6.91 6.62 7.19 7.91 8.35 8.80 8.92 8.90 i I S U M M A R Y OF D A T A C r u i s e 72/16 S t a t i o n 2 D a t e C o l l e c t e d A p r i l 25/72 D e p t h m M o M o p n g / l M n 0 F e p u g / l ^ug -a t / l S u l p h i d e j j g - a t / l p H in s i tu S a l i n i t y 0/ '00 T e m p ° C 0 608 8.01 28.811 8.23 5 9.52 -0.3 4.3 10 7.94 29.044 7.64 20 7.89 29.269 7.32 25 *9.46 -0.3 9.2 40 522 7.86 29.315 6.91 50 *9.24 -0.3 5.3 60 7.83 29.525 6.59 75 *9.52 -0.9 13.9 80 404 7.75 30.054 6.95 100 *9.74 0 3.5 13.8 160 7.54 30.605 7.73 120 27 11.1 9.2 85 7.48 30.805 8.17 130 21 19.5 8.1 140 *9.63 60 -39 5.0 19 7.46 31.089 8.75 150 *9.46 36 60.3 8.0 160 *9.08 25 28.8 7.4 15 7.48 31.187 8.93 175 *8.91 25 8.9 5.9 180 16 31.209 200 9.02 13 3.3 16 0 7.51 31.220 8.98 210 16 7.53 S U M M A R Y OF D A T A C r u i s e 72/16 S t a t i o n 2 D a t e C o l l e c t e d A p r i l 25/72 D e p t h M o M o p M n p F e p 0 2 S u l p h i d e p H S a l i n i t y T e m p m / j g / l n g / l p§/\ j i g / I ^ug-a t / l > j g - a t / l in s i t u % o ° C 215 9.02 1.7 8.3 ~1 220 8.53 10 1.2 5.5 6 7.3 7.57 31.230 225 8.58 -0.2 .6.6 **B+1 8.36 * Error in analysis - values given are interpolation between stations 1 and 3 ** 1 meter off bottom S U M M A R Y OF D A T A C r u i s e 72/16 S t a t i o n 3 D a t e C o l l e c t e d A p r i l 25/72 D e p t h m M o ^9/1 M o p n g / l Mrip F e P u g / l S u l p h i d e , u g - a t / 1 p H in s i t u ' S a l i n i t y 0/ '00 T e m p ° C 0 660 8.06 28.314 8.52 5 8.97 -0.3 5.8 10 ' 590 7.98 29.010 7.65 20 5A3 7.90 29.245 7.36 25 9.52 -0.7 AO 520 7.85 29.306 6.88 50 9.13 1.3 9.8 60 508 7.83 29.445 6.60 75 9.57 IK?) 2.3 12.3 80 AA3 30.029 6.91 100 9.90 16(?) 3.A 16.2 229 7.68 30.541 7.51 120 9.30 16 10.2 11.9 78 7.50 30.847 8.17 130 9.2A 25 11.0 9.5 1A0 9.24 12 9.1 5.3 22 7.47 31.091 8.74 150 9.A6 15.0 7.2 160 9.30 5.6 5.3 18 7.46 31.184 8.95 180 8.91 2.2 7.6 18 7.52 31.212 8.95 200 8.97 1.0 18 0 7.49 8.98 220 8.80 -0.2 6.3 13 0 7.48 31.224 225 10 2.8 7.50 31.227 228 8.36 0 7.0 S U M M A R Y OF D A T A C r u i s e 7 2 / i 6 S t a t i o n 4 D a t e C o l l e c t e d A p r i l 25/72 D e p t h m M o M o p n g / l M n p F e p 0 2 S u l p h i d e ^ g / l JJQ/I ^ g - a t / l j j g - a t / l p H S a l i n i t y In s i t u % o T e m p ° C 0 5 10 20 25 30 50 70 75 90 100 110 115 125 130 140 150 155 160 170 180 9.13 8.91 9.19 9.24 9.19 8.64 8.97 17 18 16 8.80 -0.2 -1.0 -0.9 -1.1 2.6 6.3 9.5 4.9 -0.8 -0.8 5.7 15.5 16.9 23.9 17.0 14.9 12.0 9.3 7.0 8.4 671 542 518 498 374 153 38 11 9 8 14 8.10 27.485 7.97 7.92 8.07 7.89 7.87 7.84 7.64 7.47 7.48 7.52 28.975 29.316 29.360 29.441 29.783 30.271 30.704 7.53 31.032 7.50 31.182 31.206 31.210 8.32 7.51 7.38 7.21 6.88 6.83 7.15 7.84 8.61 8.92 8.93 8.97 S U M M A R Y OF D A T A C r u i s e 72/16 S t a t i o n 4 D a t e C o l l e c t e d A p r i l 25/72 D e p t h M o M o p M n p F e p 0 2 S u l p h i d e p H S a l i n i t y T e m p m j j g / l n g / l ^ g / l u g / l j j g - a t / l j j g - a ^ / l in s i t u % » ° C 185 9.08 -0.9 9.9 190 17 7.51 31.219 198 8.80 -0.2 7.4 * None detected S U M M A R Y OF D A T A C r u i s e 72/16 S t a t i o n 5 D a t e C o l l e c t e d A p r i l 25/72 D e p t h m M o M o p n g / l M n p F e p u g / l °2 / > jg -a t / l S u l p h i d e > i g - a t / l p H S a l i n i t y in s i t u 4o T e m p ° C 0 5 10 20 30 40 50 60 70 80 85 9.41 9.41 8.80? 9.41 -0.7 -1.2 .1.2 -1.0 3.7 16.5 24.0 17.5 21.5 144 651 566 552 536 520 491 421 8.04 27.469 7.93 7.92 7.90 7.87 7,86 7.79 29.052 29.195 29.284 29.410 29.926 30.154 8.18 7.55 7.40 7.25 6.96 6.95 7.08 -74-SUMMARY OF DATA Molybdenum i n Surface Sediments Station Mo (ppm) Mo* (ppm) (data taken by author) (from Gross, 1967) 1 (head) 77 67 2 63 35 3 32 26 4 19 28 5 ( s i l l ) 4.4 none detected * Approximate location to stations taken by author (figure 2) 

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