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Biogeochemical cycling of dissolved and particulate manganese in the northeast Pacific and Canadian western… Sim, Nari 2018

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   BIOGEOCHEMICAL CYCLING OF DISSOLVED AND PARTICULATE MANGANESE IN THE NORTHEAST PACIFIC AND CANADIAN WESTERN ARCTIC by  Nari Sim  B.Sc., The University of British Columbia, 2010  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Oceanography)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  November 2018  © Nari Sim, 2018 ii  The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the dissertation entitled: Biogeochemical Cycling of Dissolved and Particulate Manganese in the Northeast Pacific and Canadian Western Arctic  submitted by Nari Sim in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Faculty of Graduate and Postdoctoral Studies (Oceanography)  Examining Committee: Kristin Orians Supervisor  Susan Allen Supervisory Committee Member   Supervisory Committee Member Leslie Lavkulich University Examiner Allan Bertram University Examiner  Additional Supervisory Committee Members: Roger Francois Supervisory Committee Member  Supervisory Committee Member iii  Abstract  The biogeochemical cycling of manganese (Mn) in the ocean is regulated by the complex interaction between external sources, removal processes and its redox sensitive chemistry. The goal of this research was to expand our knowledge about the relative importance of each process, to assess the major controls on annual variability in Mn distributions, and to explore interaction between particulate and dissolved phases of Mn. To address these questions, the distribution of suspended particulate Mn (pMn) and dissolved Mn (dMn) in the northeast Pacific Ocean across the Line-P transect and the Beaufort Sea of the Arctic Ocean was evaluated in the context of the regional physical and chemical processes. Within the Summer Mixing Layer (SML) of the Line-P transect, it was found that eolian dust input and photo-reduction elevate dMn and the annual variability in dMn at the station nearest the shore is driven by variations in the strength of Ekman transport, which brings Mn-rich coastal water to this area. Below the SML, where UV ration is no longer available for photo-reduction, rapid oxidation is identified as the main process responsible for elevated pMn. Based on a simple advection/mixing model, it was identified that the horizontal distribution of dMn at intermediate depths is influenced either by eastward advection of NPIW or by northward advection of low dMn water, depending on the position of the boundary between the Pacific subarctic and subtropical gyres. Within the Oxygen Minimum Zone (OMZ), Mn is regulated by increased reduction across the transect. The decreasing concentration of dMn from the continent to the open ocean, and the low lithogenic pMn near the continental margin in the OMZ, are the combined result of reduction of re-suspended particles and addition of dMn from the sediments. This work also evaluated the biogeochemical cycling of dMn in the Beaufort Sea. Mn in this area is controlled more by external sources rather than internal cycling. River water, sea ice melt water, and photo-reduction dominate in the surface, while advection of water mass and the mixing with remobilized dMn from the continental margin are the dominant influences at the mid-depth in this region. iv  Lay Summary  Manganese exists at very low concentrations in the oceans, yet plays an important role as a micronutrient for marine primary producers. Manganese can also be used as a tracer for ocean processes and for other important elements. The biogeochemical cycling of manganese in the sea is governed by a complex combination of sources, removal processes, and internal cycling. The goal of this research was to elucidate these mechanisms, and to constrain the relative importance of the various sources and sinks. To achieve these goals, concentrations of particulate and dissolved manganese were analyzed in samples collected from the northeast Pacific and the Canadian Arctic Oceans. This data enabled an evaluation of the biological, chemical and physical processes controlling manganese in these study areas. These results expand our knowledge of the processes and the role of particles in determining the distribution of dissolved manganese in the ocean. v  Preface  Chapter 2: Annual variability of dissolved manganese in Northeast Pacific along Line-P: 2010-2013  In 2010 and 2012, dissolved trace metal samples were collected by Amy Cain (UBC) and Jason McAlister (UBC). In 2011 and 2013, I collected dissolved trace metal and nutrient samples aboard the CCGS John P. Tully. I performed all laboratory experiments, ICP-MS measurements, and analysis of the trace metal data (dMn and dFe). Nutrient samples were analyzed by Department of Fisheries and Ocean Sciences in 2010 – 2012 and by Chris Payne (UBC) in 2013.   Chapter 3: Distribution and Composition of Suspended Particulate Iron and Manganese in Northeast Pacific In 2013, I collected particulate trace metal samples across the Line-P along with dissolved trace metal samples. I designed the sample collection method, performed laboratory analysis, carried out ICP-MS measurement, and analyzed the measured data. I participated in the GEOTRACES International Particle Inter-calibration project and submitted measured data, which were prepared and analyzed by the same analytical method of this chapter.   Chapter 4: Dissolved Manganese and Iron in the Beaufort Sea of the Arctic Ocean: 2009-IPY GEOTRACES  In 2009, dissolved trace metal samples (dFe, dMn, and dBa) were collected by Dr. Kristin Orians, Jason McAlister, and Maureen Soon (UBC). Nutrient samples were collected and measured by Dr. Maria T. (Maite) Maldonado (UBC). I performed all trace metal laboratory work, ICP-MS measurement, and the data analysis. The dissolved barium analysis in this chapter used the same analytical method as outlined in the previously published work, of which I participated as a co-author in 2013, as part of my BSc undergraduate thesis (Giesbrecht, T., Sim, N., Orians, K.J. and Cullen, J.T., 2013. The distribution of dissolved and total dissolvable aluminum in the Beaufort Sea and Canada Basin region of the Arctic Ocean. Journal of Geophysical Research: Oceans, 118(12): 6824-6837.).  vi  I generated all figures in this dissertation (unless otherwise referenced) and wrote the text in collaboration with Dr. Kristin Orians. The main chapters (2, 3, and 4) are being prepared for publication in peer-reviewed journals, which will be co-authored as ‘Sim and Orians’. For this reason, these chapters are written in the first-person plural (i.e. we). vii  Table of Contents  Abstract ......................................................................................................................................... iii Lay Summary ............................................................................................................................... iv Preface .............................................................................................................................................v Table of Contents ........................................................................................................................ vii List of Tables ..................................................................................................................................x List of Figures ............................................................................................................................... xi List of Symbols .......................................................................................................................... xvii List of Abbreviations ............................................................................................................... xviii Acknowledgements ......................................................................................................................xx Chapter 1: Introduction ................................................................................................................1 1.1  Dissolved Manganese (dMn) in Seawater ...................................................................... 2 1.2  Dissolved Iron (dFe) in Seawater ................................................................................... 4 1.3  dMn vs dFe ..................................................................................................................... 5 1.4  Particulate Trace Metals (pTM) in Seawater .................................................................. 5 1.5  Study Area ...................................................................................................................... 7 1.5.1  Northeast Pacific: Line-P transect .............................................................................. 7 1.5.2  Canadian Western Arctic: Beaufort Sea ..................................................................... 9 1.6  Research Objectives ...................................................................................................... 11 Chapter 2: Annual Variability of dissolved Manganese in Northeast Pacific along Line-P: 2010-2013 ......................................................................................................................................13 2.1  Summary ....................................................................................................................... 13 2.2  Introduction ................................................................................................................... 14 2.3  Method .......................................................................................................................... 15 2.3.1  Study Area and Sample Collection ........................................................................... 15 2.3.2  Analytical Method .................................................................................................... 17 2.3.2.1  Evaluation of analytical method ....................................................................... 18 2.4  Results and Discussion ................................................................................................. 20 2.4.1  Hydrography of Line-P during study period ............................................................. 20 2.4.2  Overview: Distribution of dissolved Mn and Fe across Line-P ................................ 24 viii  2.4.3  Dissolved Mn in the surface mixing layers .............................................................. 28 2.4.3.1  Summer Mixing Layer: Annually variable dMn at the onshore stations .......... 28 2.4.3.2  Winter Mixing Layer: Elevation of offshore dMn in high O2 conditions ........ 34 2.4.4  Significance of advected sources at the mid-depth ................................................... 36 2.4.4.1  California Undercurrent (CUC) ........................................................................ 36 2.4.4.2  North Pacific Intermediate Water (NPIW) ....................................................... 38 2.4.5  Elevated dMn in the Oxygen Minimum Zone .......................................................... 42 2.4.6  Enhancement of dTM by eddies in 2010 and 2013 .................................................. 47 2.5  Conclusion .................................................................................................................... 49 Chapter 3: Distribution and Composition of Suspended Particulate Iron and Manganese in Northeast Pacific ..........................................................................................................................51 3.1  Summary ....................................................................................................................... 51 3.2  Introduction ................................................................................................................... 52 3.3  Method .......................................................................................................................... 53 3.3.1  Sample Collection ..................................................................................................... 53 3.3.2  Analytical Method .................................................................................................... 54 3.3.3  Instrumental analysis and Assessment ...................................................................... 55 3.4  Results and discussion .................................................................................................. 57 3.4.1  Definition of the particles and depth ranges ............................................................. 57 3.4.2  Overview: Distribution of particulate elements along Line-P .................................. 57 3.4.3  Particulate versus dissolved Mn and Fe across Line-P ............................................. 60 3.4.4  Composition of pTM and its role in determining dTM distributions ....................... 62 3.4.4.1  Particulate TM in the Summer Mixing Layer (upper 35 m) ............................. 67 3.4.4.2  Particulate TM in the Winter Mixing Layer (35 – 150 m) ............................... 69 3.4.4.3  Oxygen Minimum Zone and sedimentary input ............................................... 70 3.5  Conclusion .................................................................................................................... 71 Chapter 4: Dissolved Manganese and Iron in the Beaufort Sea of the Arctic Ocean: 2009-IPY GEOTRACES ......................................................................................................................72 4.1  Summary ....................................................................................................................... 72 4.2  Introduction ................................................................................................................... 73 4.3  Method .......................................................................................................................... 74 ix  4.3.1  Study Area: Beaufort Sea of the Arctic Ocean ......................................................... 74 4.3.2  Sampling method ...................................................................................................... 75 4.3.3  Analytical method ..................................................................................................... 76 4.4  Results and discussion .................................................................................................. 78 4.4.1  Hydrography of study area ....................................................................................... 78 4.4.2  Overview: Vertical distribution of dTM ................................................................... 80 4.4.2.1  Dissolved TM at the Canada Basin (CB) Stations ............................................ 80 4.4.2.2  Dissolved TM at the shelf station (S4) ............................................................. 82 4.4.3  Upper 100 m: external sources in pSML and removal processes in PSW ............... 83 4.4.3.1  River input in pSML ......................................................................................... 87 4.4.3.2  Sea ice melt water in pSML .............................................................................. 91 4.4.3.3  Contrasting removal processes of dMn and dFe within PSW .......................... 92 4.4.4  Mid-depth enhancement of dTM: advection from the shelf ..................................... 93 4.4.5  Dissolved TM in the Atlantic sourced water – local versus intra-basin advection ... 94 4.5  Conclusion .................................................................................................................... 97 Chapter 5: Conclusion .................................................................................................................98 5.1  Biogeochemical cycling of Mn in the northeast Pacific Line-P ................................... 98 5.2  Biogeochemical cycling of Mn in the Beaufort Sea of the Arctic Ocean ................... 100 5.3  Thesis conclusion ........................................................................................................ 102 Bibliography ...............................................................................................................................103 Appendices ..................................................................................................................................118 Appendix A Supplementary material for chapter 2 ................................................................ 118 Appendix B Supplementary material for chapter 3 ................................................................ 122 Appendix C Supplementary material for chapter 4 ................................................................ 127  x  List of Tables  Table 2.1 Seawater reference material GS (GEOTRACES intercalibration samples collected from BATS at surface) and GD (BATS at 2000m). All concentrations are in nmol kg-1. .................... 18 Table 2.2 Concentration of dMn collected during Aleksandr Vinogradov Cruises, collected in 1991 (Yang, 1993). Stations are located in northwest and central north Pacific. Only the dMn values are available. Values in parentheses are samples with n=2. .............................................. 19 Table 3.1 Laboratory inter-comparison and certified reference material results obtained using the Piranha method ............................................................................................................................. 56 Table 3.2 Trace metal to P ratios in marine phytoplankton. ........................................................ 64 Table 3.3 Trace metal to Al ratios in the earth crust. Values in bold texts are used for this work. ...................................................................................................................................................... 64 Table 4.1 Values used for the end-member analysis of the Beaufort Sea .................................... 86  Table A.1 Summary of TM sampling along Line-P from 2010 to 2013.................................... 118 Table A.2 Location of stations and bottom depths along Line-P ............................................... 118 Table A.3 Concentration of dMn and dFe along Line-P: 2010-2013 ........................................ 119 Table A.4 Concentration of duplicate samples of dMn and dFe collected from Line-P ........... 121 Table B.1 Concentration of filter blanks .................................................................................... 122 Table B.2 Elemental concentrations of Small Suspended Particle (SSP) (0.45-20 µm) ........... 123 Table B.3 Elemental concentrations of Large Suspended Particle (LSP) ( >20 µm) ................ 125 Table C.1 Concentration of dMn and dFe in the Beaufort Sea in 2009. All units are in nmol kg-1. .................................................................................................................................................... 127 Table C.2 Concentration of duplicate samples of dMn and dFe collected from the Beaufort Sea .................................................................................................................................................... 128 Table C.3 Concentration of dBa in the Beaufort Sea in 2009. All units are in nmol kg-1. ........ 129  xi  List of Figures  Figure 1.1 Major currents in the northeast Pacific. This figure is generated based on Fig. 1 of Whitney et al. (2007). Bathymetry is contoured at 500 m interval. (BC: British Columbia, WA: Washington, OR: Oregon, CA: California) .................................................................................... 8 Figure 1.2 Circulation of major water masses in the Arctic Ocean (ACW: Alaska Coastal Water, sBSW: summer Bearing Sea Water, TPD: Trans Polar Drift, RW: River Water, AW: Atlantic Water). This figure is generated based on the figure 14, a) of Steel et al. (2004), figure 4, b) of Morison et al. (2012), and figure 9 of Rudels et al. (1994). Bathymetry is contoured at 500 m interval. ......................................................................................................................................... 10 Figure 2.1 The Line-P transect in northeast Pacific. Both hydrographic stations (blue) and trace metal stations (red, labeled) are shown on the upper panel. The bathymetry and trace metal sampling resolution of 2011 are plotted on the bottom panel (red dots). ..................................... 16 Figure 2.2 Duplicated Line-P samples for a) dMn and b) dFe. Every duplicate seawater sample is marked in a different symbol. ....................................................................................................... 19 Figure 2.3 Potential temperature versus salinity for the 5 major stations along Line-P from 0 to 4000 m depth in each of the 4 years. The colour bar indicates dissolved oxygen (µmol kg-1). The OMZ  (O2 < 100 µmol kg-1) is found between isopycnal of 27.0 and 27.5 kg-1 (~200 – 2000 m). Note that shallowest sampling depth for P4 and P12 are 10 m and for P16 to P26 are 3 m in 2010. ...................................................................................................................................................... 20 Figure 2.4 Spice contour plots along Line-P from 2010-2013. An expanded view of the upper   150 m is shown above each plot. Spice is calculated from temperature-salinity-pressure data in  1 m resolution at all 26 stations across the Line-P. The overlay contour lines represent sigma-t (potential density – 1000 kg m-3). The TM sampling locations are marked in different symbols (2010 in square; 2011 in circle; 2012 in triangle; 2013 in diamond). Samples between  100 – 900 m at station P20 in 2013 are not available due to difficulties in TMR operation. Note that spiciness and sigma-t contours are based on T and S measured at all 26 stations in 1 m resolution. ..................................................................................................................................... 21 Figure 2.5 Distribution of dissolved oxygen in a) 2011, b) 2012, c) 2013 against depth in log scale (left panel) and against sigma-t (right panel). ............................................................................... 23 xii  Figure 2.6 Vertical profiles of dissolved Mn along Line-P a) from 2010 to 2013 with a linear depth scale, and b) at each station for inter-annual comparison with a logarithmic depth scale. Symbols represent the years (2010 in square; 2011 in circle; 2012 in triangle; 2013 in diamond). Colors represent the stations (P4 in black; P12 in red; P16 in green; P20 in purple; P26 in blue). ......... 25 Figure 2.7 Vertical profiles of dissolved Fe along Line-P a) from 2010 to 2013 with a linear depth scale, and b) at each station for inter-annual comparison with a logarithmic depth scale. Symbols represent the years (2010 in square; 2011 in circle; 2012 in triangle; 2013 in diamond). Colors represent the stations (P4 in black; P12 in red; P16 in green; P20 in purple; P26 in blue). ......... 26 Figure 2.8 Horizontal distribution of average dMn in the Summer Mixing Layer (0-35m). ...... 29 Figure 2.9 Mean (July-August) of dust (dry + wet) deposition in GoA area from 2010 to 2013. Plots are based on the satellite data of Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2), provided by NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) (GMAO, 2015). The spatial resolution of the data set is 0.5° × 0.625°. ................................................................................................................................. 30 Figure 2.10 Mean (July-August) of UV index in GoA area from 2010 to 2013. Plots are based on the level-3 daily global gridded Aura-OMI Spectral Surface UV-B Irradiance and Erythemal Dose product (OMUVBd), provided by NASA GES DISC (Hovila et al., 2013). The spatial resolution of the data set is 1° × 1°. ................................................................................................................ 31 Figure 2.11 a) Daily river discharge rate (in m-3 s-1) from the major watersheds located on Vancouver Island, from the Fraser River in BC mainland (dark green), and Columbia River in the USA (grey) from 2010 January 1st to 2013 December 31st. The date of sample collection at station P4 is marked with dashed lines (red). b) Two-month cumulative of coastal upwelling indices at  48 °N 125 °W. Values for late summer (July-Aug) are highlighted in red. c) Average upwelling indices over 3-weeks prior to the sampling at P4 and dMn are plotted on the same grid. The y-axis represents both upwelling indices (upper part) and dMn (lower part). ........................................ 32 Figure 2.12 Distribution of dMn at each station for upper 500m. The colored symbols represent the maxima dMn found in WML (35-150 m). .............................................................................. 34 Figure 2.13 Cross section contour plot of fluorescence (upper panel) and nitrate+nitrite (lower panel) across the Line-P in 2012. Open circle indicates the depth where the highest dMn is found within the WML at the offshore stations. ..................................................................................... 35 xiii  Figure 2.14 Vertical profiles of spice, depth, dMn and dFe against the sigma-t at station P4, P12, and P16 in a) 2011, b) 2012, and c) 2013.  The CUC is expected to be found at station P4 along the core isopycnal of  26.5 kg m-3 (dotted red lines). ................................................................... 37 Figure 2.15 a) Dissolved Mn along the 26.8 kg m-3 isopycnal across Line-P, from 2010 to 2013 (open symbols). Closed symbols: calculated dMn using an advection/diffusion model. Vertical grey lines: dMn concentration ranges when there are more than 2 samples between the isopycnals of 26.75 and 26.85 kg m-3 (2010: n = 2 at P20 and P26, 2011: n = 3 at all stations, 2013: n=3 at P4 and P12, n=2 at P16 and P26). b) – e) Maps of surface circulation in the GoA from 2010 to 2013 (Fisheries and Oceans Canada, http://isdm-gdsi.gc.ca/isdm-gdsi/argo/canadian-products/Argo-circulation-eng.html). Scale (right top corner): current speeds associated with contour separation. Dashed lines: boundary between north Pacific subarctic and subtropical gyres. Note that the dashed lines cross the Line-P transect in 2010 and 2012, but not in 2011 or 2013. The boundary contour lines which influence the Line-P transect are highlighted in thick dashed lines. Black symbols: stations of previous studies (V4, V5: Landing et al., 1985; GP2, BD15, BD16: Mawji et al., 2015; 14: Brown et al., 2012). The blue line: the Line-P transect. ......................................................... 40 Figure 2.16 Concentration dMn, dFe, and dissolved oxygen below sigma-t of 26.3 kg m-3 in a) 2011, b) 2012, and c) 2013. The vertical and horizontal lines indicate the boundary for the Oxygen Minimum Zone (100 µmol kg-1) and North Pacific Intermediate water (26.8 kg m-3) respectively. Filled symbols indicate the maximum concentration found in the OMZ. .................................... 43 Figure 2.17 Concentration of dMn in intermediate waters. Panel a) shows all values within the Oxygen Minimum Zone (grey) where the oxygen concentration is lower than 100 µmol kg-1, at the core isopycnal of 26.5 kg m-3 (cyan) representing California Under Current at the onshore stations, and at 26.8 kg-3 (green) representing North Pacific Intermediate Water. The approximate depth range of OMZ is 250 – 2000 m (sigma-t > ~27.0 kg m-1). The mean concentration of measured dMn within the OMZ (black, closed) is also shown. The mean value of P20 in 2013 is based on the sample data collected below 1000 m only (purple). Panels b) and c) show dissolved Mn against N* and dFe, respectively, from 2011 – 2013 in the OMZ. ........................................ 45 Figure 2.18 Vertical profiles of dMn and dFe a) at P12 and b) at P16 for upper 300m. The years influenced by mesoscale eddies are highlighted in color (2010 in red, 2013 in green). ............... 48 Figure 3.1 Cross section contour plots of a) SSP and b) LSP for pCd, pP, pAl, pFe, and pMn across the Line-P transect. Units are in nmol kg-1 for all. Note that the depth scale is non-linear to xiv  better view the surface distribution of each element. Note the samples between 15 and 1200 m are absent at P20 due to difficulties in TMR operation. Black dots indicate the sample location. .... 58 Figure 3.2 The cross section contour plot of a) nitrate + nitrite, b) Fluorescence, and c) pCd/pP of the TSP. The vertical profiles of pCd:pP are also shown on d). Note the different depth scales for a) and b) versus c) and d). ............................................................................................................. 60 Figure 3.3 Vertical distribution of dissolved and total suspended particulate a) Fe and b) Mn. Dotted lines at 35 m and 150 m indicate the boundaries between SML and WML and between WML and OMZ, respectively. The CUC is found at ~175 m at P4. The NPIW is found at ~200 m from P26 to P12. Maxima of dMn and pMn within the WML are marked in red (b). Note the different concentration scale for pMn compared to dMn. The data from P20 are not reported due to the sample loss during the TMR operation. .............................................................................. 61 Figure 3.4 a) Vertical profiles of total suspended pMn across the Line-P. Colored area represents the contribution of each component. b) Vertical profiles of pMn to pAl ratio for total suspended particles (TSP), small suspended particles (SSP), and large suspended particles (LSP). Vertical dashed lines are crustal abundance of Mn to Al (0.0033:1) (Shaw et al., 1967). c) The vertical profiles of pMn to pP ratio for TSP, SSP, and LSP. Vertical dashed lines denote the extended Refield ratio between Mn and P (0.0004:1) (Martin et al., 1976; Martin and Knauer, 1973). ..... 63 Figure 3.5 a) Vertical profiles of total suspended pFe across the Line-P. Colored area represents the contribution of each component. Dotted area indicates the overestimated lithogenic pFe (see text). b) Vertical profiles of pFe to pAl ratio for total suspended particles (TSP), small suspended particles (SSP), and large suspended particles (LSP). Vertical dashed lines are crustal abundance of Fe to Al (0.19:1) (Shaw et al., 1967). c) The vertical profiles of pFe to pP ratio for TSP, SSP, and LSP. Vertical dashed lines denote the plankton organic tissue composition ratio between Fe and P (0.005:1) (Martin et al., 1976; Martin and Knauer, 1973). ................................................. 65 Figure 3.6 a) The relationship between pFe and pAl. b) Particulate Fe is plotted against their non-lithogenic components across the Line-P, where non-lithogenic pFe = pFe – pAl × (Fe:Al)crustal ratio. Lithogenic component is significant when the data points are more deviated from y=x line. ..... 66 Figure 3.7 a) Vertical profiles of Mn (II) oxidation rates at 4 major stations. b) Percentage of total Mn which is dissolved across Line-P. Each station is marked with a different color. ................. 68 xv  Figure 4.1 Map of Canadian western Arctic showing 7 sampling stations of this study. Stations L1 – L3 and S2 – S4 are referred to as Canada Basin (CB) stations and shelf stations, respectively. ...................................................................................................................................................... 75 Figure 4.2 Duplicate Arctic samples plotted against each other for a) dMn and b) dFe. ............ 77 Figure 4.3 a) T-S plot of all stations. b) Vertical profile of temperature and salinity at station L2. Note that the y-axis is in log scale. ............................................................................................... 78 Figure 4.4 Vertical distribution of a) dMn and b) dFe at the Canada Basin stations (L1 – L3) a) from surface to 3500 m. The area between 70 – 3500 m (below the dashed line of a) and c)) is expanded for b) dMn and  d) dFe. Note that the depth is in a log scale to show upper layer distributions clearly. The temperature profile of station L2 is overlaid on each plot to identify water masses. .......................................................................................................................................... 81 Figure 4.5 Vertical distribution of a) dMn and b) dFe at L1 and S4 in the Beaufort Sea. Grey symbols denote the data points of CB stations (L1.1 to L3). ........................................................ 82 Figure 4.6 Cross section contour plots of a) salinity, b) temperature (ºC), c) O2 (µmol kg-1), d) sigma-t (kg m-3), e) spiciness (kg m-3), f) AOU (µmol kg-1), g) dFe (nmol kg-1), h) dMn   (nmol kg-1), i) dBa (nmol kg-1), j) transmissivity (%), k) N* (µmol kg-1), l) Fluorescence (µg L-1), and  m) NO32- (µmol kg-1) from off the coast of the North America continent (red star on the map (n)) towards the interior of the Canada Basin. .............................................................................. 84 Figure 4.7 a) Percentage composition of sea ice melt (SIM) water, river water (RW), and seawater (SW) in the Beaufort Sea. b) Horizontal distribution of transmissivity, dMn, and dFe within the pSML(upper 15m). Note that the transmissivity scale is reversed. Individual transmissivity values between 5 to 15 m are plotted in grey square (1m resolution). .................................................... 87 Figure 4.8 a) Dissolved Mn plotted against salinity. Open squares indicate all measured dMn of this study. The best-fit line (dashed) is based on the values with salinity lower than 32.5. Likewise, closed squares (red) denote dMn at S4 with salinity lower than 32.5. The solid line is the best-fit line based on the red symbols.  b) Dissolved Mn in the lowest salinity surface waters at each station, plotted against the distance to the river mouth. Solid black line is the (exponential)  best-fit line extrapolated to the zero distance (i.e. Mackenzie River mouth). Red triangle indicates the estimated dMnRiver (12.2 ± 4.1 nmol kg-1). The measured Mackenzie River concentrations have a range of 16.1 – 43.9 nmol kg-1. .................................................................................................. 90 xvi  Figure 4.9 Area-averaged chlorophyll a concentration (141°W, 68°N, 128°W, 80°N) observed at the surface of the Beaufort Sea. The plot is generated based on the NASA satellite data (SeaWiFs Global Monthly Mapped – 9 km Chlorophyll a) with 8-day temporal resolution (SeaWiFS Project, 2003). ............................................................................................................................................ 92 Figure 4.10 Horizontal distribution of a) dMn and b) dFe in the AW. Dashed red and black lines indicate the mean concentration of previously reported values of Eurasian Basin and all measured values of this study in Canada Basin, respectively. The x-axis (Distance from L1) is determined based on the cross section map (Figure 4.6, n))............................................................................ 95 Figure 5.1 Schematic diagram of Mn biogeochemical cycling across Line-P .......................... 100 Figure 5.2 Schematic diagram of Mn biogeochemical cycling in the Beaufort Sea .................. 101   xvii  List of Symbols  Al   Aluminum Ba   Barium CaCO3   Calcium carbonate Cd   Cadmium  Fe   Iron H2O2    Hydrogen peroxide H2SO4    Sulfuric acid HCl    Hydrochloric acid HNO3    Nitric Acid M   Molarity (1 M = 1 mole ∙ litre-1)  µmol    micromole (1 mole = 1000 µmol) µL   microliter (1 mL = 1000 µL) Mn   Manganese  NO2-   Nitrite NO32-    Nitrate O2    Oxygen OH-   Hydroxide P   Phosphorous pH   Measure of acidity (pH = -log[H+]) pOH   Measure of basicity (pOH = -log[OH-], pOH = 14 – pH) PO4   Phosphate Si(OH)4  Silicic acid  xviii  List of Abbreviations  AC    Alaska Current ACW    Alaska Coastal Water AO   Arctic Oscillation AW   Atlantic Water BG   Beaufort Gyre CB   Canada Basin CC    California Current CTD    Conductivity, Temperature, Depth instrument CUC    California Under Current dTM    dissolved Trace Metal EB   Eurasian Basin GoA    Gulf of Alaska HEPA filter   High Efficiency Particulate Air filter HNLC    High Nutrient Low Chlorophyl HR - ICPMS   High Resolution - Inductively Coupled Plasma Mass Spectrometer HTV    Hydrothermal Vents LDPE    Low Density Polyethylene LSP   Large Suspended Particle ( > 20µm in this study) MERRA  Modern Era Retrospective-analysis for Research and Applications NASA   National Aeronautics and Space Administration NPC    North Pacific Current NPIW    North Pacific Intermediate Water OMZ    Oxygen Minimum Zone OSP    Ocean Station Papa (50 ºN 145 ºW) POC    Particulate Organic Carbon POM    Particulate Organic Matter pSML   polar Surface Mixing Layer PSW   Pacific Summer Water pTM    particulate Trace Metal xix  pTMauthi  Authigenic particulate Trace Metal pTMbio   Biogenic particulate Trace Metal pTMlitho  Lithogenic particulate Trace Metal PWW   Pacific Winter Water RR   Regular Rosette RW   River Water S    Salinity (g kg-1) SAFe   Sampling and Analysis of Fe (iron) reference material SeaWiFS  Sea viewing Wide Field of view Sensor SIM   Sea Ice Melt water SML   Summer Mixing Layer SOD    Superoxide Dismutase SSH   Sea Surface Height SSP    Small Suspended Particle (0.45 – 20 µm in this study) T    Temperature (°C) TM   Trace Metal TMR   Trace Metal Rosette TPD    Trans Polar Drift  TSP    Total Suspended Particle (TSP = SSP + LSP) USGS   United States Geological Survey UV   Ultraviolet WML   Winter Mixing Layer  xx  Acknowledgements  First and foremost, I would like to express my gratitude to my supervisor, Dr. Kristin Orians. Thank you for always being available for discussion and being patient with me. I cannot thank enough for your mentorship, guidance, and especially the extensive editorial support.   I also would like to thank my supervisory committee, Dr. Susan Allen and Dr. Roger Francois for their support and guidance in my research. I appreciate for your thoughtful comments and insights. I also would like to thank Dr. Maite (Maria) Maldonado for providing me insights on developing the sampling method for the particulate trace metals. Thank you, Dr. Maldonado, especially for giving me an opportunity to participate the GEOTRACES particle inter-calibration project and for always being open for discussion about the particles.   I also thank to Maureen Soon for her expertise and wisdom in laboratory work. Maureen, I was lucky to have you during my long journey of PhD degree. Thank you for always being supportive whenever I ask for your help at the lab. Special thanks to Vivian Lai, as well, for training me for the ICMP-MS use and for always being available for discussion about the instrument and analytical procedure.   I also thank my labmates, Ania Posacka, Amy Cain, Manuel Colombo, and Jason McAlister for sharing ideas and for being always available for discussion. Special thanks to Jingxuan Li for going through the long particle digestion process together. I also appreciate Cindy Yu, for sparing time to discuss about the mathematical stuff.    I am also grateful to captains and crews of CCGS J. P. Tully, and scientists at the Institute of Ocean Sciences for making this work possible at the sea. Special thanks to Lisa Miller, for providing the pH data of Line-P and detailed follow up about the updated values.   I also appreciate the University of British Columbia, Department of Earth Ocean and Atmospheric Sciences, and NSERC for financial support.    Finally, I would like to extend my appreciation to my family and friends for their love and support. There is no word that can fully express my gratitude for the selfless love and support of my Mom. I would have not been able to go through this long journey without her encouragement.   1 Chapter 1: Introduction  The distribution of trace metals is shaped by complex interactions between their own biogeochemical characteristics and physical processes in the oceans. Hence, it requires inter-disciplinary knowledge from a molecular scale (e.g. transfer of oxygen or electron) to the planetary scale (e.g. global ocean circulation pattern) to assess the mechanisms controlling trace metal distributions. In seawater, trace metal concentrations can be as low as femto- (10-15) or even atto- (10-18) molar (e.g., iridium: 680 amol kg-1 (Anbar et al., 1996)), which is extremely low level in comparison to major elements, such as sodium (468 mmol kg-1) or magnesium (53 mmol kg-1) (Bruland and Lohan, 1983). Indeed, their low concentrations and the complex seawater matrix created a challenge for early trace metal research, and reliable trace metal data was first available in the mid-1970’s (Boyle and Edmond, 1975; Schaule and Patterson, 1981). These studies reported consistent and smooth vertical profiles for trace metals, emphasizing the importance of clean sampling and careful sample handling to acquire accurate results. Since then, our understanding of trace metal cycles has rapidly increased with advances in clean sampling and laboratory techniques, as well the development of highly sensitive instruments. Manganese (Mn) is an element which has been analyzed since the early stages of trace metal research (Campbell and Yeats, 1982; Klinkhammer and Bender, 1980; Landing and Bruland, 1980). To date, it has been revealed that Mn not only has a variety of sources and sinks at different depths in the water column, but is also controlled by its redox sensitive chemistry. However, we still lack knowledge about which processes are the most significant in controlling Mn distributions in the water column, what causes annual variability in Mn distributions, and how particulate and dissolved phases of Mn interplay within the water column. To address these questions and to better constrain the interactions between sources, sinks, and the biogeochemical cycling of Mn in the oceans, this thesis presents Mn data from the northeast Pacific and the Canadian western Arctic Ocean. In many sections of this dissertation, iron (Fe) is also discussed to aid in the interpretation of Mn biogeochemical cycles.   2 1.1 Dissolved Manganese (dMn) in Seawater  Manganese (Mn) is a trace metal in the ocean, existing at nanomolar levels. It is the twelfth most abundant element in earth’s crust with 0.1% of total abundance (Wedepohl, 1995), yet its average dissolved concentration in the ocean is only about 0.06 – 10.0 nmol kg-1 (Landing and Bruland, 1980; Landing and Bruland, 1987; Sohrin and Bruland, 2011). Within the water column, dMn shows modified scavenged profiles, controlled by a complex combination of oceanic processes and its redox sensitive chemistry. It has elevated concentrations near external sources, typically at the surface and/or at mid-depth, and decreasing concentrations away from these sources.   The surface maxima of dMn is due to aeolian input (Landing and Bruland, 1980) and fluvial input (Elderfield, 1976), combined with photo-reduction of manganese oxides (Klinkhammer and Bender, 1980). Aeolian input is a key external source, as greater than 30% of atmospheric Mn can be dissolved into the ocean (pH 8) within 5 – 10 minutes regardless of aerosol type (i.e. polluted, mineral or clean marine air aerosols) (Guieu et al., 1994). This dissolution can be further enhanced by photo-reduction since UV light speeds up the dissolution of manganese oxides 7 – 60 times (Sunda and Huntsman, 1994; Sunda et al., 1983). This process however is restricted to the surface layer where UV light is available. River water also provides a source of dissolved Mn. The concentration of Mn in river water is 10 – 25 times higher than in open ocean surface waters (Aguilar-Islas and Bruland, 2006; Bender et al., 1977). Below the surface mixing layer, dissolved Mn decreases rapidly with depth due oxidation and scavenging onto particle surfaces (Martin and Knauer, 1980).   A secondary maxima of dMn is often found at mid-depth due to the presence of hydrothermal vents (HTV) (Klinkhammer et al., 1977) or due to remobilized dMn from the adjacent continental margin (Heggie et al., 1987). A high dMn is also observed when oxygen concentration decreases below 100µmol kg-1 (Martin and Knauer, 1985), which is caused by the internal cycling of Mn due to its redox sensitive chemistry in the ocean. Mn exists as two dominant states in seawater, insoluble Mn(IV) (MnO2 (s)) and soluble Mn(II) (Mn2+ or MnCl+) (Sunda and Huntsman, 1994). The redox equilibrium reaction shows that a higher oxidation rate results in more oxidative scavenging and higher reduction rate leads to increase of dMn in the water column.  3  ܯܱ݊ଶሺSሻ    ൅   2ܪା    .ೝ೐೏ೠ೎೟೔೚೙ሱۛ ۛۛ ۛۛ ۛۛ ሮۛ೚ೣ೔೏ೌ೟೔೚೙ርۛۛ ۛۛ ۛۛ ሲۛ       ܯ݊ଶା    ൅    ଵଶ ܱଶ   ൅     ܪଶܱ            Since Mn(II) is thermodynamically unstable in the oxygenated seawater, it tends to be oxidized to Mn-oxides (MnOx) in oxygen replete zone (Roitz and Bruland, 1997). Conversely, a faster reduction rate and/or a slower oxidation rate under low oxygen conditions leads to the dissolution of Mn-oxides and an increase in dissolved Mn. Indeed, a secondary maxima of dMn is often found at mid-depth, coinciding with the Oxygen Minimum Zone (OMZ: O2 < 100µmol kg-1).  Two hypotheses have been proposed to explain the mechanisms behind the mid-depth enhancement of dMn. Early studies suggests that the secondary maximum of dMn in the open ocean could be the result of combined effect of fast in-situ reduction and remineralization of Mn in low oxygen conditions, as well as laterally transported Mn rich water from the continental margin (Landing and Bruland, 1980; Martin and Knauer, 1984). Alternatively, a study using a kinetic model suggests that this mid-depth enhancement is driven by a slower oxidation rate of Mn(II) rather than a faster reduction rate under these conditions (Johnson et al., 1996). In the OMZ, which usually coincides with a high carbon flux, there is more remineralization of Mn(II) than under oxygen rich conditions. Their model result suggested that dMn is enriched in the OMZ since remineralization is increased and removal by in-situ oxidation is minimized.   Near the bottom of the ocean, dMn can also be supplied from the sediments. Particulate Mn buried in the sediments undergoes a series of chemical reactions (i.e. sedimentary diagenesis). Within the anoxic or suboxic sediments Mn is reduced from its oxides and oxyhydroxides to dissolved Mn. If the redox boundary is close to the sediment surface, this results in diffusion of reduced Mn into the water column above the sediments, otherwise a Mn oxide crust is often formed at the surface of the sediment (José et al., 2016).     4  1.2 Dissolved Iron (dFe) in Seawater Iron is one of the most well studied trace elements, since iron fertilization experiments demonstrated that primary production is directly related to the iron availability in many parts of the ocean (Coale et al., 1996; Martin et al., 1990; Martin et al., 1989). Iron is an essential micronutrient for phytoplankton growth, utilized in electron transfer reactions for photosynthesis and nitrogen fixation (Bruland et al., 1991; Johnson et al., 1997; Kustka et al., 2003). Iron is the main factor that inhibits phytoplankton growth in High Nutrient and Low Chlorophyll (HNLC) regions, such as Southern Ocean, equatorial Pacific Ocean, and North Pacific Ocean (Martin et al., 1994; Martin et al., 1989). Despite its importance for primary production, iron is scarce in the ocean environment. Fe is fourth most abundant element in earth’s crust, yet the concentration of dissolved iron (Fe) does not exceed 2 nmol kg-1 in world oceans and can be as low as  0.01 nmol kg-1 (Turner and Hunter, 2001). There are number of reasons for such low concentrations for Fe. First, although atmospheric dust deposition is a significant source of Fe, the low solubility of Fe(III) in seawater (due to high pH and oxidation potential) makes Fe scarce in the ocean. Additionally, Fe is scavenged from the water column by adsorption onto particle surfaces and uptake by biological processes. Due to its low availability and importance in biochemical metabolism, phytoplankton readily consume Fe when dFe becomes available (Turner and Hunter, 2001). Indeed, dFe at the surface tends to be depleted in world oceans. Below the photic zone, some portion of dFe is returned to the water column by remineralization of sinking particles. Near the continents, sedimentary pore water fluxes can also be significant, especially under low oxygen conditions. Lastly, dFe can also be enhanced at mid-depth near mid ocean ridges, as hydrothermal vents introduce high dFe into the water column. These hydrothermal plumes can be laterally transported ~ 4300 km in the ocean (Resing et al., 2015).   5 1.3 dMn vs dFe Similar to Fe, Mn is also a bioactive element. It is used in the water splitting catalytic enzyme (i.e. oxygen evolving complex) of photosystem II (PS II) during photosynthesis (Pospíšil, 2009). Additionally, Mn replaces Fe in the antioxidant enzyme, superoxide dismutase (SOD), in  Fe-limited environment and maintains the efficiency of PSII (Peers and Price, 2004) by converting  reactive oxygen to stable molecular oxygen. Co-limitation of Fe and Mn in the oceans has been observed in areas with low dFe and low dMn, such as in the Southern Ocean (Middag et al., 2012).  Similar to Mn, iron is also controlled by redox chemistry. It has a faster oxidation rate than Mn (Balzer, 1982) and forms insoluble oxides in oxic seawater (Hudson and Morel, 1990). Hence, it tends to be readily oxidized and precipitated in oxic environment, mainly to ferric oxides  (i.e. Fe2O3).  Both dFe (Cullen et al., 2009) and dMn (Johnson et al., 1992) are enhanced in low oxygen conditions. For example, dFe and dMn are found to be elevated in the water column near the continental margin off the coast of BC (Cullen et al., 2009) and southern California (Johnson et al., 1992), when the oxygen is low. Dissolved Fe, in particular, decreases with distance from the continental margin, where oxygen levels increase towards the open ocean (Cullen et al., 2009).   1.4 Particulate Trace Metals (pTM) in Seawater Oceanic trace metals can be differentiated into dissolved and particulate phases. The dissolved fraction has been operationally defined as that which passes through a 0.2 µm (or 0.45 µm) pore size membrane filter. Particulate phases are those that are captured on a 0.2 µm (or 0.45 µm) membrane filter (Bruland and Lohan, 1983). Particulate trace metals (pTM) are a key part of trace metal cycling in the ocean, as they play an important role as sources and sinks for dTM. Depending on their origins and chemical characteristics, the pool of oceanic particles can be characterized as lithogenic, biogenic, or authigenic (Ohnemus and Lam, 2015). Lithogenic particles are delivered from terrestrial sources, such as windblown dust, resuspended particles from benthic sediments and continental margins (Lam and Bishop, 2008), as well as weathered minerals delivered by rivers (Poulton and Canfield, 2005). Dust particles delivered to the photic zone from the atmosphere are 6 a potential source for dTM, as UV light promotes photo-reduction and dissolution in the surface water (Sunda and Huntsman, 1994). Particles can also remove dTM from the water column via adsorption and aggregation. Biogenic particles are those formed by biological processes, including both dead and living organisms, particulate organic matter (POM), and the skeletal structures of plankton, such as calcium carbonate (CaCO3) and biogenic silica (Opal) (Bishop et al., 1980). There are also metal-specific particles generated by marine organisms such as barite (BaSO4) (Ganeshram et al., 2003). Active uptake by phytoplankton and adsorption of metals onto biogenic particles remove dTM in the upper ocean, while remineralization regenerates dTM deeper in the water column. Authigenic particles are generated via abiotic internal cycling of trace metals in seawater. Depending on the environmental conditions (pH, oxygen level, UV radiation, availability of bacteria) and the elements’ chemical characteristics (redox chemistry or chemical affinity to certain ligands), exchange between dissolved and particulate phases can occur within the water column. For instance, the precipitation of dFe and dMn into their hydroxide and/or oxide forms under oxic conditions can lower dTM concentration in the water column (Field and Sherrell, 2000a; Johnson et al., 1992). The analysis of suspended particles, collected with discreet Go-Flo bottles or in-situ pumps (Cullen and Sherrell, 1999; Planquette and Sherrell, 2012), can trace external sources of trace metals, such as particulate Fe transport from the continental shelf (Shigemitsu et al., 2013), or identify the origin of particles in the water column or in the phytoplankton biomass (Ho et al., 2007).          7 1.5 Study Area 1.5.1 Northeast Pacific: Line-P transect The Line-P transect is one of the oldest and longest oceanic time series, which includes 26 stations from off the coast of Vancouver Island to Ocean Station Papa (OSP, P26). The OSP is located at 50.00º N and 145.00º W in the Gulf of Alaska (GoA) about 1600km west of North America. It was a permanent weather station from 1949 to 1981 which provided weather observations and navigational assistance. In 1981, continual observations were discontinued, and the stations were sampled by ship 2-5 times a year. Since then, various oceanographic data (i.e. salinity, temperature, oxygen, nutrient concentration, phytoplankton and zooplankton) have been sampled by ship across the Line-P.   The surface and intermediate layers of the Line-P transect are affected by the cyclonic Alaska gyre (Figure 1.1). At the surface, the easterly North Pacific Current (NPC), which separates warm and salty subtropical water from cool and fresh subarctic water, flows towards north America and bifurcates into a northward Alaska Current (AC) and a southward California Current (CC) (Kawabe and Fujio, 2010). In general, the bifurcation of AC and CC happens between station P12 and P16, depending on the position of NPC (Freeland, 2006). The near-shore stations (P1 – P12) are known as nitrate limited region (Whitney et al., 2007) and open ocean area (P20 – P26) is known as a High Nutrient and Low Chlorophyll (HNLC) region, where Fe is the major limiting factor which inhibits phytoplankton growth (Boyd and Harrison, 1999; Martin et al., 1994). At the intermediate depth (~200 m), the western side of the Line-P transect is influenced by the North Pacific Intermediate water (NPIW) (You, 2005). In winter, cold water sinks in the Sea of Ohotsk and travels south and eastward (Ueno and Yasuda, 2003). This water mass is transported to the Line-P area along the core isopycnal of σθ =26.8 kg m-3. The eastern side of the transect is affected by the California Under Current (CUC: a core isopycnal of σθ=26.5 kg m-3), which carries warm, salty, and low oxygen Pacific equatorial water from the south (Meinvielle and Johnson, 2013b).  8  Figure 1.1 Major currents in the northeast Pacific. This figure is generated based on Fig. 1 of Whitney et al. (2007). Bathymetry is contoured at 500 m interval. (BC: British Columbia, WA: Washington, OR: Oregon, CA: California)  (Whitney et al., 2007) Many studies along Line-P have been conducted over the past several decades. Changes in temperature, salinity, (Crawford et al., 2007), and a decline in oxygen (Whitney et al., 2007) are well documented over past 50 years. Although studies on dissolved trace metals (e.g. Al (Cain, 2014), Pb (Charters, 2012), Cu (Posacka et al., 2017; Semeniuk et al., 2009), Fe(II) (Schallenberg et al., 2015), Zn (Janssen and Cullen, 2015), and Ga (McAlister, 2015)) have been recently reported and particulate organic carbon (POC) (Bishop et al., 1999) data are also available, neither dMn nor pTM have been well studied within this area.   9 1.5.2 Canadian Western Arctic: Beaufort Sea The study area is located in the southern part of the Canadian Basin of the Arctic Ocean, in the Beaufort Sea off the coast of the Mackenzie River estuary (Figure 1.2). The Beaufort sea is composed of multiple layers of water from different origins (McLaughlin et al., 2004).  The surface water (i.e. Polar Surface Mixed Layer) is fresher (S < 29) than any other ocean due to the high contribution of riverine water, as well as sea ice melt (Guay and Falkner, 1997; Guay and Falkner, 1998; Macdonald et al., 1995). The freshwater accumulation is intensified within the Beaufort Gyre when high Arctic Oscillation (AO) anomalies are observed. During the sampling period (2009, late summer), the study area was in a high AO cyclonic mode, which intensified the convergence of Ekman transport within the Beaufort Gyre, increasing freshwater storage and elevating Eurasian River inputs from the Lena, Yenisey, and Ob Rivers (Morison et al., 2012).  The intermediate layer is composed of Pacific waters, which are fresher and high in nutrients (Taylor et al., 2003). Water from the Pacific trifurcates as it enters the Arctic Ocean through the narrow Bering Strait when the AO is high (Steele et al., 2004). One branch directly flows eastwards along the Alaska coast (Alaska Coast Water, ACW) which carries the chemical signature of the continental shelf to the study area. The second branch travels along the Chukchi Sea and eventually joins to the Beaufort Gyre with a high nutrient signature (summer Bering Sea Water, sBSW) (Jones et al., 1998; Shimada et al., 2001). The last branch, which does not directly affect the study area, travels northward, joins the Trans Polar Drift (TDP), and exits towards the Atlantic Ocean. Below the Pacific layer, denser Atlantic water is found. This warmer and saltier Atlantic water enters through Fram Strait and the Barents Sea (Taylor et al., 2003), and circulates cyclonically within the Beaufort Gyre (Karcher et al., 2012). At the bottom of the Beaufort Sea, cold and salty Arctic Deep Water (ADW) is found, which is formed by deep shelf convection (Jones et al., 1995). Due to the geographical isolation of the Canada Basin by the Lomonosov and Mendeleev Ridges, the age of Arctic deep layer is suspected to be about 500 years (Macdonald and Carmack, 1991).      10     Figure 1.2 Circulation of major water masses in the Arctic Ocean (ACW: Alaska Coastal Water, sBSW: summer Bearing Sea Water, TPD: Trans Polar Drift, RW: River Water, AW: Atlantic Water). This figure is generated based on the figure 14, a) of Steel et al. (2004), figure 4, b) of Morison et al. (2012), and figure 9 of Rudels et al. (1994). Bathymetry is contoured at 500 m interval. (Rudels et al., 1994)     (Morison et al., 2012)   11 1.6 Research Objectives The goal of this work is to evaluate the sources, sinks, and internal cycling of dissolved Mn in the northeast Pacific and western Arctic Oceans, and to explore the roles of suspended particles in Mn cycling. During past few decades, our knowledge of dissolved Mn in seawater has increased considerably. More than most elements, Mn is affected by a large number of sources and sinks, as well as its unique chemistry in seawater. Eolian dust, river input, photo-reduction, remobilization and mixing from the continental margin, sedimentary inputs, hydrothermal input, in-situ oxidation and reduction in oxygen deficient and replete areas, removal by aggregation and scavenging process all contribute to Mn cycling in the oceans. Although we know much about these mechanisms independently, it is still not clear which are most significant in controlling dMn distributions. For instance, we know that the elevated surface concentration of dMn is the combined result of eolian dust, river input, and photo-reduction, yet we do not know how they interplay with each other and how important each is in shaping the vertical and horizontal distribution of dMn in the ocean. To address these questions, this study focuses on two study areas, one located in the northeast Pacific Ocean and another located in the Arctic Ocean. Dissolved trace metal samples were collected across Line-P, one of the oldest and longest oceanic research transect located off the coast of the British Columbia, Canada. In chapter 2, based on 299 filtered trace metal samples from the five major stations of Line-P transect (~1600 km long) in every August from 2010 to 2013, I 1) investigated the relative contribution of various sources of dMn in the surface and Oxygen Minimum Zone, 2) identified the significance of advected/mixing sources from the open ocean and from the continental shelf at the mid-depth, and 3) assessed the influence of a mesoscale eddy from Haida Gwaii. To better understand dMn cycling in the ocean, as well as to evaluate the interaction between particulate and dissolved phases of Mn, I also analyzed the suspended particles in two size fractions collected from the Line-P transect in 2013 (Chapter 3). The main objective of this chapter was to elucidate the role of particulate matter in trace metal cycling. To achieve this goal, I classified the particulate TM origins using particulate aluminum and phosphorous as lithogenic and biogenic indexes, respectively. Based on particulate composition and the dominant particle sizes at various depths along Line-P, I determined influence of particles on dissolved metals in this study area. In chapter 4, I assessed controls of dissolved Mn in the Beaufort Sea of the Arctic Ocean. The importance of river water and sea ice melt water 12 at the surface, advection and/or mixing from the continental shelf and slope, as well as a significance of Atlantic sourced water were evaluated in the context of the regional features of this area. Lastly, the focus of this dissertation is primarily on dissolved Mn, yet dissolved Fe, which shares the similar sources and sinks with dMn, is also discussed where it helps to better understand the biogeochemical cycling of dissolved Mn.  13 Chapter 2: Annual Variability of dissolved Manganese in Northeast Pacific along Line-P: 2010-2013  2.1 Summary The distribution of dissolved manganese (dMn) in the northeast Pacific across the Line-P transect was evaluated to investigate the mechanisms responsible for the spatial and temporal variability of dMn. A total of 299 filtered seawater samples (< 0.4 µm) collected in August at the five major stations each year from 2010 to 2013 were successfully analyzed. Vertical profiles of dMn showed clear distinction between onshore and offshore stations. Within the Summer Mixing layer (SML), we observed high dMn concentrations in all years driven by external sources, such as river water, coastal sediments or eolian dust, as well as photo-reduction. At the onshore stations, the absolute concentration of dMn at the surface was annually variable, depending on the strength of the Ekman transport. Within the subsurface layer, dMn decreased rapidly with depth down to 150 m due to particle scavenging. Within the Oxygen Minimum Zone (OMZ), near the continental margin, we observed elevated and annually variable dMn. The high dMn concentration is likely due to mixing of remobilized Mn from the continental margin, which varies year-to-year depending on the intensity of sedimentary Mn reduction process. At the offshore stations, dMn showed subsurface maxima, within the Winter Mixing Layer (WML) rather than surface maxima. We attribute this to the combined effect of biological drawdown of dMn in the surface during the spring and summer, where iron (Fe) is depleted in this High Nutrient and Low Chlorophyll (HNLC) region, and remnant dMn deeper in the WML, from earlier in the year. Using a simple advection and diffusion model, we identified that dMn found in North Pacific Intermediate Water (NPIW) at the western end of the transect can be advected as far as the outermost of the onshore stations in 2011 and 2013, while dMn in the central area of the transect is likely diluted by low dMn water from the south in 2010 and 2012. Within the OMZ, dMn showed elevated and annually variable concentrations, which is likely to be related to the abundance of potentially reducible particles in the water column. Lastly, eddies found in 2010 and 2013 modified the vertical distributions of dMn. Dissolved Mn is significantly enhanced within the surface mixing layers as high dissolved and potentially reducible particulate trace metals were transported from the coastal area to the open ocean by these eddies. 14 2.2 Introduction Manganese (Mn) is a redox sensitive trace element in the ocean. In low oxygen conditions, Mn in the dissolved form exists primarily as Mn(II) (e.g. Mn2+ or MnCl+), while it forms insoluble Mn-oxides (MnOx) in oxic seawater. (Roitz and Bruland, 1997). The latter is the major sink for dissolved Mn (dMn), as the oxidation process removes dMn from water column. It is also known that Mn(III) can exist as an intermediate during bacterial mediated oxidation of Mn(II) (Johnson, 2006). In the north Pacific, dMn displays a modified scavenged type profile (Sohrin and Bruland, 2011; Sunda and Huntsman, 1994). Its distribution reflects external sources (at the surface, at mid-ocean ridges, and near the sediments), scavenging removal away from these sources, as well as internal cycling in Oxygen Minimum Zones (OMZ: O2 < 100 µM). In particular, dMn shows elevated concentration in the surface layer due to surface external sources, such as rivers which contain 10 to 25 times more dMn than the ocean (Aguilar-Islas and Bruland, 2006; Elderfield, 1976) and eolian dust input which delivers potentially reducible Mn into the ocean  (Mendez et al., 2010; Statham et al., 1998). Additionally, photo-reduction enhances the level of dMn at the surface as UV radiation speeds up the dissolution of Mn-oxides 7 to 60 times (Sunda and Huntsman, 1994; Sunda et al., 1983). The mid-depth enhancement of dMn can also be observed near the mid-ocean ridges and hydrothermal vents (HTV) as they emit dMn enriched fluid into the water column (Klinkhammer et al., 1977; Resing et al., 2015). Recent studies discovered that dMn from HTV can travel as far as 4000 km (Resing et al., 2015). Subsequently, Fitzsimmons et al. (2017), attribute this to the possible association of dMn with microbial capsules which prevent exchange with sinking particles and allow it to advect a long distance. In the open ocean, insoluble Mn-oxides can be converted to soluble Mn(II) via in-situ reduction when oxygen is sufficiently low. Indeed, elevated dMn is found at mid-depth coincident with the OMZ. This mid-depth feature is more intense when O2 is lower (Middag et al., 2011a; Statham et al., 1998; Tebo, 1991). In addition, in coastal areas, reduced Mn(II) is mobilized from continental margin sediments, and can be laterally transported to the open ocean (Lam and Bishop, 2008).  In this study, we observed dMn over several years from 2010 to 2013, at 5 major stations in the northeast Pacific, from the coast of north America to the Gulf of Alaska. With this spatial and temporal resolution, in conjunction with ancillary hydrographic data, we aim to assess the relative 15 contributions of various sources of dMn to the surface layers (Section 2.4.3), identify the significance of advected sources for dMn at intermediate depth (Section 2.4.4), evaluate the cycling of dMn in relation to the biogeochemical tracers in the low oxygen regions (Section 2.4.5) and determine the influences of an mesoscale eddy on dMn observed in 2010 and 2013 (Section 2.4.6).  Dissolved iron (dFe), which shares similar sources and sinks with dMn, is also briefly reviewed in sections 2.4.5 and 2.4.6 to better understand dMn cycling in the OMZ and within the eddy influenced surface layer.   2.3 Method  2.3.1 Study Area and Sample Collection The Line-P transect, a set of 26 oceanographic stations from off the coast of Vancouver Island to the Ocean Station Papa (OSP), is located in the northeast Pacific at the Gulf of Alaska (Figure 2.1). The seafloor of this study area deepens from P1 (150 m) to P26 (4300 m). Station P26, also known as OSP, is approximately 1600 km away from the west coast of Vancouver Island and has a bottom depth of 4300 m. The Line-P transect has five major stations (P4, P12, P16, P20, and P26) along this transect where both hydrographic data (e.g. temperature, conductivity, dissolved oxygen) and seawater samples for chemical analyses (e.g. pH, trace metal and/or nutrient concentrations) were collected. Major stations are often divided into onshore (P4 and P12) and offshore stations (P16, P20, and P26) according to their major currents and water masses. The surface layer across  Line-P is affected by the easterly North Pacific Current (NPC) which bifurcates near station P16 into the northward Alaska Current and the southward California Current (Cummins and Freeland, 2007). At intermediate depths, the influence of North Pacific Intermediate Water (NPIW) is observed at the 26.8 kg m-3 isopycnal at the western end of the transect (You, 2005), and the California Undercurrent influences the coastal area at the 26.5 kg m-3 isopycnal (Meinvielle and Johnson, 2013b). 16  Figure 2.1 The Line-P transect in northeast Pacific. Both hydrographic stations (blue) and trace metal stations (red, labeled) are shown on the upper panel. The bathymetry and trace metal sampling resolution of 2011 are plotted on the bottom panel (red dots).   We collected seawater samples and hydrographic data along Line-P every August between 2010 and 2013 (Table A.1). During each cruise, hydrographic data was acquired by the Institute of Ocean Sciences part of Fisheries and Oceans, Canada. Salinity (S), temperature (T), transmissivity, and dissolved oxygen (O2) data were recorded using a CTD with an oxygen sensor at each station. Detailed sampling methods and hydrography data are publicly available at IOS archive (www.waterproperties.ca/linep). Seawater samples were collected at the five major stations (P4, P12, P16, P20, P26) from the surface to 2000 m using a trace metal clean sampling system with slight modifications each year. In 2010, samples were collected in three different ways. Surface samples were collected by hand from a Zodiac. Seawater from 5 to 40 m was sampled by a Teflon pump, and filtered in a HEPA laminar flow hood into pre-cleaned sampling bottles. Samples below 17 40 m deep were collected using Niskin-X bottles suspended to the Kevlar line. In 2011, a trace metal rosette (TMR) was used to collect all seawater samples. The TMR, mounted with 12 (12 L) GoFlo bottles and a CTD at the bottom, was deployed at all major stations. The sampling resolution of seawater was the highest in this year. The CTD recorded real time T, S, and dissolved O2. The data was then processed in 1 m resolution after the cruise. In 2012, the TMR was used to collect samples down to 1800 m. At OSP, Niskin-X bottles were used to collect samples below 1800 m. Similarly, in 2013, the TMR was used for samples in the upper 2000 m and Niskin-X bottles were used for samples below 2000 m at P26. Every TM clean seawater sample was filtered through a 0.45μm AcroPak-500 capsule filter (Pall Corporation) and collected into pre-cleaned sampling bottles. All filtered samples were acidified to pH=1.7 by adding 1 mL of 12 M ultrapure HCl (Seastar Baseline) per 1 L of seawater sample on board.   Sampling bottles, as well as all plasticware which may come in contact with seawater samples  (i.e. pipette tips for sample acidification), were intensively cleaned according to the GEOTRACES protocol (Cutter et al., 2017). The Low Density Polyethylene (LDPE) bottles (BelArt) were leached with 5% organic detergent (Extran), 6 M HCl (Environmental grade), and 0.7 M HNO3 (Seastar Chemicals) at least for a month for each step. The bottles were then rinsed with seawater samples for multiple times before the sample collection.    2.3.2 Analytical Method  Dissolved Fe and Mn were measured in the seawater samples by isotope dilution using the magnesium induced co-precipitation method as outlined in previous studies (Heumann, 1982; Mendez et al., 2010; Saito and Schneider, 2006). Since Mn is a monoisotopic element, and Fe and Mn are equally recovered by magnesium hydroxide precipitation, the concentration of Mn was determined based on the concentration of Fe and its isotope spike (Fe-57) (Saito and Schneider, 2006). All laboratory work was performed in a class-100 laminar fume hood. Briefly, an aliquot of Fe-57 enriched isotope spike was added to seawater samples (50 ml) as an internal standard. This isotope-seawater mixture was then preconcentrated by adding optima grade ammonium hydroxide NH4(OH) in order to obtain a MgOH pellet which contains Fe and Mn scavenged from 18 the seawater. The MgOH pellet was then dissolved into 1% optima grade nitric acid (HNO3) for measurement by high resolution ICP-MS (Element 2, Thermo-Finnigan). The detection limit of this instrument for Mn and Fe was 5.32 pmol kg-1 and 9.89 pmol kg-1 (n=7), respectively.    2.3.2.1 Evaluation of analytical method The analytical method was evaluated in three different ways. First, to test the intra-laboratory reproducibility and the precision of the analytical method used in this study, we measured dTM concentrations of GEOTRACES inter-calibration samples collected from Bermuda Atlantic Time-series (BAT) at two different depths (surface and 2000m). The consensus values of dFe and dMn are mean concentrations reported by 22 and 9 different laboratories with a variety of analytical methods, respectively. The average of 5 replicates of BAT samples measured by this study showed good agreement with consensus values (Table 2.1) (www.geotraces.org).  Table 2.1 Seawater reference material GS (GEOTRACES intercalibration samples collected from BATS at surface) and GD (BATS at 2000m). All concentrations are in nmol kg-1. dTM GS GD Consensus value This study (n = 5) Consensus value This study (n = 5) dFe 0.546 ± 0.046 0.523  ± 0.033 1.00 ± 0.10 1.052  ± 0.073 dMn 1.50 ± 0.11 1.577  ± 0.047 0.21 ± 0.03 0.201  ± 0.018   The dissolved TM samples for this thesis (i.e. 299 Pacific samples and 101 Arctic samples  (Chapter 4) were analyzed in 11 batches and measured on 11 different days. To test the consistency of the method and the performance of the instrument over time, seawater samples collected in 1991  (from the central North Pacific) were analyzed at the beginning of each batch using the same isotope dilution MgOH method. These results show good agreement with the reported values of dMn from these samples (Yang, 1993) as shown in Table 2.2.   19 Table 2.2 Concentration of dMn collected during Aleksandr Vinogradov Cruises, collected in 1991 (Yang, 1993). Stations are located in northwest and central north Pacific. Only the dMn values are available. Values in parentheses are samples with n=2.  Station Name Station location Depth dMn reported (nmol kg-1) dMn measured (nmol kg-1) Latitude (ºN) Longitude (ºW) Mean SD % RSD n HS1 38.1430 145.5090 250 1.629 1.626 0.013 0.79 3 HS14 16.2760 168.2980 1200 0.337 (0.33, 0.35) - - 2 HS16 17.1400 168.7000 900 0.313 0.312 0.018 5.75 7 HS16 17.1400 168.7000 1500 0.260 (0.29, 0.28) - - 2   For another test of reproducibility, some of the Line-P samples were analyzed in duplicate. In chemical oceanography, true duplicate samples (i.e. a sample collected at the same location, depth, and time by two different casts) are often not available due to logistical constraints. Instead, we measured duplicate samples drawn from the same Go-Flo bottle collected in two different sampling LDPE bottles. This not only tests reproducibility of the analytical method, but also identifies potential contamination by the sampling bottles. As they are duplicate samples with  n = 2, measured values were plotted against each other instead of reporting standard deviations or relative standard deviations (Figure 2.2). Total of 16 duplicate samples showed   5.4 % and 4.1% of standard error of linear regression for dMn and dFe, respectively.   a) dMnDuplicate sample #1 (nmol kg-1)0.0 0.5 1.0 1.5 2.0 2.5Duplicate sample #2 (nmol kg-1 )0.00.51.01.52.02.5y = 1.011x + 0.011 R2 = 0.99b) dFeDuplicate sample #1 (nmol kg-1)0.0 0.5 1.0 1.5 2.0 2.5Duplicate sample #2 (nmol kg-1 )0.00.51.01.52.02.5y = 1.022 x - 0.005  R2 = 0.99 Figure 2.2 Duplicated Line-P samples for a) dMn and b) dFe. Every duplicate seawater sample is marked in a different symbol.  20 2.4 Results and Discussion 2.4.1 Hydrography of Line-P during study period To examine the hydrography of the Line-P area, plots of potential temperature versus salinity  (T-S plots) (Figure 2.3) and spiciness contour plots (Figure 2.4) are used. The T-S plots show the water mass composition of the given area, while the spiciness can differentiate warmer/saltier waters (high spiciness value) from colder/fresher waters (lower spiciness value) for waters along the same isopycnal surface (Flament, 2002).   Figure 2.3 Potential temperature versus salinity for the 5 major stations along Line-P from 0 to 4000 m depth in each of the 4 years. The colour bar indicates dissolved oxygen (µmol kg-1). The OMZ  (O2 < 100 µmol kg-1) is found between isopycnal of 27.0 and 27.5 kg-1 (~200 – 2000 m). Note that shallowest sampling depth for P4 and P12 are 10 m and for P16 to P26 are 3 m in 2010. 21  Figure 2.4 Spice contour plots along Line-P from 2010-2013. An expanded view of the upper 150 m is shown above each plot. Spice is calculated from temperature-salinity-pressure data in 1 m resolution at all 26 stations across the Line-P. The overlay contour lines represent sigma-t (potential density – 1000 kg m-3). The TM sampling locations are marked in different symbols (2010 in square; 2011 in circle; 2012 in triangle; 2013 in diamond). Samples between 100 – 900 m at station P20 in 2013 are not available due to difficulties in TMR operation. Note that spiciness and sigma-t contours are based on T and S measured at all 26 stations in 1 m resolution. 22 The T-S plot indicates that the Summer Mixing Layer (SML; 0 – 35 m; σθ < 25.5 kg m-3) is stratified, with high temperature and low salinity water across Line-P in all years. Station P4 has the lowest salinity at the surface (S < 32.5) due to the influence of fresh water input from rivers (Figure 2.3). The annual variability of the SML is more clearly illustrated with a spice contour plot. For example, high spice in the SML in 2013 (~0.5 kg m-3) in comparison to 2012  (0.10 kg m-3) is the result of a high temperature anomaly (2.5 – 4.5 °C) in 2013 (www.waterproperties.ca/linep). Similarly, higher temperatures between P12 and P16 in 2010 caused elevated spice values (~0.3 kg m-3).  The subsurface layer, also known as the Winter Mixing Layer (WML) is found between 35 and 150 m. The WML exists between the isopycnals of 25.5 and 26.0 kg m-3, and shows increasing salinity with depth, and uniform low temperature (Figure 2.3). The difference between the summer and winter mixing layers is more evident with the spice contour plots (Figure 2.4). The SML has higher spice values (0 – 0.5 kg m-3) than the WML (-1.3 – -0.9 kg m-3) underneath it. This stratification persists across the transect in all years as temperature is 7 – 10 °C lower in the WML than in the SML in August. In 2013, the stratification between these two layers is most intense due to a high temperature anomaly in the SML and low temperature anomaly (-0.5 °C) and salinity  (-0.4 – -0.1) anomalies in the WML. In all years, both SML and WML are oxygen replete  (O2 > 150 µmol kg-1), but the WML has ~50 µmol kg-1 greater O2 as its temperature is lower than the SML (Figure 2.5).  23 0 100 200 300Sigma-t (kg m-3 )23.524.024.525.025.526.026.527.027.528.0NPIW26.8Oxygen (mol kg-1)0 100 200 300Sigma-t (kg m-3 )23.524.024.525.025.526.026.527.027.528.0NPIW26.82011Oxygen (mol kg-1)0 100 200 300Depth (m) 305010020010002000300010P4P12 P16P20P26 20120 100 200 300Depth (m) 30501002001000200030001020130 100 200 300Depth (m) 305010020010002000300010a)b)c)0 100 200 300Sigma-t (kg m-3 )23.524.024.525.025.526.026.527.027.528.0NPIW26.8 Figure 2.5 Distribution of dissolved oxygen in a) 2011, b) 2012, c) 2013 against depth in log scale (left panel) and against sigma-t (right panel). 24 Below the surface mixing layers, warm and salty California Under Current (CUC) with spice values between -0.2 and -0.4 are found at station P4 and P12 along the 26.5 kg m-3 isopycnal (Meinvielle and Johnson, 2013a) (Figure 2.4). Coastal upwelling caused by southward winds and Ekman transport brings lower oxygen water to the upper layer (Jardine, 1990). On the western side of the transect, North Pacific Intermediate Water (NPIW) with a core isopycnal of 26.8 kg m-3 advects colder and fresh water from the western Pacific to OSP and P20 (Talley, 1993). Hence, we observe low spice on the west side of the transect between 26.5 and 26.8 kg m-3. The OMZ is found between 200 and 3000 m (26.8 < σt < 27.8 kg m-3) (Figure 2.5), where the concentration of dissolved O2 is lower than 100 µmol kg-1 throughout this depth range. The lowest O2 is found at ~1000 m (7.6 µmol kg-1) across the Line-P transect, which does not reach the suboxic level (defined as O2 < 4.5 µmol L-1; (Karstensen et al., 2008)).    2.4.2 Overview: Distribution of dissolved Mn and Fe across Line-P To visualize annual and spatial variability of dMn across the Line-P transect, distributions of dMn analyzed at the major stations are plotted in two different ways. First, dMn profiles are plotted by the sampling year (Figure 2.6, a)) to highlight the geographical differences between onshore (P4 and P12) and offshore stations (P16, P20, and P26). In these plots, dMn from all five major stations in each year are plotted on one grid with a linear depth scale. Second, to highlight the annual variability of dMn, the vertical profiles are laid out by stations (Figure 2.6, b)).  For example, profiles on the P26 plot show dMn values from all years (2010 to 2013). To better observe changes in the upper layers, the profile depths are plotted in a log scale.  The horizontal lines indicate the boundaries between SML and WLM (35m) and between WML and the OMZ (150m). Likewise, the profiles of dFe are also plotted in the same format as dMn profiles (Figure 2.7 , a) and b)). Although the focus of this work is to assess controls on the spatial and temporal distribution of dMn along Line-P, a general description of dFe in the world ocean and its distribution along the Line-P transect are also described in this section as the analytical method of this work measures dFe concentrations together with dMn, and dFe will be discussed in later sections (Section 2.4.5 and 2.4.6) to help better understand dMn cycling. The measured values of both dMn and dFe are listed in Table A.3 of Appendix A.   25 2010dMn (nmol kg-1)0 1 2 3 4 6 9 12Depth (m)0500100015002000P4P12P16P20P262011dMn (nmol kg-1)0 1 2 3 4 6 9 12P4P12P16P20P262012dMn (nmol kg-1)0 1 2 3 4 6 9 12P4P12 P16P20P262013dMn (nmol kg-1)0 1 2 3 4 6 9 12P4P12P16P20 P26P260 1 2 3Depth (m)10255010020050010002000300P200 1 2 3P16dMn (nmol kg-1)0 1 2 3P120 1 2 3 4 5 6P40 2 4 6 8 10 122010201120122013a)b)(eddy)(eddy) Figure 2.6 Vertical profiles of dissolved Mn along Line-P a) from 2010 to 2013 with a linear depth scale, and b) at each station for inter-annual comparison with a logarithmic depth scale. Symbols represent the years (2010 in square; 2011 in circle; 2012 in triangle; 2013 in diamond). Colors represent the stations (P4 in black; P12 in red; P16 in green; P20 in purple; P26 in blue).   26 2011dFe (nmol kg-1)0 1 2P4P12P16P20P262010dFe (nmol kg-1)0 1 2Depth (m)0500100015002000P4P12P16P20P262012dFe (nmol kg-1)0 1 2P4P12P16P20P262013dFe (nmol kg-1)0 1 2P4P12P16P20P26a)P260 1 2Depth (m)10255010020030050010002000P200 1 2P16dFe (nmol kg-1)0 1 2P120 1 2P40 1 22010201120122013b)  Figure 2.7 Vertical profiles of dissolved Fe along Line-P a) from 2010 to 2013 with a linear depth scale, and b) at each station for inter-annual comparison with a logarithmic depth scale. Symbols represent the years (2010 in square; 2011 in circle; 2012 in triangle; 2013 in diamond). Colors represent the stations (P4 in black; P12 in red; P16 in green; P20 in purple; P26 in blue). 27 In 2010, the highest dMn is found in the surface mixing layer at station P4 (8.1 nmol kg-1 at 25m) (Figure 2.6, b)).  Station P12 also shows a high surface dMn concentration (5.0 nmol kg-1 at 25m), which is 40 – 70 % greater than in other years, due to the presence of a downwelling eddy (Figure 2.6, b)) (Section 2.4.6). The rest of stations have less than 1 nmol kg-1 of dMn in the surface layer. We observed low dMn at 150 – 200 m depth (0.3 – 0.6 nmol kg-1) at the offshore stations where NPIW is found. In 2011, we observed a clear separation between onshore versus offshore stations. At onshore stations (P4, P12), surface enriched dMn decreases with depth down to 150 m and gradually increases beneath 150 m down to the deepest depth sampled. The offshore stations however show the highest dMn below the surface in the WML (~75 m) (1.7 nmol kg-1) rather than in the SML (0.9 nmol kg-1). Dissolved Mn then reaches a minimum at the bottom of the WML (150 m). As oxygen level decreases below 100 µmol kg-1, dMn gradually increases and reaches a secondary maximum at ~400 m. The onshore versus offshore separation is also observed in 2012, but not as prominent as in 2011. Station P4 and P12 show greater concentrations with continuously increasing levels below 150 m depth. The maximum dMn is found within the SML at the onshore stations and within the WML at the offshore stations. Within the OMZ (below 150m,  O2 < 100 µmol kg-1), dMn gradually increases with depth down to the deepest sampling depth at the onshore stations (P4: 1200 m, P12: 2000 m), whereas the offshore dMn shows the secondary maxima in the upper part of the OMZ (300 – 500 m). The vertical distribution of dMn in 2013 is similar to 2011 and 2012 with the same contrasts between onshore and offshore stations. However, the secondary maxima at the offshore stations are significantly greater in 2013  (e.g. P16: 1.3 nmol kg-1) than in other years (e.g. P16: 0.8 nmol kg-1 in 2011).   Dissolved iron, on the other hand, shows low interannual variability but some geographical variability across the transect (Figure 2.7). Distribution of dFe in this study area shows typical nutrient type profiles in all years across the transect. The dFe is the lowest at the surface, and stays low until 100 m, then gradually increases with depth, mainly due to biological uptake within the photic zone and remineralization at depth (Wells et al., 1995). Similar to Mn, Fe is also introduced by eolian and riverine inputs at the surface and regenerated by organic remineralization at the depth (Morel et al., 2003). Despite its surface external sources, dFe along Line-P transect shows depleted surface concentrations due to its high demand by phytoplankton and the low solubility of Fe (III) particles. Although dFe shows similar vertical distributions across the transect, the concentration 28 range near the coast is about 2 times greater than at offshore stations. For example, the range of dFe at station P4 in 2013 is from 0.2 nmol kg-1 at the surface to 2.0 nmol kg-1 at the depth, while dFe at OSP is ranged from 0.2 to 0.6 nmol kg-1. This reflects additional dFe sources to the coastal area, such as riverine water or a flux of reduced dFe from the continental margins (Lippiatt et al., 2010). At mid-depth in the coastal area, dFe may also be remobilized from the continental slope where the oxygen concentration is low. This dFe has been observed to be laterally transported to the open ocean similar to dMn (Cullen et al., 2009; Lam and Bishop, 2008).    2.4.3 Dissolved Mn in the surface mixing layers  2.4.3.1 Summer Mixing Layer: Annually variable dMn at the onshore stations Dissolved Mn is affected by a number of external sources (e.g. riverine water, shelf sediments, dust input), internal cycling (e.g. photo-reduction) and physical processes (e.g. coastal upwelling, wind-driven surface currents) in the uppermost layer. Typically, the horizontal distribution of dMn in the surface mixing layer is expected to display the highest concentration in the coastal region and decreasing levels with distance from the shore (Middag et al., 2011b; Wu et al., 2014).   The horizontal distribution of dMn in the Summer Mixing Layer (SML: upper 35 m) displayed two interesting features across the transect (Figure 2.8). First, the level of dMn decreases with the distance from the shore in all sampling years as seen in other oceans (e.g. Atlantic and Arctic) (Middag et al., 2011b; Wu et al., 2014). Second, annually variable dMn (2.4 – 8.4 nmol kg-1) is observed at the station nearest to the shore (P4), whereas the offshore stations show lower and less variable dMn (0.9 – 1.1nmol kg-1). Based on these observations, this section will evaluate the potential factors which lead to the high interannual variability of dMn at the onshore stations, such as variations in dust input, riverine input, coastal upwelling and offshore transport, and drivers of photo-reduction.   29 StationP4P12P16P20P26dMn (nmol kg-1 )0246810 2010201120122013(eddy) Figure 2.8 Horizontal distribution of average dMn in the Summer Mixing Layer (0-35m).    Windblown dust Dust input is one of the important external sources for dMn as Mn has a relatively fast dissolution rate. Regardless of the aerosol type (i.e. polluted, mineral or clean marine air aerosols), at least 30% of atmospheric Mn is known to be dissolved into the ocean (pH 8) within 5 to10 minutes (Guieu et al., 1994). Dry and wet deposition into the GoA area (Figure 2.9) indicates that dust deposition is low and annually consistent at the onshore stations. Although a large amount of dust is observed at the BC continent, this influence does not reach the onshore stations of Line-P. Hence, this source in unlikely to cause the enhancement and variations of dMn we observe at the onshore stations. In 2011 and 2013, however, dust deposition is ~5 times greater at station P26 compared to the onshore stations (i.e. P4 and P12). Despite this elevation, the dMn at station P26 does not show variation in concentrations year-to-year (Figure 2.8). This may indicate that dust input does not cause a significant annual variation of dMn although it is a major external source for dMn in the open ocean. Conversely, it may be the result of discrepancies of time window between dust deposition data (mean of monthly dust input from July to August) and dMn data (collected from mid- to end- of August). Knowing the dust deposition in a short period (e.g. 1 – 2 days prior to the sampling time) may help identify if the enhancement of dust deposition at P26 in 2011 and 2013 was a sustained behavior during entire months of July and August or if it was driven by an instantaneous 30 event between July and August. However, daily data was not available for the dry and wet dust deposition to validate these possibilities.    Figure 2.9 Mean (July-August) of dust (dry + wet) deposition in GoA area from 2010 to 2013. Plots are based on the satellite data of Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2), provided by NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) (GMAO, 2015). The spatial resolution of the data set is 0.5° × 0.625°.    Photo-reduction of Mn-oxides Particles originating from north American riverine sources (McAlister, 2015) or upwelled from the continental margin (Chase et al., 2005) may also contribute on the dMn enhancement at P4. As laboratory experiments indicate, UV radiation can speed up the reduction of Mn-oxides in the surface layer and increases dMn in the surface ocean (Sunda and Huntsman, 1994). This photo-reduction process can generally increase the level of dMn in the SML, however its contribution to the dMn annual variability we observed is unclear. We observed higher UV index at P4 (~6) than at the offshore stations (~5) (Figure 2.10), which may contribute to the enhancement of dMn in the coastal area where more particles are also available (Figure 2.9). However, no significant interannual variations in UV index values were observed, so this cannot explain the differences we observe between years at the coastal stations.  31  Figure 2.10 Mean (July-August) of UV index in GoA area from 2010 to 2013. Plots are based on the level-3 daily global gridded Aura-OMI Spectral Surface UV-B Irradiance and Erythemal Dose product (OMUVBd), provided by NASA GES DISC (Hovila et al., 2013). The spatial resolution of the data set is  1° × 1°.   Riverine input, shelf sediments and Ekman transport Another external source of dMn is from river water. As rivers contain 10 – 25 times more dMn than seawater (Aguilar-Islas and Bruland, 2006; Martin and Whitfield, 1983; Middag et al., 2011b), fluctuation in the river discharge rate could cause the variable enhancement of dMn near the coast. In order to identify possible episodes of high or low riverine inputs which could impact dMn, we examined the river discharge rate gauged at the estuaries of a major river on Vancouver Island (Gold River) and the North America continent (Fraser and Columbia Rivers) during the study period (Figure 2.11, a)) (https://wateroffice.ec.gc.ca/; https://waterdata.usgs.gov/usa/nwis/).   32 2010 - 2013Month                  Jan  Mar  May  Jul  Sep  Nov  Jan  Rate of river discharge (m3 s-1)10100100010000 Vancouver Island: Gold River (08HC001) BC mainland: Fraser River Hope (08MF005)US: Columbia River (USGS: 14246900)Sampling date at P448 oN 125 oWMonthJ-F M-A M-J J-A S-O N-DUpwelling Indices (m3  s-1  100 meters of coastline-1)-60-40-200204060801001202010201120122013b) c)a)Year2010 2011 2012 2013dMn (nmol kg-1 ) 0510152025303540Upwelling IndicesdMn at P4 (nmol kg-1)P4: 48.4 oN 126.4 oW48 oN 125 oWUpwelling Indices (m3  s-1  100 m coastal line -1 ) Figure 2.11 a) Daily river discharge rate (in m-3 s-1) from the major watersheds located on Vancouver Island, from the Fraser River in BC mainland (dark green), and Columbia River in the USA (grey) from 2010 January 1st to 2013 December 31st. The date of sample collection at station P4 is marked with dashed lines (red). b) Two-month cumulative of coastal upwelling indices at 48 °N 125 °W. Values for late summer (July-Aug) are highlighted in red. c) Average upwelling indices over 3-weeks prior to the sampling at P4 and dMn are plotted on the same grid. The y-axis represents both upwelling indices (upper part) and dMn (lower part).  The drainage of the coastal river (Gold River; located on the Vancouver Island) follows the high precipitation in winter, while the Fraser River discharge follows the increasing temperature in early summer due to glacier/snow melting. During the study period (2010 – 2013), we observed that the discharge rate was similar during the sampling period in all years (Figure 2.11, a)). There were no 33 significant drought or flooding events recorded which could lead to large fluctuations in discharge rate. Hence, the higher dMn at P4 in 2013 (8.4 nmol kg-1) in comparison to the dMn in 2010  (2. 5 nmol kg-1) (Figure 2.8) is not likely to be the result of episodic enhancement of freshwater discharge from the rivers adjacent to the study area. Another major river source, the Columbia River, is discharged from the west coast of the USA, between Washington and Oregon, yet no variations in discharge rate was observed between the sampling years (Figure 2.11, a)). Additionally, the impact of the Columbia River water on the onshore stations along Line-P at the time of sampling, is not expected to be as significant as the local rivers in BC, due to the southerly flow of the California Current in summer (Davis et al., 2014).  Assuming that the rate of trace metal introduced by the river is annually consistent during the sampling years, we hypothesize that varying the strength of Ekman transport may cause the differences in dMn observed at P4. In summer, the eastern side of the transect is affected by southward winds, leading to westward Ekman transport and upwelling. The stronger wind stress results in enhanced Ekman transport and greater coastal upwelling. To identify the intensity of the Ekman transport in each year, two-month average upwelling indices are plotted in Figure 2.11, b) based on data provided by the Pacific Fisheries Environmental Laboratory (PFEL) of NOAA (https://www.pfeg.noaa.gov/products/las.html). These upwelling indices are determined based on the Ekman transport of water mass caused by the wind stress within the upper 50 – 100 m. Greater positive numbers represent stronger upwelling, and more importantly, greater seaward advection (westward Ekman transport) of coastal sources. Therefore, we interpreted the high upwelling indices as indicators of enhanced westward transport of waters from the coastal region which may contain high level of dMn, both from river input and/or from shelf sediments (Aguilar-Islas and Bruland, 2006). The mean upwelling indices over 3-weeks prior to the sampling period also show that the advection of coastal waters is the greatest in 2013 and the lowest in 2011, which coincides with the level of dMn at station P4 (Figure 2.11, c)) and agrees with 2 month cumulative upwelling indices (Figure 2.11, b)). Based on this positive correlation between the upwelling indices and dMn concentration, we argue that variations in the strength of Ekman transport lead to the observed annual variability in dMn at P4.   34 2.4.3.2 Winter Mixing Layer: Elevation of offshore dMn in high O2 conditions The Winter Mixing Layer (WML) is found between 35 and 150 m, which can be identified as a broad band of low spice waters across the Line-P transect (Figure 2.4) (Freeland, 2013). The WML is in contact with the atmosphere during the previous winter, and becomes separated from the SML as the surface warms up in the spring and summer. The WML therefore has lower temperature and elevated dissolved oxygen concentrations (Figure 2.5).   P26dMn (nmol kg-1)0 1 2Depth (m)10253550100150753005005201120122013P20dMn (nmol kg-1)0 1 2201120122013P16dMn (nmol kg-1)0 1 2201120122013(eddy)P12dMn (nmol kg-1)0 1 2 122010201120122013P4dMn (nmol kg-1)0 1 2 122010201120122013 Figure 2.12 Distribution of dMn at each station for upper 500m. The colored symbols represent the maxima dMn found in WML (35-150 m).   At the offshore stations, the highest values of dMn are generally found at ~75m in the WML (Figure 2.12), rather than in the surface. Since the oxygen concentration is the highest in this layer, in-situ reduction of Mn-oxides cannot be the reason for the enhanced dMn. In addition, remineralization of dMn from sinking biogenic particles cannot fully explain the enhanced dMn since the apparent oxygen utilization (AOU) indicates that organic respiration is 2 to 10 times greater at the onshore stations (30 – 49 µmol kg-1) than open ocean area (3 – 17 µmol kg-1). A more plausible explanation would be that biological drawdown of dMn by primary producers occurs in the SML after stratification separates the SML from the WML. This idea can be clearly visualized with cross section contour plots of fluorescence and nutrients (Figure 2.13) as offshore 35 dMn maximum within the WML is identified beneath the highest fluorescence maximum where the nutricline is present. Mn is one of the essential micronutrients in the ocean, and Mn enhances phytoplankton growth in high light conditions (Sunda and Huntsman, 1998). Mn can substitute for Fe in the antioxidant enzyme superoxide dismutase in high nutrient and low chlorophyll regions like Line-P area (Peers and Price, 2004). Additionally, during summer season, dMn uptake is enhanced by phytoplankton when dFe is depleted at the upper layers (Figure 2.7). We suspect that this drawdown at the SML is masked at the onshore stations by the higher external Mn sources and/or by the replete dFe concentrations within this non-HNLC area. The subsurface maximum and seasonal surface drawdown is evident at the offshore stations since external sources are minimal and there dMn consumption by phytoplankton in the SML is enhanced due to Fe limitation. As a result, dMn has surface maxima (in the SML) at the onshore stations and subsurface maxima (in the WML) at the offshore stations.       Figure 2.13 Cross section contour plot of fluorescence (upper panel) and nitrate+nitrite (lower panel) across the Line-P in 2012. Open circle indicates the depth where the highest dMn is found within the WML at the offshore stations.  36 2.4.4 Significance of advected sources at the mid-depth  2.4.4.1 California Undercurrent (CUC) The California Under Current (CUC) with its core isopycnal of 26.5 kg m-3 (Thomson and Krassovski, 2010) is found at ~150 – 200 m at station P4 in all years (Figure 2.14). Relatively higher spice values at station P4 compared to station P12 or P16 along the isopycnal of  26.5 kg m-3 identify the warmer and saltier CUC in all years (Figure 2.14). Since this water mass travels north along the west coast of North America, station P4 may be expected to receive high dMn and dFe remobilized from the sediments along the continental margin (Cullen et al., 2009). However, no significant increase or decrease of dMn or dFe at station P4 is observed at the core isopycnal of the CUC. This is consistent with previous trace metal studies conducted in this area (e.g. dissolved copper (Posacka et al., 2017), dFe (II) (Schallenberg et al., 2015)), which also noted no elevation in TM levels caused by the CUC waters. In 2011, dMn at P4 shows a similar concentration at P12 and P16 (~0.6 nmol kg-1) (Figure 2.14, a)). In contrast, dMn at P4 is greater than at the other two stations in both 2012 and 2013 (Figure 2.14, b) and c)). Similarly, dFe is greater at P4 than at P12 and P16 in all years. Despite the enhanced dMn and dFe at P4 compared to other stations, the enhancement is not centered around the isopycnal surface associated with the core of the CUC (26.5 kg m-3). The level of dMn and dFe continuously increases from 75 m (isopycnal of 25.4 kg m-3) to the deepest sample point (1200 m: 27.5 kg m-3) and the highest concentration is observed at deeper depth (~1000 m: 27.2 kg m-3) than where CUC is found. However, since the vertical profiles of spice clearly indicates that P4 is influenced by CUC at the isopycnal of 26.5 kg m-3, any dMn or dFe signal from the CUC is likely masked by a local source, such as remobilized dMn and dFe or reduction of resuspended particles from the continental margin off the coast of B.C..   37 a) 2011-0.9 -0.6 -0.3 0.0Sigma-t (kg m-3 )26.026.226.426.626.827.027.227.427.627.8b) 2012-0.9 -0.6 -0.3 0.0Sigma-t (kg m-3 )26.026.226.426.626.827.027.227.427.627.8c) 2013Spice (kg m-3)-0.9 -0.6 -0.3 0.0Sigma-t (kg m-3 )26.026.226.426.626.827.027.227.427.627.8Spice (kg m-3) dMn (nmol kg-1) dFe (nmol kg-1)Spice (kg m-3) dMn (nmol kg-1) dFe (nmol kg-1)Depth (m)100 1000 0 1 2 0 1 2 3100 1000 0 1 2 0 1 2 3P4P12P16Depth (m)100 1000Depth (m)dMn (nmol kg-1)0 1 2dFe (nmol kg-1)0 1 2 3P4P12P16P4P12P16Figure 2.14 Vertical profiles of spice, depth, dMn and dFe against the sigma-t at station P4, P12, and P16 in a) 2011, b) 2012, and c) 2013.  The CUC is expected to be found at station P4 along the core isopycnal of  26.5 kg m-3 (dotted red lines).    38 2.4.4.2 North Pacific Intermediate Water (NPIW)  At intermediate depths (~150 – 200 m), the western side of the transect is affected by North Pacific Intermediate Water (NPIW), which is generated in the northwest Pacific and flows towards OSP along the core isopycnal of 26.8 kg m-3 (Bostock et al., 2010; You, 2005). The NPIW is found at ~150 – 200 m at station P26 and P20 and can be identified by low spice values  (-0.8 – -0.7 kg m-3) due to its relatively low temperature (Figure 2.4). The NPIW has lower O2 levels by the time it reaches OSP due to its long time since ventilation, however the oxygen level is still higher than 100 µmol kg-1. On the other hand, the eastern side of the transect at this isopycnal tends to be affected by water mixed from the continental slope as described in previous studies (Lam et al., 2006; Martin et al., 1985; Wu et al., 2014). In this section, we will evaluate the influence of advected source (i.e. NPIW) on the dMn distribution along the isopycnal of  26.8 kg m-3.   To evaluate this, expected dMn supported by advection was calculated using a simple advection/diffusion model equation as outlined in previous studies with a slight modification (von Langen et al., 1997; Wu et al., 2014). Assuming that ocean is at steady state, photo-reduction, eolian dust, and river water do not contribute to dMn at this depth, and vertical mixing and particle scavenging (i.e. non-oxidative scavenging) are not significant, the input of dMn by horizontal advection/mixing should balance the output via Mn(II) oxidation under steady state (Landing and Bruland, 1987; Wu et al., 2014). Then, the expected dMn along the core isopycnal of  26.8 kg m-3 is calculated based on the following equation,   ߈௫ ߲ଶሾܯ݊ሿ߲ݔଶ ൅ ߱௫߲ሾܯ݊ሿ߲ݔ ൌ  ݇଴ሾܱଶሿሾܱܪିሿଶሾ݀ܯ݊ሿ௠௘௔௦௨௥௘ௗ  where ݇଴  is the rate constant of homogenous Mn(II) oxidation by dissolved O2  (1.96×10-2 µM-3 s-1) (von Langen et al., 1997), ߈௫ is horizontal eddy diffusivity (5×103 m2 s-1) (Huh and Ku, 1998), and ߱௫ is the velocity of NPIW along Line-P (0.022 m s-1) (Ueno and Yasuda, 2003). The concentration of hydroxide (OH-) was calculated from pH values provided by IOS (Dickson et al., 2007) and the measured values of oxygen ([O2]) and dMn ([dMn]measured) found 39 between the isopycnal of 26.75 and 26.85 kg m-3 were used. Lastly, station P26 and P4 are defined as the initial and final points for the expected dMn calculation respectively. The details of the calculation is outlined in Appendix A.1. The final product of this model is then the expected dMn concentration. By comparing the measured dMn to the calculated values, we can identify 1) if there are inputs other than the horizontal advection/mixing along Line-P  (dMnmeasured > dMncalculated), 2) if dMn is mostly supported by an advected source and mixing along the Line-P (dMnmeasured = dMncalculated), or 3) if an additional removal process other than the oxidative scavenging process is occurring along Line-P or if there is an advection of low dMn waters into the region (dMnmeasured < dMncalculated). To identify the importance of advection/mixing by the NPIW and to estimate how far dMn can be transported along the transect, the mean concentration of dTM along the core isopycnal of 26.8 kg m-3 and model calculated dMn are plotted in the same grid (Figure 2.15, a)).   40 2010P4P12P16P20P26dMn (nmol kg-1 )0.00.20.40.60.81.01.21.42011StationP4P12P16P20P26range of measured dMndMn: MeasureddMn: Model calculated, advected from OSP2012P4P12P16P20P262013P4P12P16P20P26a) Figure 2.15 a) Dissolved Mn along the 26.8 kg m-3 isopycnal across Line-P, from 2010 to 2013 (open symbols). Closed symbols: calculated dMn using an advection/diffusion model. Vertical grey lines: dMn concentration ranges when there are more than 2 samples between the isopycnals of 26.75 and 26.85 kg m-3 (2010: n = 2 at P20 and P26, 2011: n = 3 at all stations, 2013: n=3 at P4 and P12, n=2 at P16 and P26). b) – e) Maps of surface circulation in the GoA from 2010 to 2013 (Fisheries and Oceans Canada, http://isdm-gdsi.gc.ca/isdm-gdsi/argo/canadian-products/Argo-circulation-eng.html). Scale (right top corner): current speeds associated with contour separation. Dashed lines: boundary between north Pacific subarctic and subtropical gyres. Note that the dashed lines cross the Line-P transect in 2010 and 2012, but not in 2011 or 2013. The boundary contour lines which influence the Line-P transect are highlighted in thick dashed lines. Black symbols: stations of previous studies (V4, V5: Landing et al., 1985; GP2, BD15, BD16: Mawji et al., 2015; 14: Brown et al., 2012). The blue line: the Line-P transect.  41 By definition, the model results and the measurements agree at the two ends of the transect, P26 and P4. In 2010, the value used for the “measured dMn” at station P4 (Figure 2.15, a); marked in grey) is the mean of the measured dMn at P4 from 2011 to 2013, since no dTM sample was collected shallower than 40 m at P4 in 2010. In all years, the highest dMn along this isopycnal is seen at P4, due to mixing with high dMn water from the continental margin. In 2011 and 2013, measured and calculated dMn show good agreement across the transect, which suggests that dMn is supported by advection and mixing along the core isopycnal of NPIW along the Line-P. On the other hand, measured dMn in 2010 and 2012 is ~50 % lower than the calculated dMn. This indicates either an additional removal mechanism, other than oxidative scavenging, or more likely, the north-south advection of a low dMn water mass to this region in those years. The additional removal process is unlikely as the removal by the particle scavenging would have to be at least 50 to 100 times greater than the oxidative scavenging rate and only in 2010 and 2012. The latter hypothesis, north-south advection of low dMn to the Line-P transect, is then explored by comparing the circulation patterns in the northeast Pacific from 2010 to 2013 (Figure 2.15, b) – e)). These circulation contour plots are generated based on the Argo floats data (Freeland, 2006) by Fisheries and Oceans Canada. The dashed lines indicate the boundary between the north Pacific subpolar and subtropical gyres (Cummins and Freeland, 2007), the position of which varies year-to-year (e.g.(Sydeman et al., 2011). All major stations of the Line-P are found within the subpolar gyre (i.e. Alaska Gyre) in 2011 and 2013, when the level of dMn is consistent with the advection model. In 2010 and 2012, on the other hand, station P4 and P12 are within the subtropical gyre while station P16 to P26 are in the subarctic gyre. The boundaries of both gyres in 2010 and 2012 are further north than in 2011 and 2013, suggesting that all of Line-P may be more affected by the subtropical gyre in 2010 and 2012. Since there is a concentration gradient of dMn from north to south in the Pacific, the advection and mixing of high or low dMn may explain the variations in horizontal distribution of dMn in 2010 and 2012. The reported concentration range of dMn at  ~ 30°N is ~ 0.4 – 0.5 nmol kg-1 (Figure 2.15, b) – e): V4 and V5) (Martin and Knauer, 1983), while it is ~ 0.7 – 1.4 nmol kg-1 at GP2, BD15, and BD16 (Mawji et al., 2015) and ~ 1 nmol kg-1 at station 14 (Brown et al., 2012) in the subarctic gyre. Although there is a significant gap from station V4 or V5 to the Line-P transect (~2200 km), if the subtropical gyre contains low level of dMn in general, the northward advection/mixing may dilute the dMn found in Line-P when the boundary between two gyres is found more northerly (i.e. 2010 and 2012). Conversely, when the 42 subarctic gyre expands and affects the entire Line-P transect, dMn is supported by horizontal advection and mixing along the core isopycnal of the NPIW across the Line-P.    2.4.5 Elevated dMn in the Oxygen Minimum Zone   The Oxygen Minimum Zone (OMZ) in the study area has a broad depth range (250 – 2000 m) with its lowest oxygen concentration at ~1000 m (7 – 8 µmol kg-1) (Figure 2.5). Previous studies propose that dMn increases in the OMZ are due to a combination of remineralization of organic matter, a slower oxidation rate of Mn under low pH and low O2, mixing from the continental margins, and/or from hydrothermal inputs (Johnson et al., 1992; Klinkhammer and Bender, 1980; Lam and Bishop, 2008; Weiss, 1977). This section aims to evaluate the importance of remobilized dMn from the continental margin, as well as the significance of remineralization and reduction of Mn in the low oxygen conditions.   Figure 2.16 shows the profiles of dMn and dFe within the OMZ for the years when deeper waters were sampled (2011 – 2013). In all of these years, a clear separation between onshore and offshore stations is observed. At the onshore stations (P4, P12), both elements have increasing concentrations with increasing depth and little interannual variability. The general increasing trend of dTM below 300m is likely affected by the continental slope. The maximum concentrations of dTM are found in the bottom samples, closest to the continental slope, which suggests remobilization of Mn and Fe from the slope to the water column. Station P12 also shows dTM maxima at the deepest depth sampled (2000 m). This elevation is considered to be the combined effect of lateral mixing from P4 and/or resuspension or reduction of Mn from the seamount found nearby at ~1800 m.   43 P26d[Mn] (nmol kg-1)0.0 0.5 1.0 1.5Sigma-t(kg m-3)26.526.326.827.027.527.827.30 100 200P20d[Mn] (nmol kg-1)0.0 0.5 1.0 1.50 100 200P16d[Mn] (nmol kg-1)0.0 0.5 1.0 1.50 100 200P12d[Mn] (nmol kg-1)0 1 20 100 200P4d[Mn] (nmol kg-1)0 1 2Sigma-t(kg m-3)26.526.326.827.027.527.827.30 100 200dFeO2dMna) 2011P260.0 0.5 1.0 1.5Sigma-t(kg m-3)26.526.326.827.027.527.827.3O2 (mol kg-1)0 100 200P200.0 0.5 1.0 1.5O2 (mol kg-1)0 100 200P160.0 0.5 1.0 1.5O2 (mol kg-1)0 100 200P120 1 2O2 (mol kg-1)0 100 200P40 1 2Sigma-t(kg m-3)26.526.326.827.027.527.827.3O2 (mol kg-1)0 100 200c) 2013P260.0 0.5 1.0 1.5Sigma-t(kg m-3)26.526.326.827.027.527.827.30 100 200P200.0 0.5 1.0 1.50 100 200P160 100 2000.0 0.5 1.0 1.5P120 1 20 100 200P40 1 2Sigma-t(kg m-3)26.526.326.827.027.527.827.30 100 200b) 2012 Figure 2.16 Concentration dMn, dFe, and dissolved oxygen below sigma-t of 26.3 kg m-3 in a) 2011, b) 2012, and c) 2013. The vertical and horizontal lines indicate the boundary for the Oxygen Minimum Zone (100 µmol kg-1) and North Pacific Intermediate water (26.8 kg m-3) respectively. Filled symbols indicate the maximum concentration found in the OMZ. 44  The N* tracer (N* = NO3 – 16∙PO4 + 2.9) is an indicator of nitrogen fixation, denitrification and/or anammox in the ocean based on deviations from the N:P linear relationship (Gruber and Sarmiento, 1997). Positive N* values indicate excess nitrate in the water column, suggesting influence from nitrogen fixation. Conversely, negative N* values indicate removal of nitrate via denitrification and/or annamox in the water column or in the sediments in low oxygen conditions. A more negative N* value can be interpreted as a greater influence of denitrification in the water column or in the sediments. In this study area, within the OMZ, dissolved oxygen (DO) shows no significant variations in vertical distribution from one station to another along line P (Figure 2.16). Despite this similarity in DO, N* values are more negative (e.g. -6 – -4.5 µmol kg-1 at P4) close to the continental margin compared to the offshore stations (-4 – -2 µmol kg-1) (Figure 2.17, b)). This suggests that the water column near the continental slope is affected by sedimentary denitrification and/or annamox. Conditions that lead to denitrification are also likely to lead to Mn reduction and eventually to the remobilization of dMn to the water column (José et al., 2016). Indeed, we observed 2 to 4 times greater dMn at P4 (e.g. 2.0 nmol kg-1 at P4 in 2011) than at P26  (e.g. 0.4 nmol kg-1).   Additionally, we also observed that the strength of denitrification influences the dMn concentration in the water column. In other words, the concentration of dMn is greater when N* values are more negative. This can be visualized by dMn to N* plot (Figure 2.17, b)). The higher dMn is observed when N* is more negative, and they also showed a strong negative linear relationship each other. At station P4, more negative N* (-5.5 – -2 µmol kg-1) is observed in 2011 and relatively less negative N* values in 2013 (-4 – -2 µmol kg-1), suggesting that the continental margin can be a major contributor to the enhanced dMn when sedimentary denitrification is more intensified.   45 a)2011N* (mol kg-1)-8 -6 -4 -2 0dMn (nmol kg-1 )0.00.51.01.52.02.5P4P12P16-262012N* (mol kg-1)-8 -6 -4 -2 02013N* (mol kg-1)-8 -6 -4 -2 0dMn (nmol kg-1 )0.00.51.01.52.02.52000 mb)2011P4P12P16P20 P26dMn (nmol kg-1 )0.00.30.60.91.21.51.82.12.42.7 OMZCUCNPIWMean dMn2012P4P12P16P20P262013P4P12P16P20P26dMn (nmol kg-1 )0.00.30.60.91.21.51.82.12.42.72011dFe (nmol kg-1)0.0 0.5 1.0 1.5 2.0dMn (nmol kg-1 )0.00.51.01.52.02.5 P4P12P16P20P262012dFe (nmol kg-1)0.0 0.5 1.0 1.5 2.02013dFe (nmol kg-1)0.0 0.5 1.0 1.5 2.0dMn (nmol kg-1 )0.00.51.01.52.02.5c) Figure 2.17 Concentration of dMn in intermediate waters. Panel a) shows all values within the Oxygen Minimum Zone (grey) where the oxygen concentration is lower than 100 µmol kg-1, at the core isopycnal of 26.5 kg m-3 (cyan) representing California Under Current at the onshore stations, and at 26.8 kg-3 (green) representing North Pacific Intermediate Water. The approximate depth range of OMZ is 250 – 2000 m (sigma-t > ~27.0 kg m-1). The mean concentration of measured dMn within the OMZ (black, closed) is also shown. The mean value of P20 in 2013 is based on the sample data collected below 1000 m only (purple). Panels b) and c) show dissolved Mn against N* and dFe, respectively, from 2011 – 2013 in the OMZ.  46  Although both dMn and dFe show similar vertical trends at onshore stations, they do not show a strong correlation in the open ocean (Figure 2.17, c)). This suggests that mixing of remobilized dMn and dFe from the continental slope is the dominant source for the stations near the continental margin or close to the coast (P12: ~ 300 km off the coast of BC) as this flux is not observed further west than P12. The offshore stations show lower and uniform dMn in comparison to the onshore stations (Figure 2.17, a)). In most cases, dMn has a secondary maxima just below the NPIW  (26.8 kg m-3), at the top of the OMZ, where O2 level starts to drop below 100 µmol kg-1. In contrast, dissolved Fe has its maxima deeper, close to the center of the OMZ. This discrepancy might be a result of rapid reduction of Mn which depletes potentially reducible particulate Mn within the OMZ and/or slower regeneration of Fe in the low oxygen conditions. However, the exact mechanism behind this remains unclear.   The enhancement of dMn in the OMZ along Line-P is not as pronounced as in other locations, such as the tropical Pacific (18°N, 108°W) (Landing and Bruland, 1987) or the Black Sea (Tebo, 1991). We suspect two possible reasons for this difference. First, the minimum oxygen concentrations in this study area do not reach the suboxic level (defined as O2 < 4.5 µmol L-1 ) (Karstensen et al., 2008). In addition, there may be fewer sources of potentially reducible particles along Line-P, sinking down from the upper layers to the OMZ due to lack of significant dust input from the continents or lateral input from the continental shelf (Lamborg et al., 2008). The distribution and mean dMn shows annual variability at offshore stations. Although samples between 100 – 1000 m were not successfully collected from P20 in 2013, dMn at the offshore stations in 2013 do have higher concentrations than in 2011 or 2012.    47 2.4.6 Enhancement of dTM by eddies in 2010 and 2013 Mesoscale anticyclonic eddies formed at the eastern part of the GoA have been shown to impact the distribution of dissolved trace metals in this region (Crawford and Whitney, 1999). These eddies bring coastal waters, which are often high in dTM from the continental shelf, rivers, and possibly upwelled coastal water, out to the open ocean (Nishioka et al., 2001). For dMn and dFe in particular, the core of these eddies generally contain enhanced concentrations relative to the edge of the eddies (Brown et al., 2012). Haida Eddies have a low density core water and are spawned near Haida Gwaii (formerly known as the Queen Charlotte Islands). A typical Haida eddy has a diameter of 150-300 km, a core depth of 500-600 m at the center, and transports  3000 – 6000 km3 of coastal seawater towards the open ocean and can travel south to the Line-P area (Crawford and Whitney, 1999; Crispo, 2007).     These mesoscale eddies in GoA are downwelling, warm core eddies (i.e. Ekman transport pushes warm coastal water to the core), which results in an elevation of sea surface. Indeed, satellite images of sea surface height can trace the eddy formation and its movement (Crawford, 2005). According to the sea surface altimetry plots extracted from the Colorado Center for Astrodynamics Research (http://ccar.colorado.edu/colors/index.html), two eddy events were observed during the 4 sampling expeditions along line P, 2010-2013.   In 2010, a Haida eddy generated at the southern tip of the Queen Charlotte Island intersected the Line-P transect near station P12 during the sampling period (Cain, 2014). In this year, the concentration of dMn at the surface at P12 (4.8 – 5.0 nmol kg-1) is 2.5 times greater than non-eddy years (0.5 – 2.0 nmol kg-1) (Figure 2.18, a)).  The Haida eddy in 2010 was 3.5 months old when it reached P12. The dMn profile we report suggests that its core still had high dMn originating from the continental region. A previous study of dTM in Haida eddies showed that surface dMn was 1.3 times higher than in surrounding waters, which is likely caused by high dMn transported from the coastal area (Crispo, 2007). This observation agrees with previously reported dissolved aluminum and gallium, which have similar eolian and riverine sources and sinks (i.e. particle scavenging) as Mn (Cain, 2014; McAlister, 2015).  48 2013 - P16dMn (nmol kg-1)0 1 2Depth (m)05010015020025030020102011201220132010 - P12dMn (nmol kg-1)0 1 2 3 4 5Depth (m)0501001502002503002011201220132010b)dFe (nmol kg-1)0.2 0.4 0.6 0.8a)dFe (nmol kg-1)0.2 0.4 0.6 0.8 Figure 2.18 Vertical profiles of dMn and dFe a) at P12 and b) at P16 for upper 300m. The years influenced by mesoscale eddies are highlighted in color (2010 in red, 2013 in green).   The dFe, on the other hand, shows low concentration in the surface (to 25m) and higher levels than usual between 25m and 100m. Coastally derived dFe would likely be consumed rapidly in the surface layer due to biological activity during its seawards passage of the eddy. The chlorophyll concentration at the surface in 2010 (0.46 – 0.58 µM) is ~2.9 times greater than non-eddy years (0.15 – 0.20 µM), suggesting that the delivery of high dFe by eddies could have reinforced the biological activity. In addition to the biological removal, Crispo (2007) also suggests that oxidation of Fe and/or particle scavenging can export dFe below the upper halocline. Hence, we interpret increased dFe from 25 to 50 m as an effect of decreasing dFe drawdown by phytoplankton causing the concentration maximum at 50m, rather than mixing of high dFe at 50m.    In 2013, P16 is influenced by an eddy generated at the northern tip of Vancouver Island. It was formed in mid-January, reached to the Line-P transect, and dissipated at P16 a week before the sampling (i.e. elevated Sea Surface Height (SSH) was no longer detectable at the time of sampling). Interestingly enough, we observed no significant variations in dFe vertical distribution caused by the presence of the eddy (Figure 2.18, b)). Its concentration is depleted at the surface (0.1 nmol kg-1) and gradually increased with depth down to 300 m. We suspect that phytoplankton uptake after eddy dissipation depleted dFe at upper 40m. Dissolved Mn at P16 in 2013 also shows 49 a similar vertical distribution to the non-eddy years, except that it displays an elevated concentration (2.0 nmol kg-1) at 10 m. We suggest that the surface enrichment is caused by photo-reduction of particulate Mn (pMn) brought by the eddy. The concentration of particulate Al is observed to be ~3 times greater at P16 than at the non-eddy stations (Chapter 3), which suggests that the eddy in 2013 transported high lithogenic pTM to the open ocean. However, pMn which shares similar source to pAl, showed no considerable elevation at P16. Hence, we propose that elevated surface dMn is a result of photo-reduction of pMn which may have been occurring during the eddy transport and/or persisted even after the eddy dissipation.    2.5 Conclusion  This work presents multi-year distributions of dissolved Mn and Fe across the Line-P transect located in the northeast Pacific. We assessed spatial and temporal variability of dTM in the context of regional oceanographic features found in this study area. In most cases, both dissolved Mn and Fe demonstrated clear separation in vertical and horizontal trends at onshore (P4, P12) versus offshore stations (P16, P20, P26). In the SML, enhanced and annually variable dMn was found at the onshore stations. We found that background dMn is likely sustained by riverine water, flux from the coastal sediments, and photo-reduction, whereas the annual variability of dMn is correlated to the strength of Ekman transport, which affects the amount of coastal water reaching these stations. At the offshore stations, photo-reduction and eolian inputs are significant sources for both dMn and dFe. Although the primary maximum of dMn is found within the SML at the onshore stations, offshore stations show dMn maxima within the Winter Mixing Layer (WML) where the oxygen concentration is the highest. These subsurface dMn enhancements are suggested to be remnants of the high dMn generated during the previous winter with biological drawdown of dMn in the SML, rather than the reduction of dMn in the WML during the summer season. Although evidence for significant dMn and dFe enhancement by the CUC at ~175 m at station P4 was not observed, NPIW and the continental slope are found to be important sources for dMn. A simple advection/diffusion model result and zonal distribution of dMn indicate that dMn found at OSP can be advected as far as P12 along the core NPIW isopycnal (26.8 kg m-3). Likewise, mixing of remobilized dMn from the continental slope is found to be a significant source for onshore 50 stations. In some years, low dMn waters from the south appears to have been advected into this region lowering dMn in the center of the Line-P region. Within the Oxygen Minimum Zone (OMZ), both dMn and dFe show increasing concentrations with depth at the onshore stations, with their maxima in the bottom samples. Highly negative N* values at onshore stations suggests remobilization of dMn from the continental slope as Mn reduction likely occurs when denitrification is enhanced. At the offshore stations, the secondary maxima of dMn are found at the top of the OMZ (where O2 starts to drop below 100 µmol kg-1), just below the NPIW, possibly because of slow oxidation of Mn within the OMZ and introduction of potentially reducible Mn-oxides brought with the NPIW. Dissolved Fe, on the other hand, show its maxima near or below 1000 m due to remineralization. Lastly, the influence of eddies found in 2010 and 2013 is also examined. In 2010, when seawater samples were collected in the presence of the eddy, dMn showed elevated concentrations in the SML due to high dTM delivery by the eddy. Dissolved Fe also showed enhanced concentrations within the SML in general. Within the upper 40 m, where fluorescence maximum was observed, was depleted with dFe due to phytoplankton uptake. In 2013, when seawater samples were collected a week after the eddy had dissipated, as observed by sea surface satellite altimetry, no significant elevation of dFe was observed. Dissolved Mn, however, showed ~ 50% higher surface concentration relative to the non-eddy years, possibly due to the introduction of reducible pMn by the eddy and subsequent photo-reduction.   51 Chapter 3: Distribution and Composition of Suspended Particulate Iron and Manganese in Northeast Pacific  3.1 Summary The distribution of particulate Fe (pFe) and Mn (pMn) collected across Line-P in the northeast Pacific is examined to evaluate their role in dissolved metal cycling. A total of 76 membrane filter samples were collected in two different size fractions (0.45-20 µm and > 20 µm) in the summer of 2013. Using particulate phosphorus (pP) and Al (pAl) as biogenic and lithogenic indexes, we estimated the biogenic, lithogenic, and authigenic contributions to pFe and pMn. In the Summer Mixing Layer (SML), pFe is primarily associated with biogenic particles in the smaller size category, thus pFe acts as a sink for dissolved Fe (dFe) since dFe is taken up by small phytoplankton. At the onshore stations, a significant lithogenic contribution was also observed for pFe, which is likely delivered by rivers and coastal sediments via strong Ekman transport in this sampling year. Although no significant elevation of total pFe was observed at P16, there was evidence of lithogenic particles transported within a mesoscale eddy. Below the SML, pFe increases with depth to the deepest samples collected, and the increase is greatest at station P4, due to re-suspended sediments from the continental margin. In contrast, pMn in the SML is observed to be a source for dissolved Mn (dMn). Although the oxidation rate of Mn(II) is the greatest at the surface, the photo-reduction of Mn-oxides, delivered to the surface by rivers and eolian dust, enhances dMn in the SML. Indeed, pMn in this layer has a low lithogenic content as these particles are readily reduced to Mn(II) (dMn). However, the eddy transecting the Line-P enhanced the lithogenic component of pMn at station P16, which was transported from the coastal area of the Vancouver Island. In the Winter Mixing Layer (WML), we found high authigenic pMn across the transect, driven by the oxidation of dMn which prevails in the absence of UV radiation. Within the Oxygen Minimum Zone (OMZ: O2 < 100µmol kg-1), the level of total pMn was low due to enhanced reduction, which then added dMn into the water. In general, an inverse relationship was observed between pMn and dMn within this layer.    52 3.2 Introduction Marine particles play an essential role in trace metal cycling in the ocean, as they can act as sources (i.e. regeneration, dissolution, abiotic reduction) or as sinks (i.e. adsorption and scavenging, biological uptake) for dissolved metals. Particles in the ocean exist in a variety of sizes and concentrations and are typically separated from the dissolved metals with 0.2 µm or 0.45 µm pore size filters (Bruland and Lohan, 1983). Large size particles (hundreds of microns to centimeter scales) are influenced by gravity and sink through the water column (Stemmann et al., 2004), whereas smaller particles (usually under 100 microns) are suspended within the water column and can go through several aggregation and/or disaggregation cycles. The concentration of particulate elements in the oceans depends on their production or destruction in the water column and on their external sources. For example, elevated particle concentrations in the surface mixing layer could be from biological production, associated with high phytoplankton biomass, or delivery of terrigenous materials from the continent (e.g. aeolian dust input or weathered minerals from rivers). Additionally, particles can be formed or destroyed under specific physical/chemical conditions in the water column (e.g. level of dissolved oxygen or availability of UV radiation).   In general, marine particles can be grouped into three components based on their origins and cycling in the ocean (Ohnemus and Lam, 2015). First, particles with terrigenous sources such as windblown dust, weathered minerals from rivers, or re-suspended particles from nepheloid zones and continental margins are called lithogenic (Poulton and Canfield, 2005). Particulate aluminum (pAl) is often used as a tracer for lithogenic sources (Ohnemus and Lam, 2015) as it is highly abundant in terrigenous materials (>8%) (Wedepohl, 1995), and does not have a significant biological role. Second, biogenic particles are those associated with dead or living organisms. Particulate phosphorus (pP) is a tracer of biogenic particles in seawater as phosphorus is an essential macronutrient for primary producers (Ho et al., 2007).  The last component is authigenic, the term for particles generated by internal cycling (Field and Sherrell, 2000b). For example, precipitation of oxides and hydroxides of redox sensitive metals, such as Mn and Fe, can occur under high oxygen conditions and at redox boundaries (Feely et al., 1996; Mandernack and Tebo, 1993). 53 In this study, two size fractions of particles (Small Suspended Particles, SSP: 0.45-20 µm and Large Suspended Particles, LSM; > 20 µm) were collected across 5 major stations along Line-P. We processed a total of 76 filter samples to evaluate the spatial distribution of particulate iron (pFe) and manganese (pMn). This chapter aims to assess the role of particulate matter in trace metal cycling along Line-P. To achieve this goal, we identified the major components of pFe and pMn found in the Summer Mixing Layer (SML), the Winter Mixing Layer (WML), and in the Oxygen Minimum Zone (OMZ) across the transect, using pAl and pP as lithogenic and biogenic tracers, respectively. We also use pCd and the pCd/pP ratio to investigate differential remineralization patterns. This information, combined with information on the different sizes of the pTM, was used to evaluate how the dissolved metals are influenced by particles.   3.3 Method  3.3.1 Sample Collection Particulate trace metal samples were collected at five major stations along Line-P from August 20th to September 6th in 2013. A trace metal rosette, mounted with 12 (12 L) Go-Flo bottles (General Oceanics, FL, USA) and a CTD (Seabird) attached to a Kevlar line, was deployed at the major stations to collect seawater samples in the upper 2000 m. The detailed description of the study area, as well as the seawater collection procedures, are outlined in the previous chapter (Chapter 2).   To collect pTM samples, unfiltered seawater samples (6 – 7 L) were drawn from each Go-Flo bottle into a pre-cleaned 10 L Cubitainer® with a quick serve tap (Qorpak®). The tap was then connected to two filter holders (Millipore™) in series using C-Flex tubing, so that the seawater samples could be filtered through 47-mm membrane disc filters with two different pore sizes and substrates. Polycarbonate filters with 20 µm pose size (WhatmanTM) were used to collect Large Suspended Particles (LSP). Since the flow rate of polycarbonate filters with a pore size of 0.45 µm is extremely slow, Supor® polyethersulfone filters (Cole-Palmer©) were used to collect the Small Suspended Particles (i.e. sizes greater than 0.45 µm and smaller than 20 µm). In order to speed up the flow, a peristaltic pump (Cole-Palmer®) was used on the C-Flex tubing connecting the 54 Cubitainer to the filter holders. The waste water was collected at the end to determine the volume filtered. After filtration, filters were removed in a class 100 laminar flow bench, folded twice, and stored in pre-cleaned HDPE vials at -20 °C until analysis. All sampling containers, filtration apparatus, and membrane filters were acid-cleaned according to previous studies (Cullen and Sherrell, 1999; Ohnemus et al., 2014) and GEOTRACES protocol (Cutter et al., 2017).    3.3.2 Analytical Method A total of 76 filter samples were digested using the Piranha method as described by Ohnemus et al. (2014) with minor modifications. All analysis was done in class 100 laminar flow hoods in a clean laboratory at UBC with Optima grade reagents (Fisher Scientific). First, the filter sample was placed into pre-cleaned digestion vial (15 ml Teflon vial; Savillex) and left uncovered overnight at room temperature in a TM clean hood to ensure the drying of excess moisture. Then, a 3:1 mixture (2 ml, v/v) of concentrated sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) was added to the digestion vial and heated to 110 °C for 1 hour. The purpose of this step was to digest the filter itself, as well as to dissolve organic matter on the filter. In order to completely digest the sample, it was necessary to add additional H2O2 (4 × 0.4 ml) every hour. The sample was then dried at 245 °C until it turned into a dark brown deposit. During the course of drying, inner walls of the digestion vials were rinsed with 1.0 ml 8M HNO3 (5 × 200 µl). After complete dryness,  4 ml of an acid mixture (4M in HCl, HNO3- and HF) was added and refluxed at 110 °C for 4 hours, to assure full dissolution of any solids remaining in the sample solution. After refluxing, the sample was dried at 110 °C until a small pellet was obtained. A mixture of HNO3 and H2O2 (1 ml : 1 ml) was added, refluxed, and dried down. The final product, a small white pellet (~0.015 g), was then dissolved into 1.0 ml of 1% HNO3 , spiked with 10ppb indium (In), for the measurement with  HR-ICPMS (ELEMENT2, Thermo ScientificTM).     55 3.3.3 Instrumental analysis and Assessment  A total of 13 elements were measured for both small suspended particulate (SSP; 0.45-20 µm) and large suspended particulate (LSP; >20 µm) samples. Blank filters (n=3) of each filter type were processed with the same analytical method. The list of elements and their concentrations are available in Appendix B (Table B.1 – B.3). To validate the analytical method, two different sets of samples were used – certified reference material BCR-414 (Bowie et al., 2010) and GEOTRACES inter-comparison samples collected from the Pacific Ocean (Lam, personal communication). Triplicates of flow-through blank filters (GT4422SB), particulate samples collected at 45 m at the SAFe station (GT4422ST), and at  130 m in the Santa Barbara Basin (GT4965ST) went through the same analytical method as described above. At least 10 labs participated in the GEOTRACES inter-calibration program with various digestion and measurement methods. The reported mean, median, and relative standard deviation values are listed in Table 3.1. The measured values are in good agreement with the consensus values. The data set was successfully submitted to the GEOTRACES intercalibration program (GEOTRACES, 2016) 56 Table 3.1 Laboratory inter-comparison and certified reference material results obtained using the Piranha method Al Fe Mn Cu Zn Pb Ba V P Cd Co Sr NiInstrument Blank (nmol kg -1 ) measured mean (n=17) 6.6E+00 2.8E+00 4.0E-02 2.3E-02 4.1E-01 3.9E-04 1.6E-01 2.1E-02 2.2E+00 1.4E-03 1.4E-02 1.7E+00 1.0E-02standard deviation 2.7E-01 1.3E-02 5.6E-03 5.9E-04 3.5E-03 9.6E-05 1.9E-03 1.4E-03 2.3E-01 2.4E-04 4.3E-04 8.7E-03 1.9E-02RSD (%) 4.1 0.5 13.9 2.6 0.9 24.8 1.2 6.5 10.5 17.7 3.1 0.5 184.1instrument detection limit 0.822 0.040 0.017 0.002 0.011 0.0003 0.006 0.004 0.688 0.001 0.001 0.026 0.056Filter blank (GT4422 SB) (pmol sample -1 )consensus mean (n ≥ 10) 1.3E+03 6.3E+02 2.7E+01 2.4E+02 1.3E+02 3.8E+00 2.7E+01 8.7E+00 1.5E+04 2.0E+00 2.5E+00 4.3E+03 -consensus median 3.3E+02 2.9E+02 1.6E+01 1.5E+02 3.4E+01 2.0E+00 2.1E+01 7.7E+00 1.4E+04 1.0E+00 1.5E+00 4.1E+03 -RSD (%) 273 186 161 171 720 134 95 54 26 152 81 24 -measured mean (n=3) 1.5E+03 4.2E+02 1.9E+01 1.6E+02 2.1E+02 7.3E-01 1.9E+01 7.3E+00 2.0E+04 6.7E-01 1.3E+00 4.1E+03 2.6E+01standard deviation 9.0E+02 2.5E+02 2.9E+00 1.5E+01 2.3E+02 9.5E-02 6.4E+00 6.6E-01 7.1E+02 7.0E-02 1.0E-01 4.3E+02 4.3E+00RSD (%) 902 252 3 15 232 0 6 1 715 0 0 427 4Oligotrophic region (GT4422 ST) (pmol sample -1 )consensus mean (n ≥ 10) 1.1E+04 4.0E+03 1.2E+02 5.2E+02 7.3E+02 1.5E+01 2.1E+02 4.1E+01 7.7E+04 8.6E+00 1.3E+01 5.8E+03 -consensus median 1.0E+04 3.5E+03 9.4E+01 3.6E+02 1.7E+02 1.3E+01 2.1E+02 4.1E+01 7.6E+04 6.8E+00 1.2E+01 5.8E+03 -RSD (%) 31 66 84 108 210 65 23 16 16 76 33 14 -measured mean (n=3) 1.1E+04 3.9E+03 9.1E+01 2.2E+02 - 7.1E+00 1.6E+02 4.2E+01 8.1E+04 4.4E+00 1.2E+01 3.3E+03 -standard deviation 1.4E+03 1.1E+03 8.3E+00 7.6E+00 - 8.2E-01 5.8E+00 2.9E+00 3.7E+03 4.4E-01 1.1E+00 3.5E+02 -RSD (%) 13 29 9 3 - 12 4 7 5 10 9 11 -Santa Barbara Basin (GT4965 ST) (pmol sample -1 )consensus mean (n ≥ 10) 9.2E+05 3.0E+05 2.7E+03 7.4E+02 2.1E+03 7.0E+01 5.3E+03 1.3E+03 1.2E+05 8.6E+01 7.5E+01 1.1E+04 -consensus median 9.4E+05 3.2E+05 2.7E+03 5.7E+02 1.4E+03 6.7E+01 5.6E+03 1.2E+03 1.2E+05 8.5E+01 7.7E+01 1.1E+04 -RSD (%) 18 18 17 106 103 41 23 17 17 15 15 10 -measured mean (n=3) 9.4E+05 3.3E+05 2.9E+03 4.1E+02 2.2E+03 5.5E+01 4.4E+03 1.3E+03 1.1E+05 8.2E+01 6.7E+01 7.5E+03 6.8E+02standard deviation 2.4E+04 9.9E+03 9.5E+01 4.7E+01 7.2E+02 1.7E+01 5.8E+02 3.7E+01 1.4E+03 4.7E+00 7.3E+00 3.9E+02 2.4E+01RSD (%) 3 3 3 11 33 30 13 3 1 6 11 5 4Certified Reference Material: BCR-414  (µg g -1 )consensus mean 2.2E+03 1.9E+03 3.0E+02 3.0E+01 1.1E+02 4.0E+00 3.0E+01 8.1E+00 1.3E+04 3.8E-01 1.4E+00 2.6E+02 1.9E+01standard deviation 8.0E+02 1.9E+02 1.3E+01 1.3E+00 2.5E+00 1.9E-01 4.8E+00 1.8E-01 5.0E+03 1.4E-02 6.0E-02 2.5E+01 8.0E-01RSD (%) 37 10 4 4 2 5 16 2 39 4 4 10 4measured mean (n=4) 3.0E+03 2.0E+03 2.9E+02 3.0E+01 9.1E+01 2.5E+00 2.6E+01 1.0E+01 1.5E+04 3.7E-01 1.2E+00 1.9E+02 2.1E+01standard deviation 8.3E+02 3.3E+02 4.2E+01 4.6E+00 2.5E+01 3.6E-01 4.1E+00 1.5E+00 2.8E+03 4.4E-02 8.2E-01 4.0E+01 2.8E+00RSD (%) 28 17 14 15 27 14 16 14 18 12 70 21 13recovery (%) 138 106 97 103 81 63 89 129 119 96 82 73 113  57 3.4 Results and discussion  3.4.1 Definition of the particles and depth ranges  In this work, we define Small Suspended Particles (SSP) as the particles with sizes between 0.45 and 20 µm and Large Suspended Particles (LSP) as the particles with sizes larger than 20 µm. The Total Suspended Particles (TSP) is the sum of the SSP and the LSP (TSP = SSP + LSP). As described in Chapter 2, the upper 2000 m of the Line-P area contains a Summer Mixing Layer (SML: 0 – 35 m), a Winter Mixing Layer (WML: 35 –150 m), and an Oxygen Minimum Zone (OMZ: 150 – 2000 m). Of the 13 elements measured in the suspended particles, this work will primarily focus on particulate pFe and pMn. In each layer, we aim to identify the major components of pFe and pMn (i.e. lithogenic, biogenic, and authigenic), using pP and pAl as tracers for biogenic and terrigenous sources, respectively, and to investigate the influence of particles on the distribution of the dissolved metals. We also use pCd and the pCd/pP ratio to investigate differential remineralization patterns.   3.4.2 Overview: Distribution of particulate elements along Line-P  To compare the vertical and horizontal distributions of all five elements (Al, P, Cd, Fe, Mn), cross section plots for each element, in the two different size fractions (SSP and LSP), are presented in Figure 3.1. In general, the range of SSP is 2-8 times greater than that of LSP for all five elements. The smaller size particles are the dominant fraction for both biogenic (pP) and lithogenic (pAl) particles in this study area. The range of P in SSP (1.6 - 57.8 nmol kg-1) is 8 times greater than in LSP (0.2 - 7.7 nmol kg-1). Similarly, Al in SSP (0.3-16 nmol kg-1) is 6 times greater than in LSP  (0.1-2.6 nmol kg-1). In addition, Al and Fe in both SSP and LSP show similar vertical and horizontal distributions across Line-P. Their lowest concentrations are observed in the SML and in offshore OMZ regions. They are enhanced near the continental margin and gradually decrease towards the open ocean, in both size classes. A similar pattern is seen for pMn at the onshore stations (P4 and P12), with some variations observed at mid-depth (500 – 1500m).    58   Figure 3.1 Cross section contour plots of a) SSP and b) LSP for pCd, pP, pAl, pFe, and pMn across the Line-P transect. Units are in nmol kg-1 for all. Note that the depth scale is non-linear to better view the surface distribution of each element. Note the samples between 15 and 1200 m are absent at P20 due to difficulties in TMR operation. Black dots indicate the sample location.    59 Particulate cadmium (pCd) and pP show similar vertical and horizontal distributions across the transect (Figure 3.1). Similar to phosphorous, Cd is known to be an essential nutrient for primary producers, especially for diatoms, utilized as a cofactor of carbonic anhydrase in the carbon concentrating mechanism (Alterio et al., 2015). Dissolved Cd shows nutrient type profiles in the ocean, depleted at the surface, reaching maximum concentration at ~ 1000 m, and gradual decreasing concentrations below ~1000 m (Bruland, 1980; Bruland et al., 1994). The particulate Cd, however, typically shows a maximum close to the surface and gradual decreasing concentration with depth (Bruland et al., 1994; Harris and Fabris, 1979). In this study area, both elements are enriched in the SSP in the upper waters (pCd: 0 – 500 m and pP: 0 – 200m). The high concentration of both pCd and pP in the upper 100 m is due to biogenic particles at the chlorophyll maximum (Figure 3.2, b)), and the decrease in both elements below this is due to remineralization. In contrast, pCd and pP in the LSP display uniformly low surface concentrations, with a noticeable enrichment at station P16 (Figure 3.1). This localized enhancement may be from the eddy observed in this region (Section 2.4.6), which is expected to have transported large quantities of particles to this area (Brown et al., 2012). However, this enhancement is not observed for pCd and pP in the SSP. We suspect that the higher abundance of biogenic particles masked the eddy signature for both pP and pCd in the SSP.    In seawater, a linear relationship is found between dCd and dP, typically with two distinct slopes, one in the surface layer and another below the nutricline (Cullen, 2006). This change in slope is thought to be the result of preferential uptake of Cd by the primary producers in Fe limited environments (Cullen, 2006) and/or deeper regeneration of Cd compared to P (Frew and Hunter, 1992). In agreement with these previous studies, we also observed a sharp increase in pCd:pP in the upper 100 m (Figure 3.2, d)) in this region, which may suggest that P is preferentially remineralized in the upper nutricline, below the fluorescence maximum (Figure 3.2, a), b)). Additionally, a decrease of pCd:pP between 100 and 1000 m suggests that remineralization of Cd occurs deeper than phosphorous regeneration. However, we did not observe greater pCd:pP ratios in the HNLC (e.g. OSP; Fe-limited area) relative to in the non-HNLC (e.g. P4; non-Fe-limited area) stations (Figure 3.2, d)), likely due to low sampling resolution. Although the exact mechanism behind the relationship between pCd and pP remineralization remains unclear, it is still worth noting that we not only found a preferential removal of pP over pCd within the upper 60 nutricline across the Line-P transect, but also observed that most remineralization occurs in upper 1000 m of this study area.    Figure 3.2 The cross section contour plot of a) nitrate + nitrite, b) Fluorescence, and c) pCd/pP of the TSP. The vertical profiles of pCd:pP are also shown on d). Note the different depth scales for a) and b) versus c) and d).    3.4.3 Particulate versus dissolved Mn and Fe across Line-P Total suspended particulate metals (pTMTSP) and dissolved metals (dTM) are plotted together to contrast the vertical distributions of these two phases across the transect (Figure 3.3, a), b)). Similar to dTM distribution as described in chapter 2, pTMTSP also shows geographical heterogeneity between onshore versus offshore stations, as well as variations in vertical distributions within the SML, WML, and OMZ. In the SML, pFeTSP concentrations (0.1 – 0.6 nmol kg-1), are greater than dFe (0.08 – 0.3 nmol kg-1) likely due to biological uptake (Figure 3.3, a)) (Section 3.4.4.1). 61 Particulate Mn, on the other hand, shows a concentration range (0.03 – 0.1 nmol kg-1), which is 30 to 100 times lower than dMn (0.9 – 11 nmol kg-1) (Figure 3.3, b)). The highest concentration of pMnTSP is observed at station P4, closest to the coast. Although we observed an eddy near station P16 (Section 2.4.6) during the sampling period, no significant enhancement of either pFeTSP or pMnTSP was identified within the SML at this station.   P26dFe, pFeTSP (nmol kg-1)0 1 2Depth (m)10251001505001000200025050P160 1 2P120 1 2dFepFeTSPP40 1 2 3 4P26dMn (nmol kg-1)0 1 2 3Depth (m)10251001505001000200025050pMnTSP (nmol kg-1)0.0 0.1 0.2 0.3P160 1 2 30.0 0.1 0.2 0.3P120 1 2 30.0 0.1 0.2 0.3P40 2 4 6 8 10 12 140.0 0.1 0.2 0.3 0.4dMnpMnTSPb)a) Figure 3.3 Vertical distribution of dissolved and total suspended particulate a) Fe and b) Mn. Dotted lines at 35 m and 150 m indicate the boundaries between SML and WML and between WML and OMZ, respectively. The CUC is found at ~175 m at P4. The NPIW is found at ~200 m from P26 to P12. Maxima of dMn and pMn within the WML are marked in red (b). Note the different concentration scale for pMn compared to dMn. The data from P20 are not reported due to the sample loss during the TMR operation.  62 In the WML (35 – 150 m), where the oxygen concentration is the highest (Figure 2.5), we observed an increasing concentration of pFeTSP with depth at station P4 (0.3 to 2.0 nmol kg-1), and a relatively uniform vertical distribution at P12 and P16 (~0.4 nmol kg-1) (Figure 3.3, a)). This variation is not observed in dFe, which shows gradually increasing concentrations with depth across the transect. Dissolved Mn and pMnTSP also display distinctive horizontal distributions across the transect (Figure 3.3, b)). In particular, dMn in the WML decreases with the depth at the onshore stations and is enhanced at the offshore stations due to the remnant of dMn from the previous winter and biological uptake in the SML (Section 2.4.3.2). In contrast, pMnTSP shows the highest concentrations within this layer across the transect, which is likely related to the internal cycling of Mn in the high oxygen condition (Figure 2.5).   Below 150 m, the oxygen concentration decreases rapidly and becomes lower than 100 µM (OMZ) at ~200 m (Figure 2.4). This low O2 persists to the deepest depth sampled (2000 m) at all stations. Within this layer, pMnTSP is the lowest where dMn is elevated, typically at ~ 500 m (Figure 3.3, b)). For example, dMn reaches its maximum (1.3 nmol kg-1) when pMnTSP is the lowest  (0.03 nmol kg-1) at 500 m at station P16, which is likely due to in-situ reduction under low oxygen conditions (Section 3.4.4.3). In contrast, both dissolved and particulate Fe increase with depth down to 1000 m at all stations (Figure 3.3, a)). Below 1000 m, the onshore stations show greater enhancement (1.7 – 3.5 nmol kg-1) relative to offshore stations (~ 0.7 nmol kg-1).    3.4.4 Composition of pTM and its role in determining dTM distributions To evaluate the role of suspended particles as sources and sinks for dTM in each hydrographic layer along Line-P, we 1) estimate the concentration of each component (i.e. lithogenic, biogenic, authigenic) and 2) assess the relative composition of each component in total suspended particles. First, the pMn and pFe concentration of each component is calculated based on the measured pMn, pFe, pP, and pAl values (Figure 3.4). Assuming that the measured pMn concentration is the sum of three components, lithogenic pMn (pMnlitho) and biogenic pMn (pMnbio) are estimated according to pP×(Mn:P)redfield ratio and pAl×(Mn:Al)crustal ratio, respectively. The last component, authigenic pMn (pMnauthi), is then calculated by subtracting the sum of pMnlitho and pMnbio from the measured pMn concentration. 63 (pMn:pP)SSP0.00 0.05 0.10(pMn:pAl)SSP0.0 0.1 0.2(pMn:pP)LSP0.00 0.05 0.10P4P12P16P26(pMn:pP)TSP0.00 0.05 0.10Depth (m)10501001502505001000200025Mn:P Redfield ratio(pMn:pAl)TSP0.0 0.1 0.2Depth (m)10501001502505001000200025Mn:Al crustal ratio(pMn:pAl)LSP0.0 0.1 0.2c)b)P4pMnTSP (nmol kg-1)0.0 0.1 0.2 0.3 0.4 0.53510255075100150300400100015002000600200AuthigenicLithogenicBiogenicP12pMnTSP (nmol kg-1)0.0 0.1 0.2 0.3 0.53510255075100150300400100015002000600200P16pMnTSP (nmol kg-1)0.0 0.1 0.2 0.3 0.53510255075100150300400100015002000600200P26pMnTSP (nmol kg-1)0.0 0.1 0.2 0.3 0.5Depth (m)3510255075100150300400100015002000600200a)Figure 3.4 a) Vertical profiles of total suspended pMn across the Line-P. Colored area represents the contribution of each component. b) Vertical profiles of pMn to pAl ratio for total suspended particles (TSP), small suspended particles (SSP), and large suspended particles (LSP). Vertical dashed lines are crustal abundance of Mn to Al (0.0033:1) (Shaw et al., 1967). c) The vertical profiles of pMn to pP ratio for TSP, SSP, and LSP. Vertical dashed lines denote the extended Refield ratio between Mn and P (0.0004:1) (Martin et al., 1976; Martin and Knauer, 1973).  We used previously reported values of (Mn:P)Redfiled ratio and (Mn:Al)crustal ratio, which best represent the environmental conditions of Line-P region. For (Mn:P)Redfiled ratio, the mean of two values reported by Martin and Knauer (1973) and Martin et al. (1976) is used (1: 3.85 × 10-4) (Table 3.2), which are the ratios of Mn to P found in phytoplankton collected from the oligotrophic north Pacific. For (Mn:Al)crustal ratio, the value reported by Shaw et al. (1967) is used (1: 3.3 × 10-3), which represents the Canadian surface Precambrian shield composition and agrees well with the composition of the upper continental crust (Table 3.3). The vertical profiles of total suspended pMn with its calculated sub-components shaded in different colors are shown in Figure 3.4, a). In general, biogenic particles are significant in the upper layer across the transect, whereas lithogenic particles are elevated at onshore stations (P4 and P12) near external sources (i.e. continental 64 margin). Additionally, pMnauthi displays elevated concentration within the WML (Section 3.4.4.2) and decreasing concentrations with depth in the OMZ, except in the deepest waters at P12 (Section 3.4.4.3).   Table 3.2 Trace metal to P ratios in marine phytoplankton. Studies Redfield Ratio      Mn:P Fe:P      Martin and Knauer (1973) 3.9E-04 5.2E-03 oligotrophic North Pacific, open ocean Martin et al. (1976) 3.8E-04 5.0E-03 oligotrophic North Pacific, open ocean Collier and Edmond (1984) 3.4E-04 4.6E-03 oligotrophic North Pacific  Ho et al. (2003) 3.8E-03 7.5E-03 nutrient replete laboratory culture (Collier and Edmond, 1984; Ho et al., 2003; Martin et al., 1976; Martin and Knauer, 1973)  Table 3.3 Trace metal to Al ratios in the earth crust. Values in bold texts are used for this work.   Studies Crustal ratio  Average composition of  Mn:Al Fe:Al P:Al Yaroshevsky (2006) 6.1E-03 2.8E-01 1.0E-02 continental crust 6.0E-03 3.4E-01 8.4E-03 oceanic crust Taylor (1964) 5.7E-03 3.3E-01 1.1E-02 continental crust Taylor and McLennan (1995) 3.7E-03 2.1E-01 7.6E-03 upper continental crust Wedepohl (1995) 3.3E-03 1.9E-01 7.5E-03 upper continental crust Shaw et al. (1967) 3.3E-03 1.9E-01 - continental surface Precambrian shield in Canada (Taylor, 1964; Taylor and McLennan, 1995; Wedepohl, 1995; Yaroshevsky, 2006)  Second, to identify the dominant component and particle sizes of pMn within each layer, we compared the (pMn:pAl)measured to the crustal abundance and the (pMn:pP)measured to the extended Redfield ratio for total, small, and large suspended particles (Figure 3.4, b)). When the particles are dominated by terrigenous sources, the calculated ratios should be close to the crustal ratio between Mn and Al ((Mn:Al)crustal ratio = 0.0033:1) (Shaw et al., 1967).  Similarly, the contribution of biogenic particles is examined using the ratio between pMn and pP (Figure 3.4, c)). When the pMn sample contains high biogenic particles, the (pMn:pP)measured will follow the extended Redfield ratio ((Mn:P)Redfield ratio = 0.0004:1) (Martin and Knauer, 1973). We observe that the vertical trends in TSP generally follow that of SSP, as the concentration of SSP is ~ 10 times greater than that of LSP.  65 With the same procedure as applied to pMn, each component of pFe is calculated according to the equation: Measured pFe = pP×(Fe:P)redfield ratio + pAl×(Fe:Al)crustal ratio + pFeauthi (Figure 3.5, a). The calculated results indicate that majority of pFe is the lithogenic particles. In particular, station P4 (i.e. closest to the continental margin) shows the greatest pFelitho concentration at all depths. Additionally, the characteristics of pFe particles in the different size fractions are also determined based on the difference between (pFe:pAl)measured and (Fe:Al)crustal ratio (= 0.19:1;(Shaw et al., 1967) and between (pFe:pP)measured and (Fe:P)Redfield ratio (= 0.005:1;(Martin and Knauer, 1973) (Figure 3.5, b), c)).  a)P12pFeTSP (nmol kg-1)0 1 2 43510255075100150300400100015002000600200P16pFeTSP (nmol kg-1)0 1 2 43510255075100150300400100015002000600200P26pFeTSP (nmol kg-1)0 1 2 4Depth (m)3510255075100150300400100015002000600200P4pFeTSP (nmol kg-1)0 1 2 3 43510255075100150300400100015002000600200AuthigenicLithogenicBiogenic(pFe:pP)SSP0.0 0.5(pFe:pAl)SSP0.0 0.5 1.0(pFe:pP)LSP0.0 0.5 1.0(pFe:pAl)LSP0.0 0.5 1.0 1.5P4P12P16P26(pFe:pP)TSP0.0 0.5 1.0Depth (m)3510255075100150300400100015002000600200Fe:P Redfield ratio(pFe:pAl)TSP0.0 0.5 1.0 1.5Depth (m)3510255075100150300400100015002000600200Fe:Al  crustal ratiob) c)Figure 3.5 a) Vertical profiles of total suspended pFe across the Line-P. Colored area represents the contribution of each component. Dotted area indicates the overestimated lithogenic pFe (see text). b) Vertical profiles of pFe to pAl ratio for total suspended particles (TSP), small suspended particles (SSP), and large suspended particles (LSP). Vertical dashed lines are crustal abundance of Fe to Al (0.19:1) (Shaw et al., 1967). c) The vertical profiles of pFe to pP ratio for TSP, SSP, and LSP. Vertical dashed lines denote the plankton organic tissue composition ratio between Fe and P (0.005:1) (Martin et al., 1976; Martin and Knauer, 1973).  66 Unlike pMn, we found that the lithogenic component of Fe is overestimated (1.1 to 1.3 times) at some depths (Figure 3.5, a); dotted area). Particulate Fe and Al show a robust linear relationship across the Line-P (R2 = 0.9) (Figure 3.6, a)), suggesting that most of the pFe in seawater is lithogenic particles. However, the Fe to Al ratio of this region (0.16) is smaller than the reported crustal ratio of Fe:Al (0.19 to 0.34: Table 3.3). This discrepancy of Fe:Al ratios may then result in an overestimation of calculated lithogenic component. The overestimated pFelitho shows up as negative x-values on the pFe verus non-lithogenic pFe plot (Figure 3.6, b)). For example, the sample collected at 1600 m at P12 displays the most significant overestimation (Figure 3.6, b): closed dot), where the measured pFe:pAl is the lowest (i.e. 0.14) compared to the reported (pFe:pAl)crustal ratio (i.e. 0.19) (Figure 3.6, a)).   a)pAl (nmol kg-1)0 5 10 15 20pFe (nmol kg-1 )0.00.51.01.52.02.53.03.54.0P4P12y=0.14x+0.23 (R2=0.93)P16P26best-fit line of all stationsy=0.16x+0.25 (R2=0.88)non-lithogenic pFe (nmol kg-1)-1 0 1 2 3 4pFe (nmol kg-1 )01234P4P12P12, 1600 mP16P26y=xb) Figure 3.6 a) The relationship between pFe and pAl. b) Particulate Fe is plotted against their non-lithogenic components across the Line-P, where non-lithogenic pFe = pFe – pAl × (Fe:Al)crustal ratio. Lithogenic component is significant when the data points are more deviated from y=x line.   67 3.4.4.1 Particulate TM in the Summer Mixing Layer (upper 35 m)  In the upper 35 m, the observed (pFe:pP)TSP indicates that the majority of pFe is in biogenic particles, in agreement with the extended Redfield ratio (Figure 3.5, c)). The smaller size fraction, (pFe:pP)SSP, exhibits stronger biogenic characteristics than the larger particles. Indeed, we conclude that pFe in the surface layer is dominated by biological particles with sizes smaller than 20 microns. This observation agrees with a previous study, which reported that 80 % of phytoplankton are smaller than 20 micron during the summer season in this study area (Boyd and Harrison, 1999). Hence, biological uptake depletes dFe and increases pFe in this layer  (Figure 3.3, a)).   In addition to the biogenic particles, high pFelitho concentrations are also observed at station P4 and P16 (Figure 3.5, a)). The origin of lithogenic particles at station P4 is likely river water which contains weathered minerals from the continents (Ittekkot et al., 1991) and/or resuspended particles from the coastal area. Both are transported further west during the sampling period by enhanced Ekman transport during summer wind conditions (i.e. Southward wind; seaward surface water; shoreward deeper water) (Section 2.4.3.1). On the other hand, particles at station P16 are likely terrigenous and delivered from the marginal area of Vancouver Island by a mesoscale eddy (Section 2.4.6) (Brown et al., 2012; Lippiatt et al., 2011). Although it is unclear if lithogenic particles at P4 and P16 represent a source or a sink for the dFe in the SML, we can confirm that strong Ekman transport and mesoscale eddies deliver pFe to the Line-P area.   For pMn, it is important to also consider redox cycling, which affects the balance between soluble Mn(II) and insoluble Mn(IV). Since the relative rate of reduction versus oxidation determines which process prevails, we estimated the inorganic Mn(II) oxidation rate using the following equation (Johnson et al., 1996; Wu et al., 2014):  ܫ݊݋ݎ݃ܽ݊݅ܿ ܯ݊ሺܫܫሻ݋ݔ݅݀ܽݐ݅݋݊ ݎܽݐ݁ ൌ ݇଴ሾܱଶሿሾܱܪିሿଶሾܯ݊ଶାሿ where ݇଴  is the previously reported rate constant of Mn(II) oxidation by dissolved oxygen  (6.2 × 10-4 µM-3 year-1) (von Langen et al., 1997), [O2] is the measured oxygen concentrations, 68 [OH-] is the concentration of hydroxide derived from the in-situ pH (Dickson et al., 2007), and [Mn2+] is the measured dMn.   This calculation indicates that the fastest oxidation rate should occur in the upper layer  (Figure 3.7, a)), mainly due to higher concentration of dissolved oxygen relative to the lower layers. The higher concentration of authigenic pMn relative to biogenic and lithogenic pMn (Figure 3.4, a)) is consistent with a faster oxidation rate, as the majority of pMn is generated within the SML. However, most of the Mn is found in the dissolved phase (85%) (Figure 3.7, b)), suggesting that reduction dominates in these waters. Despite the presence of external sources of pMn (i.e. rivers, eolian dust, coastal water) and high Mn(II) oxidation rate, pMn concentration is 33 to 120 times lower (0.03 – 0.1 nmol kg-1) than dMn (1 – 12 nmol kg-1) in the SML. Photo-reduction plays a crucial role in the conversion of pMn to dMn, as the rate of reduction can be up to 7 – 60 times faster with UV radiation (Sunda and Huntsman, 1994). Hence, we conclude that Mn-oxides from external terrigenous sources are reduced via photo-reduction in the surface waters along Line-P.   dMn/(dMn + pMn) (%)60 80 100Depth (m)1050100150250500100020003525P4P12P16P26Mn(II) oxidation rate(nmol kg-1 yr-1)10-5 10-4 10-3 10-2 10-1 100Depth (m)1050100150250500100020003525Figure 3.7 a) Vertical profiles of Mn (II) oxidation rates at 4 major stations. b) Percentage of total Mn which is dissolved across Line-P. Each station is marked with a different color.   69 3.4.4.2 Particulate TM in the Winter Mixing Layer (35 – 150 m)  Within the WML, total pMn is high across the transect (0.1 – 0.4 nmol kg-1) with low pMnbio, moderate pMnlitho, and high pMnauthi fractions (Figure 3.4, a)). In the upper part of the WML  (35 – 75 m), smaller particles are more biogenic than larger particles (Figure 3.4, c)). Although pMnbio is generally low in the WML (Figure 3.4 a), it is higher at P16, where an eddy may have enhanced phytoplankton growth (section 2.4.6). Indeed, elevated pMnbio at P16 may be the signature of enhanced fluorescence caused by an eddy transecting this area (Figure 3.2, b)). Lithogenic pMn is elevated at station P4, likely due to sedimentary resuspension from the continental margin (Figure 3.4 a), yet rest of stations show low pMnlitho levels compared to P4. We suspect that this is likely related to the greater level of LSP compared to SSP (Figure 3.1, b)), as larger size particles can sink more rapidly relative to smaller particles rather than being transported laterally. Authigenic pMn is more than 90% of total pMn within this layer across the entire transect. The absence of photo-reduction at this depth and the high O2 concentration  (340 nmol kg-1) (Figure 2.5, c)) likely contribute to a high oxidation rate (Figure 3.7, a)), thus enhancing the production of authigenic pMn. In addition to the high pMn, we also observed enhanced dMn concentrations at the offshore stations in the WML (Figure 2.12), which is likely the remnant of high dMn generated at the surface during the previous winter. In this highly oxygenated environment, higher dMn allows for more pMn generation via rapid oxidation. However, since dMn is much greater than pMn (~10 times), we did not observe a significant decrease in dMn by this oxidative removal.    Similar to pMn, pFebio is also high in the upper 100 m (Figure 3.5, a)), dominated by the smaller size particles (Figure 3.5, c)). It also shows a significantly elevated pFebio at 50 m at P16, where an eddy was observed. In this layer, lithogenic particles from the continental margin are enhanced at station P4 (Figure 3.5, a)) and are advected towards P16, with horizontally decreasing concentrations from P4 (2 nmol kg-1) to P16 (0.6 nmol kg-1). Lastly, a decreasing biogenic pFe, as well as increasing lithogenic and authigenic pFe with depth (Figure 3.5, a)) demonstrate the importance of biogenic cycling on the distribution of dFe and pFe in this region. Indeed, the remineralization of biogenic particles is responsible for the increasing dFe with depth in the WML Figure 3.3, a)). 70 3.4.4.3 Oxygen Minimum Zone and sedimentary input  In the Oxygen Minimum Zone (OMZ, O2 < 100µM), there is more pFe in lithogenic particles, suggesting an external particle input from the continental margin (Figure 3.5 a)). This pFe is observed to be advected to P16, with decreasing pFelitho from P4 to P16. At P26, pFelitho is low and vertically uniform in the OMZ, likely due to limited eolian dust input, sinking through the upper layers. Authigenic pFe, on the other hand, is enhanced within the OMZ at P26. It is not likely that pFe is generated via in-situ oxidation, as dFe is stable in suboxic waters, but this could be the result of Fe oxidizing bacteria (Heller et al., 2017), which regenerate pFe in low oxygen conditions. Further study is needed to determine the role of Fe-oxidizing bacteria and the exact mechanism behind the high authigenic pFe at P26. Similar to the WML, the pFebio decreases with depth in the OMZ (Figure 3.5, a)). Indeed, we conclude that dFe is governed primarily by the remineralization of organic matter.  Within the OMZ, we observe a dMn maxima and pMn minima across the transect. The lowest Mn(II) oxidation rate is also found within this layer, implying that reduction of MnOx is the dominant process (Figure 3.7, a)). Indeed, we find ~ 98 % of the Mn is in the dissolved form in the centre of the OMZ (Figure 3.7, b)). Similar to pFe, lithogenic fraction of pMn is higher near the continental margin, driven by the sediment re-suspension (Lam et al., 2006). However, since this enrichment is less pronounced for pMn compared to pFe, we suspect that pMn introduced to the water column adjacent to the continental slope at P4 is readily reduced under low O2 condition (Lam and Bishop, 2008). The similar distribution of pMn and dMn is also observed at the rest of stations within the OMZ. Station P16, for example, also shows that decreasing Mn(II) oxidation rate from 150 m down to ~1000 m, decreasing pMn (0.1 to 0.03 nmol kg-1), and increasing dMn (0.6 to 1.3 nmol kg-1), which likely indicates that pMn in OMZ is reduced in a low oxygen condition. At station P12, below 1100 m, we observe a high pMn in the authigenic fraction, likely supported by the input from a seamount and in-situ oxidation. As the oxygen level (Figure 2.5) and the Mn(II) oxidation rate (Figure 3.7, a)) increase with depth below 1100 m, re-mobilized dMn from the sediments may be oxidized and increase the authigenic particles in this region. Lastly, we did not capture the signal of NPIW due to low sampling resolution and the loss of many P20 samples.  71 3.5 Conclusion We measured the concentration of 5 trace elements in particles, collected in two different size fractions. We found that particulate Mn and Fe along Line-P are dominated by small suspended particles (SSP: 0.45 – 20µm), of which concentrations are typically ~6 times greater than large suspended particles (LSP: >20µm). The analyses of pFe, compared to pAl and pP, indicates that the majority of pFe is from terrigenous sources. The decreasing biogenic pFe and increasing dFe with depth suggest that the level of dFe in the water column depends on remineralization of the particulate phase. At the surface, the majority of pFe is biological and smaller than 20 microns. Below the surface, both in the WML and the OMZ, terrigenous particles originated from the continental margin dominate at the onshore stations.   Within the SML, the authigenic pMn takes up a large portion of total pMn likely due to high Mn(II) oxidation rate, yet its concentration is 33 to 120 times lower than dMn. Enhanced reduction rates in the presence of UV radiation in these high O2 waters causes rapid cycling between authigenic pMn and dMn, leading to elevated levels of dMn and a higher authigenic fraction of pMn. Within the WML, both dissolved and particulate phases of Mn are the highest. Although rapid oxidation can generate pMn in the WML, we did not observe a decrease in dMn at the offshore stations. In the OMZ, the low concentration of pMn shows both lithogenic and authigenic characteristics, suggesting that the higher dMn concentration is attributed to the reduction of particles in this low oxygen environment.   72 Chapter 4: Dissolved Manganese and Iron in the Beaufort Sea of the Arctic Ocean: 2009-IPY GEOTRACES   4.1 Summary  The vertical and horizontal profiles of dissolved manganese (dMn) and iron (dFe) collected from the Beaufort Sea were examined to assess the mechanisms controlling their distribution. As part of the Canadian IPY GEOTRACES program, a total of 101 trace metal clean seawater samples  (< 0.4 µm) were collected at 7 stations in August/September of 2009. In the Beaufort Sea, both dMn and dFe showed highly structured profiles at all stations. In most cases, the highest dMn was observed in the polar Surface Mixing Layer (pSML). The shelf station, in particular, showed  ~50 % greater level of dMn than the open ocean stations within this layer due to river input and sea ice melt, which introduce high dMn and/or potentially reducible pMn to the seawater. Unlike in other oceans (e.g. Northeast Pacific), dFe in this study area showed elevated concentrations at the surface and depleted concentrations in the subsurface layer, where Pacific Summer Water is found. This unique structure of vertical profile is likely the result of dFe drawdown by phytoplankton during the spring bloom before the sampling period (i.e. late June to mid-July) and subsequent external input of dFe to the surface waters after the boom, before the sampling period (i.e. late August to early September). Below the pSML, at the center of the PWW (~150 m deep), we observed elevated dMn and dFe. Based on the N* values and enhanced dTM concentrations within the PWW, we concluded that the combined effect of in-situ remineralization, remobilization of dTM from the continental margin, and the advection of dTM rich water from the Chukchi Sea enhanced both dMn and dFe in this study area. Lastly, within the Atlantic Layer  (200 – 1200 m), the greater dMn and dFe near the continental margin than at the open ocean area and the greater mean concentration of dMn and dFe in Eurasian Basin than in the Beaufort Sea suggested that both elements in this region came mostly from the continental margin, rather than advected from the Eurasian Basin.    73 4.2 Introduction Distribution of dissolved Mn (dMn) and Fe (dFe) in the Arctic Ocean is governed by unique hydrographical and geographical features of this Polar region. The Beaufort Sea in the Arctic Ocean is highly stratified with multiple layers originating from different sources. In particular, the polar surface layer is composed of Pacific inflow water which is highly modified by river input, sea ice melt water, and shelf waters (Macdonald et al., 1989; Macdonald and Gobeil, 2012; Melling et al., 2008). Each of these sources exerts a significant role on both dMn and dFe distributions in the Beaufort Sea. The high river discharge during the melting season (Proshutinsky et al., 2009) of the Arctic (May to September) is known to supply high amount of nutrients and trace elements into the adjacent seas (Emmerton et al., 2008; Klunder et al., 2012a). The sea ice melt at the surface also supplies a significant amount of trace elements into the water column as it not only introduces high level of dTM (Aguilar‐Islas et al., 2008), but also releases entrained sedimentary or eolian minerals to the water column (Measures, 1999). Fresh water source within the upper layer can be distinguished using a number of tracers, such as oxygen isotopes (Östlund and Hut, 1984), alkalinity (Lansard et al., 2012), or barium (e.g.(Guay et al., 2009) in conjunction with salinity. In particular, dissolved barium (dBa) is a trace metal in seawater, which can be used as a tracer of fresh water sources since dBa varies from > 500 nmol kg-1 in the Mackenzie River to  < 5 nmol kg-1 in sea ice melt water (Guay and Falkner, 1997; Guay and Falkner, 1998; Taylor et al., 2003). Therefore, dBa, in conjunction with salinity, can be used to estimate the relative composition of river and sea ice melt water within uppermost layer (usually shallower than  10 – 15 m (Carmack and Macdonald, 2002)) and may provide insight on impact of fresh water sources on the trace metal cycling and distribution (e.g.(Giesbrecht et al., 2013). In the sub-surface layer (100 – 200 m), remobilized dMn and dFe from the sediments may also contribute to their concentrations. Pacific origin waters from the Chukchi Sea introduce high nutrients and re-mobilized trace elements from the sediments to the Beaufort Sea (Kondo et al., 2016; Yamamoto-Kawai et al., 2006). The latter process, the sedimentary flux of dTM, may also be observed near the continental margin locally (Löwemark et al., 2014; Middag et al., 2011b; Naidu et al., 1997). Although both elements are removed by scavenging, removal of dFe is observed to be more significant within the photic zone due to greater biological uptake compared to dMn (Taylor et al., 2013). In the Beaufort Sea, both dMn and dFe show vertically uniform concentrations below the 74 Pacific layers, where Atlantic sourced water and Canada Basin Deep water are present, indicating the absence of external sources like hydrothermal vents (Klunder et al., 2012b; Middag et al., 2011b).  For this study, seawater samples were collected from the Beaufort Sea in the Arctic Ocean during the Canadian GEOTRACES program in 2009, as part of the International Polar Year (IPY). We analyzed a total of 101 seawater samples to observe the spatial distribution of both dMn and dFe. This work aims to elucidate the importance of external surface sources (i.e. river water versus sea ice melt water) for both elements using dBa as a fresh water tracer (Section 4.4.3), to investigate the contribution of shelf and sedimentary sources near the continental margin, as well as the influx of trace metal rich Pacific Winter Water, to subsurface waters (Section 4.4.4), and to evaluate the significance of scavenging processes for dMn and dFe in the Atlantic waters during transport along the Eurasian continental margin (Section 4.4.5).    4.3 Method 4.3.1 Study Area: Beaufort Sea of the Arctic Ocean The Beaufort Sea is a marginal sea in the Arctic Ocean, located adjacent to the Canadian Archipelago (Figure 4.1). It is located at the southern part of the Canada Basin (CB), the area offshore of the Mackenzie Delta. For this work, seawater samples as well as hydrographic data (e.g. temperature, salinity, oxygen) were collected at two shelf stations (S2, S4) and five Canada Basin (CB) stations (L1, L1.1, L1.5, L2, L3) (Figure 4.1). The shelf stations (S2 and S4) are shallower and are located close to the shore. The shallowest station, S2, is less than 100 km away from the Mackenzie River delta, and has a bottom depth of ~200 m. The CB stations are located at the southern interior of the Canada Basin. The seafloor of the transect deepens from L1  (2000 m) to L3 (4000 m), which is the northernmost station located ~ 600 km away from the shore.    75  Figure 4.1 Map of Canadian western Arctic showing 7 sampling stations of this study. Stations L1 – L3 and S2 – S4 are referred to as Canada Basin (CB) stations and shelf stations, respectively.   4.3.2 Sampling method  Samples were collected from the Beaufort Sea of the Arctic Ocean (Figure 4.1) in the summer of 2009 (from August 29 to September 8) during Leg 3a of CCGS Amundsen Expedition (ArcticNet 0903) (Melling et al., 2012). Samples for dissolved Mn and Fe were collected at stations L1 – L3 and S4 using a Trace Metal clean Rosette (TMR) system mounted with 12 (12 L) Go-Flo bottles, as described by Giesbrecht et al. (2013). Seawater samples were filtered through 0.45 µm AcroPak Supor capsule filters and collected into pre-cleaned LDPE bottles. All samples were acidified onboard in the laminar flow hood with HEPA filters by adding 500 L of 12 M HCl (Seastar Chemicals) to 500 mL of seawater. Similarly, samples for dBa were acquired at 5 stations (L1, L1.1, L2, L3, and S2) using a Regular Rosette (RR) system mounted with Niskin-X bottles (Figure 4.1). The filtered seawater samples (0.45 µm AcroPak Supor capsule filter) were collected into 125 mL high density polyethylene bottles and acidified with 125 µL of 12 M HCl (Seastar Chemicals) onboard.  76 Both the TMR and RR systems were equipped with a CTD with an oxygen sensor, while only the RR system was equipped with additional sensors for transmissivity and fluorescence. Therefore, salinity, temperature, and dissolved oxygen are recorded at all 7 stations, whereas transmissivity and fluorescence were only acquired at station S2, L1, L1.1, L2, and L3. Although transmissivity and fluorescence data are not available for S4 and L1.5, the extrapolation between stations gave us smooth estimated values for the missing stations (Section 4.4.3). All measured trace metal concentration values are listed in Table C.1 of Appendix C. Lastly, unfiltered seawater samples were also drawn from the Go-Flo bottles on TMR to obtain the concentration of macronutrients (NO2-, NO32-, Si(OH)4, PO43-) at all CB stations and station S4. These values were used to calculate the N* tracer for section 4.4.4.    4.3.3 Analytical method  Concentration of dFe and dMn were measured using isotope dilution followed by magnesium induced co-precipitation (Heumann, 1982; Mendez et al., 2010; Saito and Schneider, 2006). As outlined in chapter 2, Fe-57 spike was added to 50 mL of seawater and preconcentrated ~33 times by precipitation with NH4OH. All samples were measured by HR-ICPMS (Element 2). In addition to the intercalibrations described in chapter 2, five samples representing different geographical locations and depths of this study area were measured in duplicate to estimate method precision and analytical reproducibility (Appendix C: Table C.2). Measured values of duplicates showed a good agreement each other (Figure 4.2). The standard error of linear regression is 5.1 % for dMn and 5.3 % for dFe.   77 dMnDuplicate sample #1 (nmol kg-1)0.0 0.5 1.0 1.5 2.0Duplicate sample #2 (nmol kg-1 )0.00.51.01.52.0y = 0.991x - 0.002 R2 = 0.99dFeDuplicate sample #1 (nmol kg-1)0.0 0.5 1.0 1.5 2.0Duplicate sample #2 (nmol kg-1 )0.00.51.01.52.0y = 0.975 x - 0.038  R2 = 0.98a) b) Figure 4.2 Duplicate Arctic samples plotted against each other for a) dMn and b) dFe.    The concentrations of dBa were also determined by isotope dilution (Heumann, 1992; Klinkhammer and Chan, 1990). As its concentration in seawater was high enough to measure with HR-ICPMS (dBa limit of detection (3) = 0.001 nmol kg-1 (n=7)), a preconcentration step was not necessary for dBa analysis. The analytical method and inter-laboratory comparison results are described in the previous study (Giesbrecht et al., 2013). Briefly, a mixture of seawater (0.5 mL) and Ba-135 isotope spike (0.5 mL) was diluted with 9 mL trace metal clean 1% HNO3 (Seastar Chemicals). To achieve the best accuracy, the Ba-135 / Ba-138 ratio of sample-isotope mixture was maintained between 0.6 and 1 for all dBa samples (Adams et al., 1988). We also analyzed a Ba inter-laboratory comparison sample collected at 86° 38.29 N and 177° 33.38 E (2000 m depth) as a part of ARK-XXII/2 Polarstern expedition in 2007 (Roeske et al., 2012). The measured value of this study (6.72 ± 0.07 nmol kg-1, n=3) is well within the error range of consensus value  (6.67 ± 0.42 nmol kg-1).    78 4.4 Results and discussion 4.4.1 Hydrography of study area  The Arctic Ocean shows a highly stratified vertical structure as it is fed by a number of sources with different salinity and temperature. In this study area we observed 7 distinct water masses, in agreement with previous studies (e.g.(Jones et al., 1998; Jones et al., 1995; Rudels, 2015; Steele et al., 2004). Using a T-S plot, as well as vertical temperature profiles (Figure 4.3), the stratified structure of this study area is briefly described here.   Figure 4.3 a) T-S plot of all stations. b) Vertical profile of temperature and salinity at station L2. Note that the y-axis is in log scale.   In the Beaufort Sea, the polar Surface Mixing Layer (pSML: upper 20 m) (Figure 4.3, b)) is modified by river, sea ice melt water, and precipitation during the summer (Yamamoto-Kawai et al., 2008). Since it is highly diluted by fresh water sources, the pSML has low salinity (S < 27) at all stations. Temperature however shows differences between CB and shelf stations. In general, shelf stations are ~2°C warmer than CB stations (Figure 4.3, a)) as they are influenced by warm river water (~16°C) due to their proximity to the Mackenzie Delta (Yang and Peterson, 2017). 79 Below the pSML, between 20 – 50 m, we observe the near Surface Temperature Maximum (nSTM) which shows elevated temperature due to entrapped solar radiation at 20 m and the remnant of the previous Winter’s Mixed Layer (rWML) which represents a relatively lower temperature than nSTM at 40 m (Jackson et al., 2011).   The Pacific waters are found at 50 – 200 m, which can be subdivided into seasonally warmer and fresher Pacific Summer Water (PSW: 29 < S < 32.5) and the colder and saltier Pacific Winter Water (PWW: 32.5 < S < 33.5) (Figure 4.2, b)). Pacific waters enter the Arctic Ocean through the narrow passage of the Bering Strait and trifurcate at the south of the Chukchi Sea. Two of these branches are modified by coastal and shelf environment in the Arctic Ocean and form PSW and PWW in the Beaufort Sea. The eastward flowing branch, the Alaskan Coastal Water (ACW), is the source water of PSW and carries shelf derived fresh water along the coast to the study area and to the interior of the Beaufort Gyre (Jackson et al., 2011; Woodgate et al., 2005). A northward branch of Pacific water flows through the Bering and Chukchi Seas (Jackson et al., 2011) and carries high nutrients and a strong sedimentary denitrification signature from the Bering and Chukchi shelf to the study area (Kondo et al., 2016) (Figure 1.2). This is the source of the colder and saltier PWW, located below the PSW at 100 – 200 m (Figure 4.3, b)). In the Canada Basin, a minimum of ~ -1.5 °C is observed at the bottom of this layer. The last branch flows towards the central pole (Trans Polar Drift: TPD), so does not influence our study region. In the Canada Basin, both pSML and Pacific layers (upper 200 m) are in an anticyclonic circulation regime (Figure 1.2).  Below 200 m, waters sourced from Atlantic Ocean enter through Fram Strait, travel along the Eurasian continental margin, and subduct below the Pacific layers in the Beaufort Sea (Jones et al., 1998). Hence, we observe an increase of both temperature and salinity between 200 and  400 m until it reaches the core of the Atlantic Water (AW: σθ = 27.8 kg m-3) (Figure 4.3, b)). This layer exhibits cyclonic circulation, with a narrow salinity rage (34.8 - 34.9) but a wide depth range (200 – 1200m) (Figure 1.2). Below 1200 m, the Canada Basin Deep Water (CBDW) is found (Carmack et al., 2012; Jones et al., 1995) with its estimated isolation time of ~500 years (Timmermans et al., 2003; Timmermans and Garrett, 2006).    80 4.4.2 Overview: Vertical distribution of dTM  4.4.2.1 Dissolved TM at the Canada Basin (CB) Stations Dissolved Mn displays a typical scavenged type profile at the CB stations (L1, L1.1, L1.5, L2, and L3) (Figure 4.4, a)). The highest dMn (3.4 – 6.7 nmol kg-1) is observed in the pSML, where external sources (e.g. river water, sea ice melt water, eolian dust) enter the ocean. Below the pSML down to 150m, dMn sharply decreases with depth (from 4.6 to 0.4 nmol kg-1), followed by a small increase at ~150 m where PWW is found (Figure 4.4, b)). The dMn increases up to 1.4 nmol kg-1 at this depth, then decreases again down to 350 m. Below 350 m, dMn shows uniformly low concentrations (~0.2 nmol kg-1), except below 1250 m at station L1 where dMn increases again up to 1.3 nmol kg-1. At 1800 m, 200 m above the sediment interface, the concentration at L1 is  ~7 times greater than at the other stations at that depth.   While Arctic dMn exists in a similar concentration ranges with Pacific or Atlantic Oceans, surface dFe in the Canadian Basin is elevated compared to the Pacific or Atlantic Oceans. In the Beaufort Sea, dFe shows slightly elevated concentrations in the pSML and the lowest concentrations at the subsurface layer between 70 – 80 m (i.e. PSW) (Figure 4.4, c)). Similar to dMn, the level of dFe then increases within the PWW with a maxima (0.5 – 0.7 nmol kg-1) at ~150 m. This enhancement is the greatest at station L1, moderate at L1.5 and L3, and the lowest at L1.1 and L2 (Figure 4.4, d)). Below 150 m, down to 350 m, dFe decreases to 0.4 nmol kg-1 at station L1 and to  ~0.2 nmol kg-1 at stations L1.1 to L3. Station L1 shows an elevated concentration (0.5 nmol kg-1) between 1000 – 1250 m, whereas the rest of stations show uniform concentrations with depth.           81    dMn (nmol kg-1)0 2 4 6 8Depth (m)101001000Temperature (C)-1.5 -1.0 -0.5 0.0 0.5 1.0L1L1.1L1.5L2L3L2: Ta) b) dMn (nmol kg-1)0.0 0.5 1.0 1.5 8.01001000Temperature (C)-1.5 -1.0 -0.5 0.0 0.5 1.0L1L1.1L1.5L2L3L2: TdFe (nmol kg-1)0.0 0.5 1.0Depth (m)101001000Temperature (C)-1.5 -1.0 -0.5 0.0 0.5 1.0L1L1.1L1.5L2L3L2: Tc) d)dFe (nmol kg-1)0.0 0.5 1.01001000Temperature (C)-1.5 -1.0 -0.5 0.0 0.5 1.0L1L1.1L1.5L2L3L2: T Figure 4.4 Vertical distribution of a) dMn and b) dFe at the Canada Basin stations (L1 – L3) a) from surface to 3500 m. The area between 70 – 3500 m (below the dashed line of a) and c)) is expanded for b) dMn and  d) dFe. Note that the depth is in a log scale to show upper layer distributions clearly. The temperature profile of station L2 is overlaid on each plot to identify water masses.     82 4.4.2.2 Dissolved TM at the shelf station (S4)  The shelf station (S4) shows more variations in the dTM vertical profiles compared to the Canada Basin stations (L1 – L3) (Figure 4.5). The highest dMn is observed in the pSML (7.9 nmol kg-1) adjacent to the shelf break where we expect remobilized dTM flux into the water column (Figure 4.5, a)). From 10 m to 50 m, dMn rapidly decreases with depth (to 2.3 nmol kg-1). Between 50 and 200 m, adjacent to the continental slope, dMn shows a noticeable enrichment at S4, with concentrations ~ 3.5 times higher than at similar depth in the CB stations. In contrast, the surface dFe is similar to that observed at the CB stations (Figure 4.5, b)). Gradually decreasing dFe is observed with depth down to 30 m, then dFe increases rapidly and reaches its highest concentration (1.8 nmol kg-1) at the same depth where dMn enrichment is observed (150 m).    dMn (nmol kg-1)0 2 4 6 8 10Depth (m)101001000Temperature (C)-1 0 1 2L1S4S4: TdFe (nmol kg-1)0.0 0.5 1.0 1.5 2.0101001000Temperature (C)-1 0 1 2L1S4S4: Ta) b) Figure 4.5 Vertical distribution of a) dMn and b) dFe at L1 and S4 in the Beaufort Sea. Grey symbols denote the data points of CB stations (L1.1 to L3).     83 4.4.3 Upper 100 m: external sources in pSML and removal processes in PSW Within the pSML, both dMn and dFe show elevated concentrations due to two major external sources (i.e. river water and ice melt water), yet they display distinctive horizontal distributions across the transect (Figure 4.6, g) and h)). In particular, the concentration of dMn decreases from the coastal area (9.0 nmol kg-1) to the open ocean (3.4 nmol kg-1), whereas dFe shows no clear horizontal variations in its concentrations. Within the PSW, below the pSML down to 100 m, the concentrations of both elements rapidly decrease with depth. The level of dMn decreases to ~1.1 nmol kg-1, which is 3 – 9 times lower than dMn in the pSML (Figure 4.6, h)). Similarly, dFe rapidly decreases to 0.1 nmol kg-1 within the PSW, and shows a broad band of depleted concentrations across the transect between 15 – 100 m (Figure 4.6, g)).  These observations highlight three key features. First, dMn and dFe in the pSML are highly influenced by external sources. Second, these surface external sources are more significant in the coastal area, specifically for dMn. Third, external sources do not influence waters below 20 m due to strong stratification. To evaluate how the potential sources contribute to the dMn and dFe distributions in the pSML, we examined the relative composition of two major external sources (i.e. river water and sea ice melt) and evaluated the impact of each source on the dMn and dFe distributions. We also described the mechanisms controlling the distribution of both elements below the pSML, within the PSW.   84  Figure 4.6 Cross section contour plots of a) salinity, b) temperature (ºC), c) O2 (µmol kg-1), d) sigma-t (kg m-3), e) spiciness (kg m-3), f) AOU (µmol kg-1), g) dFe (nmol kg-1), h) dMn (nmol kg-1), i) dBa (nmol kg-1), j) transmissivity (%), k) N* (µmol kg-1), l) Fluorescence (µg L-1), and  m) NO32- (µmol kg-1) from off the coast of the North America continent (red star on the map (n)) towards the interior of the Canada Basin. 85 To quantify the relative contribution of Sea Ice Melt (SIM), River Water (RW), and Seawater (SW) in the pSML, an end-member analysis was performed using in-situ concentrations of dissolved barium and salinity as described in previous studies (Giesbrecht et al., 2013; Lansard et al., 2012; Taylor et al., 2003; Yamamoto‐Kawai et al., 2009). Assuming that the SML of the Beaufort Sea is composed of River Water (RW), Sea Ice Melt (SIM) water, and Pacific Water (PW), the fraction of each component ௜݂  is calculated based on the equations:   ோ݂ௐ ൅  ௌ݂ூெ ൅  ௉݂ௐ ൌ 1 ோ݂ௐܵோௐ ൅  ௌ݂ூெ ௌܵூெ ൅  ௌ݂ௐܵ௉ௐ ൌ ܵ௠௘௔௦௨௥௘ௗ ோ݂ௐ݀ܤܽோௐ ൅  ௌ݂ூெ݀ܤܽௌூெ ൅  ௌ݂ௐ݀ܤܽ௉ௐ ൌ  ݀ܤܽ௠௘௔௦௨௥௘ௗ  where ௜݂ is the fraction of end-member i (i.e. i = RW = River Water:  i = SIM = Sea Ice Melt water: i = PW = Pacific Water), ௜ܵ  is salinity, and ݀ܤܽ௜  is dissolved Ba. This set of equations is the variation of previous studies, which use the oxygen isotope or PO4* (PO4* = PO43- + O2/175 – 1.95 µmol kg-1) (e.g.(Ekwurzel et al., 2001; Yamamoto-Kawai et al., 2008). The end-member values used for this calculation are listed in Table 4.1. For this analysis, we assumed that river runoff from the Eurasian Continent is not significant compared to the Mackenzie River input in this location. Although we could not identify or distinguish the influence of the Eurasian River input into this study area, if its contribution were significantly high in this study year, our current end-member analysis may have underestimated the percentage contribution of RW since the level of Ba in the Eurasian River is ~4 times lower than in the Mackenzie River (120 nmol kg-1) (Taylor et al., 2003).       86 Table 4.1 Values used for the end-member analysis of the Beaufort Sea  End-member, i Salinity, S dBa (in nmol kg-1)  Sea Ice Melt water 4 ± 1a ≤ 5b,c River Water (Mackenzie River) 0c 520c Pacific Water 32.5 ± 0.2d 65 – 70e 65 ± 5c a from Yamamoto-Kawai et al. (2009) b from Taylor et al. (2003) and Guay et al. (2009) c from Guay and Falkner (1997) d from Steele et al. (2004) e This study: dBa = 67.5 nmol kg-1 is used as PW end-member  (Guay and Falkner, 1997; Guay et al., 2009; Steele et al., 2004; Taylor et al., 2003; Yamamoto‐Kawai et al., 2009)  This calculation was done for the stations where dBa is available (i.e. L1, L1.1, L2, L3, and S2). Although water mass composition of station S4 is not available due to absence of dBa data from this location, station S2 may reflect the hydrographic conditions of S4 as both stations are located near the North America continent at the shelf break with bottom depths of ~ 300 m (Figure 4.6, i)). The results calculated using the equations indicate that the contribution of river water to pSML is ~ 20 % at station S2, L1, and L1.1 and ~ 15 % at station L2 and L3 (Figure 4.7, a)), suggesting that river water is a considerable external source in this region. In contrast, sea ice melt water takes up the lowest percentage contribution of three sources, yet it shows a more variable contribution across the transect. Its contribution is the highest at S2 (~ 10 %) and the lowest at L1 (~ 4 %). Additionally, we also observed that the transmissivity (Figure 4.7 b)) shows general inverse relationship with the total fresh water inputs (Figure 4.7 a)). For example, at the station nearest to the continent, the lowest transmissivity is observed when the sum of SIM and RW are the greatest. This likely suggests that fresh water sources may introduce particles to the study area. As the transmissivity at this depth (15 m) is lower than at the fluorescence maximum (~75 m) (Figure 4.6, j), l)), the particles in this layer are suspected to be inorganic materials or dead organic matters. This could be a potential source for dTM in the water column via photo-reduction at the surface or remineralization at the depth.     87  StationS2 L1 L1.1 L2 L3Composition (%)05101520253060708090SIMRWSWTotal Fresh water = SIM + RWa) b)Distance from shore (km)100 200 300 400 500 600Transmissivity (%)83848586878889dMn (nmol kg-1 )024681012dFe (nmol kg-1 )-1.5-1.0-0.50.00.51.0Transmissivity Mean transmissivity (upper 15m)dMn dFeS4             L1       L1.1                L2         L3 Figure 4.7 a) Percentage composition of sea ice melt (SIM) water, river water (RW), and seawater (SW) in the Beaufort Sea. b) Horizontal distribution of transmissivity, dMn, and dFe within the pSML(upper 15m). Note that the transmissivity scale is reversed. Individual transmissivity values between 5 to 15 m are plotted in grey square (1m resolution).    4.4.3.1 River input in pSML To determine the significance of dMn delivered by the Mackenzie River (dMnriver), two graphical analyses are performed. First, the dMn concentration in the Mackenzie River is estimated by linear regression and extrapolation. In upper 100 m, within pSML and PSW, dMn at station S4 showed a robust correlation (R2= 0.98) with the salinity (Figure 4.8, a)). Likewise, dMn found at all stations also displayed good negative relationship with the salinity (R2 = 0.78). The extrapolation of the best-fit line to salinity = 0 provided an estimated dMnriver concentration range of  27 – 41 nmol kg-1. These values are lower than results calculated by the same method at a station closer to the Mackenzie Delta of 170 nmol kg-1 (Cid et al., 2012), but are well within the measured dMn range (16 – 44 nM) in the Mackenzie River (Peterson et al., 2016). The estimated dMnriver also agrees well with the end-member analysis results (i.e. the river water exerts ~20% contribution within the pSML: Figure 4.7, a)) as seawater dMn (7.9 nmol kg-1 at S4) is ~ 5 times lower than the 88 estimated dMnriver (41 nmol kg-1). Despite the good agreement, however, this estimation may contain several uncertainties. The extrapolation analysis assumes that dMn is a non-reactive element, yet dMn is known to be removed by particle scavenging (e.g.(Jones and Murray, 1985; Whitfield and Turner, 1987). Additionally, as the measured dMn used for this analysis contains other sources of freshwater, such as SIM and Pacific-sourced waters, extrapolation may have overestimated the concentration of dMnriver. Nevertheless, the dMn-S relationship and extrapolation indicate that river water is a significant external source for dMn in the Beaufort Sea.   Another graphical analysis has been performed by plotting the dMn samples with the lowest salinities at each station against the distance from the Mackenzie River mouth (Figure 4.8, b)). As station S4 (i.e. closest to the Mackenzie River) is located ~270 km away from the river mouth, we also included a previously report of dMn collected at the estuary of the Mackenzie River (Cid et al., 2012) (Station A018 in their work). This station is located at ~100 km away from the Mackenzie River mouth with the dMn concentration of 10.5 nmol kg-1 at S = 25. We observed exponentially decreasing concentrations with distance from the river mouth (R2 = 0.84). Assuming that the removal by scavenging is first-order (e.g.(Weiss, 1977), the extrapolated best-fit line estimated 12.2 nmol kg-1 of dMnriver, which is lower than the actual dMnriver (16 – 44 nM). This analysis also has uncertainty in the distance from the river mouth, as we used the shortest distance from the Mackenzie River to the stations in the Beaufort Sea, rather than the distance of the river plume travels due to lack of data to constrain the flow path. For example, although the distance from MR-station to L1 is ~310 km, the river plume may take a longer path to this location. This will then shift dMn at L1 to the right. Despite this uncertainty, the decrease in dMn away from the river, the underestimated dMnriver, as well as more rapid decrease of dMn near the coastal area than the open ocean area, suggest that river-sourced dMn may be both diluted and scavenged during its path to the interior of the Canada Basin.   Dissolved Fe also shows some decrease in concentration from S4 to L2 and high value at L3, which is not as consistent of a trend as dMn (Figure 4.7 b)), possibly due to additional removal by primary production. As dFe does not show a linear relationship with salinity or distance from the MR-station, graphical analyses were not applicable for dFe. Additionally, a large increase of dFe observed at the surface of station L3 complicates the interpretation. If this feature is real, it could 89 be the result of sea ice melting which contained exceptionally high dFe. However, we did not observe considerable hydrographical differences at this station compared to the other CB stations. Alternatively, this could be due to contamination at the time of sampling (i.e. contaminataion in the original Go-Flo bottles). However, we can rule out the possibility of contamination during sample processing and analysis since the results from other participants on this research cruise agree well with our results at this station (Cullen, personal communication). 90 Salinity0 5 10 15 20 25 30 35dMn (nmol kg-1 )051015202530354045dMn S>32.5dMn S<32.5Best -fit line based on all measured dMn withdMn at S4  S<32.5Best-fit line based on dMn at S4  with S<32.5Mackenzie River (Peterson et al., 2016) Salinity24 26 28 30 32 34 36dMn (nmol kg-1 )0246810Y = -1.26X + 41.45R 2 = 0.98Y = -0.82X + 27.44R 2 = 0.78a)b)L1L1.5Distance to the river mouth (km)0 200 400 600 800dMn (nmol kg-1 )051015202530354045 Mackenzie River  (Peterson et al., 2016) Reported value of Cid et al. (2012)S4L1.5L1.1L1L2L3Predicted dMnbest-fit line: y = 12.22*e-0.002  R2=0.8495% Prediction Band  Figure 4.8 a) Dissolved Mn plotted against salinity. Open squares indicate all measured dMn of this study. The best-fit line (dashed) is based on the values with salinity lower than 32.5. Likewise, closed squares (red) denote dMn at S4 with salinity lower than 32.5. The solid line is the best-fit line based on the red symbols.  b) Dissolved Mn in the lowest salinity surface waters at each station, plotted against the distance to the river mouth. Solid black line is the (exponential) best-fit line extrapolated to the zero distance (i.e. Mackenzie River mouth). Red triangle indicates the estimated dMnRiver (12.2 ± 4.1 nmol kg-1). The measured Mackenzie River concentrations have a range of 16.1 – 43.9 nmol kg-1. 91 4.4.3.2 Sea ice melt water in pSML Sea ice melting (SIM) may also enhance the level of dMn and dFe by directly introducing dTM or labile particles into the surface seawater. It is reported that the melting of multiyear sea ice significantly enhances surface dTM concentrations in the water underneath in general (Tovar‐Sánchez et al., 2010). Another study conducted in the Antarctic also found a high level of dissolvable pMn (~ 23 nM) or dMn (~10 nM) injected by sea ice melt (Grotti et al., 2005). In the Arctic Ocean, the reported concentration of dMn in sea ice collected in the Canadian Archipelago is 2 to 4 times greater than in the seawater (Campbell and Yeats, 1982). Likewise, Measures (1999) reported dissolved Fe and Al enhancement near sea ice which contains a high amount of sediments. Sea ice melt water in the Bering Sea was found to increase the level of dFe and possibly contribute to the phytoplankton bloom in the early spring (Aguilar‐Islas et al., 2008). Indeed, sea ice can certainly enhance the level of dMn and dFe in the Beaufort Sea in general.   We observed that the estimated relative contribution of SIM is noticeably higher at the shelf station (9.0 %) than at the CB stations (2.8 – 4.7 %) (Figure 4.7, a)). Shelf sea ice contains sedimentary particles, incorporated during sea ice formation. Hence, the melting of shelf derived sea ice can release more particles into the seawater (McAlister and Orians, 2015). Sea ice in the interior of the Canada Basin may also contain eolian dust delivered during previous winters, which can be released upon melting and enhance the dTM level in the water column. In addition, photo-reduction at the surface (Sunda and Huntsman, 1994) can be more significant in this region, as the study area is exposed to the direct UV radiation during the sampling period (i.e. the highest seasonal melting). The station nearest the coast shows the lowest transmissivity (i.e. high suspended particles) in the water column. Although we cannot differentiate between biogenic particles and inorganic particles released by SIM, we observed a high particle abundance where the SIM is high. This may suggest that SIM introduces potentially reducible particles near the coastal region, which likely contribute to the enhanced dTM.   92 4.4.3.3 Contrasting removal processes of dMn and dFe within PSW Within the PSW, both dMn and dFe decrease with the depth. However, their removal mechanisms and/or rates are expected to be different due to the high biological demand of dFe in the ocean. Although Mn is an essential micronutrient for marine primary producers, it is not a limiting nutrient in the world oceans. We propose that the rapid removal of dMn in the PSW of this study area is likely due mostly to scavenging, rather than active biological uptake. The removal of dFe in the Beaufort Sea, however, is expected to be mostly from biological uptake as it is a limiting nutrient in this region (Taylor et al., 2013). During the sampling period of this study, we likely have captured depleted dFe between 15 – 100 m due to biological drawdown and a slightly elevated dFe at the surface due to external inputs (i.e. SIM) after the bloom. The area averaged surface chlorophyll a concentration shows that phytoplankton bloom occurred mid- to end- of July (Figure 4.9). The lowest chlorophyll a concentration (0.8 mg m-3) at the surface in late August, as well as the deep fluorescence maximum (~100 m) and depleted nitrate (Figure 4.6, l) and m)) likely indicate that phytoplankton stripped dFe and nutrients out of the upper 100 m during the early bloom. The surface dFe during the sampling period could then be increased due to external sources in the pSML after the bloom.   Date (day-month-year)15-Jun-09 29-Jun-09 13-Jul-09 27-Jul-09 10-Aug-09 24-Aug-09 07-Sep-09Chlorophyll a concentration (mg m-3 )0123456sampling period Figure 4.9 Area-averaged chlorophyll a concentration (141°W, 68°N, 128°W, 80°N) observed at the surface of the Beaufort Sea. The plot is generated based on the NASA satellite data (SeaWiFs Global Monthly Mapped – 9 km Chlorophyll a) with 8-day temporal resolution (SeaWiFS Project, 2003).  93 In conclusion, both river and sea ice melt water enhance the dTM concentration at the surface. About 2/3 of the fresh water originates from rivers, and much of the dMn in river water is diluted by mixing as it is advected towards the open ocean. Sea ice melt water also enhances the dMn concentration, especially in the coastal area, by introducing high dMn and/or potentially reducible pMn into water column. Due to high biological demand of dFe, its external sources were not clearly identified. We suspect that injection of dFe by SIM may have enhanced the phytoplankton bloom before our sampling period (Figure 4.9: late June to mid-July), thus removing most of the dFe in the surface layer. Additional external input after the bloom may be responsible for the small dFe enhancement observed in the surface layer at the time of sampling.   4.4.4 Mid-depth enhancement of dTM: advection from the shelf Elevated dMn is observed within the PWW, between 100 and 200 m, at all stations (Figure 4.4, b) and Figure 4.5, a)). We suggest that this enhancement is the result of advection from the marginal seas, rather than in-situ reduction. Although the oxygen concentration in the PWW is the lowest we observed in this region (240 µM) at 200 m, it is far above the level of an Oxygen Minimum Zone (100 µM) (Figure 4.6, c)). Hence, reduction of Mn is not likely to be significant (e.g.(Lewis and Luther, 2000; Martin and Knauer, 1984). A more plausible reason for this enhancement is the combination of PWW advected from the Bearing and Chukchi Seas and remobilization of dMn from the continental shelf, as well as in-situ degradation of organic material (i.e. remineralization).   The PWW in the Beaufort Sea is advected from the Bering and Chukchi Seas, which transport a high sedimentary denitrification signature. This water mass can be identified with a low N* value (i.e. N* = NO3 – 16*PO4 + 2.9) (Gruber and Sarmiento 1997) since it has a lower N:P ratio relative to the Atlantic sourced water. As Kondo et al. (2016) described, the low N* values (< -11 µM) found in the water column with high oxygen concentrations near the continental shelf indicate sedimentary denitrification and/or annamox. These conditions also are likely to lead to the remobilization of dMn into the water column via Mn-oxide reduction in the sediments (Kondo et al., 2016). Another recent study conducted in the Chukchi Sea and the southern part of Canada Basin (Cid et al., 2012) also reported a highly elevated dMn (19.7 nmol kg-1) in the shelf area relative to the interior of Canada Basin (3.25 nmol kg-1). In this study, we also observed a low N* 94 of ~ -14 µM which coincides with the mid-depth dTM enhancement (Figure 4.4, b) and c)), suggesting that the dMn at this depth is sourced by advection from the Bering or Chukchi Seas with the PWW. Interestingly, although this elevation is observed at all stations in a similar concentration rages (1.0 – 1.3 nmol kg-1), station S4 shows ~5 times greater dMn (5.2 nmol kg-1) at this depth. As N* values are similar at all CB stations and S4, we suggest that the remobilized dMn from the local continental margin also contributes to the enhancement at ~150 m. This idea is also supported by the sediment core study conducted in the Canada Basin (Macdonald and Gobeil, 2012), which discovered that shelf stations show elevated dMn concentration near the sediment-water interface.   Likewise, a noticeable dFe enrichment (0.1 to 0.6 nmol kg-1) is observed at 100 – 150 m (Figure 4.4, d) and Figure 4.5, b)) as it is also influenced by shelf modified PWW (8.2 nmol kg-1; (Cid et al., 2012) and by remobilized dFe from the continental margin. However, the level of dFe increase (~65 %) is more pronounced than dMn (~18 %). We suspect that this difference is due to remineralization. Although both elements are released by the remineralization of biogenic particles, dFe increases to a greater extent, as the elemental ratio between Fe and Mn in phytoplankton tissue is greater (Fe:Mn = 50:4) (Bruland et al., 1991). Hence, we propose that the dFe enrichment at 100 – 200 m is supported by both in-situ remineralization and the same sources which lead to the dMn maximum at this depth (i.e. advection of PWW with high dTM and additional remobilization of dTM from the continental shelf).    4.4.5 Dissolved TM in the Atlantic sourced water – local versus intra-basin advection Below the PWW layer, we find Atlantic sourced water, with its core isopycnal of 27.8 kg m-3, which flows around the Eurasian Basin (EB) and subducts underneath the Pacific layers (Rudels et al., 2006). In this layer, both dMn and dFe show depleted concentrations from 200 m to  ~1200 m with generally decreasing concentrations from the continental margin towards the open ocean (Figure 4.6, g) and h)). To observe the horizontal distributions of dMn and dFe in detail, the concentration ranges of both elements found in this layer are plotted across the transect (Figure 4.10).   95 Distance from L1 (km)0 100 200 300 400dMn (nmol kg-1 )0.10.20.30.40.50.6dMn in Atlantic source waterBest-fit line L1 - L2Mean dMn in AW: EBMean dMn in AW: This studyDistance from L1(km)0 100 200 300 400dFe (nmol kg-1 )0.10.20.30.40.50.6dFe in Atlantic source waterMean dFe in AW: EBMean dFe in AW: This studyL1 L1.1 L1.5 L2 L3 L1 L1.1 L1.5 L2 L3a) b) Figure 4.10 Horizontal distribution of a) dMn and b) dFe in the AW. Dashed red and black lines indicate the mean concentration of previously reported values of Eurasian Basin and all measured values of this study in Canada Basin, respectively. The x-axis (Distance from L1) is determined based on the cross section map (Figure 4.6, n)).   The dMn concentration is the highest at station L1 (0.33 nmol kg-1) (Figure 4.10, a)), which is likely the signature of laterally mixed dMn, re-mobilized from the continental margin (Heggie et al., 1987). The level of dMn in the AW then decreases towards the interior of the CB and shows the lowest concentration at L2 (0.19 nmol kg-1), suggesting that scavenging and mixing are removing dMn from the onshore area towards the central basin. Similar to dMn, dFe also shows a strong signature of laterally sourced dFe at station L1 (Figure 4.10, b)). From station L1 to L1.1, the level of dFe decreases from ~4.5 nmol kg-1 to 2.5 nmol kg-1, which may suggest that the majority of dFe is scavenged rapidly near L1 likely due to its faster oxidization rate (on timescales of minutes to hour) in the oxic environment (Santana-Casiano et al., 2005).  Conversely, high dFe concentration at station L1 may indicate a greater input of remobilized dFe from the continental 96 margin than dMn, as it is seen within the PWW layer on Figure 4.5 (section 4.4.4). Regardless, dFe is removed more rapidly compared to dMn from the onshore area towards the open ocean.  Since this layer is composed with Atlantic sourced water, we also expect dTM to be advected from the Eurasian Basin. Differentiating between local advective sources and basin-scale advected sources is difficult with the current dataset. However, by comparing the mean dMn and dFe concentrations of two basins, we can gain some insights regarding the importance of interbasin transport. As AW travels a long distance (~4000 km) from the Eurasian Basis (EB) to the Canada Basin (CB) (Smith et al., 2011), dTM may be scavenged and removed along this path (dTMCB < dTMEB). Conversely, dTM may be enhanced during its transit adjacent to this wide shelf area (dTMCB > dTMEB), if AW is fed by high dMn (~15 nmol kg-1) and dFe (~8.2 nmol kg-1) from the Chukchi shelf during its path from the Eurasian Basin to the Canada Basin (Kondo et al., 2016).   Observations show that scavenging removal is greater than shelf input during transit for the AW, and that there is a net removal of dTM from the EB. The mean concentration of dMn found in the Eurasian Basin along the core isopycnal of 27.8 kg m-3 (0.32 ± 0.11 nmol kg-1, n=18) (Mawji et al., 2015; Middag et al., 2011b) is ~50% greater than it found in the Canada Basin  (0.24 ± 0.07 nmol kg-1, n=32) (Figure 4.10, a)). Similarly, the mean dFe in the CB  (0.27 ± 0.08 nmol kg-1, n=32) shows lower concentration than in the EB (0.51 ± 0.14 nmol kg-1, n=18) (Klunder et al., 2012a; Mawji et al., 2015) (Figure 4.10, b)) or in the Chukchi Sea (Kondo et al., 2016). Since we see evidence for local sources from the continental boundary in the Canadian basin, the amount of dMn and dFe removed during advection from the Eurasian Basic must be even greater than the difference between mean concentrations of CB and EB.     97 4.5 Conclusion  This work presents the vertical and horizontal distribution of dissolved Mn and Fe in the Beaufort Sea. Both elements showed highly structured vertical profiles at the CB and shelf stations. Dissolved Mn was highest at the surface, decreased rapidly in the subsurface PSW layer, and had a slight enhancement at mid-depth in the PWW. Using the end member analysis, we estimated that ~20% of pSML is composed of river water. The extrapolation of upper layer dMn at one station (S4) to zero salinity provided a rough estimate of dMn in the Mackenzie River  (27 – 40 nmol kg-1), which agrees well with the measured dMnRiver (16 – 44 nmol kg-1). Another extrapolation of dMn within the lowest salinity waters across several stations, plotted against the distance of each station to the Mackenzie River mouth, underestimated the dMn in the river  (14.5 nmol kg-1). As there are significant uncertainties in both estimates, it is difficult to quantify the amount of the river-sourced dMn which is diluted or scavenged during its transit to the study area. The sea ice melt water, which makes up 5 – 10 % of the water in the pSML, also a significant source for dMn as it released both dissolved and particulate Mn into the water column. Dissolved Fe also showed elevated surface concentrations, relative to the subsurface PSW, but to a lesser extent than dMn. We suspect that the spring bloom, which occurred before the sampling period, likely removed most of the dFe in the upper 100 m. Additional input after the bloom likely contributed to the surface concentration observed in late August. In the PWW, both elements show elevated concentrations at ~150 m, with a larger elevation at the stations closest to the continental shelf than at the stations in the open ocean. The combined effect of in-situ remineralization, remobilization of dTM from the continental margin, and the advection of dTM rich water from the Chukchi Sea enhanced both dMn and dFe in this study area. The in-situ remineralization, however, is likely more prominent for dFe compared to dMn. Lastly, we assessed the advected sources within the Atlantic layer. Based on the horizontal distribution of both elements in this study area, showing that laterally advected dTM from the continental margin can locally enhance the dTM concentration, as well as inter-comparison of mean dMn and dFe found in CB and EB, we propose that there is net scavenging removal dTM in the Atlantic sourced water during its long path to the study area.    98 Chapter 5: Conclusion   This thesis presents the biogeochemical cycling of manganese in the northeast Pacific and the western Canadian Arctic oceans. In seawater, Mn is regulated by complex interactions amongst sources, sinks and its internal cycling. This dissertation aimed to elucidate the potential mechanisms shaping the Mn distribution in seawater and to help constrain the relative significance of each source and sink based on observations of Mn in the water column. The following sections contain brief summaries on the biogeochemical cycling of Mn in each study location.     5.1 Biogeochemical cycling of Mn in the northeast Pacific Line-P Based on dissolved (Chapter 2) and particulate (Chapter 3) trace metal data, the major processes that control the biogeochemical cycling of Mn in the northeast Pacific across the Line-P transect are outlined here. In general, the distribution of dMn displays distinction between onshore (i.e. P4 and P12) and offshore stations (i.e. P16, P20, P 26) in each layer of the Line-P transect.   1) Within the Summer Mixing Layer (SML), variations in the strength of Ekman transport was the most important factor in controlling the annually variability of dMn at the onshore station (P4) as stronger Ekman transport delivered high-dMn coastal waters to this station. It is observed that large portion of pMn is authigenics, which is likely the result of fast oxidation in the SML. However, since majority of Mn is found in dissolved phase (85%) within this layer, it was concluded that rapid photoreduction of lithogenic particles, delivered via eolian dust and river input, enhanced surface dMn and lowered pMn.  2) Within the Winter Mixing Layer (WML), where the oxygen level was highest, rapid oxidation was the major control on particulate Mn. The large portion of pMn in the authigenic fraction suggests that oxidation enhanced particulate Mn across the transect. However, it was unclear how this process influenced the dMn, as dMn in the WML was higher than in the SML at the offshore stations while it decreased with depth at the onshore stations. I proposed that high dMn in the WML at the offshore stations was a remnant of dMn generated at the surface 99 during the previous winter, by eolian dust and photo-reduction. Observation of dMn in other seasons would be useful to test this hypothesis.    3) Using a simple advection and diffusion model, it was determined that dMn found along the isopycnal 26.8 kg m-3 from station P26 to P16 or P12 is influenced by the advected water masses. The comparison between measured dMn and model-calculated dMn suggests that dMn along this isopycnal is mostly supported by advection of NPIW when the subarctic and subtropical gyre boundaries are located further south and the subarctic gyre encompasses the entire Line-P transect. In the years when these boundaries are located northerly and cross Line-P transect between P12 and P16, the low dMn waters from the south appear to be advected and dilute the dMn found in the Line-P area.   4) Within the Oxygen Minimum Zone (OMZ), where oxygen is below 100 µM, the continental margin is the main source of both dissolved and particulate Mn. In the OMZ, pMn is highest at station P4, adjacent to the continental margin, and gradually decreases toward the open ocean. Particulate Fe has a similar horizontal distribution in this layer, yet its lithogenic fraction is much greater than that of pMn. Based on these observations and knowing that Fe has a slower reduction rate than Mn, it was concluded that lithogenic Mn particles from the continental margin are readily reduced within the OMZ. Hence, the high dMn in the OMZ at station P4 is likely the combined result of re-mobilized dMn and in-situ reduction of lithogenic pMn originated from the continental margin. At the offshore stations, in-situ reduction is likely the main control, as the advection/mixing of both dissolved and particulate Mn from the continental margin is restricted to the onshore stations.   5) Lastly, eddies were observed to transport particulate and dissolved TM rich coastal water to the open ocean. While the lithogenic fractions of both pMn and pFe are enhanced at the station where the eddy was found, pMnlitho increased to a much lower extent than pFelitho. It was concluded that a large portion of the terrigenous pMn transported by the eddy was converted to dMn by photoreduction.    100 Lastly, figure 5.1 summarizes the biogeochemical cycling of Mn across the Line-P transect. The synthesized results and findings of this work (Chapter 2 and 3) are highlighted in red texts and thicker lines.   Figure 5.1 Schematic diagram of Mn biogeochemical cycling across Line-P  5.2 Biogeochemical cycling of Mn in the Beaufort Sea of the Arctic Ocean Dissolved Mn in the Beaufort Sea was influenced by different source waters and mixing, more than by in-situ reduction or oxidation process, due to relatively high O2 concentrations. In the polar Surface Mixed Layer (pSML), river water and sea ice melt water enhanced dMn significantly. The sea ice melt water, in particular, introduced not only dissolved Mn, but also particulate Mn, which could be subsequently reduced via photo-reduction. Within the Pacific Winter Water (PWW), enhanced dMn at the Canada Basin stations (L1 – L3) was the combined result of local 101 remineralization and advection of high dTM from the Chukchi Sea. The enhancement at station S4 in the PWW, on the other hand, was caused by remobilized dMn from the sediments, as the lowest N* values near this area suggested sedimentary Mn-reduction was likely occurring along with denitrification. Based on the mean concentration of dMn found in the Eurasian Basin compared to this study area, as well as the elevated concentration near the continental shelf, it was concluded that dMn in the Atlantic layer is more likely supported by local sources than by advection from the Eurasian Basin. Future work in the Southern part of the Beaufort Sea, near the Mackenzie River input, would be useful to provide more detailed information about the fresh water impacts on this area. Additionally, having TM samples in higher spatial resolution would improve our understanding of the role of fresh water inputs on dTM distributions and cycling in the Beaufort Sea surface layer. Figure 5.2 summarizes the biogeochemical cycling of Mn in this study area. The synthesized results and findings of this work (Chapter 4) are highlighted in red texts and thicker lines.   Figure 5.2 Schematic diagram of Mn biogeochemical cycling in the Beaufort Sea  102 5.3 Thesis conclusion  Based on the suspended particulate and multi-year dissolved Mn samples collected in the northeast Pacific, a comprehensive analysis of the mechanisms controlling Mn in each hydrographic layer across Line-P transect was presented in this dissertation. Several lines of evidence showed that dMn is regulated by 1) dust input, photo-reduction, and most importantly, coastal water input by the annually variable Ekman transport in the SML, 2) oxidation and the remnant of high dMn water generated during the previous winter within the WML, 3) an advected source at the mid-depth by the NPIW, 4) inputs from the continental margin and in-situ reduction in the OMZ, and 5) occasional presence of mesoscale eddies which transported high TM from the coastal area to the open ocean. This work also contributed to our current knowledge about dMn cycling in the Beaufort Sea. Dissolved Mn in this area was controlled by 1) fresh water sources in the pSML, 2) advection and remineralization in the PWW, 3) mixing with high dMn water from the continental margin near the shelf area and within the AW layer.   103 Bibliography Adams, F., Gijbels, R. and Van Grieken, R., 1988. Inorganic Mass Spectrometry. Chemical analysis, 95. Wiley. 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Tully Aug 20 - Sept 6 86   Table A.2 Location of stations and bottom depths along Line-P Station Latitude (°N) Longitude (°W) Bottom Depth (m) P1 48°34.5 125°30.0 120 P2 48°36.0 126°00.0 114 P3 48°37.5 126°20.0 750 P4 48°39.0 126°40.0 1300 P5 48°41.5 127°10.0 2100 P6 48°44.6 127°40.0 2500 P7 48°46.6 128°10.0 2450 P8 48°49.0 128°40.0 2440 P9 48°51.4 129°10.0 2340 P10 48°53.6 129°40.0 2660 P11 48°56.0 130°10.0 2700 P12 48°58.2 130°40.0 3300 P13 49°02.6 131°40.0 2875 P14 49°07.4 132°40.0 3275 P15 49°12.0 133°40.0 3200 P16 49°17.0 134°40.0 3550 P17 49°21.0 135°40.0 3200 P18 49°26.0 136°40.0 3775 P19 49°30.0 137°40.0 3850 P20 49°34.0 138°40.0 3890 P21 49°38.0 139°40.0 3840 P22 49°42.0 140°40.0 3880 P23 49°46.0 141°40.0 3970 P24 49°50.2 142°40.0 3910 P25 50°00.0 143°36.3 3890 P26 50°00.0 145°00.0 4300   119 Table A.3 Concentration of dMn and dFe along Line-P: 2010-2013 Year Depth (m) d[Mn] (nmol kg-1) d[Fe] (nmol kg-1) P4 P12 P16 P20 P26 P4 P12 P16 P20 P26 2010 0 7.164 4.764 0.610 0.827   0.582 0.076 0.426 0.050    5 6.131 4.638 0.505 0.624 0.827 0.586 0.081 0.229 0.116 0.061   10 6.720 4.748 0.572 0.902 0.896 0.967 0.147 0.044 0.130 0.036   25 8.085 4.985 0.827 0.410 1.063 0.557 0.323 0.058 0.203 0.061   40 1.711 2.333  0.250 0.924 0.183 0.517  0.026 0.058   75   1.138 0.998 0.640 1.172  0.275 0.293 0.266 0.088   100   0.522 0.571 0.335 1.147  0.292 0.183 0.153 0.118   150    0.434 0.469 0.636   0.189 0.170 0.474   200   0.656 0.387 0.270 0.753  0.585 0.209 0.187 0.371   300   0.788 0.517 0.849 0.897  0.773 0.478 0.398 0.482   400    0.639  0.998   0.425  0.502   600      0.765     0.592   800         0.510         0.547 2011 10 3.038 2.016 1.007 0.840 0.857 0.175 0.359 0.100 0.097 0.037   25 1.859 1.344 1.257 0.854 1.440 0.158 0.122 0.249 0.042 0.188   35 2.669      0.276       40 1.307 1.488  0.563 1.624 0.196 0.059  0.039 0.093   50 1.275 1.214 1.234 0.756 1.716 0.248 0.093 0.117 0.042 0.087   75 1.020 1.096 1.124 0.964 1.521 0.257 0.109 0.196 0.089 0.105   100 1.061 0.800 1.051 0.541 1.525 0.390 0.237 0.134 0.111 0.081   130   0.691 0.625 0.818   0.341 0.392 0.205   150 0.441 0.414 0.582 0.524 0.601 0.538 0.336 0.316 0.472 0.280   175 0.647   0.711   185 0.593 0.717 0.406 0.410   200 0.534 0.677 0.576 0.734 0.733 0.439 0.597 0.325 0.466 0.369   250 0.649 0.788     0.784 0.721      275   0.792      0.499     300 0.792 0.898 0.682 0.835 0.774 0.940 0.723 0.513 0.641 0.563   350              360 0.777      0.929       400 0.986 1.276 0.710 0.769 0.839 1.136 1.072 0.559 0.622 0.633   600 1.453 1.319 0.692 0.739 0.671 1.750 0.978 0.739 0.630 0.654   675  1.292      0.955      700 1.336 1.440     1.370 1.248      800 1.446 1.466 0.529 0.510 0.538 1.395 1.155 0.686 0.666 0.727   900 1.465      1.446       1000 1.556 1.302  0.443 0.447 1.529 1.110  0.700 0.707   1100 1.599  0.540 0.524 0.445 1.628  0.636 0.645 0.696   1200 2.002 1.367 0.548 0.553 0.441 2.241 1.382 0.642 0.634 0.670   1400  0.832 0.477 0.394 0.404  0.978 0.892 0.649 0.660   1600  0.856 0.378 0.415 0.385  0.935 0.785 0.782 0.656   1800  1.127 0.352 0.336 0.325  1.054 0.663 0.645 0.639   2000   2.476 0.305 0.304 0.303   1.795 0.646 0.602 0.674   120 Table A.3 continues Year Depth (m) d[Mn] (nmol kg-1) d[Fe] (nmol kg-1)  P4 P12 P16 P20 P26 P4 P12 P16 P20 P26  2012 10 9.903 1.332 0.212 0.917 0.854 0.382 0.392 0.038 0.039 0.062    25 1.756 1.963 0.637 0.841 1.103 0.112 0.102 0.048 0.038 0.019    50 1.431 1.294 0.960 (0.264) 1.346 0.356 0.071 0.025 (0.002) 0.051    75 1.346 0.842 1.312 0.884 1.587 0.297 0.086 0.206 0.012 0.084    100 0.881 0.450 0.680 1.223 1.263 0.316 0.044 0.172 0.104 0.109    200 1.196 0.156 0.384 0.553 0.768 1.343 0.220 0.307 0.398 0.754    400 1.145 0.394 0.525 0.607 0.671 1.971 0.406 0.536 0.596 0.612    600 1.320 0.665 0.488 0.412 0.678 2.269 0.553 0.651 0.467 0.645    800 1.625 0.523 0.435 0.266 0.257 1.796 0.677 0.513 0.761 0.585    1000 1.590 0.706 0.491 0.204 0.402 1.697 0.972 0.285 0.601 0.620    1200 1.616  0.421  0.175 1.924  0.631  0.722    1400  0.717 0.313  0.190  1.139 0.756  0.584    1800  1.509 0.175 0.099 0.113  1.426 0.627 0.505 1.071    2000     0.296     0.585    2100     0.276     0.580    2500       0.233       0.558  2013 10 11.616 2.944 2.029 0.338 0.961 0.258 0.155 0.078 0.060 0.050    25 5.228 1.747 0.938 0.710 1.035 0.287 0.048 0.047 0.093 0.068    50 2.140 1.987 1.657  1.516 0.226 0.148 0.188  0.110    75  1.636 2.103  1.170  0.264 0.206  0.120    100 0.930 0.756 1.335 (0.705) 1.025 0.380 0.132 0.205 (0.086) 0.156    130 1.499      0.568        150 0.568 0.560 0.622 0.288 0.380 0.266    200 0.761 0.430 0.499 0.542 0.970 0.345 0.259 0.469    250 0.703 0.508 0.517 0.369    300  0.754      0.651       350     0.979     0.514    360 0.521      1.499        400 1.014 0.654 1.114  0.886 1.793 0.813 0.765  0.014    450  0.738      0.726       500  0.850   0.722  0.756   0.571    550   1.339      0.990      600 1.011 0.732 1.322  0.428 1.736 0.844 0.989  0.600    650     0.234     0.628    700   1.186      0.991      800 0.809 0.723 0.934  0.219 1.674 0.823 0.808  0.502    900   0.726 0.272 0.256   0.741 0.533 0.615    1000 1.047 0.715  0.278 0.236 1.303 0.825  1.014 0.581    1100  0.772 0.614 0.343    1.002 0.683 0.533     1200 1.414   0.250 0.264 2.007   0.532 0.757    1300  0.478      0.788       1400  0.446 0.509 0.230 0.446  0.685 0.691 0.561 0.539    1600  0.459 0.445  0.055  0.879 0.751  0.638    1800  0.677 0.353 0.075 0.063  0.907 0.791 0.495 0.623    2000  0.766 0.241 0.066 0.055  1.796 0.741 0.481 0.691    2500     0.138     0.695    3000     0.178     0.625    3500     0.206     0.594    4000         0.197         0.596  *The sampling depth may not be correct for the values in the parentheses. Excluded for the analysis 121        Table A.4 Concentration of duplicate samples of dMn and dFe collected from Line-P Year Event Station Depth (m) d[Mn] (nmol kg-1) d[Fe] (nmol kg-1) Mean Raw Values Mean Raw Values 2010 29 P12 300 0.788 (0.766,0.810) 0.773 (0.807,0.783)  58 P16 400 0.639 (0.644,0.633) 0.425 (0.409,0.440) 2011 11 P4 150 0.441 (0.446,0.437) 0.538 (0.543,0.532)  11 P4 200 0.534 (0.526,0.541) 0.439 (0.671,0.713)  17 P4 600 1.453 (1.442,1.465) 1.75 (1.688, 1.812)  17 P4 1200 2.002 (2.018,1.985) 2.241 (2.231,2.251) 32 P12 400 1.276 (1.309,1.243) 1.072 (1.082,1.062) 32 P12 700 1.44 (1.391,1.488) 1.248 (1.208,1.289)  32 P12 1200 1.367 (1.328,1.407) 1.382 (1.385,1.380)  32 P12 1400 0.832 (0.861,0.803) 0.978 (0.999,0.956)  41 P16 25 1.257 (1.199,1.315) 0.249 (0.242,0.256)  41 P16 50 1.234 (1.196,1.272) 0.117 (0.115,0.118)  69 P26 150 0.601 (0.582,0.619) 0.28 (0.298,0.261)  72 P26 1600 0.385 (0.384,0.385) 0.656 (0.640,0.671) 2013 84 P26 150 0.622 (0.592,0.652) 0.266 (0.249,0.282)    76 P26 400 0.886 (0.880,0.892) 0.525 (0.515,0.535)    122 Appendix B  Supplementary material for chapter 3    Table B.1 Concentration of filter blanks Al Fe Mn Cu Zn Pb Ba Th V Ni Co P CdFilter blank (0.45 µm pore size) (nmol filter-1)mean (n=3) 1.2E+00 1.7E-01 4.8E-02 6.2E-02 2.2E-01 4.5E-03 1.9E-01 1.2E-03 6.0E-02 6.5E-02 4.6E-02 3.5E-01 1.8E-03standard deviation 1.5E-01 2.6E-02 1.4E-03 5.4E-04 2.2E-02 1.3E-04 1.0E-02 1.5E-05 5.7E-04 6.5E-03 6.0E-04 4.7E-02 8.2E-05RSD (%) 13 15 3 1 10 3 5 1 1 10 1 14 5Filter blank (20 µm pore size) (nmol filter-1)mean (n=3) 7.2E-01 4.6E-01 5.0E-02 8.0E-02 7.7E-02 6.9E-03 2.3E-02 1.2E-03 6.1E-02 1.9E-01 4.6E-02 2.1E-01 1.7E-03standard deviation 8.6E-02 6.0E-03 1.0E-03 2.9E-03 1.1E-02 3.9E-04 2.1E-03 2.2E-05 1.2E-03 1.2E-02 1.0E-03 3.3E-02 4.5E-05RSD (%) 12 1 2 4 14 6 9 2 2 6 2 15 3      123  Table B.2 Elemental concentrations of Small Suspended Particle (SSP) (0.45-20 µm) Station Depth (m) Particulate elements: smaller size fractionation (nmol kg-1) Al Fe Mn Cu Zn Pb Ba Th V Ni Co P Cd P4 10 2.057 0.410 0.095 0.030 0.125 8.9E-04 0.065 2.1E-05 0.011 0.032 0.003 35.35 7.9E-03 P4 50 0.742 0.167 0.025 0.032 0.041 4.6E-04 0.081 6.0E-06 0.005 0.015 0.001 11.55 9.7E-03 P4 100 3.946 1.025 0.183 0.044 0.112 1.1E-03 0.139 2.5E-05 0.011 0.015 0.003 8.34 1.2E-02 P4 120 8.186 1.755 0.388 0.050 0.110 2.0E-03 0.077 4.1E-05 0.015 0.018 0.005 8.71 1.0E-02 P4 600 15.961 3.064 0.048 0.029 0.052 1.2E-03 0.206 5.9E-05 0.019 0.012 0.003 4.91 1.9E-03 P4 1000 11.608 2.339 0.047 0.028 0.054 7.3E-04 0.173 4.8E-05 0.014 0.009 0.005 2.56 5.0E-04 P12 10 0.391 0.151 0.02 0.045 0.026 5.7E-04 0.008 6.0E-06 0.008 0.092 0.002 27.31 1.1E-02 P12 50 0.625 0.283 0.034 0.041 0.029 7.8E-04 0.239 1.2E-05 0.021 0.074 0.003 14.37 1.1E-02 P12 100 0.452 0.190 0.096 0.019 0.021 3.0E-04 0.034 5.0E-06 0.011 0.014 0.002 4.30 6.1E-03 P12 300 1.277 0.334 0.024 0.022 0.011 2.5E-04 0.084 7.0E-06 0.013 0.006 0.001 3.64 2.3E-03 P12 400 4.098 0.744 0.049 0.034 0.082 5.8E-04 0.281 1.7E-05 0.023 0.018 0.002 5.75 2.9E-03 P12 600 4.384 0.950 0.036 0.032 0.077 6.2E-04 0.259 1.9E-05 0.016 0.015 0.002 3.48 1.1E-03 P12 1100 8.583 1.655 0.079 0.036 0.060 7.1E-04 0.321 3.3E-05 0.016 0.014 0.002 2.59 5.8E-04 P12 1600 11.767 1.591 0.267 0.056 0.069 5.6E-04 0.070 1.0E-05 0.016 0.015 0.002 2.55 2.2E-04 P12 2000 6.140 1.251 0.278 0.036 0.062 4.6E-04 0.053 1.0E-05 0.012 0.043 0.002 3.72 1.6E-04   124 Table B.2 continues Station Depth (m) Particulate elements: smaller size fractionation (nmol kg-1) Al Fe Mn Cu Zn Pb Ba Th V Ni Co P Cd P16 10 3.556 0.529 0.031 0.05 0.227 1.2E-03 0.116 4.0E-05 0.016 0.046 0.006 33.00 1.9E-02 P16 50 1.539 0.228 0.057 0.034 0.172 9.9E-04 0.212 2.4E-05 0.035 0.03 0.004 45.80 1.4E-02 P16 100 3.361 0.559 0.121 0.031 0.133 8.2E-04 0.318 7.2E-05 0.023 0.014 0.002 16.48 1.5E-02 P16 200 1.567 0.458 0.081 0.035 0.109 9.2E-04 0.260 2.1E-05 0.021 0.013 0.002 6.84 8.3E-03 P16 250 1.975 0.530 0.073 0.030 0.067 6.3E-04 0.099 2.1E-05 0.022 0.009 0.002 6.48 5.6E-03 P16 550 4.431 0.804 0.031 0.035 0.050 4.1E-04 0.230 8.2E-05 0.012 0.008 0.003 4.18 3.5E-03 P16 800 2.938 0.680 0.040 0.027 0.054 3.8E-04 0.252 3.7E-05 0.012 0.008 0.001 2.46 9.3E-04 P16 1100 0.913 0.260 0.031 0.077 0.028 1.3E-03 0.010 2.3E-05 0.013 0.045 0.006 3.51 5.1E-04 P16 1600 1.027 0.333 0.059 0.031 0.045 2.8E-04 0.265 2.1E-05 0.007 0.006 0.003 4.73 2.6E-04 P16 2000 1.783 0.515 0.066 0.039 0.016 3.0E-04 0.273 3.5E-05 0.008 0.012 0.002 2.74 2.5E-04 P26 10 0.502 0.228 0.058 0.063 0.134 1.9E-03 0.043 2.2E-05 0.016 0.061 0.008 57.85 1.8E-02 P26 50 0.397 0.129 0.030 0.025 0.010 3.0E-04 0.197 1.6E-05 0.005 0.035 0.001 3.38 1.0E-03 P26 75 1.298 0.563 0.062 0.030 0.046 4.7E-04 0.429 3.8E-05 0.005 0.017 0.002 2.96 6.2E-04 P26 100 0.666 0.188 0.164 0.029 0.033 1.2E-03 0.224 1.9E-05 0.007 0.071 0.003 7.81 1.1E-02 P26 350 0.785 0.390 0.060 0.044 0.009 8.5E-04 0.315 3.5E-05 0.008 0.212 0.002 4.03 4.1E-03 P26 500 0.655 0.351 0.035 0.051 0.141 1.8E-03 0.135 1.8E-05 0.014 0.061 0.003 20.71 1.4E-02 P26 1000 1.167 0.742 0.048 0.031 0.024 4.2E-04 0.278 3.9E-05 0.005 0.013 0.003 3.16 5.0E-04 P26 1200 0.974 0.576 0.038 0.041 0.010 5.4E-04 0.230 2.8E-05 0.006 0.285 0.001 2.40 3.9E-04 P26 1600 0.861 0.299 0.030 0.032 0.011 2.5E-04 0.296 2.3E-05 0.005 0.049 0.001 2.56 2.8E-04 P26 2000 1.215 0.409 0.030 0.031 0.024 2.0E-04 0.233 2.7E-05 0.004 0.007 0.002 1.99 1.9E-04  125  Table B.3 Elemental concentrations of Large Suspended Particle (LSP) ( >20 µm) Station Depth (m) Particulate elements: larger size fractionation (nmol kg-1) Al Fe Mn Cu Zn Pb Ba Th V Ni Co P Cd P4 10 0.301 0.152 0.010 0.004 0.031 6.3E-04 0.025 3.00E-06 0.003 0.003 - 1.76 7.3E-04 P4 50 1.214 0.173 0.005 0.006 0.016 3.6E-04 0.019 1.60E-05 0.002 0.003 0.027 1.39 6.7E-04 P4 100 0.987 0.228 0.016 0.003 0.008 1.5E-04 0.046 8.00E-06 0.002 - 0.006 0.815 4.4E-04 P4 120 1.181 0.279 0.046 0.004 0.019 3.6E-04 0.043 7.00E-06 0.003 - 0.003 0.790 2.5E-04 P4 600 2.608 0.532 0.006 0.004 0.022 9.5E-05 0.026 1.00E-05 0.005 0.002 0.001 0.748 1.8E-04 P4 1000 1.845 0.167 0.003 0.004 0.030 - 0.016 5.00E-06 0.003 - - 0.410 1.2E-04 P12 10 0.187 0.041 0.010 0.008 0.018 2.0E-04 0.019 5.00E-06 0.005 0.015 0.003 4.00 1.7E-03 P12 50 0.145 0.079 0.007 0.012 0.010 1.2E-04 0.019 4.00E-06 0.013 0.057 - 1.51 8.6E-04 P12 100 0.243 0.04 0.028 0.004 0.008 1.2E-04 0.029 2.00E-06 0.010 0.010 0.001 0.680 2.0E-04 P12 300 0.914 0.257 0.020 0.009 0.032 4.6E-04 0.065 5.00E-06 0.015 0.031 0.001 0.729 1.7E-04 P12 400 0.972 0.110 0.004 0.004 0.028 7.8E-05 0.030 9.00E-06 0.01 0.004 - 0.705 2.1E-04 P12 600 0.511 0.078 0.002 0.001 0.018 - 0.020 7.00E-06 0.004 0.010 0.001 0.281 1.2E-04 P12 1100 0.612 0.113 0.002 0.003 0.018 - 0.018 1.00E-05 0.003 0.007 - 0.406 1.5E-04 P12 1600 0.743 0.133 0.012 0.003 0.007 1.8E-05 0.021 9.00E-06 0.005 0.005 0.010 0.263 4.3E-05 P12 2000 0.635 0.132 0.022 0.007 0.006 5.5E-05 0.023 1.00E-05 0.003 0.074 - 0.222 2.7E-05   126 Table B.3 continues Station Depth (m) Particulate elements: larger size fractionation (nmol kg-1) Al Fe Mn Cu Zn Pb Ba Th V Ni Co P Cd P16 10 0.561 0.090 0.02 0.005 0.051 4.40E-05 0.028 9.00E-06 0.002 0.001 0.002 1.23 7.80E-04 P16 50 0.441 0.074 0.005 0.005 0.024 9.40E-05 0.018 9.00E-06 0.016 - 0.002 1.70 1.50E-03 P16 100 0.377 0.144 0.03 0.008 0.013 4.60E-04 0.030 8.00E-06 0.009 0.023 - 1.15 5.80E-04 P16 200 0.293 0.090 0.009 0.012 0.016 4.40E-04 0.185 5.00E-06 0.005 0.005 0.003 7.69 3.70E-03 P16 250 0.276 0.057 0.003 0.002 0.013 - 0.016 5.00E-06 0.004 - 0.001 0.429 1.80E-04 P16 550 0.444 0.08 0.002 0.005 0.008 - 0.013 7.00E-06 0.003 - 0.004 0.785 8.70E-05 P16 800 0.248 0.045 0.001 0.001 0.002 - 0.010 5.00E-06 0.002 - - 0.213 5.90E-05 P16 1100 0.343 0.096 0.004 0.005 0.006 9.20E-05 0.039 7.00E-06 0.010 - 0.001 0.773 2.10E-04 P16 1600 0.146 0.047 0.004 0.003 0.007 - 0.033 6.00E-06 0.003 - 0.002 0.214 6.10E-05 P16 2000 0.311 0.055 0.004 0.006 0.017 2.60E-05 0.023 1.20E-05 0.003 0.001 0.001 0.501 3.00E-05 P26 10 0.210 0.283 0.010 0.034 0.023 8.30E-04 0.012 3.00E-06 0.007 0.351 0.001 4.41 2.10E-03 P26 50 0.173 0.113 0.006 0.025 0.013 5.90E-04 0.176 3.00E-06 0.003 0.300 - 1.46 7.90E-04 P26 75 0.174 0.045 0.002 0.005 0.010 7.20E-05 0.036 5.00E-06 0.002 0.017 - 0.384 4.90E-05 P26 100 0.171 0.053 0.004 0.013 0.012 2.00E-04 0.035 4.00E-06 0.003 0.157 - 0.293 1.70E-04 P26 350 0.339 0.279 0.007 0.03 0.011 4.40E-04 0.026 3.00E-06 0.003 0.331 - 0.585 1.10E-04 P26 500 0.097 0.125 0.004 0.018 0.001 3.40E-04 0.037 3.00E-06 0.002 0.267 - 0.303 5.60E-05 P26 1000 0.255 0.086 0.007 0.012 0.111 1.20E-04 0.044 6.00E-06 0.003 0.029 - 2.96 2.10E-04 P26 1200 0.184 0.839 0.009 0.07 0.019 1.20E-03 0.086 6.00E-06 0.006 1.01 0.002 0.523 8.00E-05 P26 1600 0.141 0.113 0.001 0.015 0.006 1.00E-03 0.019 2.00E-06 0.003 0.162 - 0.307 5.50E-05 P26 2000 0.215 0.037 0.002 0.003 0.005 - 0.029 5.00E-06 0.002 0.003 - 0.291 6.10E-05 127 Appendix C  Supplementary material for chapter 4 Table C.1 Concentration of dMn and dFe in the Beaufort Sea in 2009. All units are in nmol kg-1. Station Depth (m) dMn dFe Station Depth (m) dMn dFe Station Depth (m) dMn dFe L1 9 5.339 0.515 L2 8 4.622 0.227 L1.5 10 6.736 0.340 L1 15 5.716 0.243 L2 20 4.800 0.191 L1.5 19 5.810 0.276 L1 31 4.066 0.191 L2 55 1.377 0.141 L1.5 40 3.627 0.188 L1 50 2.226 0.181 L2 80 0.659 0.242 L1.5 90 0.941 0.297 L1 70 1.587 0.213 L2 120 1.215 0.371 L1.5 140 1.168 0.533 L1 90 1.252 0.472 L2 181 0.780 0.449 L1.5 190 1.275 0.556 L1 120 1.366 0.566 L2 270 0.411 0.254 L1.5 280 0.531 0.341 L1 150 1.222 0.574 L2 360 0.216 0.217 L1.5 380 0.235 0.242 L1 175 1.052 0.602 L2 400 0.207 0.220 L1.5 450 0.290 0.195 L1 200 0.918 0.657 L2 440 0.161 0.217 L1.5 600 0.249 0.234 L1 250 0.563 0.582 L2 551 0.149 0.238 L1.5 800 0.255 0.304 L1 300 0.631 0.543 L2 †700 0.233 0.238 L1.5 1001 0.280 0.322 L1 400 0.447 0.428 L2 †800 0.389 0.166 S4 7 7.970 0.535 L1 500 0.267 0.415 L2 899 0.139 0.213 S4 8 8.922 0.479 L1 600 0.257 0.387 L2 1094 0.123 0.214 S4 17 4.953 0.274 L1 749 0.275 0.381 L2 1300 0.085 0.206 S4 25 3.972 0.270 L1 1000 0.406 0.471 L2 1500 0.095 0.253 S4 50 2.269 0.382 L1 1250 0.328 0.477 L2 1700 0.082 0.265 S4 90 3.279 1.006 L1 1500 0.694 0.391 L2 1900 0.133 0.295 S4 120 3.491 1.402 L1 1800 1.387 0.284 L2 2100 0.068 0.255 S4 150 5.162 1.848 L1.1 8 5.813 0.255 L2 2300 0.146 0.269 S4 200 1.463 1.002 L1.1 20 5.903 0.192 L2 2501 0.143 0.264 S4 240 1.342 0.919 L1.1 40 2.156 0.123 L2 2701 0.150 0.246 S4 275 1.678 0.810 L1.1 60 1.578 0.129 L2 2950 0.121 0.288     L1.1 75 1.337 0.178 L3 10 3.443 0.840     L1.1 90 1.095 0.258 L3 30 2.837 0.185     L1.1 111 0.976 0.344 L3 55 1.703 0.191     L1.1 130 1.149 0.407 L3 140 1.039 0.520     L1.1 170 1.053 0.460 L3 180 1.147 0.592     L1.1 211 0.823 0.459 L3 260 0.389 0.293     L1.1 270 0.474 0.298 L3 360 0.174 0.239     L1.1 361 0.230 0.256 L3 440 0.324 0.244     L1.1 400 0.377 0.286 L3 600 0.138 0.287     L1.1 425 0.271 0.246 L3 800 0.280 0.308     L1.1 500 0.262 0.253 L3 1000 0.198 0.240     L1.1 651 0.267 0.287 L3 1200 0.215 0.219     L1.1 801 0.246 0.227          L1.1 1000 0.231 0.257          L1.1 1250 0.298 0.289          L1.1 1500 0.342 0.324          L1.1 1751 0.213 0.225          L1.1 2001 0.093 0.213          L1.1 2251 0.091 0.234          L1.1 2400 0.068 0.344            128         Table C.2 Concentration of duplicate samples of dMn and dFe collected from the Beaufort Sea Event Station Depth (m) dMn (nmol kg-1) dFe (nmol kg-1) Measurement 1 Measurement 2 Measurement 1 Measurement 2 24 L1 200 0.958 0.877 0.614 0.699 †59/67 L1.1 425 0.262 0.280 0.253 0.239 33 L1.5 1001 0.285 0.275 0.340 0.304 35 L2 2950 0.130 0.113 0.310 0.265 78 S4 240 1.325 1.358 0.928 0.910 †Sample collected at the same depth and location by two different casts   129   Table C.3 Concentration of dBa in the Beaufort Sea in 2009. All units are in nmol kg-1. Station Depth (m) dBa Station Depth (m) dBa L1 2 64.665 L2 3 71.224 L1 10 65.092 L2 30 71.045 L1 22 66.548 L2 55 65.388 L1 50 64.877 L2 100 67.514 L1 85 69.881 L2 125 68.382 L1 126 75.475 L2 150 69.787 L1 150 71.815 L2 200 50.887 L1 200 56.800 L2 250 41.649 L1 250 49.522 L2 300 42.420 L1 300 45.515 L2 400 43.645 L1  400 41.328 L2 500 43.043 L1 500 44.834 L2 600 41.679 L1 600 41.832 L2 1000 41.314 L1 800 47.318 L2 1200 43.081 L1 1000 41.762 L2 1400 37.946 L1  1200 43.067 L2 1600 45.007 L1 1400 41.526 L2 1800 44.472 L1 1700 45.586 L2 2000 46.614 L1.1 3 66.496 L2 2250 47.065 L1.1 10 70.442 L2 2500 47.868 L1.1 25 70.724 L2 2750 49.952 L1.1 70 65.900 L3 3 73.284 L1.1 140 69.563 L3 10 73.926 L1.1 175 66.277 L3 32 68.573 L1.1 200 61.561 L3 60 65.130 L1.1 250 42.488 L3 115 67.720 L1.1 300 44.107 L3 140 69.058 L1.1 350 40.936 S2 3 82.315 L1.1 400 41.072 S2 15 72.627 L1.1 450 40.962 S2 45 67.855 L1.1 500 41.968 S2 75 63.336 L1.1 600 41.856 S2 100 70.650 L1.1 800 42.292 S2a 125 70.571 L1.1 1000 42.734 S2a 150 71.493 L1.1 1400 46.149 S2a 175 72.822 L1.1 1800 46.524 S2a 200 67.234 L1.1 2000 48.043     L1.1 2250 51.456    L1.1 2500 48.730       

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