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Phytoplankton dynamics in the northeast subarctic Pacific during the 1998 El Niño, the 1999 La Niña and… Lipsen, Michael Simon 2008

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PHYTOPLANKTON DYNAMICS IN THE NORTHEAST SUBARCTIC PACIFIC DURING THE 1998 EL NIÑO, THE 1999 LA NIÑA AND 2000 WITH SPECIAL CONSIDERATION TO THE ROLE OF COCCOLITHOPHORES AND DIATOMS    by   Michael Simon Lipsen  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY  in  THE FACULTY OF GRADUATE STUDIES  (Botany)   THE UNIVERSITY OF BRITISH COLUMBIA  (Vancouver)   April 2008  ©Michael Simon Lipsen, 2008  ii Abstract Phytoplankton dynamics and chemical characteristics of the euphotic zone were measured from 1998-2000 (an El Niño/La Niña cycle) at the 5 major stations along Line P. Near-shelf  and offshore stations exhibited low seasonality in chlorophyll and moderate seasonality in particulate organic carbon (POC) production. During the 1998 El Niño, June was characterized by low chlorophyll and POC productivity due to nitrate depletion. In contrast, during the 1999 La Niña, and in 2000, higher POC productivity and nitrate occurred in June. During 1999, chlorophyll and POC productivity were similar to 1998 in late summer. Near-shelf biomass was highest in June and lowest in Feb. for the near-shelf stations. High nitrate, low chlorophyll (HNLC) stations had the highest chlorophyll in Feb. followed by June. The coccolithophore assemblage was usually numerically dominated by Emiliania huxleyi, particularly in June. Along the transect, coccolithophore abundance was much higher in June during the 1998 El Niño than in the 1999 La Niña, with Aug./Sept. abundance of both years being very low. Higher abundances were measured along the transect in June and the late summer of 2000 with sporadic ‘blooms’ of >1000 cells ml-1 at some stations. Particulate inorganic carbon (PIC) production was high along the transect during June 1998, and low during both winters, June 1999 and during late summers of 1998 and 1999. There was an increase in diatom biomass and >20 µm POC production during the 1998 El Niño, specifically in the farthest offshore HNLC stations, yet diatoms were rarely found to dominate total phytoplankton biomass or production. However, there were some sporadic examples of anomalously high diatom biomass (carbon and abundance) as well as >20 μm POC production, specifically at P12 in Aug./Sept 2000. The same major diatom species were found throughout Line P (near-shelf, P16, and HNLC). Integrated silica production measured by 32Si ranged from 0.2 to 4.7 mmol Si m-2 d-1 between 1999-2000. Silicic acid and nitrate were never limiting at all stations in Feb. and generally increased in concentration along Line P during all seasons.  iii TABLE OF CONTENTS ABSTRACT....................................................................................................................... ii TABLE OF CONTENTS ................................................................................................ iii LIST OF TABLES .......................................................................................................... vii LIST OF FIGURES ......................................................................................................... xi LIST OF ABBREVIATIONS ....................................................................................... xvi CO-AUTHORSHIP STATEMENT ............................................................................ xvii ACKNOWLEDGEMENTS ........................................................................................ xviii CHAPTER 1 : INTRODUCTION TO PHYTOPLANKTON PROCESSES OF THE NE SUBARCTIC PACIFIC............................................................................................. 1 1.1 BACKGROUND................................................................................................... 1 1.1.1 The NE subarctic Pacific............................................................................. 1 1.1.2 1997-1999 El Niño/Southern Oscillation (ENSO) ...................................... 2 1.1.3 Nitrate and iron ........................................................................................... 4 1.1.4 Silicate ......................................................................................................... 5 1.2 BIOLOGY........................................................................................................... 6 1.2.1 Primary productivity ................................................................................... 6 1.2.2 Coccolithophores along Line P ................................................................... 7 1.2.3 Siliceous phytoplankton (diatoms and silicoflagellates) along Line P ....... 8 1.3 OVERVIEW OF THIS THESIS................................................................................ 9 1.4 THESIS OBJECTIVES .......................................................................................... 9 1.5 TABLES ........................................................................................................... 12 1.6 FIGURES.......................................................................................................... 13 1.7 REFERENCES ................................................................................................... 15 CHAPTER 2 : SPATIAL AND TEMPORAL VARIABILITY IN SIZE- FRACTIONATED ORGANIC PRIMARY PRODUCTION, CHLOROPHYLL BIOMASS AND PHOTOSYNTHETIC PERFORMANCE IN THE NE SUBARCTIC PACIFIC DURING EL NIÑO (1998), LA NIÑA (1999) AND 2000 . 21 2.1 INTRODUCTION ............................................................................................... 21 2.2 MATERIALS AND METHODS ............................................................................ 22 2.2.1 Sampling location...................................................................................... 22 2.2.2 Study area.................................................................................................. 23 2.2.3 Sample collection and processing ............................................................. 23 2.2.4 Chlorophyll a and POC ’primary’ production.......................................... 24 2.2.5 Photosynthesis versus irradiance measurements (P vs. E) ....................... 25 2.2.6 Deck incubation photosynthesis versus irradiance (P vs. E) .................... 26 2.2.7 POC and nutrients..................................................................................... 26 2.2.8 Contour plotting ........................................................................................ 27 2.2.9 Statistical testing ....................................................................................... 27 2.3 RESULTS ......................................................................................................... 27  iv 2.3.1 Euphotic zone properties ........................................................................... 27 2.3.2 Nutrients .................................................................................................... 28 2.3.3 Phytoplankton biomass.............................................................................. 28 2.3.4 Particulate organic carbon ....................................................................... 30 2.3.5 POC production......................................................................................... 30 2.3.6 Size-fractionated biomass and production ................................................ 32 2.3.7 Integrated chlorophyll a-specific total POC production........................... 32 2.3.8 Carbon specific phytoplankton growth rates ............................................ 33 2.3.9 Photosynthesis versus irradiance (P vs. E) characteristics ...................... 33 2.3.10 Depth-variation in photosynthetic performance ..................................... 35 2.4 DISCUSSION .................................................................................................... 36 2.4.1 Variations in biomass and particulate organic carbon............................. 36 2.4.2 Seasonal variations in POC production.................................................... 38 2.4.3 Historic P26 POC production ................................................................... 38 2.4.4 Interannual variability during 1998 (El Niño), 1999 (La Niña) and 2000 39 2.4.5 Phytoplankton growth rates ...................................................................... 42 2.4.6 Size-fractionated biomass and production ................................................ 43 2.4.7 Photosynthesis vs. irradiance (P vs. E) relationships ............................... 44 2.4.8 Control of production by PAR along Line P ............................................. 46 2.4.9 Factors controlling carbon production ..................................................... 48 2.4.10 Fate of POC............................................................................................. 49 2.5 CONCLUSIONS................................................................................................. 50 2.6 TABLES ........................................................................................................... 51 2.7 FIGURES.......................................................................................................... 60 2.8 REFERENCES ................................................................................................... 79 CHAPTER 3 : SPATIAL AND TEMPORAL VARIABILITY IN COCCOLITHOPHORE ABUNDANCE AND PRODUCTION OF PIC AND POC IN THE NE SUBARCTIC PACIFIC DURING EL NIÑO (1998), LA NIÑA (1999) AND 2000......................................................................................................................... 88 3.1 INTRODUCTION ............................................................................................... 88 3.2 METHODS ....................................................................................................... 91 3.2.1 Sampling protocols.................................................................................... 91 3.2.2 T, S, light, nutrients and chlorophyll ......................................................... 91 3.2.3 POC and PIC incubations ......................................................................... 92 3.2.4 Separation of 14C labeled POC and PIC................................................... 93 3.2.5 Coccolithophore enumeration ................................................................... 93 3.2.6 Statistical testing ....................................................................................... 94 3.2.7 Contour plotting ........................................................................................ 94 3.3 RESULTS ......................................................................................................... 95 3.3.1 Physical and chemical conditions ............................................................. 95 3.3.2 Coccolithophore abundance and community structure............................. 95 3.3.3 Phytoplankton biomass, POC and PIC production................................... 96 3.3.4 PIC:POC production ratios ...................................................................... 98 3.4 DISCUSSION .................................................................................................... 99 3.4.1 Seasonal and spatial variations in coccolithophore abundance............... 99 3.4.2 Interannual variability: El Niño, La Niña, and 2000.............................. 100  v 3.4.3 PIC production vs. coccolithophore abundance ..................................... 101 3.4.4 PIC and POC production ........................................................................ 102 3.4.5 Bottom-up controls: nutrients, Fe, light and PIC production ................. 103 3.4.6 Top-down controls................................................................................... 105 3.4.7 Satellite images........................................................................................ 106 3.5 CONCLUSIONS............................................................................................... 107 3.6 TABLES ......................................................................................................... 109 3.7 FIGURES........................................................................................................ 113 3.8 REFERENCES ................................................................................................. 120 CHAPTER 4 : SILICEOUS PHYTOPLANKTON ABUNDANCE AND SILICA PRODUCTION RATES ALONG LINE P IN THE NE PACIFIC 1998-2000........ 129 4.1 INTRODUCTION ............................................................................................. 129 4.2 METHODS ..................................................................................................... 131 4.2.1 Sample collection..................................................................................... 131 4.2.2 Light and nutrients .................................................................................. 131 4.2.3 Particulate organic carbon (POC).......................................................... 132 4.2.4 Chlorophyll a and POC production ........................................................ 132 4.2.5 Siliceous phytoplankton enumeration and identification ........................ 132 4.2.6 Siliceous phytoplankton carbon quota calculations................................ 133 4.2.7 Biogenic silica ......................................................................................... 133 4.2.8 Silica production rates (32Si) ................................................................... 133 4.2.9 Statistical analysis ................................................................................... 134 4.2.10 Contour plotting .................................................................................... 134 4.3 RESULTS ....................................................................................................... 135 4.3.1 Physical conditions.................................................................................. 135 4.3.2 Silicic acid and nitrate concentrations.................................................... 135 4.3.3 Particulate Si (bSi) .................................................................................. 136 4.3.4 Large size fraction (>20 µm) biomass and production........................... 137 4.3.5 Siliceous phytoplankton abundance and carbon..................................... 138 4.3.6 Diatom species......................................................................................... 139 4.3.7 Silica production rates ............................................................................ 140 4.4 DISCUSSION .................................................................................................. 140 4.4.1 Siliceous biomass and community structure............................................ 140 4.4.2 Variations in diatom biomass and carbon production ............................ 142 4.4.3 Diatom biomass and production: El Niño, La Niña and 2000................ 143 4.4.4 Diatom community structure ................................................................... 144 4.4.5 Dissolved nitrate (NO3-) and silicate [Si(OH)4] utilization .................... 145 4.4.6 Seasonal and spatial variations in silica production .............................. 146 4.4.7 Fe, light and diatom production.............................................................. 147 4.4.8 Comparison of Line P POC, PIC and silica production ......................... 148 4.4.9 Comparison of silica production with other oceanic provinces.............. 149 4.5 CONCLUSION................................................................................................. 150 4.6 TABLES ......................................................................................................... 151 4.7 FIGURES........................................................................................................ 161 4.8 REFERENCES ................................................................................................. 170  vi CHAPTER 5 : GENERAL CONCLUSIONS ............................................................ 179 5.1 INTRODUCTION ............................................................................................. 179 5.2 LINE P FROM PRESENT TO THE FUTURE ......................................................... 179 5.3 FATE OF PHYTOPLANKTON ALONG A WARMER LINE P .................................. 180 5.4 INCREASING ACIDIFICATION SCENARIO ALONG LINE P.................................. 181 5.5 SUMMARY..................................................................................................... 183 5.6 LIMITS OF THIS WORK ................................................................................... 183 5.7 FUTURE STUDIES .......................................................................................... 185 5.8 REFERENCES ................................................................................................. 187 APPENDIX A: PUBLICATIONS ARISING FROM THIS THESIS...................... 190 APPENDIX B: LINE P SIZE-FRACTIONATED CHLOROPHYLL A................. 191 APPENDIX C: SIZE-FRACTIONATED POC AND PIC PRODUCTION ........... 197 APPENDIX D: IOS WEBSITE DATA....................................................................... 203 APPENDIX E: SIZE FRACTIONATED CHLOROPHYLL A WITH DEPTH.... 209 APPENDIX F: DEPTH PROFILES OF SIZE-FRACTIONATED POC PRODUCTION ............................................................................................................. 212 APPENDIX G: DEPTH PROFILES OF SIZE FRACTIONATED CHL SPECIFIC POC PRODUCTION.................................................................................................... 215 APPENDIX H: PHOTOSYNTHETRON 24 H INCUBATION PARAMETERS.. 218  vii List of Tables Table 1.1. List of major stations along Line P and their position, average depth and distance from Vancouver Island, British Columbia. P26 is equivalent to Ocean Station Papa (OSP). .................................................................................................. 12 Table 2.1. Location and depths of stations sampled along Line P for this study. Table adapted from the Line P Time Series Program website of Fisheries and Ocean Canada (http://www.pac.dfo-mpo.gc.ca/sci/osap/projects/linepdata/lineplist_e.htm). ................................................................................................................................... 51 Table 2.2. Dates of cruises, depth (m) of the euphotic zone (Zeu) as defined by 1% of surface irradiance, mixed layer depth (MLD) as determined by Freeland et al. (1997), daily surface irradiance (Io), temperature, salinity, surface nitrate and integrated chlorophyll a and POC production. Surface nitrate concentrations were obtained from the Fisheries and Ocean Canada Line P Oceanic Data web site (http://www-sci.pac.dfo-mpo.gc.ca/osap/data/linep/linepselectdata_e.htm). Surface DFe (100-55% I0) from Keith Johnson, Dr. C. S. Wong (pers. comm.), or obtained from Nishioka (2001). ND = not detectable. LS = lost sample. Detection limit of our nitrate analysis was ~0.1 uM..................................................................................... 52 Table 2.3. Average integrated Chl a and POC production and ±1 SD for Line P. All seasons includes all 8 cruises. There were only 2 cruises in Feb and 3 cruises in each of June and Aug./Sept. during the 3 year (1998-2000) sampling period. ................. 53 Table 2.4. Phytoplankton growth rates (d-1) as estimated from the turnover of algal carbon (μc, d-1) following Boyd and Harrison (1999). Percent autotrophic phytoplankton carbon (% Auto Carbon) was estimated using C:Chl a values and total integrated chl a and expressed as a percentage of particulate organic carbon (POC) for each station (see text for details). Cruise growth rate means were estimated using all the growth rates from a single cruise and seasonal growth rate mean was averaged over a whole season (winter, late spring, and late summer) for all data available. Values in parenthesis represent ± 1 s.e. of the mean. LS = lost sample. See Table 2.2 for dates of cruise number. ................................................... 54 Table 2.5. Photosynthetron incubations for samples from 55% I0 for all three years (1998- 2000). Photosynthetic vs. irradiance parameters include αB and βB [mg C (mg chl a)- 1 (mol photons m-2 s-1)-1], PBmax (mg C (mg chl a)-1 h-1), and Ek (μmol photons m-2 s- 1) and were derived following Platt et al. (1980) and Lewis and Smith (1983). The average and SE for each of the three seasons is also given. June and Aug./Sept. values are combined (n=12) to form averages for that time period by region (near- shelf and HNLC). Combined values are the mean for all cruises (n=8). See Table 2.2 for specific cruise dates. See Fig. 2.12 for plots of P v. E. ....................................... 55 Table 2.6. Deck incubations profiling POC production over the euphotic zone (6 depths). Photosynthetic parameters include αB and βB [mg C (mg chl a)-1 d-1 (mol photons m- 2 s-1)-1], PBmax (mg C (mg chl a)-1 d-1), and Ek (mol photons m-2 d-1).  Parameters were determined as described in the text. Values under the ‘All’ column are a combination of all the samples from all five stations for a particular cruise and  viii correspond to the modeled curves in Fig. 2.15. June and Aug./Sept. values are combined (n=12) to form averages of that time period by region (near-shelf and HNLC).Combined average is for all 8 cruises over 3 seasons and 3 years at each station. See Fig. 2.13 for plots of P v. E. .................................................................. 56 Table 2.7. Pearson’s correlation matrix for phytoplankton and other selected parameters in the mixed layer for all five stations from all 8 cruises (n=40).  Integrated values from the mixed layer were used for chlorophyll (Chl 0.2, 5, 20 μm size-fractionated and Chl total) and POC production (PP 0.2-5, 5-20, >20 μm size-fractionated and PP total). PBmax is the value from 55% Io. Specific growth rates (μ) were equivalent to Table 2.3. Light was the three-day average of the mixed layer from the time of sampling (see Putland et al., 2004). All nutrients (NO3-, Si(OH)4 and Fe) were tested as mixed layer averages. ........................................................................................... 57 Table 2.8. Pearson’s correlation matrix for phytoplankton and other selected parameters in the mixed layer for stations located near the shelf (P04 and P12) from all 8 cruises (n=16).  See Table 2.7 for details.............................................................................. 58 Table 2.9. Pearson’s correlation matrix for phytoplankton and other selected parameters in the mixed layer for HNLC stations (P20 and P16) from all cruises (n=16).  See Table 2.7 for details. ................................................................................................. 59 Table 3.1. Baseline data for all Line P stations sampled during 1998-2000, including the euphotic zone (Zeu), mixed layer depth (MLD) and daily surface irradiance (Io) for 8 cruises at 5 stations. Surface temperature and salinity are from Fisheries and Oceans Canada Line P data site (http://www.pac.dfo-mpo.gc.ca/sci/osap/projects/linepdata). See methods for details. Integrated values of Chlorophyll a, POC production and PIC production are from the euphotic zone. Station P26 is Ocean Station Papa (OSP). LS = lost sample.......................................................................................... 109 Table 3.2. Surface macronutrient concentrations for 5 stations and 8 cruises along Line P. Data were obtained from the Fisheries and Ocean Canada Line P Oceanic Data web site (http://www-sci.pac.dfo-mpo.gc.ca/osap/data/linep/linepselectdata_e.htm). Nutrients were measured by the Institute of Ocean Sciences (Sydney, British Columbia, Canada) following Barwell-Clarke and Whitney (1996). The detection limit for nitrate is 0.05 µM, and 0.2 µM for silicic acid (Frank Whitney pers. comm.). ND = not detectable. ................................................................................. 110 Table 3.3. Integrated (to 1% Io ) coccolithophore cell numbers (108 cells m-2) for 5 stations and 8 cruises. ‘Others’ refer to species found in either low concentrations or single occurrences. .................................................................................................. 111 Table 3.4. Average integrated (to 1% Io ) POC and PIC production from each station (mg C m-2 d-1) and the ratio of PIC:POC production. Values in parenthesis are the range of the averaged values. PIC:POC was calculated as the ratio of the average integrated PIC and POC production from each station........................................... 112 Table 4.1. Dates of cruises, depth (m) of the euphotic zone (Zeu) as defined by 1% of surface irradiance, mixed layer depth (MLD) as determined by Freeland et al. (1997), surface nitrate and integrated chlorophyll a and POC production. Surface nitrate and silicic acid concentrations were obtained from the Fisheries and Ocean  ix Canada Line P Oceanic Data web site (http://www-sci.pac.dfo- mpo.gc.ca/osap/data/linep/linepselectdata_e.htm). Average biogenic silica (bSi) represents a depth-weighted average in the euphotic zone. Sampling for silica production (ρSi) did not start until June 1999. ND = not detectable.  See (Chapter 3) for more values. LS = lost sample. ......................................................................... 151 Table 4.2. Average integrated diatom and siliceous (diatoms plus silicoflagellates) carbon, silica production (ρSi) biogenic silica (bSi), Chl a and POC productivity (PP). Chl a and POC productivity are divided into the > 20 µm size fraction and the total (Tot.) values (0-20 plus >20 µm size fractions). Eight cruises were conducted in 3 seasons. Feb. encompasses only 2 cruises (1998 and 1999). June and Aug./Sept. includes 3 cruises. Silica production was not measured in Feb. for any cruise. SD equals ±1 standard deviation................................................................................... 152 Table 4.3. Proportion of the contribution of siliceous phytoplankton (centric and pennate diatoms) and >20 µm size fraction to total POC, chlorophyll a, and POC production and the proportion of silicoflagellate carbon to total siliceous (diatom plus silicoflagellate) carbon. Proportions derived from integrated values in the euphotic zone. LS=lost sample. Average is the mean for all samples per station or for the whole study (all). .................................................................................................... 153 Table 4.4. Cell abundance (weighted average) of siliceous phytoplankton (silicoflagellates, pennate and centric diatoms) and carbon concentrations of centric and pennate diatoms for all stations and cruises. Cell abundance and integrated carbon concentrations are from the four light depths (100, 55, 10, 1%). See Chapter 2 for dates and depths of the euphotic zone. ........................................................... 154 Table 4.5. List of diatoms identified from samples collected along Line P from 1998 to 2000. ‘S’ in the column indicates that the species was found in the area designated as ‘near-shelf’ (P04 and/or P12). ‘T’ indicates the species was found at the transition station (P16).  ‘H’ indicates the species was found in the HNLC region (P20 and/or P26). There was no cruise for Feb. 2000. Species with the highest diatom abundances (measured by carbon) are marked with an asterisk (*). ...................... 155 Table 4.6. Pearson’s correlation matrix for diatoms (centric and pennate) and other selected parameters in the euphotic zone for all five stations from all 8 cruises during 1998-2000 (n=40).  Integrated values from the mixed layer were used for diatom carbon (centric, pennate and total), biogenic silica (bSi) chlorophyll (Chl 5- 20, >20 µm size-fractionated and Chl total) and POC production (PP 5-20, >20 µm size-fractionated and PP total) and nutrients (NO3-, Si(OH)4 and Fe). Si/N was tested as a ratio of the integrated values of Si(OH)4 and NO3- in the mixed layer. See Table 4.1 and Chapter 2 for values. .................................................................................. 156 Table 4.7. Pearson’s correlation matrix for diatoms and other selected parameters in the euphotic zone for stations located near the shelf (P04 and P12) from all 8 cruises (n=16).  See Table 4.6 for details............................................................................ 157 Table 4.8. Pearson’s correlation matrix for diatoms and other selected parameters in the euphotic zone for HNLC stations (P20 and P26) from all 8 cruises (n=16).  See Table 4.6 for details. ............................................................................................... 158  x Table 4.9. Major diatom species found at P26 (OSP) and P20 (this study). The nomenclature used by the authors has been retained. Note that for this study, winter refers to Feb., spring refers to June and Summer/Fall refers to Aug./Sept. Adapted from Harrison et al (2004). ..................................................................................... 159 Table 4.10. Some regional biogenic ρSi estimates (adapted from (Shipe and Brzezinski, 2001)). Annual production rates were not calculated for Line P due to a lack of any measurements in the winter and early spring.......................................................... 160  xi List of Figures Fig. 1.1. The subarctic NE Pacific showing the positions of the major hydrographic stations that were sampled during this study, overlaid on the SeaWiFS Level-3 standard mapped chlorophyll image for 1998. This image shows the position of the transition in chlorophyll concentration between the lower chlorophyll, oligotrophic subtropical gyre in the south and the higher chlorophyll, HNLC (high nitrate, low chlorophyll) subarctic region in the north, generally recognized as north of 42-45°N (Longhurst, 1998). The chlorophyll image was provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE. Gray contours are the 10 yr mean wind-forced circulation stream flow functions from Rienecker et al. (1996). The red dashed line is the approximate boundary of the NE subarctic Pacific HNLC region defined as the area where summer nitrate was consistently > 1 μM in1998- 2000 (Whitney and Welch, 2002). Figure adapted from Nelson Sherry (unpublished). ........................................................................................................... 13 Fig. 1.2. A monthly multivariate ENSO index, or MEI (Wolter and Timlin, 1998). MEI measures the intensity of (top) the 1997-98 El Niño (bold) relative to three strong El Niño events, and (bottom) the 1998-99 La Niña (bold) relative to recent La Niña events. Data obtained from http://www.cdc.noaa.gov/people/klaus.wolter/MEI/table.html. Table adapted from Hayward et al. (1999). Note that each El Niño / La Niña period covers two years and are separated into two, 12 month periods separated by a vertical line...................... 14 Fig. 2.1.Map of the portion of the NE subarctic Pacific Ocean showing the five major sampling stations P04, 12, 16, 20 and 26 along line P.  Inset shows general surface circulation in that area............................................................................................... 60 Fig. 2.2. Vertical contours of phytoplankton standing stocks as total Chl (mg chl a m-3) during 1998-2000. Dots represent the six sampling depths (100, 55, 30, 10, 3.5 and 1% of I0) for each of the 5 stations along Line P for 8 cruises. The dark dashed line corresponds to the mixed layer depth. No data for P04 in February1999 due to lost samples. Solid black line indicates area below 1% I0 and therefore this area contains no measured data. Haida eddy in Sep 1998 had a Note subsurface POC max at P12 and P16 due to Haida eddy (Whitney and Robert, 2002). ........................................ 61 Fig. 2.3. Vertical profiles of phytoplankton standing stocks (mg chl a m-3) for all 5 stations and all 3 years along Line P. Depths represent the 6 light depths (100, 55, 30, 10, 3.5 and 1% I0). Deepest sample represents the bottom of the photic zone. Same data as Fig. 2.2. ............................................................................................... 62 Fig. 2.4. Integrated chlorophyll a concentrations (mg chl a m-2) in the 0.2-5, 5-20, and >20 µm size fractions (bars) and total integrated POC production (PP) (solid lines) for all five stations and all three years along Line P. Note the different scale for POC production in the winter. ........................................................................................... 63 Fig. 2.5. Vertical contours of particulate organic carbon (µmol kg-1) for all five stations and all three years along Line P. Black dots represent actual sampling locations at each station at the six light depths (100, 55, 30, 10, 3.5 and 1% I0). The deepest  xii samples represent the base of the photic zone and the area below the photic zone (solid line) is shown as a solid white area. The dashed lines indicate the mixed layer depth. Note that the x and y axis represent very different distance scales................ 64 Fig. 2.6. Vertical Profiles of particulate organic carbon (µmol kg-1) for all five stations and all three years along Line P (same data as Fig. 2.5). Depths represent the 6 light depths (100, 55, 30, 10, 3.5 and 1% IO ) and the deepest samples represents the bottom of the photic zone. ........................................................................................ 65 Fig. 2.7. Vertical contours (see text for methods) of total POC (primary) production (mg C m-3 d-1) during 1998-2000. Dots represent the six sampling depths (100, 55, 30, 10, 3.5 and 1% of I0) for each of the 5 stations along Line P for 8 cruises. The dark dashed line corresponds to the mixed layer depth. No data for P04 in February 1999 due to lost samples. Solid black line indicates area below 1% I0 and therefore contains no measured data. ....................................................................................... 66 Fig. 2.8. Phytoplankton POC (primary) production (mg C m-3 d-1) for all stations and all years along Line P. Depths represent the 6 light depths (100, 55, 30, 10, 3.5 and 1 I0). Deepest sample represents the bottom of the photic zone. Same data as Fig. 2.7. ................................................................................................................................... 67 Fig. 2.9. Relative proportion of water column integrated size-fractionated POC production as a fraction of the total production for all five stations and all three years along Line P. Missing column for P04 in February 1999 denotes lost sample. ....... 68 Fig. 2.10. Water column integrated Chl a-specific carbon uptake (mg C (mg Chl a m-2)-1 d-1) for 1998-2000 with surface nitrate (μM, closed circles) and surface dissolved iron (DFe, nM, open circles) values. There are no data for P04 in  February 1999 (9901) due to lost samples. Note the different scale for DFe in winter. ................... 69 Fig. 2.11. Chl a-specific carbon uptake (mg C (mg Chl a)-1 d-1) for 1998-2000. There are no uptake data for February 1999 due to lost samples.............................................. 70 Fig. 2.12. Maximum rate of POC production normalized to chlorophyll a (PBmax) and light saturation onset irradiance (Ek) versus surface irradiance (I0). PBmax and Ek derived from photosynthetron experiments at 55% I0 from each station of each cruise.. There was a significant positive relationship between PBmax and I0 (r2 = 0.1354, p<0.05) while the relationship between Ek and I0 was not significant (r2= 0.0064, p>0.05) (n=40). ............................................................................................ 71 Fig. 2.13. Biomass specific photosynthesis (PB) versus irradiance curves (P v. E) for water samples collected in June and Aug./Sept. 2000 from 100, 55, 10 and 1% surface irradiance (Io) and incubated in the photosynthetron for 4 h from all five stations along Line P. The June P04 1% Io sample was lost. See Fig. 2.14 for P v. E parameters. ................................................................................................................ 72 Fig. 2.14. Photososynthetic performance parameters αB and PBmax derived from P v. E curves for water samples collected in June and Aug./Sept. 2000 (derived from Fig. 2.13). Depths are 100, 55, 10 and 1% of surface irradiance (see Table 2.2). The sample at 1% I0 for P04 was lost. ............................................................................. 73  xiii Fig. 2.15. Biomass specific photosynthesis (PB) versus irradiance for deck-incubated surface experiments (24 h) from water sampled at 55% I0. Samples are grouped according to season (Feb., June and Aug./Sept.). There was no cruise in February 2000. Dashed lines are for 1998. Solid lines are for 1999, and dash-dot-dash lines are for 2000. See Table 2.6 for P v. E parameters. ................................................... 74 Fig. 2.16. Photosynthetron deck incubated biomass specific photosynthesis normalized to chlorophyll a (PBmax) and light saturation onset irradiance (Ek) versus surface irradiance (I0) derived from depth-integrated POC production experiments (n=40). There was not a significant relationship between PBmax and I (r2 = 0.0921, p>0.05) while the relationship between Ek and I was significant (r2= 0.1279, p<0.05)......... 75 Fig. 2.17. Depth-integrated POC production from 1984 to 2000 and 2002 at P20 and P26 obtained from 5 studies. All data are  from Boyd and Harrison (1999) and Marchetti et al. (2006b) except for the present study (16 data points). Only the present study includes values from P20 as well as P26. Cloud-free irradiance (PAR; solid line) at 50°N adapted from the model of Frouin et al. (1989). The dashed line represents the average monthly POC production for all values and their corresponding standard deviation. There were no samples in January or December. .................................... 76 Fig. 2.18. Temporal SeaWIFS chlorophyll data from 1998-2000 derived from 8 day chlorophyll 9 km data from the Borstad Assoc. website (http://www.borstad.com/gripweb/grip.html) for each station. Included on each figure is averaged data from 1997-2007 (grey) as well as 8 day SeaWiFS chlorophyll concentrations based on color (when available) for each of the 3 years of this research. Included in each figure is the surface total chlorophyll a from each station and year measured in this study. There was no February cruse in 2000................... 78 Fig. 3.1. Map of the portion of the NE subarctic Pacific Ocean showing the five major sampling stations along Line P.  Inset shows general surface circulation in that area. ................................................................................................................................. 113 Fig. 3.2. Contours represent coccolithophore abundance (cells ml-1) during 1998-2000. Dots represent the six sampling depths (100, 55, 10 and 1% of I0) for 5 stations along Line P for 8 cruises. Empty areas (white) signify <100 cell ml-1. The dark dashed line corresponds to the depth of the mixed layer. Solid grey line indicates the area below 1% I0 and therefore contains no measured data.  See section 3.2.7 for contour plotting methods. ....................................................................................... 114 Fig. 3.3. Proportion of total coccolithophore carbon (POC) in the euphotic zone associated with two numerically dominant coccolithophore species along Line P for 5 stations and 8 cruises. The group designated as ‘other’ represents various unknown coccolithophore species of various sizes as well as Syracosphaera sp and Rhabdosphaera sp. Total surface coccolithophore biomass  (pg C ml-1) for each station is represented by the solid line. ................................................................... 115 Fig. 3.4. Vertical contours of PIC production (mg C m-3 d-1) during 1998-2000. Dots represent the six sampling depths (100, 55, 30, 10, 3.5 and 1% of I0) for each of the 5 stations along Line P for 8 cruises. The dark dashed line corresponds to the mixed layer depth. No data for P04 in 1999 due to lost sample. Solid grey line indicates  xiv area below 1% I0 and therefore contains no measured data. See section 3.2.7 for contour plotting methods. ....................................................................................... 116 Fig. 3.5. Particulate inorganic to particulate organic production (PIC:POC 14C production) ratio from the integrated values (see Table 3.1) for each cruise for 1998- 2000. Dashed lines represent a PIC:POC ratio of 1................................................ 117 Fig. 3.6. POC vs. PIC production (mg C m-3 d-1) for all stations for all three years. Line represents the 1:1 ratio. Although for most samples, PIC production was of the order of ~10% of POC production, some samples in 1998 and 2000 showed PIC production rates greater than POC rates. All values for 1999 were well below the 1:1 relationship.............................................................................................................. 118 Fig. 3.7. Linear regressions of the log of the surface coccolithophore abundance and (A) surface dissolved Fe (DFe), (B) average mixed layer irradiance and (C) surface nitrate for all cruises (1998-2000). Filled circles represent HNLC stations (P20 and P26). Empty triangles are for the shelf stations (P04 and P12) and grey filled inverted triangles are for P16. Collectively, they represent all stations sampled. The dashed lines represent the regression of near-shelf stations. The dash-dot-dot lines represent the regression of HNLC stations and solid lines represent all the regression of all stations (including P16). For A, only all samples grouped together (all stations) yielded a significant correlation [log coccolithophore (all) = 5.1 – 0.51 DFe; r2=0.12]. For B, HNLC stations were significant for mixed layer irradiance [log coccolithophore (HNLC) = 4.7 + 0.04 Light; r2 = 0.29]. For surface nitrate (C), only the near-shelf stations were significant [log coccolithophore (near-shelf) = 5.1 - 0.11 Nitrate; r2=0.29]. For all significant regressions, p<0.05. .............................. 119 Fig. 4.1. Vertical contour plots of biogenic silica concentrations (bSi – µmol L-1). Dots represent the 4 sampling depths (100, 55, 10 and 1% of I0) for each of the 5 stations along Line P for 8 cruises. The dark dashed line corresponds to the mixed layer depth. Solid grey line indicates area below 1% I0 and therefore contains no measured data. ......................................................................................................................... 161 Fig. 4.2. Chl a > 20 µm (mg chl a m-3) for all 5 stations and all 3 years along Line P. Depths represent the 6 light depths (100, 55, 30, 10, 5 and 1% I0). Deepest sample represents the bottom of the photic zone (Zeu)........................................................ 162 Fig. 4.3. POC production > 20 µm (mg C m-3 d-1) for all 5 stations and all 3 years along Line P. Depths represent the 6 light depths (100, 55, 30, 10, 5 and 1% I0). Deepest sample represents the bottom of the photic zone (Zeu). .......................................... 163 Fig. 4.4. Contour plots of total diatom carbon (pennate plus centric) for all 5 stations and all 3 years (1998-2000) along Line P (mg m-3). Carbon was sampled at four depths (100, 55, 10 and 1% I0) for each station. The darkest dashed line corresponds to the mixed layer depth. The deepest sample represents the base of the photic zone. .... 164 Fig. 4.5. Silica production rates (ρSi – µmol Si L-1 d-1) for the June and Aug./Sept. cruises (1999 and 2000). ρSi was sampled at four depths (100, 55, 10 and 1% I0) for each station. The deepest sample represents the base of the photic zone. Production rates were not measured in 1998 or Feb. 1999. ...................................................... 165  xv Fig. 4.6. Gross silicon:carbon (Si:C) uptake ratios (mole to mole) for June and Aug./Sept. 1999 and 2000. Average ratio for all cruises and depths was 0.11 (± 0.23 S.D.). Silica production was only measured in June and Aug./Sept. 1999 and 2000. ...... 166 Fig. 4.7. Linear regressions of silica production rate ρSi (µmol Si L-1 d-1) vs. the > 20 µm size fraction POC production (mg C m-3 d-1), > 20 µm size fraction chl a (mg chl a m-3), total siliceous (diatom plus silicoflagellate) carbon (mg C L-1) and bSi (µmol Si L-1). All 4 regressions are significant (p<0.01)....................................................... 167 Fig. 4.8. Atmospheric mineral dust recorded at Mount Rainier National Park. Data are plotted for 1998-2000. Only one major dust event occurred during this study (May 1998). Data are from the Interagency Program for Visual Environments (IMPROVE). Note that 1999 and 2000 are the same scale as 1998. ...................... 168 Fig. 4.9. Relative magnitudes of POC, PIC and silica integrated production (ρPOC, ρPIC, ρSi mmol m-2 d-1) for the June and Aug./Sept. cruises in 1999 and 2000. See Chapter 3 for more data on PIC production.......................................................................... 169  xvi LIST OF ABBREVIATIONS  Physical and geographical abbreviations AG  Alaska Gyre GOA  Gulf of Alaska MLD  Mixed layer depth HNLC  High Nitrate, Low Chlorophyll OSP   Ocean Station Papa P26   The equivalent to OSP. Used throughout.  Chemical abbreviations bSi  Biogenic (= amorphous) silica (SiO2•(H20)x) POC  Particulate organic carbon PIC  Particulate inorganic carbon LDPE  Low Density Polyethylene HDPE  High Density Polyethylene NO3-  Nitrate Si(OH)4 Silicic acid Chl  Chlorophyll SCM  Subsurface chlorophyll a maximum DFe  Dissolved iron (<0.2 μm)  Biological abbreviations and symbols PP  POC production (=primary productivity) Pb  Biomass-specific primary productivity Pbmax  Maximum biomass-specific primary productivity Zeu  Depth of euphotic zone α Initial slope of the Photosynthesis-Irradiance curve; also, significance level of statistical tests β slope of Photosynthesis-Irradiance curve that corresponds to photoinhibition at high irradiances I0  Surface irradiance ρSi  32Si (silica) production ρPOC  POC production (=primary productivity) ρPIC  PIC production (inorganic carbon production)  Program definitions CJGOFS Canadian Joint Global Ocean Flux Study SUPER Subarctic Pacific Ecosystem Research VERTEX Vertical Exchange program IOS  Institute of Ocean Sciences NPI  North Pacific Index  xvii Co-authorship statement  This paper (Chapter 3: published) was written by me with revisional inputs from the co- authors. The exception was the last section in the discussion (Satellite Images) which was written by Jim Gower with small modifications.  Chapter 2 (Spatial and temporal variability in size-fractionated organic primary production, chlorophyll biomass and photosynthetic performance in the NE subarctic Pacific during El Niño (1998), La Niña (1999) and 2000) and Chapter 4 (Siliceous Abundance and Silica Production Rates Along Line P in the NE Pacific 1998-2000) are in the process of submission.    xviii Acknowledgements I would to express my thanks and gratitude to the many people who have, in one way or another, helped me in the rather arduous task of completing and publishing this research. It has been a long haul and I want to especially thank those that who stuck with me even when it seemed there was no end and it never seemed like I would finish. I would particularly like to thank my supervisor, Dr. Paul J. Harrison who never spoke a harsh word (even though, at times, I deserved it) and stuck with me through all these years. His dedication to oceanography and his skills in editing are unsurpassed. I especially want to thank him for his editing skills on the fly while on Christmas vacation in Northern India. With that is mind, I would also like to thank Victoria for her support for such a hard working partner. A personal thanks and eternal gratitude also needs to go to Dr. David W. ‘Bottles’ Crawford. From the beginning, he has been a co-author, mentor, lab instructor, philosophy expert, roommate, IOS liaison, drink mixer and general steady hand throughout this experience. More importantly, he is the greatest of friends who has always been there when needed. It is rare to find an individual such as David, who never has a harsh word to say to anyone, always keeps his computer clean and always knows if this situation was Irish or Scottish. I also want to apologize to him about the keyboard. I also want to thank Nancy and Candace for all their love and tolerance. I would to extend my thanks to the past and present members of my committee and examining committee, each of whom contributed in important ways to the whole process. These members include Dr. John Dower, Dr. F.J.R. ‘Max’ Taylor, Dr. Al Lewis, Dr. Curtis Suttle and Frank Whitney. A special thanks to Max Taylor who always had the strength to ask the interesting questions as well as spend countless hours helping out with taxonomic identifications. A very special thanks and gratification goes to Frank Whitney. There is truly no one else who shares the breadth of knowledge of all things chemical and biological involving Line P. Without his tireless contributions, both in print, personal advice and as Chief Scientist, I would never have gotten through all this. I especially want to thank him for all his help in the recent years. A special thanks to Kristin Orians whose passion for oceanography in terms of research and teaching will always be an inspiration. A very special thanks also needs to go out to Hugh Maclean who so tirelessly contributed to everything mechanical on and off the CCGS J. P. Tully. He has helped shaped many a neophyte into an experienced sea-going scientist. I especially want to thank him specifically for his pleasantness at 4:00 am each and every morning. The plankton can only wait for so long. I would like to thank the scientists and crew on board the CCGS J. P. Tully and the technicians working at the Institute of Ocean Sciences (IOS), Sidney BC. In particular, I would like to thank Jennifer Putland, J. Barwell-Clarke, Doug Anderson, and Angelica Peña for assistance and sample analysis. A special thanks to Frank Whitney, J. Barwell-Clarke, C.S. Wong and Keith Johnson for all the nutrient analysis and for allowing me to use their data in this work. We truly had a very special lab and I would like to thanks all the members I had a pleasure to argue with over all these years. A special thanks to Adrian Marchetti, Behzad Imanian, Tonny Wagey, Rana El-Sabaawi, Tawnya Peterson, Heather Toews, Nelson  xix Sherry, Michael Henry, Robert Strzepek, Joe Needoba and Diana Varela. A special thanks to Mingxin Guo, who we always knew really ran the Harrison Lab. A special thanks to Maureen Soon and Behzad Imanian for all their help prepping and running samples for this work. Extra appreciation goes to Behzad and for his skills in philosophy, politics, and science and his friendship that was always there from the first time I saw him behind a microscope. I would also like to thank Netsa Tsegay for putting up with all of us over so long when you knew you could always do better. A special thanks to all the members of the UBC community that include David Timothy, Tara Ivanochko (and Paul), Carol Leven, Alex Allen, Chris Payne, Veronica Oxtoby, Scott Usher, Bert Mueller, Jeanette Whitton and Patrick Keeling. A substantive thank-you to my parents Zel and Wendy and sister Jane and brother Alexander without whom I would never be the person I am today. Special thanks to all other family and friends who have influenced my life and helped with the process. I would also like to thank Dr. Michelle Wood who started it all.  The research was part of the Line P time-series and was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC).  I dedicate this to Linda who has always meant everything and truly kept me going at my darkest moments. Nothing could say more than ‘Thank You’.   In loving memory of Beckett and Woofie  1 Chapter 1 : Introduction to Phytoplankton Processes of the NE subarctic Pacific 1.1 Background 1.1.1 The NE subarctic Pacific The subarctic NE Pacific (Table 1.1) is of particular interest for understanding ocean biogeochemical processes, since it is one of the three major high nitrate, low chlorophyll (HNLC) regions of the world ocean where phytoplankton production is limited by iron supply (Martin et al., 1989; 1996). Line P (Table 1.1; Fig. 1.1), a transect from the coast (Juan de Fuca Strait) to Ocean Station Papa (OSP or P26 this study), provides a unique gradient in physical (Whitney et al., 1998) chemical (Whitney et al., 1998; Varela and Harrison, 1999a), and biological (La Roche et al., 1996; Boyd et al., 1998b; Whitney et al., 1998; Boyd and Harrison, 1999; Varela and Harrison, 1999a) parameters from slope waters to HNLC oceanic waters.  This region has one of the world’s longest running oceanic time series with oceanographic measurements dating back to 1949 at P26 and extensive biological datasets including primary productivity (PP) dating back to 1956 (Tabata, 1985). The subarctic NE Pacific has been largely defined by measurements taken over many decades at P26.  This station (Table 1.1; Fig. 1.1) is located along the SE edge of the Alaskan Gyre in the relatively slow (~ 7 km d-1), eastward moving Subarctic Current (Bograd et al., 1999).  The region is typified by a relatively shallow permanent halocline at 100-120 m that limits the maximum depth of winter mixing (Dodimead et al., 1963). The permanent halocline is overlain by a seasonal thermocline that typically begins to form in May/June, achieves a minimum of  <40 m in Aug/Sep, and is mixed down to ~ 100 m in Nov/Dec (Whitney and Freeland, 1999).  In association with the cyclonic circulation of the region, Ekman upwelling at OSP has been estimated to be ~ 30 m y-1 (Gargett, 1991). Seasonally, there is a warming and freshening along Line P from winter to summer (Feb. – Aug./Sept.).  The mixed layer temperature typically varies from 5 - 12°C at P26 and from 8 - 15°C at P04 (near-shelf, Table 1.1).  The mixed layer salinity typically varies from 32.7 - 32.5 at P26 and from 32.2 - 31.8 at P04 (Whitney and  2 Freeland, 1999). In association with the 1997/98 El Niño, there was warming in surface waters above the historical average by ~ 2°C all along Line P in September 1997 and nearer the coast (P04 - P12) in Feb 1998 (Whitney and Welch, 2002). During the following La Niña in 1999, there was on average lower surface temperatures at all stations by ~1°C and a corresponding increase in ambient nutrient concentrations (Whitney and Welch, 2002). With a few historical exceptions (see Wong and Matear, 1999), P26 is replete in macronutrients (nitrate, phosphate, and silicic acid) year round (Whitney and Freeland, 1999).  Chlorophyll a is nearly constant all year at 0.2 - 0.4 mg m-3 and primary productivity roughly doubles in the spring and summer from a winter low of ~ 300 mg C m-2 d-1 (~ 3 in winter to ~ 12 mg C m-3 d-1 in spring/summer assuming 100 m and 50 m euphotic zone depths respectively) (Boyd and Harrison, 1999).  Phytoplankton biomass is dominated by small cells, < 5 µm (Booth et al., 1993; Boyd and Harrison, 1999). Both primary productivity and total chlorophyll have been shown to increase with the addition of iron in summer (Boyd et al., 1996). Interestingly, Maldonado et al. (1999) demonstrated that phytoplankton productivity in the winter responded to a combined increase in iron and light. They suggested that phytoplankton were co-limited by these two factors during winter, and provided evidence for the importance of winter mixing for phytoplankton productivity. In contrast to P26, there is greater seasonal and interannual variability closer to shore.  During the Canadian JGOFS program (1992-97), Boyd and Harrison (1999) found that the winter mixed layer chlorophyll at P04 ranged from 0.3 - 0.8 mg m-3 and typically increased from 2 to 5-fold in spring and summer.  Winter mixed layer primary productivity at P04 ranged from 5 - 20 mg C m-3 d-1 and increased as much as 10-fold in spring and/or summer depending on the year.  In association with the seasonal phytoplankton blooms, nitrate is typically depleted in the mixed layer westward of P12 during the summer (Whitney and Freeland, 1999). 1.1.2 1997-1999 El Niño/Southern Oscillation (ENSO) The evidence for the 1997/98 El Niño was first observed during the early part of 1997 in the central Pacific. It was marked by a substantial weakening of the trade winds  3 and an increase in sea surface temperatures (McPhaden, 1999). Two months after the trade winds diminished, Kelvin waves began to propagate eastward. This resulted in a 90 m deepening of the thermocline in the eastern Pacific by late 1997 (McPhaden, 1999). In the tropical Pacific, 1998 was marked by a dramatic transition from one of the strongest El Niño events of this century, to a strong La Niña event (Hayward et al., 1999) in the central Pacific. This is recorded in various oceanic and atmospheric parameters measured throughout the Pacific and is very clear in the multivariate ENSO index (MEI). The MEI (Fig. 1.2), which is based on the six main observed variables over the tropical Pacific, shows differences in that region between one of the strongest El Niños in the past 100 years (1997-98) to the clear La Niña signal in 1998-99 (Fig. 1.2). The MEI uses sea surface temperatures, surface air temperatures, sea-level pressure, zonal (i.e., east-west) surface wind, meridional (i.e., north-south) surface wind and total amount of cloudiness (details on the computation of the MEI are available at: http://www.cdc.noaa.gov/people/klaus.wolter/MEI/table.html).  When the MEI is positive,  this signals a warm phase or El Niño event, while a negative MEI signals a cool phase or La Niña event (Wolter, 1987; Wolter and Timlin, 1998). The change in the MEI between early 1998 and the beginning of 1999 represented the largest decline (switch from an El Niño to a La Niña) in over 50 years (Hayward et al., 1999). In the Gulf of Alaska (GOA), the influence of the El Niño occurs fairly rapidly via an atmospheric component (Schwing et al., 2002; Whitney and Welch, 2002) that is followed several months later from oceanic transport along the Pacific eastern boundary current (Chelton and Davis, 1982; White, 1994; Strub and James, 2002; Whitney and Welch, 2002). Higher sea levels were recorded off the Pacific coast of the United States by the spring of 1997 (Strub and James, 2002), and did not reach the British Columbia coast until later that summer (Whitney and Welch, 2002). Higher sea levels remained until February 1998 and quickly disappeared by the spring (Whitney and Welch, 2002). Freeland (2000) described the development of the 1997-1999 ENSO event in three distinct phases. The first phase started with a superficial warming of the GOA that occurred from the onset of the El Niño until the beginning of 1998. The next phase occurred in the early spring of 1998 remained warm, but the surface anomalies weakened while deeper continental-slope temperature anomalies became stronger. The last phase  4 occurred later in 1998 and continued into 1999 where there was a rapid transition from warm water anomalies to cold anomalies. This cooling occurred mainly in the surface waters (Freeland, 2000). In the NE subarctic Pacific, previous research has demonstrated that nitrate depletion, particulate organic carbon (POC) flux and particulate inorganic (PIC) flux are enhanced by the presence of an El Niño (Wong et al., 1998; Wong and Crawford, 2002; Wong et al., 2002b). During the 1998 El Niño, Whitney and Welch (2002) reported the disappearance of upwelling along the coast of British Columbia and a shallowing of the thermocline that lead to an increased depletion of surface NO3- and Si(OH)4 that occurred earlier than average at stations on the eastern portion of Line P. The effects of this depletion on the phytoplankton standing stocks is unclear, but satellite surface chlorophyll a was remarkably low in the whole GOA during this period (Whitney and Welch, 2002). The following year during the 1999 La Niña, Whitney and Welch (2002) reported increased mixing that resulted in the mixed layers deepening up to 40 m compared to 1998. They also noted a return of the summer upwelling and an increase in ambient nutrient levels. Mackas and Galbraith (2002) recorded a general decrease in zooplankton species along the eastern portion of Line P as well as a shift in species composition from endemic zooplankton to species more typical off the mid-California coast. 1.1.3 Nitrate and iron At P26, phytoplankton use NH4+ preferentially (55%) over other nitrogenous sources for growth without any apparent seasonal trend in this preference (Varela and Harrison, 1999b). The average depth-integrated f-ratio was 0.36 (urea excluded). Measurements by Varela and Harrison (1999b) showed that smaller phytoplankton (<2 μm) consumed roughly two-thirds of the regenerated nitrogen (NH4+ and urea) year round. Nitrate uptake represented only 20% of the total nitrogen taken up by these small cells and laboratory experiments suggest that nitrate uptake may be inhibited by very low ambient NH4+ concentrations (<0.5 μm), further suppressing NO3- (Varela and Harrison, 1999a).  5 For the larger phytoplankton including diatoms, iron limitation has been shown to reduce the utilization of NO3-  since iron is an essential constituent of nitrate and nitrite reductases (Milligan and Harrison, 2000), further inhibiting the uptake of NO3- at low [Fe]. At P26, on-deck incubation experiments have demonstrated that large (>18 μm) mainly pennate diatoms (e.g. Pseudo-nitzschia sp.) grew up when 2 nM Fe was added (Boyd et al., 1996). Biophysical parameters (Fv/Fm fluorescence ratio, Boyd et al., 1998a; Suzuki et al., 2002) and biochemical markers such as the production of flavodoxin (La Roche et al., 1996) were also measured and revealed that Fe stress increased westward along Line P. Interestingly, Fv/Fm  values also suggest that near-shelf stations (P04 and P12) may also be Fe-stressed, but to a smaller degree (Boyd et al., 1998a). It is still unclear whether small cells are iron-limited. Boyd et al. (1996) saw no increase in the small size fraction, but any increase in the abundance of small cells may have been consumed by microzooplankton present in the carboy experiments. However, during the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES) that occurred in July 2002 at P26, pico- and nanophytoplankton did not increase in response to the Fe enrichment over 20 days of tracking the enriched patch (Marchetti et al., 2006a). In contrast, there was a ~50 fold increase in the microphytoplankton population that consisted almost entirely of centric and pennate diatoms. 1.1.4 Silicate Recently, there has been considerable interest in ambient nutrient ratios and nutrient utilization ratios, particularly Si:N ratios (Hutchins and Bruland, 1998; Takeda, 1998; Marchetti and Harrison, in press). Under iron limitation, silicate utilization increases or NO3-  utilization decreases and therefore the Si:N ratio increases to 2 or 3, compared to the normal ratio of about 1:1 Si:N (Brzezinski, 1985). In the NE subarctic Pacific, Whitney et al. (2005a) showed that Si limitation (rather than nitrate) may co- occur with Fe limitation, or Si limitation may be induced with increased Fe inputs as shown in the SERIES mesoscale Fe addition in the NE  Pacific (Marchetti et al., 2006a). This suggestion of increased Fe inputs enhancing Si drawdown per cell may explain the three years in the 1970s at P26 when Si concentrations declined to limiting concentrations at P26 (Wong and Matear, 1999). As a result, the coastal region along  6 Line P can be replete in Fe, but NO3- depleted in summer due to riverine input of Si(OH)4 (Whitney et al., 2005b). The transitional region (~P16) may be either NO3- or Si(OH)4 limited depending on the supply ratios from depth and the HNLC region (P20 and P26) would normally have low Fe:Si ratios. Under certain conditions, HNLC waters along Line P can become Si(OH)4 limited (Wong and Matear, 1999; Whitney et al., 2005a). Conditions found in 2002 included strong vertical stratification and an unusually shallow mixed layer that increased the mixed layer light levels and may have contributed to the lower Si(OH)4 concentrations recorded (Whitney et al., 2005a). An increase in Fe supply and an increase in the mixed layer light that reduces the Fe requirements of autotrophic cells (Maldonado and Price, 1999) could then result in diatom growth. This allows the silicate pump (Dugdale et al., 1995) to preferentially remove Si in larger proportions relative to N from the photic zone (mainly due to N recycling, especially for smaller phytoplankton cells), leading to a possible Si depletion in HNLC regions. At P26, Fe concentrations are variable (Nishioka et al., 2001). Nutrient supply and utilization was shown to vary markedly during the 1998 El Niño and the 1999 La Niña (Whitney and Welch, 2002). Specifically, Si levels were exceptionally low along much of Line P in the summer of 1998. This is in comparison to little Si(OH)4 utilization during the spring/summer of 1999. During these two years, Fe levels at P26 were markedly different between the surface and at 1000 m (Nishioka et al., 2001). Therefore there is evidence to suggest that dissolved iron or silicic acid may be limiting for autotrophic growth (especially the larger phytoplankton size classes) at any given time along Line P. Although there is an increased interest in the control of Si(OH)4 by the phytoplankton population in the NE subarctic Pacific, there are no published studies that measure the role of diatoms and their direct silica uptake rates. 1.2 Biology 1.2.1 Primary productivity At P26, primary productivity has been measured over the last 40 years and there has been an increase in the annual productivity by ~3 times. It is difficult to determine whether this is real or a result of adopting the “trace metal clean technique” in the mid  7 1980s (Fitzwater et al., 1982), or due to the regime shift that occurred in 1976–77 (Brodeur and Ware, 1992). Early measurements between 1960 to1976 estimated annual productivity to be ~60 g C m-2  y-1. In the mid-1980s to early1990s, Welschmeyer et al. (1993) and Wong et al. (1995) reported estimates of 170 and 140 g C m-2 y-1 respectively. Between 1992–97, the Canadian JGOFS group sampled P26 three times per year and reported estimates of 215 g C m-2 y-1. Their elevated estimate was due to the two times higher rates in spring and summer. This annual primary productivity is quite high considering that P26 is a HNLC region. At P26, there is low seasonal variation with spring/summer values about two times higher than winter values (Wong et al., 1995; Boyd and Harrison, 1999). It is somewhat surprising that there is no clear correlation between primary productivity and irradiance (Welschmeyer et al., 1993; Boyd and Harrison, 1999), although Fe limitation would prevent cells from responding to increased irradiance in spring, summer and fall and the relatively shallow mixed layer depth (MLD) in winter may render cells only moderately light-limited. Size-fractionated primary productivity studies indicated that small (<5 μm) cells dominated the primary productivity and these cells utilized primarily regenerated nutrients (Boyd and Harrison, 1999; Varela and Harrison, 1999b). Although size-fractionated phytoplankton biomass and POC production (primary production) have been measured along Line P (Boyd and Harrison, 1999), there are no detailed studies that have measured phytoplankton dynamics during a strong ENSO event such as occurred in 1997-1999. Additionally, there are no studies that have covered phytoplankton photosynthetic performance (e.g. photosynthesis vs. irradiance) along Line P. 1.2.2 Coccolithophores along Line P Few studies have examined coccolithophores in the NE Pacific despite scattered reports of relatively high abundances (Okada and Honjo, 1973; Honjo and Okada, 1974; Booth et al., 1982; Taylor and Waters, 1982; Booth et al., 1993). Recent sediment trap and productivity studies in this area also suggest that coccolithophores may be more important than previously thought (Wong et al., 1999; Wong and Crawford, 2002). Cyclical and long-term warming trends are occurring in the NE Pacific (Whitney et al.,  8 1998; Freeland, 2000). Associated with the warming trends along Line P are lower salinity and nutrient concentrations. It is not clear what effect these physical and chemical changes have on coccolithophore abundance. Wong et al. (2006) found coccolithophore numbers in the HNLC regions (P20 and P26) of Line P to be higher during the El Niño 1998 compared to 1999-2001. Higher coccolithophore abundance in 1998 corresponded to an average dimethylsulphide (DMS) concentration in the mixed layer that was 2 times greater (242 ± 27 µmol m−2) compared to 1999 (102 ± 25 μmol m−2) when coccolithophore numbers were much lower. Although coccolithophores are not the only DMS producers in the region, their concentrations are often higher than dinoflagellates and may be important contributors of dimethylsulphoniopropionate (DMSP), a precursor of DMS (Wong et al., 2006). Putland et al. (2004) also found coccolithophores to be important in the HNLC region of the Gulf of Alaska that included P20 and P26. They recorded a near bloom concentration of the coccolithophore, Emiliania huxleyi (0.75 x 106 cells L-1) at P26 in June 2000. Additionally, they found a significant correlation with bottom-up physical and chemical parameters. Putland et al. (2004) found the highest abundances of the coccolithophore at lower temperatures, higher nutrient concentrations, higher irradiance and higher salinity. They also found that the coccolithophore population can sporadically make up a substantial proportion of the phytoplankton carbon and reached values as high as 67%, but typically averaging <10%. There are two previous studies that measured coccolithophore abundances at some stations along Line P.  Putland et al. (2004) measured surface coccolithophore abundances in the HNLC region that included P20 and P26 in the NE subarctic Pacific. Wong et al. (2006) measured coccolithophore abundances in relation to DMS at the HNLC stations (P20 and P26) of Line P. There has not been a comprehensive study of coccolithophore abundances and species diversity along Line P. Additionally, no study has measured PIC production and its relation to coccolithophore abundances. 1.2.3 Siliceous phytoplankton (diatoms and silicoflagellates) along Line P Despite the many numerous studies that have occurred at P26 since 1949, only one other previous study has measured siliceous phytoplankton along Line P (Varela and  9 Harrison, 1999b). They found that diatoms (centric and pennates) made up generally < 20% of the total phytoplankton population at all major stations and during most seasons. Other studies have counted diatom and silicoflagellate populations at P26, either as preserved cells from the water column, or from sediment traps (see Harrison et al., 2004). In most cases, diatom cell numbers rarely dominated the phytoplankton population. However, variation in sediment trap flux recorded by Takahashi (1986) as well as a possible ‘bloom’ of diatoms recorded in the winter of 1996, possibly due to an influx of Fe from the continental margin (Lam et al., 2006) were reported. During the SERIES experiment in July 2002, the microphytoplankton assemblage which was made up of predominantly diatoms increased from <20% of the total chlorophyll a to ~ 80%, 18 days after the Fe enrichment (Marchetti et al., 2006c). Additionally, diatom species found at P26 have remained relatively similar in all the studies in that region over the last few decades (Harrison et al., 2004). No study has attempted to connect the importance of the diatom community structure and the sporadic decline in Si(OH)4 at P26, or along Line P. 1.3 Overview of this thesis This thesis extends the temporal and spatial scales of previous studies.  It provides measurements of phytoplankton standing stocks and processes taken during winter, spring, and summer over the El Niño / La Niña cycle.  It includes data from the near-shelf region to HNLC stations along the Line P transect, addressing the factors controlling primary productivity and coccolithophore/diatom populations, as conditions vary seasonally, inter-annually, and spatially in the subarctic NE Pacific. These results will help improve our ability to make robust predictions about what changes will occur in the phytoplankton processes as other biological, chemical, and physical changes occur in the environment due to possible future climate change scenarios. 1.4 Thesis Objectives The main goal of this thesis was to measure and document the phytoplankton processes that occurred along Line P during the El Niño / La Niña of 1998/1999 and year 2000. Particular attention was paid to differences in biomass and production and their  10 response to the ENSO conditions with a focus on coccolithophores and siliceous (diatoms and silicoflagellates) phytoplankton abundance and production.  Specifically, the objectives of the thesis were: 1. to determine the seasonal and spatial variations in phytoplankton abundance, productivity, and to quantify the magnitude and variability of carbon flow through the phytoplankton assemblage in the subarctic NE Pacific along a transect extending from near the shelf to an open ocean HNLC region (Chapter 2). 2. to quantify the seasonal and spatial variation in coccolithophore abundance, carbon biomass, and community structure and their relationship to particulate organic and inorganic production along Line P (Chapter 3). 3. to quantify the seasonal and spatial trends in diatom abundance, carbon biomass, and community structure and their relationship to silicic acid utilization and silica production and export along Line P (Chapter 4).  This thesis is composed of four chapters and a general conclusion section. Chapter 1 provides and introduction to the region of the NE subarctic Pacific and Line P. It provides a general description of the physical, chemical, and biological characteristics of Line P. Additionally; it describes the conditions that occur during the onset of an ENSO event and specifically discusses the known effects of El Niño and La Niña on the conditions in the Gulf of Alaska and specifically Line P. The goal was to characterize the conditions that occur seasonally along Line P with special emphasis on nutrient concentrations (specifically NO3-, Si(OH)4 and Fe) as well as previous phytoplankton biomass and production values and the limited information available on coccolithophore and diatom assembledges. Chapter 2 presents the size-fractionated biomass (chlorophyll a), POC concentrations and POC production along Line P from 1998-2000 in relation to the physical and chemical changes that occurred as a result of the 1998-99 El Niño / La Niña  11 cycle. Additionally, the chapter presents phytoplankton photosynthetic performance estimates (photosynthesis vs. irradiance; P vs E) during that same time period. The main goals were to: (1) determine the phytoplankton biomass and production that occurs during an ENSO cycle, seasonally, and with depth; and (2) determine the changes in phytoplankton photosynthetic performance in relation to light, nutrients, temperature and depth. Chapter 3 describes the coccolithophore abundances and species composition along Line P during the same three year period and their effects on POC and PIC production. The primary goals were: (1) to measure coccolithophore abundances; (2) to determine species composition of the dominant coccolithophores; (3) to estimate their contribution to total POC; and (4) to measure the rates of PIC production in terms of seasonality, depth and spatially along Line P and the variation due to the El Niño / La Niña cycle. Chapter 4 presents the abundances of siliceous phytoplankton (diatoms and silicoflagellates) and their relation to biogenic silica (bSi) concentrations, major diatom species composition, and their role in silica uptake during the period of 1998-2000. The goals were: (1) to measure diatom and silicoflagellate abundances and compare them to bSi and large size fraction (>20 μm) chlorophyll a and POC production; (2) to identify the major species of diatom found along Line P and see if there is a difference between near-shelf and HNLC stations, seasons (February, June and August/September) and years (including 1998 El Niño and 1999 La Niña); (3) to determine the contribution of siliceous phytoplankton to the total POC found along Line P; and (4) to measure and compare silica uptake rates (ρSi) during the late spring and summer of 1999 and 2000 to diatom species abundance and previously published Si(OH)4 utilization rates as well as other global ρSi values. Finally, the general conclusions for all chapters are presented after Chapter 4.  12 1.5 Tables  Table 1.1. List of major stations along Line P and their position, average depth and distance from Vancouver Island, British Columbia. P26 is equivalent to Ocean Station Papa (OSP).  Station Number Latitude Longitude Depth (m) Distance (km) Classification  P04 48° 39.0'N 126° 40.0'W 1300 87 Near-shelf  P12 48° 58.2'N 130° 40.0'W 3300 380 Near-shelf  P16 48° 17.0'N 134° 40.0'W 3550 672 Transition  P20 48° 34.0'N 138° 40.0'W 3890 961 Oceanic  P26 50° 00.0'N 145° 00.0'W 4200 1420 Oceanic   13 1.6 Figures  130°W140160 150 60°N 50 40 MS05 OSP/P26 P20 P16 P12 P4Line - P Alaska British Columbia Chlorophyll a Concentration (mg m-3) HNLC Boundary Subarctic Current N. Pacific Current West Wind Drift C alifornia C urrent A laska C urrent Alas kan Stre am Alas kan Gyre  Fig. 1.1. The subarctic NE Pacific showing the positions of the major hydrographic stations that were sampled during this study, overlaid on the SeaWiFS Level-3 standard mapped chlorophyll image for 1998. This image shows the position of the transition in chlorophyll concentration between the lower chlorophyll, oligotrophic subtropical gyre in the south and the higher chlorophyll, HNLC (high nitrate, low chlorophyll) subarctic region in the north, generally recognized as north of 42-45°N (Longhurst, 1998). The chlorophyll image was provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE. Gray contours are the 10 yr mean wind-forced circulation stream flow functions from Rienecker et al. (1996). The red dashed line is the approximate boundary of the NE subarctic Pacific HNLC region defined as the area where summer nitrate was consistently > 1 μM in1998-2000 (Whitney and Welch, 2002). Figure adapted from Nelson Sherry (unpublished).  14 -2 -1 0 1 2 3 4 1972/73 1982/83 1991/92 1997/98 El Niño Ja n1 Fe b1 M ar 1 A pr 1 M ay 1 Ju n1 Ju l1 A ug 1 S ep 1 O ct 1 N ov 1 D ec 1 Ja n2 Fe b2 M ar 2 A pr 2 M ay 2 Ju n2 Ju l2 A ug 2 S ep 2 O ct 2 N ov 2 D ec 2 St an da rd iz ed  D ep ar tu re -2 -1 0 1 2 3 4 La Niña1964/65 1970/71 1973/74 1988/89 1998/99  Fig. 1.2. A monthly multivariate ENSO index, or MEI (Wolter and Timlin, 1998). MEI measures the intensity of (top) the 1997-98 El Niño (bold) relative to three strong El Niño events, and (bottom) the 1998-99 La Niña (bold) relative to recent La Niña events. Data obtained from http://www.cdc.noaa.gov/people/klaus.wolter/MEI/table.html. Table adapted from Hayward et al. (1999). Note that each El Niño / La Niña period covers two years and are separated into two, 12 month periods separated by a vertical line.  15 1.7 References  Bograd, S.J., Thomson, R.E., Rabinovich, A.B., LeBlond, P.H., 1999. Near-surface circulation of the northeast Pacific Ocean derived from WOCE-SVP satellite- tracked drifters. Deep-Sea Research Part II-Topical Studies in Oceanography 46 (11-12), 2371-2403. Booth, B.C., Lewin, J., Norris, R.E., 1982. Nanoplankton species predominant in the sub- arctic Pacific in May and June 1978. Deep-Sea Research Part a-Oceanographic Research Papers 29 (2), 185-200. Booth, B.C., Lewin, J., Postel, J.R., 1993. Temporal variation in the structure of autotrophic and heterotrophic communities in the subarctic Pacific. Progress in Oceanography 32 (1-4), 57-99. Boyd, P., Berges, J.A., Harrison, P.J., 1998a. In vitro iron enrichment experiments at iron-rich and -poor sites in the NE subarctic Pacific. Journal of Experimental Marine Biology and Ecology 227 (1), 133-151. Boyd, P.W., Muggli, D.L., Varela, D.E., Goldblatt, R., Chretien, R., Orians, K.J., Harrison, P.J., 1996. In vitro iron enrichment experiments in the NE subarctic Pacific. Marine Ecology Progress Series 136, 179-193. Boyd, P.W., Wong, C.S., Merrill, J., Whitney, F., Snow, J., Harrison, P.J., Gower, J., 1998b. Atmospheric iron supply and enhanced vertical carbon flux in the NE subarctic Pacific: Is there a connection? Global Biogeochemical Cycles 12 (3), 429-441. Boyd, P.W., Harrison, P.J., 1999. Phytoplankton dynamics in the NE subarctic Pacific. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2405- 2432. Brodeur, R.D., Ware, D.M., 1992. Long-term variability in zooplankton biomass in the subarctic Pacific Ocean. Fisheries Oceanography 1 (1), 32-38. Brzezinski, M.A., 1985. The Si:C:N ratio of marine diatoms: Interspecific variability and the effects of some environmental variables. Journal of Phycology 21, 347-357. Chelton, D.B., Davis, R.E., 1982. Monthly mean sea level variability along the west coast of North America. Journal of Physical Oceanography 12 (8), 757-784. Dodimead, A.J., Favorite, F., Hirano, T., 1963. Salmon of the North Pacific Ocean. II. Review of the oceanography of the subarctic Pacific region. International North Pacific Commission Bulletin 13, 195.  16 Dugdale, R.C., Wilkerson, F.P., Minas, H.J., 1995. The role of a silicate pump in driving new production. Deep Sea Research 42 (5), 697-719. Fitzwater, S.E., Knauer, G.A., Martin, J.H., 1982. Metal contamination and its effect on primary production measurements. Limnology and Oceanography 27 (3), 544- 551. Freeland, H., 2000. The 1997-98 El Nino: The view from Line-P. California Cooperative Oceanic Fisheries Investigations Reports 41, 56-61. Gargett, A.E., 1991. Physical processes and the maintenance of nutrient-rich euphotic zones. Limnology and Oceanography 36 (8), 1527-1545. Harrison, P.J., Whitney, F.A., Tsuda, A., Saito, H., Tadokoro, K., 2004. Nutrient and plankton dynamics in the NE and NW gyres of the subarctic Pacific Ocean. Journal of Oceanography 60 (1), 93-117. Hayward, T.L., Baumgartner, T.R., Checkley, D.M., Durazo, R., Gaxiola-Castro, G., Hyrenbach, K.D., Mantyla, A.W., Mullin, M.M., Murphree, T., Schwing, F.B., Smith, P.E., Tegner, M.J., 1999. The state of the California Current in 1998-1999: Transition to cool-water conditions. California Cooperative Oceanic Fisheries Investigations Reports 40, 29-62. Honjo, S., Okada, H., 1974. Community structure of coccolithophores in the photic layer of the mid-Pacific. Micropaleontology 20 (2), 209-230. Hutchins, D.A., Bruland, K.W., 1998. Iron-limited diatom growth and Si:N uptake ratios in a coastal upwelling regime. Nature (London) 393, 561-564. La Roche, J., Boyd, P., McKay, R., Geider, R.J., 1996. Flavodoxin as a marker for iron stress in phytoplankton. Nature (London) 382, 802-805. Lam, P.J., Bishop, J.K.B., Henning, C.C., Marcus, M.A., Waychunas, G.A., Fung, I.Y., 2006. Wintertime phytoplankton bloom in the subarctic Pacific supported by continental margin iron. Global Biogeochemical Cycles 20 (1), Gb1006, doi:1029/2005GB002557. Longhurst, A., 1998. Ecological geography of the sea. Academic Press, San Diego. Mackas, D.L., Galbraith, M., 2002. Zooplankton community composition along the inner portion of Line P during the 1997-1998 El Nino event. Progress in Oceanography 54 (1-4), 423-437. Maldonado, M.T., Boyd, P.W., Harrison, P.J., Price, N.M., 1999. Co-limitation of phytoplankton growth by light and Fe during winter in the NE subarctic Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2475-2485.  17 Maldonado, M.T., Price, N.M., 1999. Utilization of iron bound to strong organic ligands by plankton communities in the subarctic Pacific Ocean. Deep-Sea Research Part II-Topical Studies in Oceanography 46 (11-12), 2447-2473. Marchetti, A., Juneau, P., Whitney, F.A., Wong, C.-S., Harrison, P.J., 2006a. Phytoplankton processes during a mesoscale iron enrichment in the NE subarctic Pacific: Part II - Nutrient utilization. Deep Sea Research Part II: Topical Studies in Oceanography 53 (20-22), 2114-2130. Marchetti, A., Sherry, N.D., Kiyosawa, H., Tsuda, A., Harrison, P.J., 2006b. Phytoplankton processes during a mesoscale iron enrichment in the NE subarctic Pacific: Part I - Biomass and assemblage. Deep Sea Research Part II: Topical Studies in Oceanography 53 (20-22), 2095-2113. Marchetti, A., Harrison, P.J., in press. Coupled changes in the cell morphology and elemental C, N and Si composition of the pennate diatom Pseudo-nitzschia due to iron deficiency. Limnology and Oceanography. Martin, J.H., Gordon, M., Fitzwater, S.E., Broenkow, W.W., 1989. VERTEX: phytoplankton/iron studies in the Gulf of Alaska. Deep Sea Research 36 (5), 649- 680. McPhaden, M.J., 1999. El Nino:  The child prodigy of 1997-98. Nature 398 (6728), 559- 562. Milligan, A.J., Harrison, P.J., 2000. Effects of non-steady state iron limitation on nitrogen assimilatory enzymes in the marine diatom Thalassiosira weissflogii (Bacillariophyceae). Journal of Phycology 35, 1-9. Nishioka, J., Takeda, S., Wong, C.S., Johnson, W.K., 2001. Size-fractionated iron concentrations in the northeast Pacific Ocean: distribution of soluble and small colloidal iron. Marine Chemistry 74, 157-179. Okada, H., Honjo, S., 1973. Distribution of oceanic coccolithophorids in the Pacific. Deep Sea Research 20 (4), 355-374. Putland, J.N., Whitney, F.A., Crawford, D.W., 2004. Survey of bottom-up controls of Emiliania huxleyi in the northeast subarctic Pacific. Deep Sea Research Part I: Oceanographic Research Papers 51 (12), 1793-1802. Rienecker, M.M., Atlas, R., Schubert, S.D., Willett, C.S., 1996. A comparison of surface wind products over the North Pacific Ocean. Journal of Geophysical Research- Oceans 101 (C1), 1011-1023. Schwing, F.B., Murphree, T., deWitt, L., Green, P.M., 2002. The evolution of oceanic and atmospheric anomalies in the northeast Pacific during the El Nino and La Nina events of 1995-2001. Progress in Oceanography 54 (1-4), 459-491.  18 Strub, P.T., James, C., 2002. The 1997-1998 oceanic El Nino signal along the southeast and northeast Pacific boundaries - an altimetric view. Progress in Oceanography 54 (1-4), 439-458. Suzuki, K., Liu, H.B., Saino, T., Obata, H., Takano, M., Okamura, K., Sohrin, Y., Fujishima, Y., 2002. East-west gradients in the photosynthetic potential of phytoplankton and iron concentration in the subarctic Pacific Ocean during early summer. Limnology and Oceanography 47 (6), 1581-1594. Tabata, S., 1985. Statistics of oceanographic data based on hydrographic/STD casts made at Ocean Station P during August 1956 through June 1981. Canadian Data Report of Hydrography and Ocean Sciences 31. Takahashi, K., 1986. Seasonal fluxes of pelagic diatoms in the subarctic Pacific, 1982- 1983. Deep-Sea Research Part a-Oceanographic Research Papers 33 (9), 1225- 1251. Takeda, S., 1998. Influence of iron availability on nutrient consumption ratio of diatoms in oceanic waters. Nature (London) 393, 774-777. Taylor, F.J.R., Waters, R.E., 1982. Spring phytoplankton in the subarctic Pacific Ocean. Marine Biology 67, 323-335. Varela, D.E., Harrison, P.J., 1999a. Effect of ammonium on nitrate utilization by Emiliania huxleyi, a coccolithophore from the oceanic northeastern Pacific. Marine Ecology Progress Series 186, 67-74. Varela, D.E., Harrison, P.J., 1999b. Seasonal variability in nitrogenous nutrition of phytoplankton assemblages in the northeastern subarctic Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 46, 2505-2538. Welschmeyer, N.A., Strom, S., Goericke, R., DiTullio, G.R., Belvin, M., Peterson, W., 1993. Primary production in the subarctic Pacific Ocean: Project SUPER. Progress in Oceanography 32 (1-4), 101-135. White, W.B., 1994. Slow El-Nino-Southern-Oscillation Boundary Waves. Journal of Geophysical Research-Oceans 99 (C11), 22737-22751. Whitney, F.A., Wong, C.S., Boyd, P.W., 1998. Interannual variability in nitrate supply to surface waters of the northeast Pacific Ocean. Marine Ecology Progress Series 170, 15-23. Whitney, F.A., Freeland, H.J., 1999. Variability in upper-ocean water properties in the NE Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2351-2370.  19 Whitney, F.A., Welch, D.W., 2002. Impact of the 1997-1998 El Niño and 1999 La Niña on nutrient supply in the Gulf of Alaska. Progress in Oceanography 54 (1-4), 405- 421. Whitney, F.A., Crawford, D.W., Yoshimura, T., 2005a. The uptake and export of silicon and nitrogen in HNLC waters of the NE Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 52 (7-8), 1055-1067. Whitney, F.A., Crawford, W.R., Harrison, P.J., 2005b. Physical processes that enhance nutrient transport and primary productivity in the coastal and open ocean of the subarctic NE Pacific. Deep Sea Research Part II: Topical Studies in Oceanography 52 (5-6), 681-706. Wolter, K., 1987. The southern oscillation in surface circulation and climate over the tropical Atlantic, eastern Pacific, and Indian Oceans as captured by cluster- analysis. Journal of Climate and Applied Meteorology 26 (4), 540-558. Wolter, K., Timlin, M.S., 1998. Measuring the strength of ENSO-how does 1997/98 rank? Weather 53, 315-324. Wong, C.S., Whitney, F.A., Iseki, K., Page, J.S., Zeng, J., 1995. Analysis of trends in primary productivity and chlorophyll a over two decades at Ocean Station P (50°N 145°W) in the subarctic northeast Pacific Ocean. Canadian Journal Fisheries Aquatic Sciences 121, 107-117. Wong, C.S., Whitney, F.A., Matear, R.J., Iseki, K., 1998. Enhancement of new production in the northeast subarctic Pacific ocean during negative North Pacific index events. Limnology and Oceanography 43 (7), 1418-1426. Wong, C.S., Matear, R.J., 1999. Sporadic silicate limitation of phytoplankton productivity in the subarctic NE Pacific. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2539-2555. Wong, C.S., Whitney, F.A., Crawford, D.W., Iseki, K., Matear, R.J., Johnson, W.K., Page, J.S., 1999. Seasonal and interannual variability in particle fluxes of carbon, nitrogen and silicon from time series of sediment traps at Ocean Station P, 1982- 1993: relationship to changes in subarctic primary productivity. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2735-2760. Wong, C.S., Crawford, D.W., 2002. Flux of particulate inorganic carbon to the deep subarctic Pacific correlates with El Niño. Deep Sea Research Part II: Topical Studies in Oceanography 49 (24-25), 5705-5715. Wong, C.S., Waser, N.A.D., Nojiri, Y., Whitney, F.A., Page, J.S., Zeng, J., 2002. Seasonal cycles of nutrients and dissolved inorganic carbon at high and mid latitudes in the North Pacific Ocean during the Skaugran cruises: determination of new production and nutrient uptake ratios. Deep Sea Research Part II: Topical Studies in Oceanography 49 (24-25), 5317-5338.  20 Wong, C.S., Wong, S.E., Peña, M.A., Levasseur, M., 2006. Climatic effect on DMS producers in the NE subarctic Pacific: ENSO on the upper ocean. Tellus B 58 (4), 319-326.     21 Chapter 2 : Spatial and temporal variability in size-fractionated organic primary production, chlorophyll biomass and photosynthetic performance in the NE subarctic Pacific during El Niño (1998), La Niña (1999) and 20001  2.1 Introduction Ocean Station Papa (OSP; P26) is one of the longest open ocean time series (Freeland, 2007) with water sampling starting in 1956. This long term data set has provided insights into nutrient and phytoplankton variability on time scales from seasonal to decadal variations (Harrison et al., 2004; Pena and Varela, 2007). OSP is located in the high nitrate, low chlorophyll waters (HNLC) of the subarctic Pacific where phytoplankton production and biomass are mainly controlled by iron (Maldonado et al., 1999; Nishioka et al., 2001; Denman and Pena, 2002; Whitney et al., 2005b).  Most studies at OSP report a relatively constant year round chlorophyll a concentration of 0.2 to 0.4 mg m-3 (Anderson et al., 1977; Sambrotto and Lorenzen, 1987; Frost, 1991; Miller et al., 1991; Welschmeyer et al., 1991). While the basic water column parameters such as nutrients and chlorophyll have been routinely measured, there have been few attempts to quantify C:Chl ratios along Line P. Booth et al. (1993) did calculate a range of C:Chl values for OSP, but only during the spring and summer seasons with no winter values. Accompanying the studies at OSP, there is also an extensive time series for the transect (Line P) running from the British Columbia coast to OSP. The Line P transect consists of a series of stations (P01 to P26), but only P04, 12, 16 20 and 26 are routinely sampled for all water column parameters. Therefore Line P has provided valuable insights of the changes in biogeochemical parameters from a coastal ecosystem to HNLC waters (Harrison et al. 1999). Due to summer upwelling, tidal mixing and river run-off that occurs near the coast, maximum POC production rates in the Gulf of Alaska tend to occur near shore (Forbes et al., 1986; Boyd et al., 1995b; Harrison et al., 1999; Peterson, 2005) where the  1 A version of this chapter has been/will be submitted for publication. Lipsen, M., Crawford, D., Whitney, F. and Harrison P.J. Spatial and temporal variability in size-fractionated organic primary production, chlorophyll biomass and photosynthetic performance in the NE subarctic Pacific during El Niño (1998), La Niña (1999) and 2000.    22 mixed layer is often shallow and not light limited (Whitney and Freeland, 1999). Production tends to decrease offshore and parallels a decrease in available iron (Nishioka et al., 2001; Johnson et al., 2005). The  availability of iron is known to be important in HNLC waters such as the NE Pacific (Banse, 1991b; Boyd et al., 1996; Boyd and Harrison, 1999; Maldonado et al., 1999; Boyd et al., 2004) where chlorophyll a standings stocks are lower than dissolved macronutrients could theoretically support (Banse, 1991b). Additionally, studies of nitrogen uptake by Varela and Harrison (1999b) indicate a depth-integrated ƒ-ratio range of 0.05-0.37, indicating that phytoplankton production is primarily based on regenerated nitrogen. The major source of iron to the HNLC region in the NE subarctic Pacific is much better understood now than it was 20 years ago, with iron known to be supplied by dust events (Boyd et al., 1995b; Bishop et al., 2002), offshore shelf sediment transport (Lam et al., 2006), and mesoscale eddies which carry shelf derived Fe far offshore into the oligotrophic North Pacific gyre (Johnson et al., 2005). With the exception of Boyd et al. (1999) covering the years 1992-1997 during the Canadian Joint Global Ocean Flux Study (CJGOFS), the historical perspective of Peña and Varela (2007) and coccolithophore study during the same period as this study (Putland et al., 2004), there has been no study covering the phytoplankton dynamics of the major stations along Line P during and ENSO event. This study aims to extend the research on the biological component of CJGOFS and expand the coverage by introducing some new aspects.  For example, this is the first study to combine biomass and organic production values coupled with photosynthetic performance (P vs. E) along Line P. Additionally, this study encompasses the first comprehensive measurements of phytoplankton biomass, production and nutrient dynamics during El Niño (1998) and La Niña (1999) events. 2.2 Materials and Methods 2.2.1 Sampling location Samples were collected during 8 cruises undertaken as a part of the long term monitoring of Line P and Ocean Station Papa (OSP) carried out by the Canadian    23 Department of Fisheries and Oceans from the Institute of Ocean Sciences, Sidney, BC, Canada on the CCGS John P. Tully. Cruises lasting approximately three weeks were undertaken in February (winter), June (late spring) and August/September (late summer) during 1998, 1999 and 2000 (no Feb cruise in 2000) (Table 2.1 and 2.2). Samples were taken at five stations (P04, P12, P16, P20 and P26) along Line P, starting with the most easterly station P04 approximately 70 km off the coast of Vancouver Island, and ending at station P26 (also known as Ocean Station Papa, OSP). 2.2.2 Study area There have been numerous studies that have characterized the different physical, chemical and biological characteristics along Line P and at OSP. The most eastern station (P04) is located on the continental slope (1300 m). All other stations are at depths >3000 m (Table 2.1 and Fig. 2.1).  P04 and P12 experience nitrate depletion each spring, thus have been characterized as having a productivity cycle similar to the coastal ocean (Boyd and Harrison, 1999) and are referred to in this study as near-shelf stations. P16 is a transition station, having neither the distinct characteristics of an HNLC or nitrate deplete region (Whitney et al., 1998). P20 and P26 are HNLC stations and are characterized as having a shallow winter pycnocline (Evans and Parslow, 1985), an absence of a spring diatom bloom (Parslow, 1981), dissolved iron (DFe) concentrations <0.5 nM (Martin and Gordon, 1988a; Nishioka et al., 2001; Johnson et al., 2005) and Fe-stressed phytoplankton cells (Martin et al., 1989; Marchetti et al., 2006b). 2.2.3 Sample collection and processing Samples were collected from 12 L GO-FLO® bottles equipped with silicon tubing soaked in 10% HCl for 24 h  mounted on Kevlar® line. Bottles were tripped using a Teflon® coated messenger to minimize trace metal contamination (Bruland et al., 1979; Fitzwater et al., 1982). Water was collected prior to local dawn (04:00-07:00 local time) at each station. Samples were collected from six light depths corresponding to 100, 55, 30, 10, 3.5, and 1% of surface irradiance (I0). Light depths were selected from vertical photosynthetically active radiation (PAR) profiles derived whenever possible from mid- day casts at the same station the day prior to sampling. Incident irradiance was recorded    24 and averaged at 10 min intervals with a Li-COR® light meter with a 4π quantum sensor. The mixed layer depth was derived according to the procedure used by Freeland et al. (1997). Average mixed layer underwater irradiance was calculated according to Putland et al. (2004). For a particular station, the surface irradiance was averaged for the previous 4 days using values collected along the Line P transect and this allowed for a light parameter that took into account the light regime the phytoplankton cells encountered before measurements of production and performance. This technique was used only in Pearson correlation matrices where irradiance was correlated against other variables, and should not be confused with the method employed to calculate light depths (see above). 2.2.4 Chlorophyll a and POC ’primary’ production Replicate (2 per depth) size-fractionated chlorophyll a samples (300 ml) were filtered serially through 20, 5, and 0.2 μm polycarbonate filters (47 mm diameter). The 20 and 5 μm size fraction were filtered under gravity, while the 0.2 μm size fraction was filtered using < 100 mm Hg vacuum differential (Joint et al., 1992). Filters were stored in scintillation vials with 10 ml 90% acetone at -20 C for 24 h, then analyzed for chlorophyll a on board the ship using a Turner DesignsTM 10-AU Fluorometer following Parsons et al. (1984). Size-fractionated particulate organic carbon (POC) ‘primary’ production was estimated using the 14C technique following Boyd et al. (1996). Samples (two from each depth) were placed in acid-cleaned, distilled-deionized Milli-Q® (Fitzwater et al., 1982) 250 ml Nalgene® polycarbonate bottles, and then 15 μCi of 14C as sodium bicarbonate was added to each sample. Dark bottle incubations (one from each depth) were prepared in a similar manner using 250 ml opaque polyethylene bottles. Light and dark samples were incubated in Plexiglas® incubators maintained at ambient sea surface temperature (± 2oC) using a seawater flow-through system. Bottles were placed in plastic bags wrapped in neutral density screening that corresponded to the light depth from which the sample was taken. After a 24 h incubation, all samples were size-fractionated as above. Filters were placed in scintillation vials and stored in the dark until the end of the cruise. Back in the laboratory, filters were soaked in an HCl solution with a surrounding KOH trap to    25 organic (POC) and inorganic (PIC) carbon fixation (see Chapter 3). Scintillation cocktail (Scintisafe®) was then added to all samples and analyzed one month later with a Beckman LS6000 SC scintillation counter following JGOFS protocols (Knap et al., 1996). Growth rates of the phytoplankton population were estimated using the turnover time of water-column integrated algal carbon following Boyd and Harrison (1999). Integrated chlorophyll a biomass was converted to phytoplankton carbon biomass using a C:Chl a range of 16.9-85.9 derived from OSP and P04, the end members of Line P (Peña and Varela, 2007). For stations where no C: Chl a data were available, values were the average from available stations from that cruise. Turnover time was calculated by dividing daily column integrated POC production by the integrated phytoplankton biomass. Multiplying these results by 0.69 yields instantaneous growth rates (d-1). 2.2.5 Photosynthesis versus irradiance measurements (P vs. E) Samples for P vs. E measurements were taken for all cruises in 1998 and 1999 at the 55% I0 depth. For the two cruises in 2000, samples were taken from each station at 100, 55, 10 and 1% I0. Water samples were drawn directly from the GO-FLO® into collapsible, acid-cleaned 4 L LDPE cubitainers and dispensed into 19 (16 light and 3 dark) 70 ml polycarbonate bottles (acid-cleaned with 10% HCl for > 24 h and DDW- rinsed) under low light conditions. Samples were inoculated with 15 μCi of 14C-labeled sodium bicarbonate and immediately placed in a water-cooled aluminum block set to ambient sea surface temperature (± 20C) located in a photosynthetron (Peterson, 2005) at designated light intensities and incubated for 4 h. All incubations were performed between 08:00 – 13:00 which corresponds to the period of maximum photosynthetic rates in this region (Forbes et al., 1988) at light intensities that varied between 2-2500 μmol photons m-2 s-1. Light intensities for each chamber were determined using a Biospherical QSL Quantum Scalar Laboratory Sensor at the beginning, middle and end of each cruise. After 4 h, all samples were filtered (< 100 mm Hg pressure) through 0.2 μm polycarbonate filters (25 mm diameter) and processed in an identical manner to the POC production samples.    26 The assimilation number (PBmax, maximum rate of photosynthesis normalized to chlorophyll a), alpha (αΒ, initial slope of the photosynthesis–irradiance curve normalized to chlorophyll a), beta (βΒ, slope of the curve under photoinhibition normalized to chlorophyll a), and the irradiance at the onset of light saturation (Ek) were fitted to the Platt et al. (1980) equation and the parameters were subsequently derived following Lewis and Smith (1983). 2.2.6 Deck incubation photosynthesis versus irradiance (P vs. E) Photosynthetic parameters were also derived from deck incubations (POC production values) using the relationship between 14C uptake rates and water column daily PAR. Conversely, P vs. E relationships derived from photosynthetron experiments (see above) only measured photosynthetic performance over a four hour period. Due to the differences in photosynthetic performance (Welschmeyer et al., 1993) measured over hours (photosynthetron) versus a complete photoperiod (deck incubations), no effort was made to convert values to equivalent units from the two methods. Only the trends between the two methods will be considered. 2.2.7 POC and nutrients   Particulate organic carbon and nitrogen POC (particulate organic carbon) samples were collected as above for each light depth in 4 L collapsible LDPE cubitainers that had been acid-soaked with 10% HCl > 24 h and DDW-rinsed. Samples were filtered through pre-combusted (500oC) 0.7 μm Whatman® GF/F filters using vacuum pressure (>100 mm Hg) and stored frozen (-20oC). POC samples were analyzed using a Carlo Erba Model NA-1500 Elemental Analyzer following Verado et al. (1990). Nitrate, silicic acid and dissolved iron Nitrate and silicic acid data were analyzed at sea on a Technicon Autoanalyzer following procedures described by Barwell-Clarke and Whitney (1996). Dissolved iron    27 (DFe) data from the same cruises were kindly provided by Keith Johnson and  Dr. C. S. Wong (pers. comm.) or obtained from Nishioka (2001). 2.2.8 Contour plotting Contour plots (Fig. 2.2, 2.5 and 2.7) were created using Surfer 7.0 (Golden Software) following the kriging interpolation technique utilizing the linear model with a slope of one. Disparity in the values of the x-axis (1500 km) and the y-axis (85 m) were addressed using the anisotropy function with a ratio of 0.5 and a zero angle. Although contour plots should always be interpreted with caution, our approach does yield a sufficiently conservative value that allows realistic analysis near the sampling points and a cautious analysis of trends over the whole area. 2.2.9 Statistical testing All variables were tested for normality using the Kolmogrov-Smirnov test and visual inspection of normal probability plots (Systat 11).  As the data were not normal, the non-parametric equivalent of the t-test, the Mann-Whitney test (Systat 11) to test for significant spatial and temporal differences, was used. Alpha was set at 0.05. 2.3 Results 2.3.1 Euphotic zone properties Mixed layer depths (MLD) for all stations were shallower than the 1% light level (Zeu) for all June and Aug./Sept. cruises and varied between 11 and 60 m (Table 2.2). In February, MLDs were greater than Zeu with a range from 76 to 175 m. The greatest range occurred in 1998. Surface salinity remained relatively consistent along all of Line P in February of both years. June and Aug./Sept. displayed the typical increase (Whitney and Freeland, 1999) from P04 to P26 with the largest difference occurring in June 1999 (31.58 to 32.86).    28 2.3.2 Nutrients Nitrate (Table 2.2) was not limiting at any station (>3 μM) for both winters cruises with 1999 showing slightly higher levels than 1998. In June, nitrate was typically undetectable (<0.1 μM) at P04 and P12 in 1998 and gradually increased to values >6 μM at P20 and P26. In June 2000, nitrate reached 13.2 μM at P26. Winter surface DFe (Table 2.2) concentrations were maximum (>0.5 nM) at P04 in 1998 (1.5 nM) and 1999 (1.7 nM). DFe was always maximal at P04 in June and Aug./Sept. except in Aug./Sept. 2000 where P12 values (0.13 nM) were higher than P04 (0.04 nM). The rest of the stations (P12 - P26) were generally <0.1 nM for both seasons. Throughout this study, surface DFe was never <0.1nM at P04 for all cruises with the exception of Aug./Sept. 2000 (0.05 nM). P12 was more variable and DFe > 0.1 for three cruises (June and Aug./Sept. 1998, February 1999 and Aug./Sept. 2000). At all other stations (P16-P26) surface DFe < 0.1 nM, except for P26 during Feb. 1998 and all stations during Feb 1999. 2.3.3 Phytoplankton biomass Along Line P, phytoplankton biomass was relatively constant. Average integrated (for all seasons combined) chlorophyll a values (Table 2.3) ranged from 18 to 21 mg m-2. Phytoplankton biomass for all Feb. cruises increased from a minimum at P04 (18 mg m-2) to a maximum for this study of 32 mg m-2 at P20. June and Aug./Sept cruises had maximum average integrated values at P04 and P12 with minimum average integrated values occurring at P16 and P20. In both cases, P26 was higher than P16 and P20, but not as high as P04 and P12. Total chlorophyll a values at the near-shelf station (P04) showed both seasonal and annual variability. P04 water column concentrations in Feb 1998 and 1999 varied minimally from 0.3 to 0.5 mg chl m-3 (Fig. 2.2 and 2.3) coinciding with little to no variability in depth. Total integrated values were similar between years (Table 2.2). In February, mixed layer depths for both years were below the euphotic zone for all stations (Table 2.2). During the June cruises (1998-2000), chlorophyll a values at P04 varied by the largest margin with ranges from a low of 0.2 mg m-3  in 1998 to a maximum of 1.5    29 mg m-3 at the subsurface chlorophyll a maximum (SCM) at 16 m in 1999. June 2000 also showed high values that ranged from 0.31 to 0.67 mg m-3. Integrated values (Table 2.2 and Fig. 2.4) at P04 displayed a near three-fold difference over the three years with the largest value occurring in June 1999 (34.6 mg m-2) and the lowest in June 1998 (9.5 mg m-2). Aug./Sept. P04 values had a larger range between depths in 1998  (0.2 to 0.7 mg m- 3) than between the three years suggesting a more stratified phytoplankton assemblage. Integrated average P04 values for the three years 1998, 1999, and 2000 were 14.9, 16 and 22.9 mg m-2 respectively (Fig. 2.2 and 2.3). February 1998 values at P12 resembled P04 with little vertical gradient and an integrated chlorophyll a (Table 2.2 and Fig. 2.4) value of 16.8 mg m-2.  Feb. 1999 integrated values (27.6 mg m-2) were >1.5 times higher. Maximum algal biomass (Fig. 2.2 and 2.3) occurred at P12 in late spring in 1998 (0.2-0.8 mg m-3) and 1999 (0.3-0.9 mg m-3) and during Aug./Sept. 2000. (0.3-0.7 mg m-3). In contrast, the lowest integrated chlorophyll a (Table 2.2) at P12 occurred in Aug./Sept. 1998 (10.1 mg m-2) and 1999 (14.5 mg m-2), and in  June 2000 (19.0 mg m-2) . At station P16 (middle station of Line P) water column chlorophyll values ranged from 0.1 to 0.6 mg m-3 (Fig. 2.2 and 2.3). Winter values in 1998 were two-fold higher than in 1999 with clear vertical mixing throughout the euphotic zone. June and Aug./Sept. 1999 and 2000 were relatively uniform and ranged between 0.1 and 0.2 mg m-3 with slightly higher values of 0.4 mg m-3 in Aug./Sept. 2000.  During June and Aug./Sept. 1998, P16 chlorophyll was low at the surface (0.1 mg m-3) and increased with depth with a maximum of 0.5 mg m-3 between 15 and 26 m in June and a sub-surface maximum in Aug./Sept. of 0.4 mg m-3 at 40 m. P20 vertical profiles were similar to P16 and ranged between 0.1 to 0.5 mg m-3. Integrated values (Table 2.2 and Fig. 2.4) reached a maximum in February (36.8 mg m-2) and were double the value at P16 in June (18.3 mg m-2). OSP (P26) water column samples were similar but generally higher than P20 with a range of 0.3-0.5 mg m-3 (Fig. 2.2 and 2.3) with the exception of both winter cruises where OSP had the lowest values in 1998 and was lowest second to only P16 in 1999. Maximum values (0.5 mg m-3) were found in Aug./Sept. 2000. Integrated P26 values    30 (Table 2.2 and Fig. 2.4) ranged from 12.6 mg m-2 (Aug./Sept. 1998) to a maximum of 23.4 mg m-2 (June 1999). 2.3.4 Particulate organic carbon Particulate organic carbon (POC) ranged from 1 to 14 μmol kg-1 for all three years and all stations (Fig. 2.5 and 2.6). In Feb, POC levels were relatively constant below the surface along Line P. Surface layers were variable with large values at the surface of P20 in 1998 (7.8 μmol kg-1) and P12 in 1999 (10.2 μmol kg-1) (Fig. 2.6). Concentrations were normally higher at P26 and P04 above the mixed layer in June and Aug./Sept. Maximum values were measured at the surface at P04 in June 1998 (8.2 μmol kg-1) and June 1999 (5.8 μmol kg-1), at 14 m in June 2000 (14.8 μmol kg-1) and at P26 in Aug./Sept. 1999 at 30 m (8.4 μmol kg-1). Additionally, there was a maximum below the mixed layer at P04 in Aug./Sept. 1998 at 20 m (20 μmol kg-1). 2.3.5 POC production Average integrated POC production per station showed more variability than found in integrated chlorophyll a values. Integrated POC production averaged for all cruises (Table 2.3) showed a clear maximum at P04 (512 mg C m-2 d-1) with a minimum at P20 (273 mg C m-2 d-1) and a slightly higher value at P26 (314 mg C m-2 d-1). Seasonally, average Feb. cruise values were different than June and Aug./Sept.. February integrated POC production was minimal at P04 (72 mg C m-2 d-1) and reached a maximum values at P20 (205 mg C m-2 d-1). It is important to note that POC production was measured at P04 in February only once (1998). Average integrated June values showed a maximum at P04 (615 mg C m-2 d-1) and continued to decline to P26 (170 mg C m-2 d-1). Aug./Sept. average integrated POC production was 555 mg C m-2 d-1 at P04 and declined to P20 (331 mg C m-2 d-1), but spiked to a maximum of 570 mg C m-2 d-1 at P26. POC production at P04 displayed a similar seasonal maximum range as chlorophyll a. There was an 8-fold increase in average column integrated production from February to June with a slightly lower increase between February and Aug./Sept. (Table 2.2 and Fig. 2.4). Average photic zone values for discrete samples for all stations    31 for winter 1998 were 2.5 mg C m-3 d-1 (Fig. 2.7 and 2.8) with a maximum value of 4.8 mg C m-3 d-1 at the surface. Unfortunately, samples for P04 were lost in February 1999 and there was no February cruise in 2000. However, values for P12 in 1999 averaged 2.2 mg C m-3 d-1 and previous studies at P04 reveal similar rates to those found in 1998 with low variation between depths (Boyd and Harrison, 1999). Integrated June P04 values (Table 2.2 and Fig. 2.4) demonstrated the largest variation between years (72-1390 mg C m-2 d-1). Although the difference in integrated production values between February and June 1998 at P04 were minimal (72 and 100 mg C m-2 d-1 respectively), there was a >3-fold difference between June 1998 and June 1999 (100 and 358 mg C m-2 d-1 respectively). A 13-fold difference between 1998 and 2000 (100 and 1390 mg C m-2 d-1 respectively) coincided with a SCM at 14 m in June 2000 at P04 with the highest production rates of any station or season throughout the three year study. Although Aug./Sept.P04 integrated values were similar for all three years (566, 447 and 653 mg C m-2 d-1 respectively), values for discrete samples (Fig. 2.7 and 2.8) varied. In 1998, a clear subsurface production maximum coincided with the SCM at 24 m during Aug./Sept. Conversely in 1999, production maxima were found at the surface and did not correspond to the SCM. During that cruise at P04, there was a production maximum at 10 m, corresponding to 30% of surface irradiance. Chlorophyll biomass was uniform (Fig. 2.2 and 2.3)  in the upper 20 m indicating probable light saturation at 30% Io, very similar to June of the same year. Integrated February production rates at P12 (Table 2.2 and Fig. 2.4) were twice the value at P04 in 1998 and slightly higher than P12 in 1999.  Seasonally, average integrated values were two times greater from February to June and about three times larger from winter to Aug./Sept. June 1998 showed the lowest value (84.1 mg C m-2 d-1) of any of the P12 values and was five times lower than 1999 and 2000 June values.  June 2000 production values at P12 were sharply lower than P04. As in June 1998, Aug./Sept. 1998 production was lower than the rates during the same period for 1999 and 2000. Upper water column rates were always higher and did not correspond to lower water column biomass maxima found in June 1998 and 1999 (Fig. 2.7 and 2.8). Water column production rates at P16, with the exception of June 2000, were < 10 mg C m-3 d-1 (Fig. 2.7 and 2.8) and generally had the lowest integrated production rates    32 (Table 2.2 and Fig. 2.4) of any stations. The exceptions occurred in June 1998 where P16 had the highest integrated value of any of the stations (312 mg C m-2 d-1) and June 2000 where it had the second highest value (483 mg C m-2 d-1) next to P04. Similar to P16, P20 surface values (Fig. 2.7 and 2.8) were commonly < 10 mg C m-3 d-1 with similar integrated production rates (Table 2.2 and Fig. 2.4). The only exceptions were a subsurface maximum value (Fig. 2.7 and 2.8) in June 2000 at 20 m (12.1 mg C m-3 d-1) and the surface in Aug./Sept. 2000 (13.0 mg C m-3 d-1). The 20 m value for June 2000 did not correspond to a clear SCM. Average OSP integrated values (Table 2.2 and Fig. 2.4) were marginally higher in June than February, but not statistically significant. Like most stations (except P04), production rates were higher in Aug./Sept. than in June with a greater than three-fold increase in integrated values from June. In Aug./Sept. 1998, OSP surface rates (25-27 mg C m-3 d-1) were the highest of any of the stations for that cruise (Fig. 2.7 and 2.8). 2.3.6 Size-fractionated biomass and production Production and biomass were generally dominated by the smaller (0.2-5.0 μm) size class for all stations and cruises. These small cells averaged 63% of the total biomass and 60% of the production (n=39) for all stations and seasons over the three-year period (Fig. 2.4 and 2.9). Large cells (>20 μm) averaged 14% of the total biomass and 17% of the total production for the entire study. The largest contribution by the 0.2-5.0 μm size class was generally observed in the winter samples (biomass ca. 70%, production ca. 66%). Near-shelf samples (P04 and P12) also tended to have slightly higher values (biomass ca. 70%, production ca. 66%) and were similar to P26 (biomass ca. 59%, production ca. 60%). Although cells >20 μm were never over 50% of the biomass or production, they reached values >30% for both at P20 in June 1998 (39% and 49%), P20 in June 2000 (31% and 31%), and P12 in Aug./Sept. 2000 (43% and 48%). 2.3.7 Integrated chlorophyll a-specific total POC production Chlorophyll a-specific carbon uptake rates (Fig. 2.10) ranged from 4 (P04 February 1998) to 64 mg C (mg Chl a m-2)-1 d-1 (P04 Aug./Sept. 2000). It is interesting to note the minimum and maximum values occurred during the same year (1998) and the    33 same station (P04). Mean water column values for each cruise increased seasonally with an eight-fold increase between February and Aug./Sept. 1998 and a four-fold increase in 1999. The opposite occurred in 2000 with the highest mean value in June. 2.3.8 Carbon specific phytoplankton growth rates Carbon specific growth rates (μc) were estimated using the proxy of turnover time of column integrated phytoplankton carbon (Table 2.4) derived using algal carbon to chlorophyll values (C:Chl a) from by Peña and Varela (2007). C:Chl a values were only available for P04 and OSP. Values for all other stations were derived from an average of the C:Chl a from P04 and OSP. Estimated C:Chl a values ranged from 17 (OSP February 1998) to 85 (P04 Aug./Sept. 2000) with an overall average of 57. This four-fold variation is a more accurate representation of the true C:Chl a values than the previous value of 50 used for all seasons (Boyd and Harrison, 1999). This yielded carbon specific growth rates ranging from 0.5-0.67 d-1. Carbon specific growth rates in February 1999 (0.10 d-1), June 1998 (0.13 d-1), and June 1999 (0.14 d-1) had the lowest rates of all the cruises (Table 2.4). Maximum values were measured in Aug./Sept. 1998 (0.43 d-1) and June 2000 (0.39 d-1). Seasonally, growth rates for February and June were similar (μc = 0.20 - 0.22 d-1) with the maximum mean value found in Aug./Sept. (0.31 d-1). Although there did not appear to be any consistent trends, rates tended to be maximal at the most eastern (P04), or the most western (OSP) stations with the exception of February 1998 at P12 (0.4 d-1). The largest values were found during Aug./Sept. 1998 at P26 (0.6 d-1) (Fig. 2.10) and June 2000 at P04 (0.7 d-1) which also corresponded to the highest rate of production. June 2000 also corresponded to the highest percent of phytoplankton of the particulate carbon pool at P04 (Table 2.4). 2.3.9 Photosynthesis versus irradiance (P vs. E) characteristics Photosynthetron incubations were used to derive P vs. E parameters for all stations and cruises for samples collected at the 55% surface irradiance (I0) depth (Table 2.5). The average PBmax rate was 1.8 mg C (mg chl a)-1 h-1 with a maximum value of 9.8 (P04, June 2000) and a minimum of 0.1 mg C (mg chl a)-1 h-1 (P26, February 1998).    34 About 47% of the values were <1.0 mg C (mg chl a)-1 h-1. Light saturation onset irradiance (Ek) had a > 60-fold range with a minimum of 10 (P12, June 98), a maximum of 623 (P26, June 99) and an average (3 years, 8 cruises, 5 stations) of 178 μmol photons m-2 s-1. Seasonal PBmax values along Line P yielded average maximum values at P12 in February (0.59 mg C (mg chl a)-1 h-1), and P04 in June (3.91 mg C (mg chl a)-1 h-1), while Ek yielded maximum values at P04 in February and June with little difference in Aug./Sept. Summer average PBmax rates were similar along Line P with slight increases at P04 and OSP. Higher PBmax values occurred in 1998 than in 1999 for all stations in February and Aug./Sept. June 1998 values were also higher, but to a lesser extent with the exception of P26 (1998) which was > 25-fold higher than 1999. As expected from the PBmax rates, Ek values were generally higher for 1999 than 1998 with the largest value (623 μmol photons m-2 s-1) occurring in June 1999. The lowest value recorded was at P12 in June 1998 (9.6 μmol photons m-2 s-1). When 55% I0 PBmax and Ek (Fig. 2.12) were plotted against incident surface irradiance (I0), a significant relationship was found between PBmax and I0 (r2 = 0.113, p<0.05), but not with Ek (r2= 0.0064, p>0.05). Initial slopes of the P vs. E curves (αB) were steeper at P04 and generally decreased offshore reaching a minimum at OSP (Table 2.5). Seasonally, αB was at a minimum in February, gradually increasing to an average maximum in Aug./Sept. At individual stations, the initial slope followed the general trend of maximal PBmax rates in Aug./Sept. 1998. The slopes of the hyperbolic curves corresponding to photoinhibition (βB) were generally negative (positive βB) at higher photon flux densities for most stations, indicating that most samples exhibited possible photoinhibition in situ at high light intensities. Increased measurements of photosynthetron P vs. E values were taken from four light depths (100, 55, 10 and 1% I0) for all stations for the June and Aug./Sept. cruises in 2000 (Fig. 2.14). Initial slope values (αB) for June and Aug./Sept. 2000 ranged from 0 to 0.12 mg C (mg chl a)-1 (mol photons m-2 s-1)-1 (Fig. 2.13). Although average per station αB values were slightly higher for the HNLC stations (0.4 (mg chl a)-1 (mol photons m-2 s- 1)-1) compared to the near-shelf stations (0.3(mg chl a)-1 (mol photons m-2 s-1)-1), the difference was not significant. In contrast to the near-shelf stations, which showed little    35 difference between June and Aug./Sept 2000 cruises, maximum αB values for the HNLC stations (P20 and P26) were found during Aug./Sept. PBmax values (Fig. 2.13 and 2.14) ranged from 0.5 to 9.2 mg C (mg chl a)-1 h-1 with a near-shelf average that was 1.4 times larger than the HNLC stations (not statistically significant). High values at the near-shelf station P04 in June 2000 corresponded to high POC production (Fig. 2.8). PBmax values at the HNLC stations remained variable with no clear difference between June and Aug./Sept. even though POC production was 3-times higher in Aug./Sept. 2.3.10 Depth-variation in photosynthetic performance Deck incubations profiling POC production over 6 depths in the euphotic zone were conducted in order to obtain in situ depth-dependent, Chl-specific assimilation rates and were plotted against depth dependent PAR (Fig. 2.15) to derive equivalent P vs. E parameters (PBmax, Ek, αB and βB), similar to those obtained from the photosynthetron experiments (see above) (Table 2.6). Deck incubated P vs. E derived values of PBmax and αB values were significantly correlated with the corresponding photosynthetron values (r2 =0.246 and 0.294 respectively, P<0.05). Ek and βB, however, were not significantly correlated (r2 =0.005 and 0.000 respectively, P>0.05). This is not surprising due to the limitation of the method where different depths may represent different algal communities in differing photoadaptive states, while the photosynthetron samples were derived from a single, discrete depth of 55% I0. The deck incubated samples showed a similar increase to the photosynthetron samples in PBmax from average February values to Aug./Sept. Ek was also comparable, showing a maximum value in June. Conversely, αB values were lowest in June. When PBmax and Ek (Fig. 2.16) were plotted against incident surface irradiance (I0) measured during the 24 h incubation, there was not a significant relationship between PBmax and I0 (r2 = 0.0921, p>0.05).  The relationship between Ek and I0 was significant (r2= 0.128, p<0.05) with an even stronger relationship (r2= 0.272, p<0.05) if the three values at the highest irradiances (probable photoinhibition) were removed.  36 2.4 Discussion 2.4.1 Variations in biomass and particulate organic carbon During our 3 year study, P04 showed the greatest seasonal variation in surface chlorophyll biomass (10-fold), especially during the 1999 season (0.3-1.5 mg chl a m-3) when spring growth was delayed due to the onset of La Niña (Whitney and Welch, 2002). Seasonal differences decreased offshore with variations typically <4-fold with a 2-fold or less difference at OSP. With the exception of P04 in June 1999, chlorophyll a values were never > 1 mg m-3 with an average for all stations, depths, seasons, and years of 0.3 mg m-3. This agrees with previous studies at OSP (Parslow, 1981; Welschmeyer et al., 1993; Boyd et al., 1995a; Wong et al., 1995; Harrison et al., 1999; Harrison, 2002; Marchetti et al., 2006c). The only other previous study of Line P stations other than OSP (Boyd and Harrison, 1999) also showed the same low seasonality and biomass for stations P04, P12, P16 and P20. Interestingly, the largest variation in integrated chlorophyll a values occurred at P20 between Aug./Sept. 1998 and Feb. 1999 when chlorophyll increased from 7.5 to 36.8 mg C m-2 d-1. The characteristic stable low algal standing stocks at OSP and the rest of Line P has been attributed to a relatively shallow year-round thermocline (Evans and Parslow, 1985; Boyd et al., 1995a; Boyd et al., 1995b; Freeland et al., 1997; Harrison et al., 1999; Harrison et al., 2004) which maximizes the light in the winter and minimizes macro- nutrient availability at the near-shelf stations (Whitney et al., 1998; Whitney and Freeland, 1999; Whitney et al., 2005a) and DFe availability at the HNLC stations (La Roche et al., 1996; Nishioka et al., 2001). Surface nitrate levels tended to follow the opposite pattern of surface DFe concentrations with limiting nitrate concentrations at stations near the shelf (P04 and P12) and limiting DFe in typical HNLC waters (P20 and P26) (Fig. 2.10), especially in the June and Aug./Sept. The resulting Fe stress to the algal populations in HNLC waters limits the larger phytoplankton species (>20 μm), specifically centric diatoms (Doucette et al., 1996; La Roche et al., 1996; Hutchins et al., 1998), to less than 20% of the total chlorophyll a.  37 Following the same pattern, POC concentrations showed the greatest variation at P04 with the largest value occurring in June 2000 at 30% I0 (15 μmol kg-1). February stations were relatively uniform below 15 m for both years and all stations with a range of 0.5 to 2.5 μmol kg-1. Maximum surface concentrations varied each year with a surface maximum at P20 (7.6 μmol kg-1) in 1998 and P12 (10.2 μmol kg-1) in 1999. Although published data of POC along Line P is sparse, this variability is consistent with Bishop et al. (1999) who found a surface maximum at the HNLC stations in Feb. 1996 and the near-shelf stations (P12, P07 and P06) in Feb. 1997. Their May 1996 study showed a relatively consistent POC concentration between 2.0-2.5 μmol kg-1 across Line P above 50 m. Although these concentrations were within the range of many of our measurements, there was a similar surface P04 maximum for all three years that was consistent with observed increases in algal biomass in previous studies (Boyd and Harrison, 1999; Thibault et al., 1999). Interestingly, P04 in June 2000 displayed the highest POC value of any of the cruises. This subsurface maximum (14.8 μmol kg-1 at 14m) was located at the approximate depth of the thermocline and corresponded to high values of chlorophyll a and POC production. This P04 maximum was followed by a secondary maximum at P26 in June 1998 (7.2 μmol kg-1 at 33 m) and 2000 (3.5 μmol kg- 1 at 2 m). Bishop et al. (1999) found POC maxima at either end of Line P (P04 and P26) in Aug. 1996 which agreed well with our Aug./Sept. 1999 POC data. Aug./Sept. 1998 also had a P26 surface maximum value (8.3 μmol kg-1). However, this was followed by a P04 maximum (6.5 μmol kg-1) at 33 m, below the mixed layer. In Aug./Sept. 2000, P04 had the lowest POC of any station due to nitrate depletion. Although maximum values of POC at the near-shelf station can be attributed to increased nutrient supply from the shelf and the coast (Boyd and Harrison, 1999), reasons for high values of POC (greater than P12, P16 and P20) found in June and Aug./Sept. are not clear. However, Wong et al. (1999) did find periodic high inputs of POC in all their P26 (OSP) sediment traps. Indeed, they found that June had the second highest POC flux (next to May) of all the averaged monthly data in their 200 m sediment trap suggesting a seasonal signal in POC production at P26. Generally, June and Aug./Sept. values for 1998 and 1999 were significantly (p<0.05) lower than 2000.  38 2.4.2 Seasonal variations in POC production Like the phytoplankton biomass values, station P04 displayed the highest range of production values in the euphotic zone over the three year period (0-60 mg C m-3 d-1). Integrated POC production values were also the highest at the near-shelf station with an almost 19-fold difference in values. All the other stations had ~ 6-fold difference in integrated production over all three years with the exception of P20 (3-fold). This pattern corresponds to previous Line P data (Boyd and Harrison, 1999) and is concurrent with high chlorophyll a and water-column integrated chlorophyll a specific POC production (Fig. 2.10) at P04 from this study. In 1998 and 1999, maximum POC production values generally increased through the year and were highest for all station in Aug./Sept. Although June values for those years were generally in between Feb. and Aug./Sept., P12 in 1998 and P16 in 1999 had the lowest maximum values in June instead of February. However, the highest production values for 2000 at P04 (60 mg C m-3 d-1) were  measured in June and was in fact the highest measured POC production value anywhere during this three year study. Boyd and Harrison (1999) also showed that HNLC stations showed the same pattern of maximum values found later in the summer, while stations located near the shelf (P04 and P12) were more variable and exhibited maxima in either spring (May) or summer (September). 2.4.3 Historic P26 POC production Integrated production rates at P26 measured from 1984 to 2002 (Fig. 2.17) vary ca. 3-fold between the winter minimum (247 ± 40 mg C m2 d-1 in February) and a maximum (777 ± 40 mg C m2 d-1) in September (Welschmeyer et al., 1993; Boyd and Newton, 1995; Wong et al., 1995; Babin et al., 1996; Boyd and Harrison, 1999; Marchetti et al., 2006c). In all three time periods (Feb., June and Aug./Sept), our column integrated POC production rates for P20 and P26 were lower than the monthly mean over the past 20 years. Interestingly, average monthly values show a dip in integrated POC production in July and August and a maximum in September. This finding is contrary to earlier studies (Sambrotto and Lorenzen, 1987; Booth, 1988; Welschmeyer et al., 1991; Wong et al., 1995; McClain et al., 1996; Harrison et al., 1999) where average values followed the  39 standard irradiance curve with maximum values found in June, July and August. Sambrotto (1987) showed that integrated POC production data collected from the OSP weathership program prior to 1971 from Anderson (1977) increased in the spring and was maximal at the beginning of July and decreased in fall. However, there were no data points from late July through August. Data from the weathership was not included in Fig. 2.17 due to the much lower values obtained during that time period compared to data published after 1984, probably due to differences in trace metal clean techniques (Welschmeyer et al., 1993). Data from Wong et al. (Wong et al., 1995) and a more recent cruise in 2002 (Marchetti et al., 2006c) seem to suggest lower rates of production in the late July/August period. Caution should be taken in interpreting production rates during this July/August time period due to the lack of data and more measurements are needed in the future during this interesting two month summer period. Monthly average integrated values do show a maximum in September. Welschmeyer et al. (1991) did find high production values of ca. 650 mg C m2 d-1 in September during the SUPER cruises. Although our values tended to be lower than the average with the exception of September 1998 (798 mg C m-2 d-1). 2.4.4 Interannual variability during 1998 (El Niño), 1999 (La Niña) and 2000 Although the original El Niño formed in early 1997 (McPhaden, 1999; Whitney and Welch, 2002), an increased sea surface height was not recorded off the British Columbia coast until summer 1997 and persisted along the coast through the winter of 1997-98 (Whitney and Welch, 2002), resulting in an elevated SST (Table 2.2) for most of 1998. Even though the signs of the El. Niño had dissipated by the spring of 1998 (Whitney and Welch, 2002), nitrate remained low (Table 2.2) and coincided with an increase in warmer water zooplankton (Mackas and Galbraith, 2002; Whitney and Welch, 2002) for the rest of 1998. Total phytoplankton biomass values pooled each year showed no significant difference between each other for this study. Additionally, averaged SeaWIFS surface chlorophyll (1997-2007) from Borstad Assoc. (http://www.borstad.com/gripweb/grip.html) shows little variation in chlorophyll values throughout the year (Fig. 2.18). However, Aug./Sept. chlorophyll a values were  40 significantly lower in 1998 and 1999 when compared to 2000. Total POC production values for 1998 and 1999 were significantly lower for all values when June and Aug./Sept. data were pooled together when compared to values in 2000. When separated, June and Aug./Sept. POC production values showed no significant differences when compared between years. On average, interannual variability along Line P was similar to that described by Boyd and Harrison (1999b), with near-shelf stations (P04 and P12) generally showing more variability than HNLC stations in spring (June) and summer (Aug./Sept.). P04 in June 1999 had 2-3-fold higher production and biomass than 1998 and a 2-fold increase in biomass from 1999 to 2000 followed by a 5-fold increase in POC production. There was a 14-fold increase in production from 1998 to 2000, the largest interannual increase at the same location (P04) for all three years and corresponds to high biomass concentrations recorded at the northern Gulf of Alaska shelf by Childers et al. (2005). Unlike Boyd and Harrison (1999), There was little interannual variation at P04 in Aug./Sept. Biomass and production ranged from 1-2-fold over all three years. The decreased variability found at the near-shelf station in Aug./Sept. compared to June, is probably due to the lateness in the season and the decline in nutrient availability. This contrasts with the year-to-year variability of the strength and timing of the spring bloom (Whitney et al., 1998; Boyd and Harrison, 1999). By late summer, areas of nitrate depletion can extend from the near-shelf stations to as far as P16 (Whitney et al., 1998; Whitney and Freeland, 1999). During our study, nitrate was non-detectable at P04 (Table 2.2 and Fig. 2.4) for all cruises in June and Aug./Sept. Depletion extended as far as P16 in Aug./Sept. 1998 and was low at P12 for the same period in 1999 (0.6 µM) and 2000 (0.9 µM). The lower nitrate concentrations found during the El Niño of 1998 affected the slope and shelf waters of the Gulf of Alaska (Whitney and Welch, 2002) and was probably responsible for the lower POC production rates found in June 1998 at P04-P16 compared to 1999 and 2000. Although nitrate depletion extended the farthest west along Line P in Aug./Sept. 1998, POC production rates at P04 to P16 were not significantly lower than the same period in 1999 and 2000. In part, this could be due to nutrient transport to Line P by mesoscale eddies that was enhanced in 1998 (Crawford, 2002; Whitney and Robert, 2002). Nutrients in the region are generally supplied through continuous summer upwelling along the British  41 Columbia coast (Freeland and Denman, 1982). However, during the 1998 El Niño, there appeared to be no evidence of coastal upwelling during either the June or Aug./Sept. cruises (Whitney and Welch, 2002), suppressing near-shelf POC production in June. Interestingly, POC production in Aug./Sept. 1998 at the near-shelf stations was in comparable to values recorded in 1999 and 2000, even though upwelling appeared to have returned along the BC coast by August 1999 (Whitney and Welch, 2002). Integrated POC production at P16 in 1998 in June and Aug./Sept. was similar to June and Aug./Sept. 1999 and Aug./Sept. 2000. Whitney et al. (2005a) suggest that this may be due to the remnants of the Haida-1998 eddy resulting in a higher Fe/Si ratio than would be normally expected at 100 m. They suggested that this eddy remnant may be supplying dissolved iron to the euphotic zone and thus increasing production rates. During the 1999 La Niña, the increase in the MLD along with an increase in macronutrients (Whitney and Welch, 2002; Wong et al., 2006) did not significantly change phytoplankton biomass and POC at HNLC stations. However, POC was significantly higher at P16-P26 in Aug./Sept. 1998 compared to 1999, possibly due to the variation in the MLD between El Niño and La Niña events in these waters and the availability of colder, nutrient-rich water in 1999. June and Aug./Sept. 2000 also showed a deepening of the mixed layer similar to 1999 (Wong et al., 2006) and could still be considered as part of the demise of the La  Niña cycle (Childers et al., 2005; Wong et al., 2006), contributing to the slight increase in phytoplankton biomass found at the HNLC stations during Aug./Sept. 2000. Interestingly, surface nitrate at P26 in Aug./Sept. 2000 was anomalously low (5.1 μM) as was silicic acid (3.1 μM) compared to an average nitrate value of ~15 μM measured during the Canadian JGOFS cruises between 1992- 1997 (Whitney and Freeland, 1999). These conditions may indicate a possible input of iron that may have stimulated phytoplankton growth prior to our arrival in Aug./Sept. 2000. These surface nitrate and silicic acid levels are in contrast to those found in June 2000 at P26 (13.2 and 19.9 μM respectively). During that same period, Wong et al. (2002a) found very high new production rates in the Alaska gyre that corresponded to high rates of silicic acid depletion, suggesting an increased occurrence of diatom production in the area (Childers et al., 2005).  42 2.4.5 Phytoplankton growth rates Although there are earlier estimates of algal growth rates at P26 (Booth et al., 1993; Landry et al., 1993; Boyd and Harrison, 1999), only the Boyd and Harrison (1999). study covers all of Line P. Algal growth rates for our study ranged from <0.1 to 0.7 d-1 with similar average rates per station (all seasons) of 0.2-0.3 d-1. P04 and P26 had the highest variability in growth rates of all the stations. Historical P26 growth rates varied from 0.1-0.7 d-1 derived from dilution experiments (Landry et al., 1993; Rivkin et al., 1999) and 0.2-1.4 d-1 (Booth et al., 1993; Welschmeyer et al., 1993; Boyd and Harrison, 1999) estimated by the equivalent method used in this study with the exception that in this study, a variable C:Chl a value was used instead of a constant C:Chl a = 50 that was used by Boyd and Harrison (1999). Our growth values for P26 are consistent with previous studies and ranged from 0.1-0.6 d-1. Growth rates of >0.3 d-1 occurred in Feb. 1998 (0.4 d-1), Aug./Sept. 1998 (0.6 d-1) and Aug./Sept. 1999 (0.4 d-1). Boyd and Harrison (1999) found the highest growth rates to occur at P04-P16, while this study found that the highest growth rates varied between stations, depending on the season and the year. Additionally, our maximum rates were much lower with a maximum value of 0.7 d-1 (P04 June 2000) compared to 2.2 (P16 Sept. 1995) and also well below the maximum theoretical division rates consistent with water properties along Line P (Banse, 1991a). Seasonally, the values measured for this study were 3-4 -fold smaller than the average seasonal growth rates found in Boyd and Harrison (1999). The differences between these studies may be attributed to variation in time of collection (e.g. El Niño and La Niña years in our study), but the most likely difference is the variable C:Chl a ratio that was  used in this study in contrast to the fixed C:Chl ratio of 50:1 used by Boyd and Harrison (1999). The marked variation in the C:Chl ratio from 16 to 87 reported by Pena and Varela (2007), agreed with the values derived in modeling studies (~25-75) at P26 (Booth et al., 1993; Boyd et al., 1995a; Taylor et al., 1997; Denman and Peña, 1999).  43 2.4.6 Size-fractionated biomass and production On average, cells in the smallest size fraction (0.2-5.0 µm) made up 64% (±13 s.e.) of the total chlorophyll a biomass and 61% (± 14 s.e.) of the total POC production for all cruises and seasons. This was followed by the 5.0-20 µm size fraction that made up 22% of the biomass (± 10 SD) and 23% (± 12 SD) of the production. There was little difference in the relative proportion of the 0.2-5.0 µm size class along Line P. Seasonally, phytoplankton biomass for the 0.2-5 µm size class had the highest proportion in February (68%) and decreased in June (65%) and reached a minimum (60.5%) in Aug./Sept. which was paralleled by a similar decrease in POC production of the smallest size fraction. The phytoplankton biomass in the 5.0-20 µm fraction was statistically similar in Feb. and June (ca. 18%), but increased to 29% during the Aug./Sept. time frame. The largest size fraction (>20 µm) was maximal in June for both biomass (19%) and production (20%). These relative proportions are generally in agreement with Boyd and Harrison’s (1999) Line P data and they also agree with size-fractioned biomass and POC production data found at the Haida eddy in June and September in 2000 and 2001 (Peterson, 2005) . Welschmeyer (1993) also found cells < 3 µm to make up ca. 70% of the total production at P26. Although smaller phytoplankton were not counted during this study with the exception of coccolithophores (Chapter 3), there are other studies from P26 and the NE subarctic Pacific. Taylor and Waters (1982) found spring to be dominated by cryptomonads and photosynthetic dinoflagellates at a station near P26. Booth (1993) found that during the SUPER program (1984-1987), the phytoplankton biomass was dominated mainly by autotrophic flagellates in the small size fraction. Boyd and Harrison (1999) and Varela and Harrison (1999b) found autotrophic flagellates, cyanobacteria and small pennate diatoms at P26 during the Canadian JGOFS program. In July 2002, as part of the SERIES program (Subarctic Ecosystem Response to Iron Enrichment Study), initial phytoplankton assemblages (before iron fertilization) were numerically dominated by cyanobacteria, coccolithophorids and Prymnesiophyceae (Marchetti et al., 2006c). Although coccolithophores (specifically Emiliania huxleyi) were found at near bloom levels along Line P twice during our study (P26 June 2000 and P12 Aug./Sept. 2000), they were rarely the dominant phytoplankton group (Chapter 3).  44 Boyd and Harrison (1999) using their size-fractionated data, fucoxanthin data from Thibault et al. (1999), and 234Th data from Charette et al. (1999), suggest that large cells dominate P04 during late spring and late summer. In our study, it was only during June 1998 that the >20 μm chlorophyll a size fraction at P04 was greater than the 3-year average of that size class. POC production in the large size class follows the same result, but for a different year (June 1999). There was elevated chlorophyll a and POC production at P04 in June (2000). In most cases, the smallest size class (0.2-5.0 μm) had the highest proportion of biomass for the near-shelf stations. Production followed the same trend for the near-shelf stations with the exception of P12 in Aug./Sept. 2000. The variation between this study’s results and Boyd and Harrison (1999) may be attributed to the later time frame of this study (June instead of May), variations experienced due to El Niño and La Niña, or the general variability of biological processes in this area. It does appear that POC and biogenic silica (bSi) fluxes are higher on average in May than June (C.S. Wong, unpub. data.) during the time period of this study. Interestingly, in our study, HNLC stations had the highest percentage of >20 μm biomass (26%) and production (27%) compared to the 3-year study averages for all stations (14 and 16% respectively). Although this proportion is not large compared to the smallest size class, diatoms, especially the smaller pennates, are consistently found in studies at P26 (Booth, 1988; Boyd et al., 1995a; Boyd and Harrison, 1999; Varela and Harrison, 1999b; Marchetti et al., 2006c). Additionally, sediment trap records at P26 show high bSi and POC flux in May and June in the 200 m trap (Wong et al., 1999) that corresponds to high silicic acid (and nitrate) utilization (Whitney and Freeland, 1999). This suggests that higher diatom activity at P26 can occur in the spring (e.g. May) and may point to a greater role of diatoms in the HNLC waters of Line P than previously reported (Boyd et al., 1995a; Boyd and Harrison, 1999; Harrison et al., 1999; Harrison, 2002). This is similar to the more pronounced diatom spring (May) bloom at occurs in the western Pacific gyre at Stn KNOT (Imai et al., 2002; Mochizuki et al., 2002). 2.4.7 Photosynthesis vs. irradiance (P vs. E) relationships There has not been any recent systematic measurement of photosynthetic parameters along Line P. However, there were measurements near the British Columbia  45 coast (Forbes et al., 1986; Peterson, 2005) and P26 (Welschmeyer et al., 1993). Forbes et al. (1986) and Peterson (2005) used the same methodology for their incubations (short term, artificial light source at a range of irradiances) that was used for the photosynthetron experiments in this study. However, Welschmeyer et al. (1993) derived their measurements over a 24 h period with natural light. An intercomparison between data from Welschmeyer et al. (1993) and results derived from short term photosynthetron experiments is difficult due to the diel differences in phytoplankton performance (Prézelin and Matlick, 1980) and fluctuations in natural daily irradiance (Lewis and Smith, 1983). It is possible to compare the deck-incubated POC production parameters (Table 2.6) to the Welschmeyer et al. (1993) data. Forbes et al. (1986) reported PBmax  averages in Hecate Strait of 7.5 ± 0.6 mg C (mg chl a)-1 h-1 and 12.3 ± 0.6 mg C (mg chl a)-1 h-1 in the Strait of Georgia. Peterson (2005) found a range from 1.3 – 18.8 mg C (mg chl a)-1 h-1 in or near the Haida Eddy when it was closer to the coast (2000) in an area similar to the near-shelf stations of this study. Near-shelf PBmax values in our study ranged from 0.1 – 6.2 mg C (mg chl a)-1 h-1 with a combined June and Aug./Sept. average of 2.3 (± 0.6 SE) mg C (mg chl a)-1 h-1 (Table 2.5). Our results are noticeably lower than those found in Forbes et al. (1986). This is most likely attributed to the fact that their stations were more coastal compared to this study. Peterson’s (2005) results outside of the Haida eddy in 2000 are closer to our range with a 55% I0  PBmax maximum of 11.6 mg C (mg chl a)-1 h-1 in June compared to our maximum of 6.2 mg C (mg chl a)-1 h-1 in June 2000 (measured 3 weeks before their sample). The Haida PBmax range decreased offshore to 1.0 – 4.9 mg C (mg chl a)-1 h-1 and is similar to the HNLC stations in our study in June and Aug./Sept. (0.2 – 7.2 mg C (mg chl a)-1 h-1; average 2.3 ± 0.7 SE mg C (mg chl a)-1 h-1). Our range was similar to the photosynthetic capacity from other HNLC regions such as the Southern Ocean (0.7-2.8 mg C (mg chl a)-1 h-1) (Saggiomo et al., 2002; Platt et al., 2003) and the equatorial Pacific (~6 mg C (mg chl a)-1 h-1) (Lindley et al., 1995; Platt et al., 2003). Values for αΒ were also similar in range. Winter PBmax HNLC values for both years (1998-1999) averaged 0.4 ± 0.1 (SE) mg C (mg chl a)-1 h-1 which is similar to the only other published winter value (0.6 mg C (mg chl a)-1 h-1) from February 1997 (Maldonado et al., 1999).  46 Interestingly, average June and Aug./Sept. values for P04 and P26 were similar (2.7 and 2.8 mg C (mg chl a)-1 h-1 respectively) and represented the highest averages as well as the stations with the largest PBmax values of all the stations (6.2 and 7.7 mg C (mg chl a)-1 h-1). This similarity between stations at either end of Line P helps to illustrate the complex nature of the biological and chemical interactions that occur along Line P. Iron availability has been shown to directly affect PBmax values. Iron-replete phytoplankton have been shown to have a higher PBmax than Fe-deficient cells, both in the lab (Greene et al., 1991) and at P26 during the SERIES iron enrichment experiment (Marchetti et al., 2006b). Although more data compiled over more years may show a greater difference in PBmax between the near-shelf and the HNLC region of Line P, our data seem to suggest that other physical and biological properties other than just iron limitation may be controlling photosynthetic performance at P26.  Our photosynthetic parameters derived from deck incubations (Table 2.6) also showed high P04 values of PBmax (54.5 mg C (mg chl a)-1 d-1) with slightly lower P26 values (43.9 - 54.5 mg C (mg chl a)-1 d-1) (Table 2.6). As would be expected, photosynthetic capacity was higher in June and Aug./Sept. for all stations compared to winter values (Fig. 2.15). Our combined average from all HNLC stations in June and Aug./Sept. (53.4 mg C (mg chl a)-1 d-1) was remarkably similar to values from the depth- integrated primary production experiments of Welschmeyer et al. (1993) (55.1 mg C (mg chl a)-1 d-1) at P26 derived in late spring and late summer 1987 and 1988. Interestingly, our αB average for the same period as above (11.1 mg C (mg chl a)-1 d-1 (mol photons m-2 s-1)-1), was also very close to the value of Welschmeyer et al. (1993) (13.0 mg C (mg chl a)-1 d-1 (mol photons m-2 s-1)-1). Contrary to Welschmeyer et al. (1993), there was a weak correlation between PBmax compared to surface irradiance (I0) from our photosynthetron experiments (Fig. 2.12) as well as a weak correlation between Ek and I0 for the deck- incubated samples (Fig. 2.16), suggesting that  light may be limiting for some samples along Line P. 2.4.8 Control of production by PAR along Line P There have been many studies elucidating the importance of iron at P26 as well as along of Line P (Martin and Fitzwater, 1988; Miller et al., 1991; Lam et al., 2001;  47 Harrison, 2006). However, the role of light in controlling primary production is much less clear (Welschmeyer et al., 1993; Boyd and Harrison, 1999; Maldonado et al., 1999). Along Line P for all cruises, there was a weak but significant positive correlation between maximum Chl-specific assimilation rates derived in the photosynthetron, and surface irradiance (Fig. 2.12). Most of this correlation is weighted towards the near-shelf station where nutrient limitation is more sporadic due to nutrient re-supply from the shelf and the coast. Like Boyd and Harrison (1999) and Welschmeyer et al. (1993), there was not a significant correlation with the HNLC samples and 24 h surface irradiance during the incubation, regardless of whether the  winter data was included. When all the stations and cruises were combined (Table 2.7), there was a strong correlation between all three size fractions of POC production with the strongest correlation occurring between 3-day average surface light and total production (r=0.62, p=0.005). A correlation between productivity and average 3-day irradiance with all the near-shelf stations (Table 2.8) shows a significant relationship between POC production in the 0.2-5.0 µm (r=0.85, p=0.005) and the 5.0-20 µm (r=0.74, p=0.005) size classes with the strongest correlation occurring with total combined POC production  (r=0.86, p=0.005). Interestingly, in the HNLC region, the only significant correlation with  average light was with the > 20 µm (r=0.61, p=0.01) size fraction, perhaps due to the decreasing iron demand at higher light intensities (Strzepek and Price, 2000). Maximum PBmax was also strongly correlated to average light for all stations and cruises (r=0.44, p=0.005) with the majority of that relationship weighted towards the near-shelf stations (r=0.69, p=0.005) further implying that light is more important in controlling phytoplankton growth at the near-shelf stations than in the HNLC region. Although this study has shown that there was a large variation in chlorophyll- specific photosynthetic performance, both in the near-shelf and HNLC stations, there was also lower chlorophyll normalized production rates at lower depths (> 30 m) compared to Welschmeyer et al. (1993). Results from this study imply that cells lower in the euphotic zone and sometimes below the mixed layer did not provide a significant contribution to the integrated production rate (Fig. 2.11). This suggests that bottom-up adaptation by either different deeper water phytoplankton species or bottom-up nutrient supply, does not appear to play the significant role found during the SUPER program and is more on  48 order with the CJGOFS results (Boyd and Harrison, 1999). Interestingly, our mean Chl- specific assimilation rate (30 mg C (mg Chl a)-1 d-1) for the HNLC stations P20 and P26 in June and Aug./Sept. was similar to Welschmeyer  et al. (1993) (31 mg C (mg Chl a)-1 d-1) and higher than reported by Boyd and Harrison. (1999), indicating possible differences in the water column or collection/analysis techniques between the Canadian JGOFS study and this study. 2.4.9 Factors controlling carbon production Near-shelf stations were generally replete for nutrients in winter and nitrate- limited in the spring and summer (especially P04), This agrees with earlier studies (Whitney et al., 1998; Boyd and Harrison, 1999; Wong et al., 2002d; Whitney et al., 2005b) . There was a strong positive correlation (r=0.57, p = 0.01) between surface nitrate and the 0.2 – 5.0 µm chlorophyll a size fraction (Table 2.8) inferring the greater efficiency of nitrate utilization of the smallest size fraction. The role of Fe at stations such as P04 is unclear (Nishioka et al., 2001; Johnson et al., 2005) and may along with nitrate, control phytoplankton performance and production. Phytoplankton biomass, POC production, and maximum Chl-specific assimilation rates were relatively low at P04 indicating light limitation concurrent with deep winter mixing (Freeland et al., 1997) and coincided with a positive significant relationship between light and POC production of the two smaller size fractions.  Fe correlated with total chlorophyll a in HNLC waters and even more so with the smallest size fraction (0.2-5 µm). For HNLC stations, there was a very strong correlation (r=0.70, p=0.005) between surface DFe and the 0.2-5.0 µm size fraction of chlorophyll a (Table 2.9) as well as the total chlorophyll biomass (r=0.67, p=0.005). Interestingly, there was a strong negative correlation (r=-0.62, p=0.01) between light and surface DFe suggesting possible co-limitation similar to that found by (Maldonado et al., 1999) in the winter at P26. Indeed, various experiments and studies have shown an induction of phytoplankton growth to iron addition at P26 both experimentally (Martin and Fitzwater, 1988; Boyd et al., 1996; Maldonado et al., 1999; Lam et al., 2001; Crawford et al., 2003) and in situ (Boyd et al., 2004; Lam et al., 2006). Other studies have also shown a change in photosynthetic performance (Marchetti et al., 2006b). However, the variation in PBmax  49 and Chl-specific carbon uptake rates that was found in June and Aug./Sept. in the HNLC regions does suggest that light plays an important role in controlling phytoplankton production and biomass and may select for phytoplankton species that can grow in low light. 2.4.10 Fate of POC Particle flux from the surface varies temporally and spatially along Line P with higher fluxes occurring at near-shelf stations (Thibault et al., 1999; Wong et al., 1999). Strong pulses of POC and bSi to deep-moored sediment traps occur sporadically, but appear to have a strong seasonal signal (Boyd and Harrison, 1999 and CS Wong, unpub. data.; Charette et al., 1999) and are consistent with offshore summer upwelling. At P26, sediment trap data show monthly average POC and bSi flux to be smaller than at the coast, but with a distinct seasonal signal with maximum rates occurring in May and June (Wong et al., 1999). A relatively stable seasonal phytoplankton biomass at the surface, but temporal variation in POC productivity, suggests that grazers and or light could be important in controlling the biomass. However, the predator-prey relationship at P26 is unclear. Studies by Goldblatt et al. (1999) and Rivkin et al. (1999; 1999) indicate that meso- and microzooplankton grazing on phytoplankton to be infrequent and to be more likely to occur on other heterotrophic protists such as ciliates. Mesozooplankton grazing along Line P seems to have only a small effect on phytoplankton production and biomass (Boyd et al., 1999a; Vezina and Savenkoff, 1999). This lack of a clear coupling between autotrophic and heterotrophic carbon combined with the stable autotrophic biomass at P26 seems to allow for a direct transfer of algal carbon to depth, especially in the spring. This may also help to explain the sporadic high pulses of bSi and POC found in P26 sediment traps (Wong et al., 1999). This study did not record an occurrence of a large increase in chlorophyll a or POC production in June on any cruise at P26, but this may be due to our late arrival in June and the short duration (1 to 3 days) of our sampling and suggests that average POC production may be higher in May than in June. Whitney et al. (Whitney et al., 2005a) did find elevated chlorophyll levels (~1.5 ug/l) and relatively depleted nutrient levels within 100 km of OSP in June 2000.  Sediment records actually show a large flux of bSi in late May/early June in 1998 (CS Wong, unpub. data.)  50 suggesting that this study missed an increase of diatom production just prior to sampling at P26 in June 1998. 2.5 Conclusions Line P stations can be grouped based on three water types, those influenced by high inputs of iron and nutrients from coastal processes, those sitting in iron impoverished HNLC waters, and those in the Transition Domain where nutrient supply is weak and nitrate depletion occurs for an extended portion of the spring and summer. The results of our study agree with previous Line P data and shows that the line can be divided into near-shelf stations (P04) with strong nitrate limitation in June and Aug./Sept. and HNLC stations (P20 and OSP) where iron plays an important role in controlling phytoplankton production and biomass. What is interesting is that the two stations at beginning and end of Line P (P04 and P26) do not vary as much as might be expected. Biomass and production were often similar at both stations even though there were clear differences in the abiotic conditions at each station. The data also appears that other than just low iron concentrations other properties such as light and macronutrient availability, may contribute to control of POC production and phytoplankton biomass in the HNLC region of Line P. There were also differences in phytoplankton biomass and POC production between El Niño (1998) and La Niña (1999), both seasonally and temporally. Average June integrated Chl a values for all of Line P increased from 1998 to 2000 in both June and Aug./Sept.. POC average integrated production decreased between June 1998 and 1999 and increased from Aug./Sept. 1998 and the same period in 1999. Interestingly, even though 2000 was similar in physical characteristics (nutrients, MLD, etc.) to 1999, it was distinctly different from either 1998 or 1999 and appears to be even different than studies from previous years. Line P appears to be temporally and spatially heterogeneous with variations in iron, light and nitrate affecting biogeochemical processes. It is clear that iron was a primary controlling factor for P20 and P26 in June and Aug./Sept. Its supply and utilization controls the production and utilization of POC in the region and has implications towards other trophic levels within the food web in the NE subarctic Pacific.  51 2.6 Tables Table 2.1. Location and depths of stations sampled along Line P for this study. Table adapted from the Line P Time Series Program website of Fisheries and Ocean Canada (http://www.pac.dfo-mpo.gc.ca/sci/osap/projects/linepdata/lineplist_e.htm).  Station Latitude North Longitude West Distance from P1 (km) Depth (m) P04 48°39.0 126°40.0 87 1300 P12 48°58.2 130°40.0 382 3300 P16 49°17.0 134°40.0 676 3550 P20 49°34.0 138°40.0 967 3890 P26 50°00.0 145°00.0 1425 4250  52 Table 2.2. Dates of cruises, depth (m) of the euphotic zone (Zeu) as defined by 1% of surface irradiance, mixed layer depth (MLD) as determined by Freeland et al. (1997), daily surface irradiance (Io), temperature, salinity, surface nitrate and integrated chlorophyll a and POC production. Surface nitrate concentrations were obtained from the Fisheries and Ocean Canada Line P Oceanic Data web site (http://www-sci.pac.dfo- mpo.gc.ca/osap/data/linep/linepselectdata_e.htm). Surface DFe (100-55% I0) from Keith Johnson, Dr. C. S. Wong (pers. comm.), or obtained from Nishioka (2001). ND = not detectable. LS = lost sample. Detection limit of our nitrate analysis was ~0.1 uM. Cruise Number Date Station Zeu (m) MLD (m) I0 (mol photons m-2 d-1) Surface Temp. (°C) Surface Salinity Int. Chl a (mg m-2) Int. POC prod. (mg C m-2 d-1) Surface Nitrate (µM) Surface DFe (nM) 9803 19-Feb-98 P04 40 175 12.6 11.0 32.62 18.3 72 3.5 1.54  21-Feb-98 P12 50 76 10.6 8.6 32.60 16.8 166 5.8 0.06  23-Feb-98 P16 60 81 7.7 7.5 32.61 26.8 195 8.4 0.04  24-Feb-98 P20 80 81 12.5 6.6 32.64 26.7 144 10.3 0.04  26-Feb-98 P26 80 94 14.7 5.4 32.67 18.9 162 13.0 0.12 9815 5-Jun-98 P04 33 24 39.1 12.6 31.97 9.5 100 ND 0.21  6-Jun-98 P12 40 17 22.8 12.2 32.31 16.9 84 ND 0.10  8-Jun-98 P16 52 22 27.8 10.9 32.67 20.0 312 4.1 0.02  9-Jun-98 P20 58 15 46.3 10.1 32.69 15.1 143 6.6 0.02  12-Jun-98 P26 50 22 18.0 9.1 32.67 18.5 189 9.9 0.07 9829 27-Aug-98 P04 33 21 44.2 16.8 32.05 14.9 566 ND 0.17  28-Aug-98 P12 45 17 24.9 16.6 32.10 10.1 324 ND 0.19  30-Aug-98 P16 55 27 28.2 16.0 32.28 12.4 460 ND 0.02  31-Aug-98 P20 60 31 24.5 14.1 32.65 7.5 405 5.1 0.02  5-Sep-98 P26 55 42 34.1 12.0 32.63 12.6 798 5.7 0.07 9901 10-Feb-99 P04 40 78 13.3 8.3 32.57 18.4 LS 8.9 1.72  14-Feb-99 P12 80 102 15.7 7.6 32.75 27.6 123 9.1 0.92  23-Feb-99 P16 75 102 4.8 6.7 32.82 20.5 123 9.2 0.25  20-Feb-99 P20 75 104 18.1 6.2 32.77 36.8 265 10.7 0.23  18-Feb-99 P26 60 114 7.7 5.2 32.83 22.4 131 14.3 0.23 9910 23-Jun-99 P04 35 12 30.3 12.2 31.58 34.6 358 ND 0.18  21-Jun-99 P12 60 21 32.1 10.0 32.82 34.0 426 6.9 0.04  19-Jun-99 P16 52 19 22.9 8.8 32.73 9.0 80 8.1 0.03  18-Jun-99 P20 65 60 42.1 8.1 32.73 18.3 225 9.4 0.05  12-Jun-99 P26 65 28 20.9 7.0 32.86 23.4 167 13.2 LS 9921 29-Aug-99 P04 35 16 32.7 15.5 31.91 16.0 447 ND 0.14  27-Aug-99 P12 45 19 43.8 14.6 32.30 14.5 365 0.6 0.06  29-Aug-99 P16 55 31 64.0 13.1 32.51 13.5 304 3.1 0.07  30-Aug-99 P20 60 26 23.3 12.3 32.68 7.1 181 7.6 0.07  2-Sep-99 P26 60 35 22.0 12.7 32.66 14.1 432 11.3 LS 2000-10 1-Jun-00 P04 50 11 61.2 11.4 31.87 21.7 1386 ND 0.17  3-Jun-00 P12 71 36 21.5 10.0 32.65 19.0 458 6.9 0.03  4-Jun-00 P16 80 32 28.0 9.1 32.66 17.7 483 8.4 0.06  6-Jun-00 P20 80 29 37.4 8.5 32.66 13.4 416 9.8 0.04  8-Jun-00 P26 80 27 26.4 7.7 32.68 18.5 152 13.2 0.02 2000-25 6-Sep-00 P04 50 21 40.8 15.0 31.80 22.9 653 ND 0.05  8-Sep-00 P12 50 27 37.6 15.5 32.29 31.6 581 0.9 0.13  9-Sep-00 P16 66 40 18.1 14.5 32.41 22.7 295 1.8 0.01  11-Sep-00 P20 75 38 37.7 13.8 32.55 16.9 407 8.2 0.03  13-Sep-00 P26 50 29 28.4 13.5 32.62 24.5 480 5.1 0.03  53 Table 2.3. Average integrated Chl a and POC production and ±1 SD for Line P. All seasons includes all 8 cruises. There were only 2 cruises in Feb and 3 cruises in each of June and Aug./Sept. during the 3 year (1998-2000) sampling period. Months Station Int. Chl a (mg m-2) S.D. Int. POC prod. (mg C m-2 d-1) S.D. ALL Seasons P04 19.5 7.4  512 443  P12 21.3 8.6  316 177  P16 17.8 5.9  282 145  P20 17.7 9.9  273 119  P26 19.1 4.3  314 238  Average all 19.1 7.2  335 247  Feb. P04 18.3 0.0  72 0  P12 22.2 7.6  145 31  P16 23.7 4.5  159 50  P20 31.7 7.1  205 86  P26 20.6 2.5  147 22  Average all 23.3 6.2  154 54  June P04 21.9 12.5  615 681  P12 23.3 9.3  322 207  P16 15.5 5.8  292 203  P20 15.6 2.5  261 140  P26 20.2 2.8  170 18  Average all 19.0 7.4  351 321  Aug./Sept. P04 17.9 4.4  555 103  P12 18.7 11.4  423 138  P16 16.2 5.6  353 93  P20 10.5 5.5  331 129  P26 17.0 6.5  570 199  Average all 16.1 6.7  446 156  54 Table 2.4. Phytoplankton growth rates (d-1) as estimated from the turnover of algal carbon (μc, d-1) following Boyd and Harrison (1999). Percent autotrophic phytoplankton carbon (% Auto Carbon) was estimated using C:Chl a values and total integrated chl a and expressed as a percentage of particulate organic carbon (POC) for each station (see text for details). Cruise growth rate means were estimated using all the growth rates from a single cruise and seasonal growth rate mean was averaged over a whole season (winter, late spring, and late summer) for all data available. Values in parenthesis represent ± 1 s.e. of the mean. LS = lost sample. See Table 2.2 for dates of cruise number. Period Cruise Station % of Auto Carbon µ (d-1) µ Cruise Mean µ Seasonal Mean February 9803 P04 34.1 0.2 (winter) P12 21.2 0.4   P16 23.0 0.3   P20 19.2 0.2   P26 28.0 0.4 0.29±0.04   9901 P04 70.0 LS   P12 93.3 0.1   P16 68.3 0.1   P20 77.9 0.1   P26 81.2 0.1 0.10±0.01 0.20±0.04  June 9815 P04 34.8 0.1 (late spring)  P12 64.3 0.1   P16 61.7 0.2   P20 50.2 0.1   P26 40.7 0.1 0.10±0.02   9910 P04 91.5 0.1   P12 88.1 0.2   P16 42.1 0.1   P20 51.2 0.2   P26 74.2 0.1 0.13±0.01   2000-10 P04 19.2 0.7   P12 80.5 0.3   P16 97.8 0.4   P20 90.9 0.4   P26 75.2 0.1 0.37±0.09 0.20±0.04  Aug./Sept. 9829 P04 63.5 0.4 (late summer)  P12 37.5 0.3   P16 35.1 0.4   P20 34.3 0.5   P26 35.1 0.6 0.43±0.06   9921 P04 33.6 0.3   P12 37.2 0.3   P16 31.7 0.3   P20 31.6 0.3   P26 24.9 0.4 0.30±0.02   2000-25 P04 79.8 0.2   P12 75.8 0.2   P16 73.8 0.1   P20 65.5 0.2   P26 64.9 0.2 0.19±0.02 0.31±0.03   55 Table 2.5. Photosynthetron incubations for samples from 55% I0 for all three years (1998-2000). Photosynthetic vs. irradiance parameters include αB and βB [mg C (mg chl a)-1 (mol photons m-2 s-1)-1], PBmax (mg C (mg chl a)-1 h-1), and Ek (μmol photons m-2 s-1) and were derived following Platt et al. (1980) and Lewis and Smith (1983). The average and SE for each of the three seasons is also given. June and Aug./Sept. values are combined (n=12) to form averages for that time period by region (near-shelf and HNLC). Combined values are the mean for all cruises (n=8). See Table 2.2 for specific cruise dates. See Fig. 2.12 for plots of P v. E.     Station P04 P12 P16   P20   P26   αB βB PBmax Ek αB βB PBmax Ek αB βB PBmax Ek αB βB PBmax Ek αB βB PBmax Ek   Cruise Feb. 9803 0.006 0.001 0.55 95 0.037 0.007 0.73 20 0.020 1.030 0.54 27 0.022 0.004 0.41 19 0.019 0.008 0.71 37  9901 0.000 0.001 0.10 599 0.003 0.002 0.46 178 0.002 0.000 0.38 229 0.001 0.000 0.10 142 0.002 0.000 0.22 138  Average 0.003 0.001 0.32 347 0.020 0.005 0.59 99 0.011 0.515 0.46 128 0.011 0.002 0.25 80 0.010 0.004 0.47 87  std error 0.003 0.000 0.23 252 0.017 0.003 0.14 79 0.009 0.515 0.08 101 0.011 0.002 0.16 62 0.009 0.004 0.24 51  June 9815 0.014 0.001 1.61 118 0.110 0.000 1.06 10 0.054 0.000 2.08 39 0.018 0.001 1.04 59 0.022 0.000 5.23 234  9910 0.003 0.000 0.37 114 0.001 0.013 0.54 410 0.001 0.011 0.58 582 0.003 0.030 1.01 338 0.000 0.025 0.19 623  2000-10 0.044 0.001 6.20 140 0.033 0.000 3.20 97 0.028 0.001 1.37 48 0.022 0.000 3.49 158 0.029 0.000 1.96 67  Average 0.020 0.001 2.73 124 0.048 0.004 1.60 172 0.028 0.004 1.34 223 0.014 0.010 1.85 185 0.017 0.009 2.46 308  std error 0.012 0.000 1.78 8 0.032 0.004 0.81 121 0.015 0.003 0.43 180 0.006 0.010 0.82 82 0.009 0.008 1.47 165  Aug./Sept. 9829 0.295 0.000 3.75 13 0.136 0.001 4.95 36 0.159 0.000 4.08 26 0.177 0.000 4.53 26 0.019 0.001 7.67 401  9921 0.001 0.000 0.23 370 0.000 0.010 0.07 435 0.002 0.026 0.86 440 0.004 0.000 0.22 62 0.002 0.000 0.42 178  2000-25 0.042 0.000 4.16 99 0.009 0.000 1.33 145 0.029 0.000 1.66 57 0.003 0.025 0.90 284 0.024 0.001 1.07 44  Average 0.113 0.000 2.71 161 0.049 0.004 2.12 205 0.063 0.009 2.20 174 0.061 0.009 1.88 124 0.015 0.001 3.05 208  std error 0.092 0.000 1.25 108 0.044 0.003 1.46 119 0.048 0.009 0.97 133 0.058 0.008 1.34 81 0.007 0.000 2.31 104  June and  Average  Near-shelf (P04 and P12) 0.057 0.002 2.29 166        HNLC 0.027 0.007 2.31 206 Aug./Sept. std error     0.025 0.001 0.60 44         0.014 0.003 0.69 52  Combined Average 0.051 0.000 2.12 193 0.041 0.004 1.54 166 0.037 0.134 1.44 181 0.031 0.008 1.46 136 0.015 0.004 2.18 215  std error 0.036 0.000 1.81 68 0.019 0.002 0.59 60 0.019 0.128 0.43 77 0.021 0.004 0.58 42 0.004 0.003 0.98 72   56 Table 2.6. Deck incubations profiling POC production over the euphotic zone (6 depths). Photosynthetic parameters include αB and βB [mg C (mg chl a)-1 d-1 (mol photons m-2 s-1)-1], PBmax (mg C (mg chl a)-1 d-1), and Ek (mol photons m-2 d-1).  Parameters were determined as described in the text. Values under the ‘All’ column are a combination of all the samples from all five stations for a particular cruise and correspond to the modeled curves in Fig. 2.15. June and Aug./Sept. values are combined (n=12) to form averages of that time period by region (near-shelf and HNLC).Combined average is for all 8 cruises over 3 seasons and 3 years at each station. See Fig. 2.13 for plots of P v. E.   Station P04 P12 P16 P20 P26 All   αB βB PBmax Ek αB βB PBmax Ek αB βB PBmax Ek αB βB PBmax Ek αB βB PBmax Ek αB βB PBmax Ek   Cruise  Feb. 9803 3.14 4.1 14.1 4.5 20.30 25.2 20.0 1.0 13.84 15.0 13.2 1.0 14.53 3.4 10.6 0.7 11.33 15.1 17.7 1.6 12.90 2.1 13.2 1.0  9901 1.79 2.1 10.3 5.8 1.79 1.0 10.3 5.8 12.89 11.9 14.9 1.2 13.66 1.0 11.4 0.8 0.19 9.9 24.9 5.2 6.08 10.0 11.6 1.9  Average 2.47 3.1 12.2 5.1 13.37 13.4 14.1 1.1 13.37 13.4 14.1 1.1 14.10 2.2 11.0 0.8 5.76 12.5 21.3 3.4 9.49 6.0 12.4 1.5  std error 0.68 1.0 1.9 0.6 0.48 1.5 0.8 0.1 0.48 1.6 0.8 0.1 0.44 1.2 0.4 0.1 5.57 2.6 3.6 1.8 3.41 4.0 0.81 0.4  June 9815 3.43 6.0 23.9 7.0 1.10 0.4 38.3 34.8 5.38 0.7 22.6 4.2 3.49 0.5 19.9 5.7 5.53 8.5 34.2 6.2 3.80 1.0 25.7 6.8  9910 1.34 0.0 59.1 44.1 1.58 -0.1 44.6 28.2 4.77 7.2 24.9 5.2 3.76 0.5 20.7 5.5 4.03 2.0 30.8 7.6 2.38 2.5 25.3 10.6  2000-10 14.93 0.8 90.0 6.0 18.04 0.1 45.3 2.5 7.18 9.9 48.7 6.8 11.36 285.8 73.2 6.4 3.55 5.9 14.3 4.0 5.47 5.6 62.4 11.4  Average 6.57 2.3 57.7 19.0 6.91 0.1 42.7 21.8 5.78 5.9 32.0 5.4 6.21 95.6 37.9 5.9 4.37 5.5 26.4 5.9 3.88 3.02 37.8 9.6  std error 4.23 1.9 19.1 12.5 5.57 0.1 2.2 9.8 0.72 2.7 8.3 0.7 2.58 95.1 17.6 0.3 0.60 1.9 6.2 1.0 0.89 1.34 12.3 1.4  Aug./Sept. 9829 17.89 15.6 103.2 5.8 31.08 45.0 133.9 4.3 17.65 11.6 110.8 6.3 40.18 4.6 114.5 2.8 22.76 19.5 121.7 5.3 23.48 8.0 118.2 5.0  9921 10.05 10.0 60.6 6.0 14.07 0.7 36.1 2.6 5.91 0.2 33.8 5.7 11.77 1.4 66.4 5.6 14.24 20.6 65.7 4.6 11.88 1.1 52.0 4.4  2000-25 6.46 11.2 51.2 7.9 11.19 -0.2 31.8 2.2 7.35 -0.1 26.9 3.7 8.69 9.0 45.4 5.2 3.93 0.3 33.9 8.6 4.78 6.2 42.8 9.0  Average 11.47 12.3 71.6 6.6 18.78 15.2 67.2 3.0 10.3 3.9 57.2 5.2 20.21 5.0 75.4 4.6 13.64 13.5 73.8 6.2 13.38 5.1 71.0 6.1  std error 3.37 1.7 16.0 0.7 6.21 14.9 33.3 0.6 3.70 3.8 26.9 0.8 10.02 2.2 20.4 0.9 5.44 6.6 25.7 1.2 5.45 2.1 23.7 1.4  June and  Average Near-shelf (P04 and P12) 10.93 7.5 59.8 12.6       HNLC 11.11 29.9 53.4 5.6 Aug./Sept. std error     2.59 3.8 9.5 4.2         3.14 23.4 10.4 0.4  Combined Average 7.38 6.2 51.5 10.9 12.97 9.1 44.8 9.6 9.37 7.0 37.0 4.2 13.43 38.3 45.3 4.1 8.19 10.2 42.9 5.4 8.85 4.55 43.9 6.3   std error 2.22 2.0 12.1 4.8 3.35 5.6 13.4 4.8 1.68 2.1 11.3 0.8 4.09 35.4 13.1 0.8 2.63 2.7 12.5 0.8 2.47 1.20 12.4 1.4   57  Table 2.7. Pearson’s correlation matrix for phytoplankton and other selected parameters in the mixed layer for all five stations from all 8 cruises (n=40).  Integrated values from the mixed layer were used for chlorophyll (Chl 0.2, 5, 20 μm size-fractionated and Chl total) and POC production (PP 0.2-5, 5-20, >20 μm size-fractionated and PP total). PBmax is the value from 55% Io. Specific growth rates (μ) were equivalent to Table 2.3. Light was the three-day average of the mixed layer from the time of sampling (see Putland et al., 2004). All nutrients (NO3-, Si(OH)4 and Fe) were tested as mixed layer averages. All  Chl 0.2 μm Chl 5 μm Chl 20 μm Chl total NO3 - Si(OH)4 Fe PP 0.2 μm PP 5 μm PP 20 μm PP total P B max µ (d-1) Light Chl 0.2 μm - Chl 5 μm 0.34* - Chl 20 μm 0.01 0.32* - Chl all 0.85* 0.70* 0.44* - NO3- 0.15 0.12 0.17 0.20 - Si(OH)4 0.12 0.08 0.17 0.16 0.97* - Fe 0.33* 0.04 0.01 0.26 0.17 0.13 - PP 0.2 μm 0.22 -0.01 -0.22 0.08 -0.28 -0.21 -0.12 - PP 5 μm -0.27 0.22 -0.22 -0.19 -0.36* -0.29 -0.15 0.52* - PP 20 μm 0.01 0.26 0.67* 0.31* -0.13 -0.06 -0.06 0.40* 0.29 - PP all 0.06 0.07 -0.09 0.04 -0.32* -0.24 -0.13 0.95* 0.71* 0.57* - PBmax -0.20 -0.19 -0.16 -0.26 -0.29 -0.22 -0.12 0.72* 0.59* 0.30 0.76* -  µ (d-1) -0.16 -0.24 -0.37* -0.32* -0.19 -0.11 -0.18 0.72* 0.67* 0.24 0.77* 0.70* - Light -0.15 -0.15 -0.03 -0.17 -0.34* -0.24 -0.23 0.60* 0.38* 0.41* 0.62* 0.44* 0.39* -   *Denotes coefficients that were significant (α=0.05)     58  Table 2.8. Pearson’s correlation matrix for phytoplankton and other selected parameters in the mixed layer for stations located near the shelf (P04 and P12) from all 8 cruises (n=16).  See Table 2.7 for details. Near-shelf  Chl 0.2 μm Chl 5 μm Chl 20 μm Chl total NO3 - Si(OH)4 Fe PP 0.2 μm PP 5 μm PP 20 μm PP total P B max µ (d-1) Light Chl 0.2 μm - Chl 5 μm 0.42 - Chl 20 μm -0.11 0.45 - Chl all 0.78* 0.81* 0.48 - NO3- 0.57* 0.13 0.03 0.45 - Si(OH)4 0.53* 0.18 0.03 0.43 0.94* - Fe 0.36 0.01 -0.02 0.24 0.66* 0.55* - PP 0.2 μm 0.33 0.05 -0.18 0.17 -0.12 0.09 -0.20 - PP 5 μm -0.19 0.15 -0.02 -0.09 -0.35 -0.08 -0.22 0.60* - PP 20 μm -0.06 0.45 0.75* 0.41 -0.09 0.06 -0.13 0.40 0.54* - PP all 0.14 0.11 0.02 0.14 -0.19 0.06 -0.21 0.95* 0.78* 0.62* - PBmax -0.05 -0.22 -0.19 -0.18 -0.26 -0.10 -0.15 0.83* 0.54* 0.34 0.82* -  µ (d-1) -0.04 -0.20 -0.29 -0.21 -0.21 -0.04 -0.24 0.80* 0.72* 0.34 0.83* 0.79* - Light 0.13 0.13 -0.10 0.09 -0.37 -0.14 -0.33 0.85* 0.74* 0.41 0.86* 0.69 0.67* -   *Denotes coefficients that were significant (α=0.05)     59 Table 2.9. Pearson’s correlation matrix for phytoplankton and other selected parameters in the mixed layer for HNLC stations (P20 and P16) from all cruises (n=16).  See Table 2.7 for details. HNLC  Chl 0.2 μm Chl 5 μm Chl 20 μm Chl total NO3 - Si(OH)4 Fe PP 0.2 μm PP 5 μm PP 20 μm PP total P B max µ (d-1) Light Chl 0.2 μm - Chl 5 μm 0.58* - Chl 20 μm 0.24 0.07 - Chl all 0.94* 0.75* 0.41 - NO3- 0.45 -0.07 0.28 0.35 - Si(OH)4 0.31 -0.23 0.29 0.20 0.97* - Fe 0.70* 0.48 0.09 0.67* 0.33 0.28 - PP 0.2 μm -0.23 0.13 -0.45 -0.21 -0.37 -0.44 -0.28 - PP 5 μm -0.33 0.29 -0.55 -0.26 -0.56* -0.54* -0.15 0.67* - PP 20 μm -0.17 0.06 0.54 0.02 0.08 0.07 -0.07 0.14 -0.07 - PP all -0.31 0.21 -0.43 -0.24 -0.45 -0.49 -0.25 0.95* 0.83* 0.23 - PBmax -0.50* 0.22 -0.12 -0.45 -0.44 -0.33 -0.41 0.58* 0.66* 0.18 0.68* - Spec µ (d-1) -0.47 -0.26 -0.66* -0.56* -0.28 -0.19 -0.30 0.66* 0.72* -0.02 0.73* 0.63* - Light -0.62* -0.27 0.36 -0.45 -0.25 -0.21 -0.62* 0.07 -0.06 0.61* 0.12 0.13 -0.03 -   *Denotes coefficients that were significant (α=0.05)    60 2.7 Figures    Fig. 2.1.Map of the portion of the NE subarctic Pacific Ocean showing the five major sampling stations P04, 12, 16, 20 and 26 along line P.  Inset shows general surface circulation in that area.      61 P26 P20 P16 P12 P4 Jun 00 P26 P20 P16 P12 P4 Feb 9980 60 40 20 0 P26 P20 P16 P12 P4 80 60 40 20 0 D e p t h  ( m ) Jun 98 1500 1000 500 Distance along Line P (km) 1500 1000 500 Aug/Sep 00 1500 1000 500 80 60 40 20 0 Jun 99 1998 1999 2000 Aug/Sep 98 Aug/Sep 99  Feb 98  Fig. 2.2. Vertical contours of phytoplankton standing stocks as total Chl (mg chl a m-3) during 1998-2000. Dots represent the six sampling depths (100, 55, 30, 10, 3.5 and 1% of I0) for each of the 5 stations along Line P for 8 cruises. The dark dashed line corresponds to the mixed layer depth. No data for P04 in February1999 due to lost samples. Solid black line indicates area below 1% I0 and therefore this area contains no measured data. Haida eddy in Sep 1998 had a Note subsurface POC max at P12 and P16 due to Haida eddy (Whitney and Robert, 2002).    62 D e p t h  ( m ) 0 20 40 60 80 mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 P4 P12 P16 P20 P26 0 20 40 60 80 1999 Feb. 1999 Aug./Sept. 1998 Feb. 1998 Aug./Sept. 1999 June 2000 June 2000 Aug./Sept 1998 June  Fig. 2.3. Vertical profiles of phytoplankton standing stocks (mg chl a m-3) for all 5 stations and all 3 years along Line P. Depths represent the 6 light depths (100, 55, 30, 10, 3.5 and 1% I0). Deepest sample represents the bottom of the photic zone. Same data as Fig. 2.2.   63 Y  A x i s  2 0 10 20 30 40 Y  A x i s  3 C h l o r o p h y l l  a  ( m g  C h l  a  m - 2 ) 0 10 20 30 40 P26 P20 P16 P12 P04 0 10 20 30 40 Y  A x i s  2 >20 μm 5-20 μm 0.2-5 μm Total int. PP (mg C m-2 d-1) 0 50 100 150 200 250 300 P26 P20 P16 P12 P04 Y  A x i s  2 I n t e g r a t e d  P P  ( m g  C  m - 2  d - 1 ) 0 200 400 600 800 1000 1200 1400 P26 P20 P16 P12 P04 0 200 400 600 800 1000 1200 1400 1998 1999 2000 Aug./Sept. JuneJune Aug./Sept. Feb. June Aug./Sept Feb.  Fig. 2.4. Integrated chlorophyll a concentrations (mg chl a m-2) in the 0.2-5, 5-20, and >20 µm size fractions (bars) and total integrated POC production (PP) (solid lines) for all five stations and all three years along Line P. Note the different scale for POC production in the winter.   64  P26 P20 P16 P12 P4 Jun 00 P26 P20 P16 P12 P4 Feb 9980 60 40 20 0 P26 P20 P16 P12 P4 80 60 40 20 0 D e p t h  ( m ) Jun 98 1500 1000 500 Distance along Line P (km) 1500 1000 500 Aug/Sep 00 1500 1000 500 80 60 40 20 0 Jun 99 1998 1999 2000 Aug/Sep 98 Aug/Sep 99  Feb 98  Fig. 2.5. Vertical contours of particulate organic carbon (µmol kg-1) for all five stations and all three years along Line P. Black dots represent actual sampling locations at each station at the six light depths (100, 55, 30, 10, 3.5 and 1% I0). The deepest samples represent the base of the photic zone and the area below the photic zone (solid line) is shown as a solid white area. The dashed lines indicate the mixed layer depth. Note that the x and y axis represent very different distance scales.   65 D e p t h  ( m ) 0 20 40 60 80 μmol kg-1 0 2 4 6 8 10 12 14 μmol kg-1 0 2 4 6 8 10 12 14 μmol kg-1 0 2 4 6 8 10 12 14 0 20 40 60 80 P04 P12 P16 P20 P26 0 20 40 60 80 1999 Feb. 1999 Aug./Sept. 1998 Feb. 1998 Aug./Sept. 1999 June 2000 June 2000 Aug./Sept 1998 June  Fig. 2.6. Vertical Profiles of particulate organic carbon (µmol kg-1) for all five stations and all three years along Line P (same data as Fig. 2.5). Depths represent the 6 light depths (100, 55, 30, 10, 3.5 and 1% IO ) and the deepest samples represents the bottom of the photic zone.   66 P26 P20 P16 P12 P4 Jun 00 P26 P20 P16 P12 P4 Feb 9980 60 40 20 0 P26 P20 P16 P12 P4 80 60 40 20 0 D e p t h  ( m ) Jun 98 1500 1000 500 Distance along Line P (km) 1500 1000 500 Aug/Sep 00 1500 1000 500 80 60 40 20 0 Jun 99 1998 1999 2000 Aug/Sep 98 Aug/Sep 99  Feb 98  Fig. 2.7. Vertical contours (see text for methods) of total POC (primary) production (mg C m-3 d-1) during 1998-2000. Dots represent the six sampling depths (100, 55, 30, 10, 3.5 and 1% of I0) for each of the 5 stations along Line P for 8 cruises. The dark dashed line corresponds to the mixed layer depth. No data for P04 in February 1999 due to lost samples. Solid black line indicates area below 1% I0 and therefore contains no measured data.   67 D e p t h  ( m ) 0 20 40 60 80 mg C m-3d-1 0 10 20 30 40 50 60 mg C m-3d-1 0 10 20 30 40 50 60 mg C m-3d-1 0 10 20 30 40 50 60 0 20 40 60 80 P4 P12 P16 P20 P26 0 20 40 60 80 1999 Feb. 1999 Aug./Sept. 1998 Feb. 1998 Aug./Sept. 1999 June 2000 June 2000 Aug./Sept 1998 June  Fig. 2.8. Phytoplankton POC (primary) production (mg C m-3 d-1) for all stations and all years along Line P. Depths represent the 6 light depths (100, 55, 30, 10, 3.5 and 1 I0). Deepest sample represents the bottom of the photic zone. Same data as Fig. 2.7.   68 N o  D a t a 0.0 0.2 0.4 0.6 0.8 1.0 R e l a t i v e  P r o p o r t i o n 0.0 0.2 0.4 0.6 0.8 1.0 P26 P20 P16 P12 P04 0.0 0.2 0.4 0.6 0.8 1.0 P26 P20 P16 P12 P04 P26 P20 P16 P12 P04 1998 1999 2000 Aug./Sept. JuneJune Aug./Sept. June Aug./Sept Feb. Feb. 0.2-5 μm 5-20 μm >20μm  Fig. 2.9. Relative proportion of water column integrated size-fractionated POC production as a fraction of the total production for all five stations and all three years along Line P. Missing column for P04 in February 1999 denotes lost sample.   69 D F e  ( n M ) 0.0 0.5 1.0 1.5 2.0 2.5 N O 3  ( μ M ) 0 3 6 9 12 15 0 10 20 30 40 50 60 70 D F e  ( n M ) 0.0 0.1 0.2 0.3 0.4 0.5 N O 3  ( μ M ) 0 3 6 9 12 15 P26 P20 P16 P12 P04 0.0 0.1 0.2 0.3 0.4 0.5 N O 3  ( μ M ) 0 3 6 9 12 15 P26 P20 P16 P12 P04 [ m g  C  ( m g C h l  a  m - 2 ) - 1  d - 1 ] 0 10 20 30 40 50 60 1998 1999 2000 P26 P20 P16 P12 P04 0 10 20 30 40 50 60 Aug./Sept. JuneJune Aug./Sept. Feb. June Aug./Sept. Feb. D F e  ( n M ) NO3 (μM) DFe (nM) Total int PP/ Chl a  Fig. 2.10. Water column integrated Chl a-specific carbon uptake (mg C (mg Chl a m-2)-1 d-1) for 1998-2000 with surface nitrate (μM, closed circles) and surface dissolved iron (DFe, nM, open circles) values. There are no data for P04 in  February 1999 (9901) due to lost samples. Note the different scale for DFe in winter.   70 D e p t h  ( m ) 0 20 40 60 80 mg C (mg chl a)-1 d-1 0 20 40 60 80 100 120 140 mg C (mg chl a)-1 d-1 0 20 40 60 80 100 120 140 mg C (mg chl a)-1 d-1 0 20 40 60 80 100 120 140 0 20 40 60 80 P4 P12 P16 P20 P26 0 20 40 60 80 1999 Feb. 1999 Aug./Sept. 1998 Feb. 1998 Aug./Sept. 1999 June 2000 June 2000 Aug./Sept 1998 June  Fig. 2.11. Chl a-specific carbon uptake (mg C (mg Chl a)-1 d-1) for 1998-2000. There are no uptake data for February 1999 due to lost samples. 71   Irradiance (mol photons m-2 d-1) 0 10 20 30 40 50 60 70 PB m ax  [m g C  (m g ch l a )-1  h -1 ] 0 2 4 6 8 10 E k  ( μm ol  p ho to ns  m -2  s -1 ) 0 100 200 300 400 500 600 700 PBmax Ek  Fig. 2.12. Maximum rate of POC production normalized to chlorophyll a (PBmax) and light saturation onset irradiance (Ek) versus surface irradiance (I0). PBmax and Ek derived from photosynthetron experiments at 55% I0 from each station of each cruise.. There was a significant positive relationship between PBmax and I0 (r2 = 0.1354, p<0.05) while the relationship between Ek and I0 was not significant (r2= 0.0064, p>0.05) (n=40). 72    June P16 PB  (m g C  m g ch l a -1  h -1 ) 0 2 4 6 8 June P04 0 2 4 6 8 10 June P26June P20 Aug/Sept. P04 0 2 4 6 8 Aug/Sept. P12 Aug/Sept. P16 0 500 1000 1500 2000 0 2 4 6 8 Aug/Sept. P20 0 500 1000 1500 2000 Aug/Sept. P26 Irradiance (μmol photons m-2 s-1) 0 500 1000 1500 2000 2500 100% Io 55% Io 10% Io 1% Io June P12 PB  ( μ g C  m g ch l a -1  h -1 ) 2 4 6 8  Fig. 2.13. Biomass specific photosynthesis (PB) versus irradiance curves (P v. E) for water samples collected in June and Aug./Sept. 2000 from 100, 55, 10 and 1% surface irradiance (Io) and incubated in the photosynthetron for 4 h from all five stations along Line P. The June P04 1% Io sample was lost. See Fig. 2.14 for P v. E parameters.   73 June 2000 αB [mg C (mg chl a)-1 (mol photons m-2 s-1)-1] 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 20 40 60 80 Aug./Sept. 2000 D e p t h  ( m ) 20 40 60 80 P04 P12 P16 P20 P26 June 2000 PBmax [mg C (mg chl a)-1 h-1] 2 4 6 8 10 Aug./Sept. 2000 Fig. 2.14. Photososynthetic performance parameters αB and PBmax derived from P v. E curves for water samples collected in June and Aug./Sept. 2000 (derived from Fig. 2.13). Depths are 100, 55, 10 and 1% of surface irradiance (see Table 2.2). The sample at 1% I0 for P04 was lost. 74   Winter (1998 & 1999) 0 5 10 15 20 25 9803 9901 June (1998-2000) PB  [ μ g C  ( μ g ch l a -1 ) d -1 ] 0 25 50 75 100 125 9815 9910 2000-10 Aug/Sept (1998-2000) Irradiance (mol photons m-2 d-1) 0 10 20 30 40 50 0 25 50 75 100 125 9829 9921 2000-10  Fig. 2.15. Biomass specific photosynthesis (PB) versus irradiance for deck-incubated surface experiments (24 h) from water sampled at 55% I0. Samples are grouped according to season (Feb., June and Aug./Sept.). There was no cruise in February 2000. Dashed lines are for 1998. Solid lines are for 1999, and dash-dot-dash lines are for 2000. See Table 2.6 for P v. E parameters. 75   Irradiance (mol photons m-2 d-1) 0 10 20 30 40 50 60 70 PB m ax  [m g C  (m g ch l a )-1  d -1 ] 0 20 40 60 80 100 120 140 160 E k  ( m ol  p ho to ns  m -2  d -1 ) 0 10 20 30 40 50 PBmax Ek  Fig. 2.16. Photosynthetron deck incubated biomass specific photosynthesis normalized to chlorophyll a (PBmax) and light saturation onset irradiance (Ek) versus surface irradiance (I0) derived from depth-integrated POC production experiments (n=40). There was not a significant relationship between PBmax and I (r2 = 0.0921, p>0.05) while the relationship between Ek and I was significant (r2= 0.1279, p<0.05).   76 Julian Day 0 50 100 150 200 250 300 350 P r o d u c t i o n  ( m g  C  m - 2  d - 1 ) 0 200 400 600 800 1000 1200 1400 1600 1800 2000 P A R  ( E i n  m - 2  d - 1 ) 0 20 40 60 80 1999-2000 Present study 1987-1988 Welschmeyer et al. (1993) 1984-1990 Wong et al. (1995) 1992-1997 Boyd and Harrison (1999) 2002 Marchetti et al. (2006)  Fig. 2.17. Depth-integrated POC production from 1984 to 2000 and 2002 at P20 and P26 obtained from 5 studies. All data are  from Boyd and Harrison (1999) and Marchetti et al. (2006b) except for the present study (16 data points). Only the present study includes values from P20 as well as P26. Cloud-free irradiance (PAR; solid line) at 50°N adapted from the model of Frouin et al. (1989). The dashed line represents the average monthly POC production for all values and their corresponding standard deviation. There were no samples in January or December. 77  P04 0.0 0.5 1.0 1.5 2.0 2.5 3.0 98 98 98 99 99 99 00 00 P12 C hl  a  m g m -3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 98 98 98 99 99 99 00 00 average 1998 Sat 1999 Sat 2000 Sat 1998 Surface98 1999 Surface99 2000 Surface00 P16 Month Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec  Jan 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 98 98 98 99 99 99 00 00 78  P20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 98 98 98 99 99 9900 00 average 1998 Sat 1999 Sat 2000 Sat 1998 Surface98 1999 Surface99 2000 Surface00 P26 Month Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec  Jan C hl  a  m g m -3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 98 98 98 99 99 99 00 00  Fig. 2.18. 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Miller, C.B., Frost, B.W., Wheeler, P.A., Landry, M.R., Welschmeyer, N.A., Powell, T., 1991. Ecological dynamics in the subarctic Pacific, a possibly iron-limited ecosystem. Limnology and Oceanography 36 (8), 1600-1615. Mochizuki, M., Shiga, N., Saito, M., Imai, K., Nojiri, Y., 2002. Seasonal changes in nutrients, chlorophyll a and the phytoplankton assemblage of the western subarctic gyre in the Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 49 (24-25), 5421-5439. Nishioka, J., Takeda, S., Wong, C.S., Johnson, W.K., 2001. Size-fractionated iron concentrations in the northeast Pacific Ocean: distribution of soluble and small colloidal iron. Marine Chemistry 74, 157-179. Parslow, J.S., 1981. Phytoplankton-zooplankton interactions: data analysis and modeling (with particular reference to Ocean Station Papa [50°N 145°W] and controlled ecosystem experiments). PhD thesis, University of British Columbia, Vancouver, Canada. Parsons, T.R., Maita, Y., Lalli, C.M., 1984. A manual of chemical and biological methods for seawater analysis. Pergamon Press, Oxford [Oxfordshire] ; New York. Peña, M.A., Varela, D.E., 2007. Seasonal and interannual variability in phytoplankton and nutrient dynamics along Line P in the NE subarctic Pacific. Progress in Oceanography 75 (2), 200-222. Peterson, T., 2005. Studies on the biological oceanography of Haida eddies, University of British Columbia, Vancouver, B.C. 85  Platt, T., Gallegos, C.L., Harrison, W.G., 1980. Photoinhibition of photosynthesis in natural assemblages of marine-phytoplankton. Journal of Marine Research 38 (4), 687-701. Platt, T., Sathyendranath, S., Edwards, A.M., Broomhead, D.S., Ulloa, O., 2003. Nitrate supply and demand in the mixed layer of the ocean. Marine Ecology Progress Series 254, 3-9. Prézelin, B.B., Matlick, H.A., 1980. Time-course of photoadaptation in the photosynthesis-irradiance relationship of a dinoflagellate exhibiting photosynthetic periodicity. Marine Biology 58, 85-96. Putland, J.N., Whitney, F.A., Crawford, D.W., 2004. Survey of bottom-up controls of Emiliania huxleyi in the northeast subarctic Pacific. Deep Sea Research Part I: Oceanographic Research Papers 51 (12), 1793-1802. Rivkin, R.B., Putland, J.N., Anderson, M.R., Deibel, D., 1999. Microzooplankton bacterivory and herbivory in the NE subarctic Pacific. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2579-2618. Saggiomo, V., Catalano, G., Mangoni, O., Budillon, G., Carrada, G.C., 2002. Primary production processes in ice-free waters of the Ross Sea (Antarctica) during the austral summer 1996. Deep Sea Research Part II: Topical Studies in Oceanography 49 (9-10), 1787-1801. Sambrotto, R.N., Lorenzen, C.J., 1987. Phytoplankton and primary production. In: Hood, D.W., Zimmerman, S.T. (Eds.), The Gulf of Alaska : physical environment and biological resources. Ocean assessments division, Alaska office, NOAA, US Minerals Management Service, OCS study. Strzepek, R.F., Price, N.M., 2000. Influence of irradiance and temperature on the iron content of the marine diatom Thalassiosira weissflogii (Bacillariophyceae). Marine Ecology Progress Series 206, 107-117. Taylor, A.H., Geider, R.J., Gilbert, F.J.H., 1997. Seasonal and latitudinal dependencies of phytoplankton carbon-to-chlorophyll a ratios: results of a modeling study. Marine Ecology Progress Series 152, 51-66. Taylor, F.J.R., Waters, R.E., 1982. Spring phytoplankton in the subarctic Pacific Ocean. Marine Biology 67, 323-335. Thibault, D., Roy, S., Wong, C.S., Bishop, J.K., 1999. The downward flux of biogenic material in the NE subarctic Pacific: importance of algal sinking and mesozooplankton herbivory. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2669-2697. 86  Varela, D.E., Harrison, P.J., 1999. Seasonal variability in nitrogenous nutrition of phytoplankton assemblages in the northeastern subarctic Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 46, 2505-2538. Verado, D.J., Froelich, P.N., McIntyre, A., 1990. Determination of organic carbon and nitrogen in marine sediments using the Carlo Erba NA-1500 Analyzer. Deep Sea Research 37, 157-165. Vezina, A.F., Savenkoff, C., 1999. Inverse modeling of carbon and nitrogen flows in the pelagic food web of the northeast subarctic Pacific. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2909-2939. Welschmeyer, N.A., Goericke, R., Strom, S., Peterson, W., 1991. Phytoplankton growth and herbivory in the subarctic Pacific: a chemotaxonomic analysis. Limnology and Oceanography 38 (8), 1631-1649. Welschmeyer, N.A., Strom, S., Goericke, R., DiTullio, G.R., Belvin, M., Peterson, W., 1993. Primary production in the subarctic Pacific Ocean: Project SUPER. Progress in Oceanography 32 (1-4), 101-135. Whitney, F., Robert, M., 2002. Structure of Haida eddies and their transport of nutrient from coastal margins into the NE Pacific Ocean. Journal of Oceanography 58 (5), 715-723. Whitney, F.A., Wong, C.S., Boyd, P.W., 1998. Interannual variability in nitrate supply to surface waters of the northeast Pacific Ocean. Marine Ecology Progress Series 170, 15-23. Whitney, F.A., Freeland, H.J., 1999. Variability in upper-ocean water properties in the NE Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2351-2370. Whitney, F.A., Welch, D.W., 2002. Impact of the 1997-1998 El Niño and 1999 La Niña on nutrient supply in the Gulf of Alaska. Progress in Oceanography 54 (1-4), 405- 421. Whitney, F.A., Crawford, D.W., Yoshimura, T., 2005a. The uptake and export of silicon and nitrogen in HNLC waters of the NE Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 52 (7-8), 1055-1067. Whitney, F.A., Crawford, W.R., Harrison, P.J., 2005b. Physical processes that enhance nutrient transport and primary productivity in the coastal and open ocean of the subarctic NE Pacific. Deep Sea Research Part II: Topical Studies in Oceanography 52 (5-6), 681-706. Wong, C.S., Whitney, F.A., Iseki, K., Page, J.S., Zeng, J., 1995. Analysis of trends in primary productivity and chlorophyll a over two decades at Ocean Station P 87  (50°N 145°W) in the subarctic northeast Pacific Ocean. Canadian Journal Fisheries Aquatic Sciences 121, 107-117. Wong, C.S., Whitney, F.A., Crawford, D.W., Iseki, K., Matear, R.J., Johnson, W.K., Page, J.S., 1999. Seasonal and interannual variability in particle fluxes of carbon, nitrogen and silicon from time series of sediment traps at Ocean Station P, 1982- 1993: relationship to changes in subarctic primary productivity. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2735-2760. Wong, C.S., Waser, N.A.D., Nojiri, Y., Johnson, W.K., Whitney, F.A., Page, J.S.C., Zeng, J., 2002a. Seasonal and interannual variability in the distribution of surface nutrients and dissolved inorganic carbon in the northern North Pacific: Influence of El Niño. Journal of Oceanography 58 (2), 227-243. Wong, C.S., Yu, Z., Waser, N.A.D., Whitney, F.A., Johnson, W.K., 2002b. Seasonal changes in the distribution of dissolved organic nitrogen in coastal and open- ocean waters in the North East Pacific: sources and sinks. Deep Sea Research Part II: Topical Studies in Oceanography 49 (24-25), 5759-5773. Wong, C.S., Wong, S.E., Peña, M.A., Levasseur, M., 2006. Climatic effect on DMS producers in the NE subarctic Pacific: ENSO on the upper ocean. Tellus B 58 (4), 319-326.   88 Chapter 3 : Spatial and Temporal Variability in Coccolithophore Abundance and Production of PIC and POC in the NE subarctic Pacific during El Niño (1998), La Niña (1999) and 20001  3.1 Introduction The oceanic biological carbon pump is a process by which dissolved CO2 is fixed as particulate carbon in surface waters before being transported into deeper waters or into the sediments. This process principally involves photosynthetic fixation of CO2 into particulate organic carbon (POC) by phytoplankton, followed by sinking of a proportion of this POC, along with detrital and fecal material from associated planktonic communities. However, the formation of POC is only one component of the biological carbon pump. Recent studies suggest that because of the resulting decrease in alkalinity, the formation of particulate inorganic carbon (PIC) by calcifying plankton has the opposite effect on surface water pCO2 to that of POC (Holligan et al., 1993; Crawford and Purdie, 1997; Haidar and Thierstein, 2001). The ratio of PIC: POC production, or more importantly the PIC: POC ratio of biogenic particles exported to deeper waters, is therefore a critical parameter driving spatial variations in air-sea gradients in pCO2. PIC formation in the surface ocean is principally mediated through calcification by coccolithophores, although foraminifera and pteropods can also make some contribution (Fabry, 1989). Coccolithophores phytoplankton, such as Emiliania huxleyi, are widespread in the world’s oceans, and their coccoliths are preserved extensively in sediments (Winter and Siesser, 1994). Recent studies have suggested that despite being above the carbonate compensation depth (CCD), a significant proportion of the PIC fixed at the surface can in fact be remineralised in the upper 1000 m (Milliman et al., 1999). This suggests that a significant amount of coccolithophore PIC can be transported to the  1 A version of this chapter has been published/accepted for publication. Lipsen, M.S., Crawford, D.W., Gower, J., Harrison, P.J., 2007. Spatial and temporal variability in coccolithophore abundance and production of PIC and POC in the NE subarctic Pacific during El Nino (1998), La Nina (1999) and 2000. Progress in Oceanography 75 (2), 304-325.   89 intermediate ocean. It is not yet known to what extent this transport is mediated by sinking of senescent coccolithophores and coccoliths, or the result of top-down grazing by zooplankton followed by sinking of fecal material (Pilskaln and Honjo, 1987; Harris, 1994). Extensive blooms occur in certain parts of the ocean, such as the North Atlantic, and are detected through satellite imagery (Brown and Yoder, 1993, 1994b, a; Gower, 2004).  A production ratio of PIC:POC of around 1 has been estimated within these blooms from changes in water column carbonate chemistry (Robertson et al., 1994), a figure consistent with studies from monocultures of E. huxleyi (Paasche, 1998, 1999, 2001). A ratio of around 1 suggests that these blooms do have a significant impact upon the air-sea gradient of pCO2 and therefore the efficiency of the biological carbon pump (Robertson et al., 1994; Crawford and Purdie, 1997). Brown and Yoder (1994b) have suggested that satellite detected coccolithophore blooms represent only a small fraction of total planktonic PIC formation in the oceans, and clearly more information is required on PIC:POC production ratios under non-bloom conditions. However, methodology has been a limitation; the standard 14C technique was designed to measure incorporation of 14C into POC, with labeled PIC being acidified and lost with the residual dissolved 14C on the filter. Paasche (1969) modified the 14C technique to assess PIC production in cultures of E. huxleyi, but this involved estimating PIC production by subtraction, using acidified and non-acidified duplicate filters. This method has been used in blooms of E. huxelyi (Fernández et al., 1993), but in non-bloom conditions the method can be limited by the low PIC production signal which can be lost in the natural variability between replicate filters. The method was then modified so that 14C incorporation into both PIC and POC could be determined from the same filter; this involved micro-diffusion and trapping of the acidified PIC fraction as CO2 (Paasche and Brubak, 1994). The post-filtration method is labor intensive however, and has not been widely adopted in routine studies of primary productivity. However, some studies have used this technique to measure PIC production by non-bloom populations of coccolithophorids in the equatorial Pacific and the Arabian Sea and they found that PIC production can contribute 1-10% of the total fixed carbon (POC+PIC), and up to 30-50% at some stations (Balch and Kilpatrick, 1996; Balch et al., 2000).  90 The northeastern subarctic Pacific is one of three major high nitrate low chlorophyll (HNLC) areas of the world’s oceans. In these HNLC areas, the concentration of chlorophyll is low and relatively invariant year round, and nitrate is rarely depleted to limiting concentrations (Martin and Fitzwater, 1988; Martin et al., 1989; Dugdale and Wilkerson, 1991; Boyd et al., 1999b). Primary productivity is significantly limited by the availability of dissolved iron (Fe), suggesting that Fe plays a pivotal role in the functioning of the biological carbon pump (Martin and Fitzwater, 1988; Coale, 1991). The subarctic Pacific is of further interest because coccolithophores are present, although blooms visible from satellites are rare. Indeed, E. huxleyi and other coccolithophores may have been underestimated in this region; E. huxleyi has been sporadically recorded in some studies (Okada and Honjo, 1973; Honjo and Okada, 1974; Booth et al., 1982; Taylor and Waters, 1982; Fabry, 1989; Booth et al., 1993; Putland et al., 2004; Wong et al., 2006) but not in others (Taylor and Waters, 1982; Boyd et al., 1995b; Boyd et al., 1999b). This discrepancy could result from a preservation artifact because E. huxleyi is not easily recognized when preserved in acid Lugol’s iodine, for example, because of the dissolution of the coccoliths. Okada and Honjo (1973) have reported that E. huxleyi were the numerically dominant coccolithophorid population in the subarctic Pacific, and a recent study (Putland et al., 2004) has confirmed that E. huxleyi concentrations ranged from <100 cells l-1 to near bloom concentrations (0.7x 106 cells l-1). Sediment trap data also indicates periods of high PIC export at P26 (Wong et al., 1999; Wong and Crawford, 2002). The factors controlling coccolithophore abundance and calcium carbonate and organic carbon production in the surface ocean are still not well understood. In addition, in situ observations of coccolithophore carbon production, especially over longer time scales of years and the influence of El Niño and La Niña events on coccolithophore abundance and production is lacking. The main objective of this study was to determine the temporal (seasonal and interannual) and spatial (near-shelf vs. oceanic) variation in coccolithophore abundance, and in PIC and POC production. In the present study, sampling occurred along a regular transect from the Canadian coast out to Ocean Station Papa in the NE subarctic Pacific during the 1998 El Niño, the 1999 La Niña and during 2000.  Factors exerting bottom-up  91 control of surface coccolithophore abundance were also assessed. This is the first study to evaluate the importance of coccolithophores together with PIC production rates in the NE subarctic Pacific. 3.2 Methods 3.2.1 Sampling protocols Sampling was conducted along Line P, a long term sampling transect used by the Institute of Ocean Sciences, Sidney, BC (Fig. 3.1) The transect consists of five major stations (P04, P12, P16, P20, and P26) with station P26 being the long term monitoring station, Ocean Station Papa (OSP). Stations P04 and P12 were considered to be near- shelf stations, P16 a transitional station and P20 and P26 were HNLC stations (Boyd and Harrison, 1999). The cruises were conducted during February, June and August/September 1998 and 1999, and in June and September 2000 (Table 3.1). GO-FLO® bottles were soaked for >48 h in 10% HCl prior to arriving at each station. At each station, six depths were sampled before dawn using 12 L GO-FLO® bottles from depths where the irradiance was 100, 55, 30, 10, 3.5 and 1% of surface irradiance (I0). The depths were derived from irradiance profiles collected on the previous day at that station and the depth of the euphotic zone (Zeu) was designated by the deepest sample (1% I0). Samples were also collected from each depth for chlorophyll, POC and PIC production and coccolithophore cell enumeration. PIC production refers to calcification (mainly by coccolithophores), while POC production refers to primary production with no correction for DOC production/excretion. 3.2.2 T, S, light, nutrients and chlorophyll Temperature, salinity and nutrients were obtained from the Line P oceanographic data web site (http://www-sci.pac.dfo-mpo.gc.ca/osap/data/linep/linepselectdata_e.htm). The mixed layer depth was derived according to the procedure used by Freeland et al. (1997). Incident irradiance was recorded and averaged at 10 min intervals with a Li- COR® light meter with a 4π quantum sensor. Average mixed layer underwater irradiance was calculated according to Putland et al. (2004). For a particular station, the surface irradiance was averaged for the previous 4 days using values collected along the Line P  92 transect and this allowed for intercomparison with the results from Putland et al. (2004). This technique was used only in comparisons with log cell densities and should not be confused with the method employed to calculate light depths (see above). Dissolved iron (<0.2 µm) concentrations were obtained from Nishioka et al. (2001) and C. S. Wong (pers. comm.) and were used to examine a possible correlation with surface coccolithophore abundance. Chlorophyll a samples were collected in 300 ml polycarbonate bottles and filtered serially through 20, 5, and 0.2 μm polycarbonate filters (47 mm diameter). The 20 and 5 μm size fractions were filtered under gravity, while the 0.2 μm size fraction was filtered using <100 mm Hg vacuum differential (Joint et al., 1993). Filters were immediately stored in scintillation vials and extracted with 90% acetone in a freezer and analyzed for chlorophyll a on board using a Turner DesignsTM 10-AU fluorometer according to Parsons et al. (1984). The size fractions were summed to give total chlorophyll. Size- fractionated data will be reported elsewhere. 3.2.3 POC and PIC incubations Duplicate 250 ml polycarbonate bottles were filled from each GO-FLO® bottle from each depth. Prior to use, the bottles were subjected to a minimum 24 h soak in 10% HCl and rinsed three times with 0.2 µM filtered seawater. Three replicate dark bottles (selected randomly from the six depths) were also filled from the GO-FLO®s. Each bottle was inoculated with 15 µCi NaH14CO3. Triplicate 100 µl subsamples were drawn from three randomly selected bottles and placed in 200 µl of ethanolamine in glass scintillation vials for subsequent analysis of total available 14C. Sample bottles were incubated around dawn in on-deck incubators cooled with surface seawater and screened with neutral density mesh screens at approximately the irradiance levels from which they were sampled. After 24 h, the polycarbonate bottles were removed from the incubators, placed in the dark in a cold room on deck, and then filtered as soon as possible (0-2 hours). The contents of all bottles were filtered serially through 20, 5 and 0.2 µm pore size polycarbonate membrane filters following the same procedure as for chlorophyll a samples described above. In order to remove as much residual dissolved inorganic 14C as  93 possible from the filters, filters were each sequentially subjected to two, 20 ml filtered seawater washes. Initial experiments established that two filtered seawater washes were sufficient to remove residual 14CO2 by testing with 14C labeled 0.2 µm filtered water followed by rinsing with unlabeled filtered seawater. All experimental and control bottles were subject to the same size-fractionation procedure. Filters were placed in glass scintillation vials, capped, and frozen. Size fractions were summed to give total POC and PIC productivity. The size- fractionated data will be reported elsewhere. 3.2.4 Separation of 14C labeled POC and PIC Onshore, the filters (light and dark) were processed to determine the 14C uptake into POC and PIC following the micro-diffusion method described in Crawford et al. (2003), based upon a modification by Paasche and Brubak (1994). This allowed the 14C uptake into PIC to be estimated from the same filter as that for 14C uptake into POC. The method is based upon the principle of acidification of 14C labeled PIC on the filter, and subsequently trapping the released 14CO2 in an alkaline (KOH) trap (Paasche and Brubak, 1994). It was previously determined that >95% of the 14CO2 released upon acidification is caught in the alkaline trap within 24 h (Manahan, 1983; Crawford et al., 1994). Scintillation cocktail (10 ml Scintisafe@) was added to all vials and thoroughly mixed. Samples were allowed to stand for a minimum of three days to allow for chemiluminescence to decay. Rates of PIC production were calculated from the alkaline trap fraction, and rates of POC production calculated from the filter fraction, according to the standard 14C protocol (Knap, 1994) after the dark bottle values for both POC and PIC were subtracted.. Total CO2 available was calculated according to Crawford et al. (2003). The detection limit for PIC production was established at 0.05mgC m-3 d-1. As with chlorophyll, values were taken from the euphotic zone to calculate integrated POC and PIC production. 3.2.5 Coccolithophore enumeration Water (250 ml) was subsampled from each GO-FLO® at each station and depth, and then processed and preserved in 2% hexamethylenetetramine-buffered formalin according to Booth et al. (1993). Subsamples (100 ml) were settled for 48 h and a  94 minimum of 100 coccolithophore cells per sample were counted at 400x magnification using an inverted microscope (Utermöhl, 1931; Booth, 1988; Peterson, 2005). Random samples were recounted at 500x magnification with a polarizing microscope (Hobro and Willen, 1977; Winter and Siesser, 1994; Putland et al., 2004) to verify enumeration of the coccolithophores. Coccolithophore numbers were separated into the four most numerous species (Emiliania huxleyi, Gephyrocapsa oceanica, Rhabdosphaera sp. and Syracosphaera sp.). Coccolithophores designated as ‘others’ were made up of several different species. Integrated coccolithophore species densities (Table 3.3) were calculated from the cell densities located within the euphotic zone. Organic carbon per cell was calculated according to Menden-Deuer and Lessard (2000). The proportion of total coccolithophore carbon (organic) in each species (see Fig. 3.3) was calculated from the organic carbon for each species integrated throughout the euphotic zone. 3.2.6 Statistical testing All variables were tested for normality using the Kolmogrov-Smirnov test and visual inspection of normal probability plots (Systat 11).  As the data were not normal, the non-parametric equivalent of the t-test, the Mann-Whitney test (Systat 11) to test for significant spatial and temporal differences, was used. Alpha was set at 0.05. 3.2.7 Contour plotting Contour plots (Fig. 3.2 and 3.4) were created using Surfer 7.0 (Golden Software) following the kriging interpolation technique utilizing the linear model with a slope of one. Disparity in the values of the x-axis (1500 km) and the y-axis (85 m) were addressed using the anisotropy function with a ratio of 0.5 and a zero angle. Although contour plots should always be looked at with caution, our approach does yield a sufficiently conservative value that allows realistic analysis near the sampling points and a cautious analysis of trends over the whole area. Distance along Line P (x-axis) starts with historical station P1 as the origin and follows the Line W-NW to P26 (1420 km from P1). See Whitney and Freeland (1999) for a full listing of stations, locations, distances along Line P and distances from shore.  95 3.3 Results 3.3.1 Physical and chemical conditions Conditions along Line P varied temporally and spatially during the years 1998 to 2000 (Table 3.1). Surface temperatures were generally warmer during the 1998 El Niño period for all three cruises when compared to the 1999 La Niña. During 2000, surface temperatures along Line P were similar to 1999 in the spring with similarly cool temperatures. In Aug/Sept 1998, P04 was also similar to 1999. However, the rest of the stations exhibited warmer temperatures in 1998 compared to 1999 and culminated in the highest surface temperature (14.1°C) recorded at P26 of any cruise during the three year period. Surface nitrate concentrations were lower in 1998 when compared to 1999 for all cruises (Table 3.2). Surface NO3 depletion in 1998 occurred as far out as P12 in June and P16 in Aug/Sept. In 1999 and 2000, surface NO3 depletion was much closer to the shelf, and only occurred at P04. Interestingly, surface nitrate (5.1 µM) and silicic acid (2.0 µM) at P26 during Aug/Sept 2000 were the lowest for that station for all eight cruises. Potentially growth limiting concentrations of silicic acid were also observed at P12 and P16 in June and Aug/Sept 1998, respectively. The euphotic zone tended to be shallower in 1998 compared to 1999 (Table 3.1) with the exception of P20 and P26 in February. The two cruises in 2000 had the deepest 1% light level for both June and Aug/Sept. For most cruises for all three years, the deepest euphotic zones tended to be found at P16 and P20. 3.3.2 Coccolithophore abundance and community structure An interannual comparison revealed that maximum abundances of coccolithophores occurred in 1998 and 2000 with an annual mean of 132 and 473 coccolithophores ml-1 respectively. During 1999, there was a significantly (p<0.001) lower average (42 coccolithophores ml-1) than the other two years (Fig. 3.2). There was no significant difference between 1998 and 2000. In February 1998, abundance was highest at stations P12 and P16 with average coccolithophore abundances in the mixed layer of 146 (SD =82) and 199 (SD=97) cells ml-1 respectively. In June, abundances were  96 much higher along the transect (mixed layer station averages ranged from 227±135 SD to 344±148 SD cells ml-1) and cells were relatively evenly dispersed within the mixed layer. In Aug/Sept, numbers were much lower, but peaked (mixed layer average of 172±149 SD cell ml-1) at the transitional station (P16). Coccolithophore densities were low throughout 1999 and averaged 48 (SD=47) cells ml-1. In 2000, surface maxima (>2000 cells ml-1) occurred both offshore (P26) in June and nearer the shelf (P12) during Aug/Sept. The small coccolithophore, E. huxleyi (measured cell diameter 6-10 µm), numerically dominated all stations in June (Table 3.3; Fig. 3.3) for all three years, and generally had the highest cell density where surface coccolithophore density was >500 cells ml-1. Although E. huxleyi had the highest densities at station P26 in Aug/Sept 2000 the coccolithophore with the highest proportion of coccolithophore POC was Syracosphaera sp. (measured cell diameter 10-30 µm). The second most numerically dominant coccolithophore in this study, Gephyrocapsa oceanica (measured cell diameter 15-27 µm), had maximum cell densities during February for both 1998 and 1999, particularly closer to the continental shelf (P04). Species composition was more variable in Aug/Sept, especially at stations with low coccolithophore abundance. However, E. huxleyi numerically dominated the two bloom periods (>1000 cells ml-1) at P26 in June and P12 in Aug/Sept 2000. Rhabdosphaera sp. (measured cell diameter 10-20 µm) and Syracosphaera sp. (measured cell diameter 10-30 µm) were also identified in the enumeration samples as were several unknown species (measured cell diameter 5-30 µm). 3.3.3 Phytoplankton biomass, POC and PIC production Winter (February) values of integrated chlorophyll a (Table 3.1) were highest at the intermediate stations (P12 to P20). POC production tended to be lower in June and varied over the three-year period with a maximum at the transition station P16 in 1998 and the near-shelf stations P04 and P12 in 1999 and 2000. Over the three year period, chlorophyll a was higher in 1999 than 1998 for June and Aug/Sept cruises. Aug/Sept 2000 had the highest chlorophyll a values of the three late summer periods. Although nutrient concentrations (Table 3.2) and mixed layer depths were on average lower in 1998 than in 1999, POC productivity values were similar (Table 3.1 and  97 3.4). POC productivity was over three times higher at P04 than the rest of the stations during the late summer of 1999. Aug/Sept values were slightly higher than June for all three years with the maximum values typically occurring at P04. June 2000 had much higher production near the shelf (P04) than either of the two previous years with chlorophyll values closer to 1998 than 1999. PIC production (Fig. 3.4) rates ranged from undetectable (<0.05 mg C m-3 d-1) to 20 mg C m-3 d-1 (Aug/Sept 2000 P26 surface) and averaged 13% of total (POC+PIC) carbon production (median = 7%) (Fig. 3.6). The highest values were measured within the mixed layer in June 1998 and Aug/Sept 2000 for all stations (Fig. 3.4). Maximum integrated PIC production rates (Table 3.1) were highest at P20 for both periods and tended to be higher for the HNLC stations (P20 and P26) than for the stations closer to the shelf. The overall correlation between non-integrated coccolithophore abundance and PIC production was not significant (r2 = 0.052, n=160). Seasonal and interannual variations were also found in POC and PIC production (Table 3.4). Average values for each season showed an increase of POC production with a minimum in Feb and a three fold increase in Aug/Sept. PIC production values were more variable with maximum average cruise values found in June for 1998, February for 1999 and Aug/Sept in 2000. Average values in Feb 1998 and 1999 were not significantly different (p>0.05) with POC production of 147 and 160 mg C m-2 d-1 respectively and PIC production rates of 13 mg C m-2 d-1 for both years. Greater variation occurred in June for all three years with average POC production increasing from 1998 (166 mg C m-2 d-1) to 2000 (579 mg C m-2 d-1). PIC production did not follow the same trend with maximum values found in June 1998 (146 mg C m-2 d-1) followed by a 3-fold reduction in 2000 (48 mg C m-2 d-1) and a minimum value of 3.8 mg C m-2 d-1 in June 1999 for all cruises. Aug/Sept showed the opposite result with PIC production of 22 mg C m-2 d-1 in 1998, a seasonal minimum in 1999 (8 mg C m-2 d-1), and a maximum in 2000 (224 mg C m-2 d-1) the latter being the highest value recorded in this study. In Aug/Sept, PIC production was significantly different in all of the three years (p<0.001) as were the three years in June (p<0.001). A significant difference in February between 1998 and 1999 in PIC production was not found.  98 The maximum average yearly PIC production was found in 2000 (2.6 mg C m-3 d- 1) followed by 1998 (1.4 mg C m-3 d-1) and 1999 (0.14 mg C m-3 d-1). The averages for 1998 and 2000 were both significantly higher (p<0.001) than the 1999 average. There was no significant difference between 1998 and 2000. In general, PIC production did not follow the same trends as POC production and areas of maximum POC production rarely corresponded to high PIC production values (Table 3.1). Maximum values of POC production (>500 mg C m-2 d-1) were found at P04 (566 mg C m-2 d-1) and P26 in Aug/Sept 1998 (798 mg C m-2 d-1) and at P04 in June 2000 (1386 mg C m-2 d-1) (Table 3.1), yet the ratio of integrated PIC:POC production did not exceed >0.04 at these times (Fig. 3.5). Aug/Sept 2000 was an exception where maximum POC productivity at P04 (653 mg C m-2 d-1) and P12 (581 mg C m-2 d-1) (Table 3.1) corresponded to PIC:POC ratios of 0.10 and 0.14 respectively (Fig. 3.5). In June 1998, three out of the five stations (P04, P12, and P20) had PIC:POC ratios >1.0 (P20 was the highest of all the cruises at 1.7), yet POC production did not exceed145 mg C C m-2 d-1. In Aug/Sept 2000, P20 had the highest POC production (405 mg C C m-2 d-1) and the PIC:POC production ratio was 1.4. Integrated PIC production reached values >60% of total carbon production (PIC and POC) at P20 in June 1998 and Aug/Sept 2000. In June 1998, the PIC:POC production ratios (Fig. 3.5) were never <0.5 for any of the stations. Aug/Sept 2000 had similar high values (>0.7), but were lower (~0.1) for the two near-shelf stations (P04 and P12). 3.3.4 PIC:POC production ratios A plot of PIC vs. POC production for all pooled samples showed that more than 50% of PIC production was less than 10% of POC production (Fig. 3.6). All samples where PIC production was equal to, or greater than POC production, occurred in HNLC waters in 1998 or 2000. Lower PIC production rates occurred in 1999 compared to 1998 and 2000, however, they were not statistically different. POC production did not follow this trend. The PIC:POC ratio spanned over more than 3 orders of magnitude, displaying the great spatial and temporal variation found in this study area.  99 The ratio of PIC:POC production averaged 0.25 for all 8 cruises with a minimum of 0.09 for all Feb cruises, a maximum of 0.39 in June and 0.21 for all Aug/Sept cruises (Table 3.4). The ratio was similar over the two winter cruises in 1998 and 1999. However, there was considerable interannual variation (range 0.02-1.03) in the spring and late summer values in 1998 and 2000. The largest total cruise PIC:POC ratio (average 1.03 for the cruise) occurred in June 1998.  PIC production was high during that period and combined with the slightly lower POC production value (compare to June 1999 and 2000), resulted in a higher PIC:POC ratio when compared to other cruises. Conversely, Aug/Sept 2000 showed the highest average total cruise PIC production, but PIC:POC was 0.55 since POC production was also high. The other PIC:POC ratios were < 0.09 with a minimum ratio of 0.02 in June 1999. 3.4 Discussion 3.4.1 Seasonal and spatial variations in coccolithophore abundance Although chlorophyll a biomass remains relatively constant seasonally and spatially along the Line P (Boyd and Harrison, 1999), physical and chemical properties were very different and may be related to the marked difference in coccolithophore abundance (Wong et al., 1995; Whitney et al., 1998; Wong et al., 2002b; Wong et al., 2002d). However, our results did not show a strong correlation of coccolithophore abundance with physical or chemical properties (see section 3.4.5). This study found near-bloom coccolithophore densities in two distinct areas (near-shelf and HNLC) in 2000 (Fig. 3.2) in June and also in Aug/Sept as well as higher densities in June 1998 along the entire Line P even during a period of lower chlorophyll (Table 3.1). Coccolithophore concentrations were high enough (>1000 cells ml-1) to be considered ‘blooms’ (Merico et al., 2004; Putland et al., 2004) at P26 in June and P12 in Aug/Sept 2000. Wong et al. (2006) found similar coccolithophore trends (measured in carbon) at P20  and P26 during the June and September of the same years. They also found higher dimethylsulphide (DMS) concentrations in June 1998 (highest) and 2000 compared to 1999. Our periods of high coccolithophore densities did not correlate well with their higher DMS values during the same periods. They found their highest DMS values in June 1998, while our higher coccolithophore densities in the HNLC region were in June  100 2000 at P26. This may be attributed to a higher occurrence of other DMS producing organisms in the area or other factors. In most cases of high (>500 cells ml-1) coccolithophore densities, E. huxleyi dominated and was rarely <75% of the total coccolithophore population (Fig. 3.3). Coccolithophid ‘blooms’ found in this study were infrequent (2 times) and they were larger (>1500 cells ml-1) than the cell densities found by Putland et al. (2004) in northeast subarctic Pacific HNLC waters (750 cells ml-1) in June. Additionally, during the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES) at P26 in July 2002 (Harrison, 2006), Marchetti et al. (2006c) found coccolithophore cell densities increased from 200 to 984 cells ml-1, ten days after the mesoscale iron enrichment. Sediment trap data collected over 10 years at P26 show periods of high PIC flux and a 10-fold variation between extreme months (Wong et al., 1999; Wong and Crawford, 2002), a much higher range than found in the POC flux. A maximum PIC flux in the 200 and 1000 m traps occurred between June and July, but did vary between years. More recent data show that the PIC flux at the 1000 m sediment trap was maximum in July 1998 (195 mg m-2 d-1), much lower in April 1999 (111 mg m-2 d-1), and marginally higher (129 mg m-2 d-1) in June 2000 (C.S. Wong, unpub. data.) although the exact source of the PIC has not been established. Satellite images support the observations of high coccolithophore densities in the region surrounding Line P (Gower, 2004) in both the HNLC and near-shelf waters and in both June and summer periods. 3.4.2 Interannual variability: El Niño, La Niña, and 2000 Our findings of significantly higher PIC production in an El Niño year with lower values in a La Niña period agrees with the study of Wong and Crawford (2002) based on sediment trap data at P26 from 1982 to 1990. They showed a higher flux of PIC and a higher rain ratio (PIC:POC flux) during El Niño years with a lower flux in La Niña periods. The PIC:POC ratios (ca. 1) of material falling into shallow traps in June/July at P26 by Wong & Crawford (2002) were very similar to the PIC:POC ratios that found during this study in surface waters for the same locations in 1998 and 2000. Coccolithophore abundances were found to be significantly higher during the El Niño, corresponding to the higher PIC production rates. Coccolithophore abundances and  101 species identification from the sediment traps of the Wong and Crawford (2002) study, especially during these periods of high flux, would be especially helpful in connecting PIC production at the surface to sinking particles below the mixed layer. The 1998 El Niño nutrient levels were noticeably lower than average with low nitrate concentrations along the whole of Line P and depleted silicic acid at the near-shelf stations (Table 3.2). Whitney et al. (2002) attributed these lower nutrients to a perceptible shallowing of the mixed layer that contributes to lower chlorophyll levels (Table 3.1). Conversely, the 1999 La Niña resulted in an increase in mixed layer depth, nutrient levels and chlorophyll along line P (Whitney and Welch, 2002; Wong et al., 2006). This was most distinct at the near-shelf stations (Table 3.1). Childers et al. (2005) also measured higher stratification and lower nutrients in 1998 compared to 1999 along the GLOBEC Seward line along the northern shelf of the Gulf of Alaska. With the diminished chlorophyll concentrations in 1998, there was an increase in PIC production and coccolithophore density, (Table 3.4, Fig. 3.2 and 3.4). Studies in the Atlantic (Balch et al., 1991; Fernández et al., 1993; Holligan et al., 1993) have also shown an increase in PIC production and coccolithophore densities under conditions of low chlorophyll. Indeed it has been shown that coccolithophores can compete well under stratified nutrient limited conditions. For example, sediment trap studies in the Santa Barbara Basin in California (De Bernardi et al., 2005) also showed an increase in coccolithophore abundance concurrent with the development of the 1997-1998 El Niño. Reduced coastal upwelling decreased diatom fluxes and resulted in increased coccolithophore flux. Conversely, even though a large E. huxleyi bloom occurred in the Bering Sea during a positive El Niño/Southern Oscillation (ENSO) event, there were no indications of a clear bloom during the period from 1978 to 1995 (Merico et al., 2003) suggesting that although a strong coccolithophore bloom can occur in the area during an El Niño period, other factors are clearly important. This emphasizes that the potential effects of growth factors is not clearly understood. 3.4.3 PIC production vs. coccolithophore abundance Coccolithophore abundance fluctuated and reached maximum values at stations at either end of Line P. Maximum values (Fig. 3.2) were found at P26 and P12 in 2000  102 (~2400 cells ml-1). These values were higher than previous values of E. huxleyi found at P26 (~750 cells ml-1) by Putland et al. (2004). Although growth experiments have shown a direct correlation between high coccolithophore densities and PIC production (Fritz, 1999; Crawford et al., 2003; Schulz et al., 2004), it has been more difficult to demonstrate this relationship for studies in the field (Balch et al., 1992; Balch and Kilpatrick, 1996). In our study, coccolithophore densities at bloom levels (P26 June 2000 and P12 Aug/Sept 2000) often, but not necessarily corresponded to higher PIC production.  Nevertheless, the rates of PIC production when normalized per cell (from integrated PIC production and integrated cell numbers) fell within the published range for PIC production (Fabry, 1989; Crawford et al., 2003) by coccolithophores in the NE subarctic Pacific (mean of 12 pg C cell-1 d-1 for June and Aug/Sept cruises combined). 3.4.4 PIC and POC production Our observed high PIC production in the NE Pacific agrees with the conclusions of Wong et al. (2002c) who suggested that significant PIC formation must be occurring to explain observed changes in water column chemistry. Crawford et al. (2003) found PIC:POC ratios to range from 0.04 to 0.1 for P26 in September 1999. In the same region, T. Peterson (unpubl. data) found a greater range of ratios approaching 0.35 in the center of the Haida eddy (north of Line P). Our values, for individual depth samples, ranged from <0.01 to >5 (Fig. 3.6). Although no other data is available from the NE subarctic Pacific, they are comparable to other large data sets (Balch and Kilpatrick, 1996; Balch et al., 2000; Graziano et al., 2000). They also correspond to the ranges found in shallow sediment traps at P26 (Wong et al., 1999; Wong and Crawford, 2002) and may better explain some of the higher “rain ratios” found in those traps. Caution must be used when considering PIC:POC ratios because coccolithophores will only make up a fraction of any field sample (Paasche, 2001). Moreover, there may be significant dissolution of PIC in the sediment traps depending on depth, preservative and age of sample (Sprengel et al., 2002). PIC production rates during E. huxleyi blooms in various regions can make up a significant portion of the total carbon fixed.  During blooms in the North Atlantic and the  103 North Sea (Holligan et al., 1993; Buitenhuis et al., 1996), PIC production contributed ~20% of total carbon production. PIC production made up 20-67% of the total carbon production in Norwegian coastal mesocosm experiments in late spring (van der Wal et al., 1995) and 37% of an E. huxleyi bloom in the Gulf of Maine (Balch et al., 1992). PIC production rates can also be affected by the presence of pteropods and foraminifera. Fabry (1989) found the average daily contribution to PIC formation from these calcium carbonate forming zooplankton to vary between 15-26% at P26. Foraminifera were infrequently found in the present study, due mainly to the small sample size and their tendency to migrate below the euphotic zone during daylight hours (Wormuth, 1981; Fabry, 1989). High PIC:POC production ratios can also be affected by PIC formation in the dark.  Dark PIC formation varies in the literature and can range from zero (Linschooten et al., 1991) to 10-15% of the light saturated rate (Paasche, 1966; Balch et al., 1992; Nimer and Merrett, 1992; Paasche and Brubak, 1994; Sekino and Shiraiwa, 1994; Paasche, 2001). Although rates of PIC production in the dark were not measured, the maximum time samples were stored in the dark before filtration was <2 hours so any dark calcification would have a minimal effect on total PIC production in a 24 hour incubation. 3.4.5 Bottom-up controls: nutrients, Fe, light and PIC production Our results did not show a strong correlation of coccolithophore abundance with physical or chemical properties. There was a weak negative correlation between surface coccolithophore abundance and surface dissolved iron (Fig. 3.7A). Martin et al. (1989) and Crawford et al. (2003) found that the addition of Fe to P26 samples increased coccolithophore concentrations during deck incubations. Lab experiments have also shown an increase in CaCO3 production with increasing iron (Fe(III)) concentrations (Schulz et al., 2004). During the SERIES mesoscale Fe enrichment at P26 in July/Aug 2002, coccolithophores increased almost 5-fold, 10 days after the initial Fe enrichment (Marchetti et al., 2006c). However, by the end of the experiment (day 18), coccolithophore numbers were half the density found before the addition of Fe. This contrasts with the significant increase in diatoms (10-fold) found over the first 20 days of  104 the Fe enrichment. Conversely, Lam et al. (2001) showed no change in PIC production after a Fe addition to P26 samples during the same period as when Crawford et al. (2003) showed an increase in PIC production. Muggli and Harrison (1997) found that E. huxleyi cells isolated from P26 had a low Fe requirement compared to a diatom from the same area. Although the effects of Fe addition were not examined in this study, the significant spatial and temporal variation found in coccolithophore densities along Line P suggest the control of coccolithophore growth is probably more complicated than the simple concentration of available Fe. Control of coccolithophore growth may also be influenced by zinc availability. The addition of zinc to P26 water has been shown to result in a 3-fold increase in coccolithophore density after 8 days (Crawford et al., 2003) compared to the control, implying a possible advantage of coccolithophores in low Fe waters with variable zinc availability. Surface concentrations of dissolved zinc at P26 can vary from 0.04 to 0.07 nM (Martin et al., 1989; Lohan et al., 2002) and increase towards the shelf with values up to 0.9 at P04 in September 1999. Lab incubation studies by Schulz et al. (2004) found that E. huxleyi increased the PIC production per cell with increasing Fe concentrations, but remained unchanged with zinc additions, even though growth rates increased with the addition of either trace metal. This implies that Fe has a direct effect on PIC production, while a deficiency in zinc does not, resulting in a CaCO3 accumulation in slow growing, low zinc systems, effectively raising the PIC:POC production ratio. Shipboard incubations have also suggested an increase of PIC:POC ratios concurrent with increased available Fe (Crawford et al., 2003).  There was a weak but significant positive correlation between surface coccolithophore abundance and underwater irradiance for HNLC stations (Fig. 3.7B). Other studies have found the same correlation with irradiance as well as salinity (Kristiansen et al., 1994; Townsend et al., 1994; van der Wal et al., 1995; Nanninga and Tyrrell, 1996; Head et al., 1998; Haidar and Thierstein, 2001). Putland et al. (2004) presented data from a similar area (HNLC) and time period (1998-2001). Our study did not corroborate their findings. The correlation with underwater irradiance was similar, but there was not any significant regression with salinity, temperature, phosphate or silicic acid (not shown). There was a weak negative correlation with surface nitrate  105 concentrations at the near-shelf stations (Fig. 3.7C), in contrast to that of Putland et al. (2004). Our highest surface coccolithophore densities did not correspond to the stations with maximum values for average mixed layer irradiance.  Instead, they tended to occur when average daily mixed layer irradiance values were around 10 µmol photons m-2 d-1. This is in contrast to Egge and Heimdal (1994) who found concentrations of E. huxleyi in Norwegian mesocosms to increase with increasing irradiance and blooms to occur when surface irradiance was >20 µmol photons m-2 d-1. Although data is presented in Fig. 3.7 as total coccolithophore cell concentrations instead of just E. huxleyi, there was the same or weaker correlations when compared to only E. huxleyi. The weaker correlations or contrary regressions found in our study compared to Putland et al. (2004) may be due to the differing spatial and temporal variation within our data. Unlike their data which was restricted to HNLC stations and mesoscale eddies in HNLC waters only during June, our study included both the near- shelf and HNLC stations and encompassed three seasons over three years. Due to the nature of our sampling, there was not a large enough sample size to restrict our analysis to only HNLC waters in June for a direct comparison with Putland et al. (2004). This suggests variable coccolithophore acclimations to different conditions and may not be easily predicted as a single response to a few variables. Further study requires more sample collection in a single area over a longer period of time. 3.4.6 Top-down controls Microzooplankton (protists and metazoan sizes <200 µm) grazing can be an important factor in controlling phytoplankton populations in both oligotrophic (Lessard and Murrell, 1998) and coastal waters (Strom et al., 2001). Consumption of phytoplankton production is extremely variable and can reach over 100% of daily production in some cases (Verity and Smetacek, 1996; Merico et al., 2004). Zooplankton grazing studies in the NE subarctic Pacific do not show a clear indication of controls on coccolithophores. Rivkin et al. (1999) demonstrated that microzooplankton tended to preferentially ingest smaller, heterotrophic prey over autotrophic ones. Indeed, they found no indication of any consistent grazing on the nanoplankton size class (2-20 µm). Goldblatt et al. (1999) found grazing by  106 mesozooplankton on nanoplankton to be infrequent and was only measured at the near- shore (P12) station. On a larger scale, mesozooplankton along line P were found to have only a small effect on phytoplankton production and biomass (Boyd et al., 1999a; Vezina and Savenkoff, 1999). Instead, the larger zooplankton group seems to exert most of their grazing pressure on the microheterotrophs (ciliates, flagellates and microcrustaceans) and thereby an indirect control on the pico- and nanoplankton populations at P26 (Landry et al., 1993; Goldblatt et al., 1999; Rivkin et al., 1999). Elsewhere, microheterotrophs have been shown to clearly graze E. huxleyi (Holligan et al., 1993; Levasseur et al., 1996) but other studies have shown preferential grazing on other organisms of the same size class over E. huxleyi (Archer et al., 2001; Fileman et al., 2002; Olson and Strom, 2002).  Low grazing pressure on coccolithophores, in conjunction with favorable physical conditions, may help explain their observed frequency at certain times along Line P and the NE subarctic Pacific. In modeling studies performed by Merico et al. (2004) on the Bering Sea shelf, E. huxleyi was able to outcompete and achieve bloom densities when microzooplankton selectively grazed the diatoms. This model infers the importance of controls on diatoms growth on the abilities of E. huxleyi to compete. Periods of low silicic acid have also been suggested as equivalent controls on diatom growth (silicate switch) that may allow smaller phytoplankton species such as coccolithophores to compete for limited nutrients such as iron (Ridgwell, 2003). This may help explain the higher PIC production and coccolithophore cell densities in HNLC waters during Aug/Sept of 2000 when silicic acid concentrations were anomalously low. Clearly more studies on the specific grazing pressures on coccolithophores in the area are necessary, because the episodic nature of the blooms observed in this study could be suggestive of variation in top-down controls. 3.4.7 Satellite images The high visibility of coccolithophore blooms in optical satellite images is well known (Balch et al., 1991).  The brightness of such blooms is due to the 20 to 50 coccoliths that are detached by the average cell as the bloom finishes its active growth phase and enters senescence.  Balch et al. (1991) and Tyrell et al. (1999) related coccolith counts to the optical properties of water during bloom conditions, quantifying the  107 expected increase in back-scatter and hence in water-leaving radiance.  Brown and Yoder (1994b) presented results of a global survey based on CZCS (Coastal Zone Color Scanner) satellite imagery collected during the period 1978 to 1986.  The survey was strongly influenced by the rather variable global distribution of data from this sensor, and showed many events in the North Atlantic, but few in the North Pacific. The more recent data from SeaWiFS cover the period of our cruises (1998-2000) and show frequent bright blooms in the Gulf of Alaska (Gower, 2004), thus supporting our observations. Inspection of the SeaWiFS monthly global composite data for the times of the cruises reported here, shows frequent increases in water brightness as measured by nLw555 (normalized water-leaving radiance at a wavelength of 555 nm), suggesting presence of coccolithophore blooms.  These bright blooms are most frequent in the summer months, June, July and August, but in June and July cloud cover in the Gulf of Alaska is sufficiently common that no satellite data are available for many areas. Unfortunately, the monthly composites show no data for most of the central Gulf in June of 1998 and 1999, for example. In June 2000, the SeaWiFS composite image shows a large area including station P26 that was brightened, probably due to a coccolithophore bloom.  The radiance increase indicated by the satellite data (from 0.3 to 0.8 mW cm-2 micron-1 steradian-1) is roughly consistent with the expected brightening due to the coccolithophore abundance shown in Fig. 3.2.  With 2473 cells ml-1 for the near-surface sample at P26 in June 2000 (Fig. 3.2), this was the highest coccolithophore abundance observed at all 5 stations over the three year study.  Other cell counts show a statistical tendency for cell densities to result in brighter water as measured by the satellite, but the correlation is poor. This poor correlation is partly to the lack of a count of detached coccoliths.  It should also be noted that the monthly composites used for convenience in these cloudy conditions, lead to relatively large errors given the spatial patchiness, expected movement and short duration of the blooms. 3.5 Conclusions High PIC production suggests a low efficiency of the biological pump. This is because pCO2 drawdown generated by a unit production of POC is much lower when this  108 POC production is accompanied by significant PIC production. Moreover, PIC in the form of coccoliths may also act as "ballast" and increase the transfer efficiency of organic matter from the surface to intermediate depths where it is remineralised (Armstrong et al., 2002; Klaas and Archer, 2002). Therefore, there are important general implications for high or increasing abundance of coccolithophores in the open ocean and whether they represent sources or sinks of CO2 largely depends on the ultimate fate of the material. Understanding the conditions which lead to increased abundance of coccolithophores is crucial. Our study has shown that Line P in the NE subarctic Pacific is a variable but significant area of coccolithophore abundance and PIC production. The data suggest stronger PIC production rates during the 1998 El Niño when compared to the 1999 La Niña, although rates were also high in 2000. Our data do not provide conclusive evidence for specific top-down or bottom-up controls.  109 3.6  Tables Table 3.1. Baseline data for all Line P stations sampled during 1998-2000, including the euphotic zone (Zeu), mixed layer depth (MLD) and daily surface irradiance (Io) for 8 cruises at 5 stations. Surface temperature and salinity are from Fisheries and Oceans Canada Line P data site (http://www.pac.dfo-mpo.gc.ca/sci/osap/projects/linepdata). See methods for details. Integrated values of Chlorophyll a, POC production and PIC production are from the euphotic zone. Station P26 is Ocean Station Papa (OSP). LS = lost sample. Cruise Number Date Station Zeu (m) MLD (m) I0 (mol photons m-2 d-1) Surface Temp. (°C) Surface Salinity Int. Chl a (mg m-2) Int. POC prod. (mg C m-2 d-1) Int. PIC prod. (mg C m-2 d-1) 9803 19-Feb-98 P04 40 175 12.6 11.0 32.62 18.3 72 1  21-Feb-98 P12 50 76 10.6 8.6 32.60 16.8 166 8  23-Feb-98 P16 60 81 7.7 7.5 32.61 26.8 195 3  24-Feb-98 P20 80 81 12.5 6.6 32.64 26.7 144 27  26-Feb-98 P26 80 94 14.7 5.4 32.67 18.9 162 28 9815 5-Jun-98 P04 33 24 39.1 12.6 31.97 9.5 100 107  6-Jun-98 P12 40 17 22.8 12.2 32.31 16.9 84 109  8-Jun-98 P16 52 22 27.8 10.9 32.67 20.0 312 164  9-Jun-98 P20 58 15 46.3 10.1 32.69 15.1 143 248  12-Jun-98 P26 50 22 18.0 9.1 32.67 18.5 189 102 9829 27-Aug-98 P04 33 21 44.2 16.8 32.05 14.9 566 10  28-Aug-98 P12 45 17 24.9 16.6 32.10 10.1 324 14  30-Aug-98 P16 55 27 28.2 16.0 32.28 12.4 460 40  31-Aug-98 P20 60 31 24.5 14.1 32.65 7.5 405 32  5-Sep-98 P26 55 42 34.1 12.0 32.63 12.6 798 14 9901 10-Feb-99 P04 40 78 13.3 8.3 32.57 18.4 LS LS  14-Feb-99 P12 80 102 15.7 7.6 32.75 27.6 123 13  23-Feb-99 P16 75 102 4.8 6.7 32.82 20.5 123 11  20-Feb-99 P20 75 104 18.1 6.2 32.77 36.8 265 14  18-Feb-99 P26 60 114 7.7 5.2 32.83 22.4 131 12 9910 23-Jun-99 P04 35 12 30.3 12.2 31.58 34.6 358 2  21-Jun-99 P12 60 21 32.1 10.0 32.82 34.0 426 3  19-Jun-99 P16 52 19 22.9 8.8 32.73 9.0 80 4  18-Jun-99 P20 65 60 42.1 8.1 32.73 18.3 225 3  12-Jun-99 P26 65 28 20.9 7.0 32.86 23.4 167 8 9921 29-Aug-99 P04 35 16 32.7 15.5 31.91 16.0 447 9  27-Aug-99 P12 45 19 43.8 14.6 32.30 14.5 365 3  29-Aug-99 P16 55 31 64.0 13.1 32.51 13.5 304 7  30-Aug-99 P20 60 26 23.3 12.3 32.68 7.1 181 4  2-Sep-99 P26 60 35 22.0 12.7 32.66 14.1 432 17 2000-10 1-Jun-00 P04 50 11 61.2 11.4 31.87 21.7 1386 58  3-Jun-00 P12 71 36 21.5 10.0 32.65 19.0 458 76  4-Jun-00 P16 80 32 28.0 9.1 32.66 17.7 483 52  6-Jun-00 P20 80 29 37.4 8.5 32.66 13.4 416 16  8-Jun-00 P26 80 27 26.4 7.7 32.68 18.5 152 40 2000-25 6-Sep-00 P04 50 21 40.8 15.0 31.80 22.9 653 67  8-Sep-00 P12 50 27 37.6 15.5 32.29 31.6 581 80  9-Sep-00 P16 66 40 18.1 14.5 32.41 22.7 295 206  11-Sep-00 P20 75 38 37.7 13.8 32.55 16.9 407 568  13-Sep-00 P26 50 29 28.4 13.5 32.62 24.5 480 197  110 Table 3.2. Surface macronutrient concentrations for 5 stations and 8 cruises along Line P. Data were obtained from the Fisheries and Ocean Canada Line P Oceanic Data web site (http://www-sci.pac.dfo-mpo.gc.ca/osap/data/linep/linepselectdata_e.htm). Nutrients were measured by the Institute of Ocean Sciences (Sydney, British Columbia, Canada) following Barwell-Clarke and Whitney (1996). The detection limit for nitrate is 0.05 µM, and 0.2 µM for silicic acid (Frank Whitney pers. comm.). ND = not detectable.  Cruise Number Station Surface Nitrate (µM) Cruise Average Surface Phosphate (µM) Cruise Average Surface Silcic Acid (µM) Cruise Average 9803 P04 3.5 8.2 0.6 0.9 5.3 11.6  P12 5.8  0.8  6.8  P16 8.4  0.9  11.4  P20 10.3  1.0  14.0  P26 13.0   1.2   20.5 9815 P04 ND 4.1 0.3 0.6 2.9 7.5  P12 ND  0.4  0.2  P16 4.1  0.7  7.6  P20 6.6  0.8  10.4  P26 9.9 1.0 16.4 9829 P04 ND 2.2 0.3 0.5 4.1 5.6  P12 ND  0.3  4.5  P16 ND  0.3  0.9  P20 5.1  0.8  9.3  P26 5.7   0.8   9.1 9901 P04 8.9 10.4 0.9 1.1 14.4 15.5  P12 9.1  1.0  14.0  P16 9.2  1.0  13.5  P20 10.7  1.1  16.1  P26 14.3   1.3   19.6 9910 P04 ND 7.5 0.2 0.8 1.6 11.4  P12 6.9  0.7  11.7  P16 8.1  0.9  11.4  P20 9.4  1.0  13.5  P26 13.2   1.2   18.7 9921 P04 ND 4.5 0.3 0.6 8.9 11.5  P12 0.6  0.4  7.2  P16 3.1  0.6  9.0  P20 7.6  0.8  12.7  P26 11.3   1.1   19.7 2000-10 P04 ND 7.7 0.4 0.9 6.4 13.3  P12 6.9  0.9  13.2  P16 8.4  1.0  13.1  P20 9.8  1.1  14.1  P26 13.2   1.3   19.9 2000-25 P04 ND 3.2 0.4 0.6 5.6 6.2  P12 0.9  0.4  6.1  P16 1.8  0.5  6.6  P20 8.2  0.9  10.8  P26 5.1  0.7  2.0  111  Table 3.3. Integrated (to 1% Io ) coccolithophore cell numbers (108 cells m-2) for 5 stations and 8 cruises. ‘Others’ refer to species found in either low concentrations or single occurrences. Cruise Station Emiliania  huxleyi Gephyrocapsa oceanica Rhabdosphaera sp. Syracosphaera sp. Others Total 9803 P04 27.0 3.0 0.0 0.0 0.0 30  P12 69.0 16.5 0.0 0.0 0.0 85  P16 103.5 24.5 1.5 0.0 0.0 129  P20 23.4 3.1 1.1 0.0 0.0 28  P26 25.4 0.0 0.0 0.0 0.0 25 9815 P04 50.1 0.0 0.0 0.0 0.0 50  P12 79.2 0.0 0.0 0.0 0.0 79  P16 111.7 0.0 0.0 0.0 0.0 112  P20 92.0 0.4 0.0 0.0 0.0 92  P26 85.4 0.0 0.0 0.0 0.0 85 9829 P04 27.8 0.0 0.3 0.0 0.0 28  P12 11.9 2.9 3.5 0.0 0.0 18  P16 69.6 4.2 15.4 0.0 3.7 93  P20 7.3 5.0 39.0 0.0 3.3 55  P26 11.1 6.2 1.9 0.0 0.0 19 9901 P04 2.3 0.3 0.2 0.0 0.1 3  P12 4.9 11.1 0.0 0.0 0.0 16  P16 55.3 11.6 0.6 0.0 0.0 67  P20 43.5 0.3 0.8 0.0 0.0 45  P26 36.1 2.8 1.1 0.0 0.0 40 9910 P04 39.5 0.0 0.0 0.0 0.0 39  P12 2.4 0.0 0.0 0.0 0.0 2  P16 10.3 0.0 0.0 0.0 0.0 10  P20 21.7 0.1 0.0 0.0 0.0 22  P26 19.9 0.0 0.0 0.0 0.0 20 9921 P04 8.3 0.0 14.1 0.0 0.0 22  P12 0.8 0.0 6.8 1.3 0.0 9  P16 1.0 0.0 0.0 10.5 0.0 12  P20 6.5 0.0 0.0 0.0 0.0 7  P26 20.8 2.9 1.8 5.8 0.0 31 2000-10 P04 187.1 6.8 0.0 5.0 0.0 199  P12 19.3 0.0 0.9 0.8 0.0 21  P16 27.8 0.0 0.0 0.2 0.0 28  P20 11.9 0.0 0.0 0.0 0.0 12  P26 989.3 0.0 0.0 0.0 0.0 989 2000-25 P04 81.0 13.3 0.0 1.1 1.6 97  P12 709.4 6.9 6.9 8.2 6.3 738  P16 187.9 0.0 9.9 0.5 42.2 241  P20 41.2 0.0 0.0 12.3 2.3 56   P26 130.5 21.4 0.6 102.7 0.0 255   112  Table 3.4. Average integrated (to 1% Io ) POC and PIC production from each station (mg C m-2 d-1) and the ratio of PIC:POC production. Values in parenthesis are the range of the averaged values. PIC:POC was calculated as the ratio of the average integrated PIC and POC production from each station.  Cruise Period POC Production PIC Production PIC:POC 9803 Feb-98 147.9 (72-195)  13.3 (1-28) 0.09 9815 Jun-98 165.5 (84-312) 146.0 (102-249) 1.03 9829 Aug/Sept-98 510.5 (324-798)  22.0 (10-40) 0.05 9901 Feb-99 160.7 (123-265)  12.5 (11-14) 0.09 9910 Jun-99 217.4 (84-353)   3.8 (2-8) 0.02 9921 Aug/Sept-99 345.8 (181-447)   8.0 (3-17) 0.02 2000-10 Jun-00 579.2 (152-1386)  48.4 (16-76) 0.12 2000-25 Aug/Sept-00 483.1 (295-653) 223.7 (67-567) 0.55  Average (±SD) 326.3 (± 177.2)  59.7 (± 81.1) 0.25  Feb Average (±SD) 154.3 (± 9.0)  12.9 (± 0.56) 0.09  June Average (±SD) 320.7 (± 224.4)  66.1 (± 72.7) 0.39  Aug/Sept Average (±SD) 446.5 (± 88.2)  84.6 (± 120.7) 0.21   113 3.7 Figures  Fig. 3.1. Map of the portion of the NE subarctic Pacific Ocean showing the five major sampling stations along Line P.  Inset shows general surface circulation in that area.    114  D e p t h  ( m ) 19991998 2000 80 60 40 20 0 80 60 40 20 0 1500 1000 500 80 60 40 20 0 1500 1000 5001500 1000 500 Distance along Line P (km) P26 P20 P16 P12 P4 P26 P20 P16 P12 P4 P26 P20 P16 P12 P4 Feb 98 Jun 98 Aug/Sep 98 Feb 99 Jun 99 Aug/Sep 99 Jun 00 Aug/Sep 00   Fig. 3.2. Contours represent coccolithophore abundance (cells ml-1) during 1998-2000. Dots represent the six sampling depths (100, 55, 10 and 1% of I0) for 5 stations along Line P for 8 cruises. Empty areas (white) signify <100 cell ml-1. The dark dashed line corresponds to the depth of the mixed layer. Solid grey line indicates the area below 1% I0 and therefore contains no measured data. See section 3.2.7 for contour plotting methods.   115 0 5e+4 1e+5 2e+5 2e+5 0.0 0.2 0.4 0.6 0.8 1.0 Y  A x i s  2 S u r f a c e  c o c c o l i t h o p h o r e  b i o m a s s  ( p g  C  m l - 1 ) 0 5e+4 1e+5 2e+5 2e+5 P-26 P-20 P-16 P-12 P-04 0 5e+4 1e+5 2e+5 2e+5 P-26 P-20 P-16 P-12 P-04P-26 P-20 P-16 P-12 P-04 P r o p o r t i o n  C o c c o l i t h o p h o r e  C a r b o n 0.0 0.2 0.4 0.6 0.8 1.0 Proportion Emiliania huxleyi carbon Proportion Gephyrocapsa oceanica carbon Proportion other coccolithophore carbon surface coccolithophore biomass (pg C ml-1) 0.0 0.2 0.4 0.6 0.8 1.0 1998 1999 2000 Aug/Sept Aug/Sept Aug/Sept JuneJuneJune Feb.Feb.  Fig. 3.3. Proportion of total coccolithophore carbon (POC) in the euphotic zone associated with two numerically dominant coccolithophore species along Line P for 5 stations and 8 cruises. The group designated as ‘other’ represents various unknown coccolithophore species of various sizes as well as Syracosphaera sp and Rhabdosphaera sp. Total surface coccolithophore biomass (pg C ml-1) for each station is represented by the solid line.   116   N o  D a t a 80 60 40 20 0 80 60 40 20 0 1500 1000 500 80 60 40 20 0 1500 1000 5001500 1000 500 D e p t h  ( m ) P26 P20 P16 P12 P4 P26 P20 P16 P12 P4 P26 P20 P16 P12 P4 Feb 98 Jun 98 Aug/Sep 98 Feb 99 Jun 99 Aug/Sep 99 Jun 00 Aug/Sep 00 19991998 2000   Fig. 3.4. Vertical contours of PIC production (mg C m-3 d-1) during 1998-2000. Dots represent the six sampling depths (100, 55, 30, 10, 3.5 and 1% of I0) for each of the 5 stations along Line P for 8 cruises. The dark dashed line corresponds to the mixed layer depth. No data for P04 in 1999 due to lost sample. Solid grey line indicates area below 1% I0 and therefore contains no measured data. See section 3.2.7 for contour plotting methods.   117 1999 PI C :P O C  14 C  P ro du ct io n 0.0 0.5 1.0 1.5 Feb June Aug/Sept 1998 0.0 0.5 1.0 1.5 2000 Station P04P12P16P20P26 0.0 0.5 1.0 1.5  Fig. 3.5. Particulate inorganic to particulate organic production (PIC:POC 14C production) ratio from the integrated values (see Table 3.1) for each cruise for 1998- 2000. Dashed lines represent a PIC:POC ratio of 1.   118 POC production (mg C m-3 d-1) 0.01 0.1 1 10 100 PI C  p ro du ct io n (m g C  m -3  d -1 ) 0.01 0.1 1 10 100 1998 1999 2000 1:1  Fig. 3.6. POC vs. PIC production (mg C m-3 d-1) for all stations for all three years. Line represents the 1:1 ratio. Although for most samples, PIC production was of the order of ~10% of POC production, some samples in 1998 and 2000 showed PIC production rates greater than POC rates. All values for 1999 were well below the 1:1 relationship.   119 Surface nitrate (μM) 0 2 4 6 8 10 12 14 16 1 2 3 4 5 6 7 HNLC stations (n=16) near shelf stations (n=16) all stations (n=40) Surface DFe (nM) 0.0 0.5 1.0 1.5 2.0 1 2 3 4 5 6 7 HNLC stations near shelf stations P16 Average mixed layer irradiance ( µmol photons m-2 d-1) 0 10 20 30 40 50 lo g co cc ol ith op ho re s (c el ls  l- 1 ) 1 2 3 4 5 6 7 B A C  Fig. 3.7. Linear regressions of the log of the surface coccolithophore abundance and (A) surface dissolved Fe (DFe), (B) average mixed layer irradiance and (C) surface nitrate for all cruises (1998-2000). Filled circles represent HNLC stations (P20 and P26). Empty triangles are for the shelf stations (P04 and P12) and grey filled inverted triangles are for P16. Collectively, they represent all stations sampled. The dashed lines represent the regression of near-shelf stations. 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Wong, C.S., Whitney, F.A., Iseki, K., Page, J.S., Zeng, J., 1995. Analysis of trends in primary productivity and chlorophyll a over two decades at Ocean Station P (50°N 145°W) in the subarctic northeast Pacific Ocean. Canadian Journal Fisheries Aquatic Sciences 121, 107-117. Wong, C.S., Whitney, F.A., Crawford, D.W., Iseki, K., Matear, R.J., Johnson, W.K., Page, J.S., 1999. Seasonal and interannual variability in particle fluxes of carbon, nitrogen and silicon from time series of sediment traps at Ocean Station P, 1982-   128 1993: relationship to changes in subarctic primary productivity. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2735-2760. Wong, C.S., Crawford, D.W., 2002. Flux of particulate inorganic carbon to the deep subarctic Pacific correlates with El Niño. Deep Sea Research Part II: Topical Studies in Oceanography 49 (24-25), 5705-5715. Wong, C.S., Waser, N.A.D., Nojiri, Y., Whitney, F.A., Page, J.S., Zeng, J., 2002a. Seasonal cycles of nutrients and dissolved inorganic carbon at high and mid latitudes in the North Pacific Ocean during the Skaugran cruises: determination of new production and nutrient uptake ratios. Deep Sea Research Part II: Topical Studies in Oceanography 49 (24-25), 5317-5338. Wong, C.S., Waser, N.A.D., Whitney, F.A., Johnson, W.K., Page, J.S., 2002b. Time- series study of the biogeochemistry of the north east subarctic Pacific: reconciliation of the Corg/N remineralization and uptake ratios with the Redfield ratios. Deep Sea Research Part II: Topical Studies in Oceanography 49 (24-25), 5717-5738. Wong, C.S., Yu, Z., Waser, N.A.D., Whitney, F.A., Johnson, W.K., 2002c. Seasonal changes in the distribution of dissolved organic nitrogen in coastal and open- ocean waters in the North East Pacific: sources and sinks. Deep Sea Research Part II: Topical Studies in Oceanography 49 (24-25), 5759-5773. Wong, C.S., Wong, S.E., Peña, M.A., Levasseur, M., 2006. Climatic effect on DMS producers in the NE subarctic Pacific: ENSO on the upper ocean. Tellus B 58 (4), 319-326. Wormuth, J.H., 1981. Vertical distributions and diel migrations of Euthecosomata in the northwest Sargasso Sea. Deep-Sea Research Part a-Oceanographic Research Papers 28 (12), 1493-1515.   129 Chapter 4 : Siliceous Phytoplankton Abundance and Silica Production Rates Along Line P in the NE Pacific 1998-20001 4.1 Introduction Ocean station Papa (OSP/P26) in the NE subarctic Pacific is the location of one of the longest oceanographic time series starting over 50 years ago with the Canadian weathership program (1956-1982). The time series has continued by the Institute of Ocean  Studies (IOS – Sydney, British Columbia) Line P World Ocean Circulation Experiment (WOCE), the Subarctic Pacific Ecosystem Research (SUPER) (Miller, 1993), the VERTical Exchange (VERTEX) program (Martin et al., 1989) and the Canadian Joint Global Ocean Flux Study (CJGOFS)(Boyd et al., 1999b). The Line P monitoring program continued after the CJGOFS program ended in 1997. As a result is that there has been almost continuous data collection at OSP (P26 this study) for more than half a century and more recently along Line P. (Peña and Bograd, 2007). As a result of this long time series, there is now a comprehensive collection of the temporal patterns of nutrients, chlorophyll a (chl a) and POC production (primary productivity) at OSP and more recently along Line P. However, data on the distribution and abundance of phytoplankton species, specifically diatoms, has been restricted mostly to OSP (Booth et al., 1982; Takahashi, 1986, 1987; Booth, 1988; Mochizuki et al., 2002; Marchetti et al., 2006c) with only one previous phytoplankton study of major stations along Line P (Varela, 1997; Varela and Harrison, 1999b) OSP is characterized in surface waters by relatively low and constant phytoplankton biomass (chlorophyll a concentrations), with seasonal variation  in POC production), dominance of small phytoplankton cells, high macronutrient concentrations year-round, and Fe limitation of phytoplankton growth (Harrison et al., 2004; Peña and Varela, 2007). As a result of this Fe limitation, surface NO3- and Si(OH)4 concentrations are not regularly depleted in the summer, but decrease to only about half of their late winter values (Whitney and Freeland, 1999). Whitney et al. (1998), characterized Line P into coastal waters where productivity is stimulated during the summer by periods of upwelling, a transition region which is not influenced by coastal  1 A version of this chapter has been/will be submitted for publication. Lipsen, M., Crawford, D., Whitney, F. and Harrison P.J. Siliceous Phytoplankton Abundance and Silica Production Rates Along Line P in the NE Pacific 1998- 2000.  130 upwelling but experiences NO3- depletion in summer, and the HNLC (high-nitrate, low- chlorophyll) region. Fe stress was measured along Line P by quantifying the biochemical marker flavodoxin in May and September 1995 (La Roche et al., 1996). They found that phytoplankton cells were not Fe stressed at stations P04 to P16, but were Fe stressed at P20 and P26. Stations on the eastern part of Line P (P04-P16) were characterized by sporadic spring and summer blooms (primary production >3 g C m-2 d-1), whereas P20 and P26 exhibited low seasonality in biomass and primary production (Boyd and Harrison, 1999). Additionally, Varela and Harrison (1999b) reported nitrogen uptake measurements along Line P that indicated phytoplankton growth utilized primarily regenerated nitrogen (ƒ-ratio range 0.05 – 0.37) rather than NO3- during all seasons along Line P. The NE subarctic Pacific is generally NO3- and Si(OH)4 replete as a result of Fe limitation (Martin et al., 1989; Boyd et al., 1996; Whitney et al., 2005a) and P20 and P26 are typical of this HNLC region. There have been sporadic incidences of Si(OH)4 depletion at P26. During three years in the 1970’s (1972, 1976, and 1979), Si(OH)4 declined to 1 µM, while NO3- remained >3 µM (Wong and Matear, 1999). More recently, anomalously low Si(OH)4 occurred in coastal and oceanic regions of Line P in 1998 and 1999 as a result of the strong El Niño that occurred in 1997-1998 (Whitney and Welch, 2002; Whitney et al., 2005b). Whitney and Welch (2002) went on to postulate that the Si(OH)4/ NO3- ratio decreased as a result of a dramatic change in winter mixing and summer upwelling during that period. The change in the supply of nutrients (Si(OH)4, NO3-, and Fe) will directly affect the diatom community structure as well as their production and biomass. Any change in the diatom community will also affect Si drawdown and export from the upper ocean to the sediments. Wong et al. (2002c) and Whitney et al. (2005a) have suggested that low silicate supply in the eastern subarctic Pacific may actually be  partially responsible for the HNLC character in the Gulf of Alaska (GOA) in combination with low Fe concentrations. Low Fe concentrations increase the Si(OH)4:NO3- uptake ratio (Hutchins and Bruland, 1998; Takeda, 1998) and result in heavier diatoms. Depending on the availability of Fe, the Si(OH)4:NO3- uptake ratios could range from 1.5 to 2.8 in the HNLC region of the GOA, increasing the importance of diatoms in nutrient drawdown. The main goal of this chapter, covering the three years between 1998 and 2000 and three seasons (February, June and August/September) along Line P, was to examine the contribution of diatoms to community phytoplankton primary production and biomass (chl a and POC) from  131 the near-shelf stations (P04 – P12) to the HNLC region (P20 – P26). This will be further augmented by examining the relationship between macronutrients (nitrate, silicic acid), dissolved iron (DFe), biogenic silica (bSi), and silica production rates (ρSi). By measuring these parameters and comparing them to historic rates of nutrient uptake and biogenic export below the mixed layer during years of an El Niño (1998), La Niña (1999) and 2000, there is an increased understanding of the contribution that diatoms make to primary production in the NE subarctic Pacific. 4.2 Methods 4.2.1 Sample collection Sampling was conducted along Line P, a 1500 km transect maintained by the Institute of Ocean Sciences, Sidney BC (see Chapter 2 and 3 for locations and details). Samples were collected at the 5 major stations along the transect (from E to W; P04, P12, P16, P20 and P26). P26 is the long term monitoring station also known as Ocean Station Papa (OSP). During this three year study (1998-2000), cruises were conducted in February (Feb.), June (June) and August / September (Aug./Sept.) in 1998 and 1999 and only in June and Aug./Sept. 2000 (Table 4.1). There was no cruise in Feb. 2000. Seawater was carefully drawn at or near dawn (local time) from 10 L, 24 h acid-soaked, seawater rinsed GO-FLO® bottles taken from six light depths (100, 55, 30, 10, 5, 1% I0). Samples for POC production (primary productivity), chlorophyll a and particulate organic carbon (POC) were taken from all six light depths. Biogenic silica (bSi), silica production (ρSi), cell enumeration was taken from 4 light depths (100, 55, 10 and 1% I0).  See Chapters 2 and 3 for more details. GO-FLO®s were always sampled first for phytoplankton enumeration, followed by nutrients, chlorophyll, POC production (see Chapters 2 and 3 for details) and silica production (ρSi). 4.2.2 Light and nutrients Nutrients (nitrate and silicic acid), for the same cruises, stations and depths as our samples, were obtained from the Line P oceanographic data web site (http://www-sci.pac.dfo- mpo.gc.ca/osap/data/linep/linepselectdata_e.htm). Dissolved iron (<0.2 µm) concentrations were obtained from Nishioka et al. (2001) and C. S. Wong (pers. comm.). The mixed layer depth  132 (MLD) was derived according to the procedure used by Freeland et al. (1997). Incident irradiance was recorded and averaged at 10 min intervals with a Li-COR® light meter with a 4π quantum sensor. 4.2.3 Particulate organic carbon (POC) Samples for POC (particulate organic carbon) were collected from each light depth into 4 L collapsible LDPE cubitainers that had been acid-soaked with 10% HCl > 24 h and DDW- rinsed followed by a > 24 h seawater rinse for each light depth. They were filtered through pre- combusted (500oC) 0.7 µm Whatman® GF/F filters using a vacuum pressure (>100 mm Hg) and stored frozen (-20oC). POC samples were analyzed using a Carlo Erba Model NA-1500 Elemental Analyzer following Verado et al. (1990). 4.2.4 Chlorophyll a and POC production Replicate (2 per depth) size-fractionated chlorophyll a samples and particulate organic carbon (POC) ‘primary’ production (300 ml) were filtered serially through 20, 5, and 0.2 µm polycarbonate filters (47 mm diameter). The 20 and 5 µm size fraction were filtered under gravity, while the 0.2 µm size fraction was filtered using < 100 mm Hg vacuum differential (Joint et al., 1992). Samples collected on the 20 µm filters will be referred to as the > 20 µm size fraction. Total (tot) chl a or POC production is the sum of all 3 size fractions (0.2-5.0, 5.0-20 and > 20 µm). See Chapters 2 and 3 for detailed methods on collection and processing of size- fractionated chlorophyll a and POC production. All productivity samples were split into inorganic (PIC) and organic (POC) production (Chapter 3). 4.2.5 Siliceous phytoplankton enumeration and identification  Siliceous phytoplankton (diatoms and silicoflagellates) samples for enumeration (1 per depth for each of 4 light depths) were drawn using dedicated clean silicon tubing into 250 ml glass bottles. Bottles were immediately placed in a light-tight box and stored in a cold room (4°C) prior to processing. Within 4 h of sampling, diatom enumeration bottles were preserved following Booth (1988; 1993)  with 2% hexamethylenetetramine-buffered formalin to be counted later using an inverted microscope (Utermöhl, 1931). On shore, subsamples (100 ml) were settled for 48 h and a minimum of 400 total phytoplankton (all classes) cells per sample  133 were counted at 400x magnification. Counting continued until a minimum of 100 diatom cells were counted or the whole sample was counted, whichever came first. Average cell abundances (Table 4.4) were calculated within the euphotic zone (100, 55, 30, 10, 3.5 and 1% I0) and presented as depth-weighted averages which were calculated by dividing the value of trapezoidal integration of the euphotic zone by the depth of the euphotic zone for each station (Crosbie and Furnas, 2001). This same technique was used for all depth-weighted values. 4.2.6 Siliceous phytoplankton carbon quota calculations For this study, only siliceous phytoplankton (diatoms and silicoflagellates) were enumerated and converted to carbon. See Chapter 3 for coccolithophore abundances and carbon. For each diatom species, volumes of each cell were determined using a combination of simple shapes (e.g. cones, cylinders, boxes, etc.) or a combination following Hillebrand et al. (1999) and Sun and Liu (2003). Organic carbon per cell was calculated according to Menden-Deuer and Lessard (2000) following the assumption that large diatoms possess proportionally less carbon due to the size of their vacuole. Silicoflagellate carbon was also estimated following Menden- Deuer and Lessard (2000). 4.2.7 Biogenic silica Biogenic silica (bSi) samples (500 ml) were analyzed following Paasche (1980) with modifications described in Brzezinski and Nelson (1995) . Samples (500 ml) were filtered onto 47 mm, 0.6 µm porosity polycarbonate filters, then dried and digested in 0.2 N NaOH, and neutralized with HCl. Dissolved Si(OH)4 was analyzed following Barwell-Clarke and Whitney (1996). 4.2.8 Silica production rates (32Si) Silica production rates (ρSi) were measured following the 32Si method of Brzezinski and Phillips (1997). Samples were collected from the same GO-FLO® used for phytoplankton cell enumeration into 300 ml polycarbonate bottles and immediately spiked with 0.045 µCi (1.7 kBq) of 32Si(OH)4 to give a total activity of ~1.5 x 10-4 µCi ml-1 (5.5 x 10-3 kBq ml-1) in the 300 ml sample. The addition of the high specific activity tracer increased the ambient dissolved Si(OH)4 by less than 0.05 µM (~0.4% dissolved Si(OH)4). Samples were incubated in Plexiglas®  134 incubators maintained at ambient sea surface temperature (± 2oC) using a seawater flow-through system. Bottles were placed in plastic bags wrapped in neutral density screening that corresponded to the light depth from which the sample was taken. After a 24 h incubation, all ρSi samples were filtered using <15 cm Hg vacuum onto 25 mm, 0.6 µm polycarbonate filters. Each sample was rinsed three times with 0.2 µm filtered seawater to eliminate excess tracer and placed in new 20 ml plastic scintillation vials, air dried for 24 h and capped for storage. Samples were stored for > 6 months to allow for secular equilibrium to occur between 32Si and the daughter isotope, 32P. Once equilibrium had been established, 1 ml of 2.5 M hydrofluoric acid was added to dissolve the biogenic silica. Twenty- four hours after the HF addition, 10 ml scintillation cocktail (Scintisafe®) was added to each sample and analyzed one month later with a Beckman LS6000 SC scintillation counter. 32Si uptake rates were determined using the logarithmic model of Brzezinski and Phillips (1997). Dissolution rates were not measured and therefore the ρSi values should be considered a measure of gross silica production rates (Brzezinski et al., 2003b). Silica production measures the silica uptake of autotrophic diatoms and silicoflagellates as well as radiolarians and choanoflagellates. Choanoflagellates have been found in the subarctic Pacific including OSP (Booth et al., 1980; Booth, 1990). Due to the small size of our incubation bottles, larger grazers were minimized from our experiments. Therefore our ρSi rates may be an overestimation. However, large zooplankton grazing on diatoms along Line P has been shown to be minimal compared to microzooplankton grazing in previous studies (Goldblatt et al., 1999). 4.2.9 Statistical analysis All variables were tested for normality using the Kolmogrov-Smirnov test and visual inspection of normal probability plots (Systat 11).  As the data were not normal, the non- parametric equivalent of the t-test, the Mann-Whitney test (Systat 11) to test for significant spatial and temporal differences, was used. Alpha was set at 0.05. 4.2.10 Contour plotting Contour plots (Fig. 4.2) were created using Surfer 7.0 (Golden Software) following the kriging interpolation technique utilizing the linear model with a slope of one. Disparity in the values of the x-axis (1500 km) and the y-axis (85 m) were addressed using the anisotropy function with a  135 ratio of 0.5 and a zero angle. Although contour plots should always be viewed at with caution, our approach does yield a sufficiently conservative value that allows realistic analysis near the sampling points and a cautious analysis of trends over the whole area. Distance along Line P (x-axis) starts with historical station P1 as the origin and follows the Line W-NW to P26 (1420 km from P1). See Whitney and Freeland (1999) for a full listing of stations, locations, distances along Line P and distances from shore. 4.3 Results 4.3.1 Physical conditions The data collected from Line P can be more easily described and compared by dividing this transect into three oceanic regimes; near-shelf, transition and HNLC (Whitney et al., 1998; Boyd and Harrison, 1999). Stations P04 and P12 are closer to shore with more of a shelf influence that results in lower (Table 4.1) macronutrient concentrations in summer (Whitney et al., 1998; Whitney and Freeland, 1999). Stations P20 and P26 (OSP) are located in HNLC waters (Boyd and Harrison, 1999) and are characterized by higher summer macronutrient values and lower concentrations of DFe (see Chapter 2). The characteristics of the transition station (P16) vary between the near-shelf stations and HNLC waters.  Conditions along Line P varied temporally and spatially during the years 1998 to 2000. Surface temperatures (Chapter 3) were generally warmer during the 1998 El Niño period for all three cruises when compared to the 1999 La Niña. This corresponded to a shallower euphotic zone (Zeu in Table 4.1) and MLD in 1998 compared to 1999 (Whitney and Welch, 2002). During 2000, surface temperatures along Line P were similar to spring 1999. Zeu was the deepest for both June and Aug./Sept. compared to 1998 and 1999 during similar times of the year. For all cruises, P20 and P26 generally had the deepest Zeu and usually corresponded to lower particulate matter in the water column (Chapter 2). 4.3.2 Silicic acid and nitrate concentrations Surface nitrate and silicic acid concentrations generally increased from east to west along Line P for all seasons and years. Nitrate depletion usually occurred at P04 in the spring and  136 propagated westward by Aug./Sept. (Table 4.1). Silicic acid concentrations were generally higher than nitrate at all stations and during all seasons, but were episodically lower than nitrate. Surface nitrate and silicic acid concentrations were lower in 1998 when compared to 1999 for all cruises (Tables Table 4.1) and corresponded to warmer temperatures (Whitney and Welch, 2002). During 1998, surface depletion of nitrate occurred as far west as P12 in June and P16 in Aug/Sept. Surface nitrate depletion was much closer to the shelf in 1999 and 2000, and only occurred at P04. Interestingly, surface nitrate (5.1 µM) and silicic acid (2.0 µM) at P26 during Aug/Sept 2000 were the lowest for that station for all eight cruises. Potentially growth limiting concentrations of silicic acid were also observed at P12 and P16 in June and Aug/Sept 1998, respectively. 4.3.3 Particulate Si (bSi) Depth-weighted average and integrated bSi (Table 4.1 and 4.2) tended to be lower at the near-shelf (P04 and P12) and the transition station (P16) and highest at the HNLC stations (P20 and P26) with high seasonal variation at all five stations. Values at discrete depths (Fig. 4.1) ranged from a minimum of 0.2 µmol L-1 (80 m during June 2000 at P20) to a maximum of 1.58 µmol L-1 (24 m during June 1998 at P20). February values of integrated bSi (Table 4.2) were highest at the western most stations (P16-P26). During June, HNLC stations were significantly higher (α<0.05) than the other stations and were more than double the average integrated value for P04 and P16. Conversely, average integrated bSi values per station for Aug./Sept. were not significantly different from each other even though P16 was less than half (8.9 mmol m-2) of the maximum found at P12 (22.2 mmol m-2). Seasonal and interannual variations were also found in bSi along Line P. The maximum average integrated values of bSi occurred in June (28.4 mmol m-2) and were nearly double the concentrations found in Feb. (16.1 mmol m-2) and Aug./Sept. (14.7 mmol m-2). However due to the large variation occurring between years, the differences were not significant (>0.05). Typically, maximum bSi concentrations were found in June. In 1998, June had the highest weighted averages (Table 4.1) for P04 (0.80 µmol L-1), P20 and P26 (0.90 µmol L-1). June 1999  137 was similar with maximum values occurring at P04 (0.82 µmol L-1) and P26 (0.74 µmol L-1). June 2000 values were lower with a Line P minimum found at P04 (0.13 µmol L-1) and a maximum of only 0.47 µmol L-1 at P26. Interestingly, the highest average weighted value found in 2000 was 0.57 µmol L-1 at P12 in Aug./Sept. In all cases, maximum bSi values (Fig. 4.1) were found at or above the MLD. 4.3.4 Large size fraction (>20 µm) biomass and production The > 20 µm size fraction for chl a and POC production contributed the least of the three size fractions, only 14% of tot chl a and 16% of tot POC production (Table 4.3) for all stations and seasons. This is in contrast to the smallest size fraction (0.2-5.0 µm) that made up 64 and 61% of the tot chl a and tot POC production respectively (Chapter 2). Maximum values for integrated > 20 µm chl a (Table 4.1 and 4.2) were typically found at P12 (beyond the shelf) and P26 (HNLC). Minimum values were found at P04 (near-shelf) and P16 (transitional). Spatial and temporal variation was high and discrete chl samples (Fig. 4.2) ranged from a minimum of undetectable (25 and 60 m in Aug./Sept. 1998 at P20) to a maximum of 0.3 mg chl a m-3 (20 m in Aug./Sept. 2000 at P12). Average (all seasons and stations) > 20 µm POC production (Table 4.1 and 4.2) was typically greatest at the near-shelf stations (P04 and P12). Minimum values were found at P16 (transition) and P26 (HNLC). Discrete > 20 µm POC production values (Fig. 4.3) ranged from undetectable to a maximum of 10.8 mg C m-3 d-1 (2 m in Aug./Sept. 2000 at P12) and coincided with the > 20 chl a maximum (Fig. 4.2) and a high bSi concentration (Fig. 4.1). In February, the average integrated > 20 µm size fraction of chl a and POC production (Table 4.2) were maximum at P16 (transition) and P20 (HNLC). Conversely in June, maximum vales for > 20 µm chl a occurred at the HNLC stations (P20 and P26), while the > 20 µm POC production occurred at P04 (near-shelf) and P20 (HNLC). During Aug./Sept., maximum values for both the large size fraction chl a and POC production occurred at P12 (near-shelf) with an average more than twice the other stations for the  > 20 µm chl a values. The high average integrated value for P12 in Aug./Sept. can be attributed to abnormally high diatom activity found only in 2000 (Tables 4.1 and 4.2 and Figs. 4.3 and 4.3). In 1998, June had the highest integrated values (Table 4.1) for P20 (6.8 mg chl a m-2 and 87 mg C m-2 d-1) for the > 20 µm size fraction. During 1999, there was more variability between  138 the large size fraction chl a and POC production with a maximum for chl in June at P04 (4.0 mg chl a m-2) and a maximum for POC production at P04 in Aug./Sept. (68 mg C m-2 d-1). Interestingly, the highest integrated value found in 2000 for the > 20 µm size fraction was 11.7 mg chl a m-2 and 320 mg C m-2 d-1 at P12 in Aug./Sept. In both cases, the high value found at P12 in Aug./Sept. of 2000 was a minimum of 4 times higher than the next highest values for that cruise. As noted previously, these high values also correspond to a high bSi concentration. For more detail on the contribution of the three size classes to chlorophyll a and POC production, see Chapter 2. 4.3.5 Siliceous phytoplankton abundance and carbon Average maximum values of diatom abundance (Table 4.4) occurred at P12 (21.7 cells ml-1) followed by P26 (8.2 cells ml-1). The minimum average abundance occurred at P16 (4.0 cells ml-1). Diatom carbon followed a similar pattern with maximum average values for all cruises occurring at P12 (485 mg m-2). Discrete (values at individual depths) total diatom carbon (Fig. 4.4) ranged from undetectable to a maximum of 101 mg m-2 (2 m in June 1998 at P12) and coincided with a high percentage contribution of diatom carbon (31%; Table 4.3) to total POC. The average cell abundance and cell carbon of silicoflagellates along Line P was minimal, and tended to be found in larger numbers closer to the shelf and never contributed more than 8% of the total siliceous phytoplankton abundance (Table 4.4). During the 1998 El Niño, diatom carbon along the whole of Line P was significantly (p<0.05) higher than during the 1999 La Niña. Specifically, winter and June of 1998 contributed significantly larger diatom carbon concentrations when compared to 1999. The largest significant differences occurred at the edge stations (P04 and P26) in February and the bordering stations P12 (near-shelf) and P16 (transition) between the two years. In Feb., the highest average diatom cell abundance (Table 4.2) and average integrated diatom carbon were found at P12 (7.8 cells ml-1 and 323 mg m-2). June had the highest values of diatom abundances and carbon with the highest average diatom abundance values occurring at P26 (16.6 cells ml-1). Diatom carbon, however, was highest at P20 (871 mg m-2). Although Aug./Sept. values had the highest average cell abundances (11.5 cells ml-1) along the whole of Line P compared to Feb. (5.1 cells ml-1) and June (8.0 cells ml-1), average integrated total diatom  139 carbon was > 3 times lower (178 mg m-2) than the Line P average for June (571 mg m-2). However, similar to Feb., Aug./Sept. average diatom cell abundance (42.7 cells ml-1) and diatom carbon (472 mg m-2) was maximum at P12. Although the near-shelf stations (P04 and P12) had the highest diatom cell abundances, they were not significantly different (p>0.05) than the HNLC stations (P20 and P26). Near-shelf diatom abundances were only significantly higher (p>0.05) during Aug./Sept. and this can mainly be attributed to the diatom production event that occurred at P12 in Aug./Sept. 2000. Average diatom carbon was higher at the HNLC stations (not significant) compared to the near- shelf. However, total diatom carbon was highest at the near-shelf stations in Aug./Sept., once again due to the diatom production event at P12 in Aug./Sept. 2000. 4.3.6 Diatom species Siliceous phytoplankton taxonomic analysis was completed at all the major stations and collected from the four light depths (100, 55, 10, 1% I0).  A list of all the major diatom species split into centric and pennates found during 1998-2000 are listed in Table 4.5 as well as the general location (near-shelf, transition and HNLC) of the individual species. Additionally species information including coccolithophore enumeration and carbon contribution can be found in Chapter 3. Although Line P tends to be dominated numerically by nanoflagellates (Varela and Harrison, 1999b), diatoms were found at every station during each cruise and their contribution to total particulate organic carbon (POC) ranged from <1 to 78% (2 m in June 1998 at P12). The diatom assemblage frequently composed of Corethron hystrix, Coscinodiscus spp., Proboscia alata, Thalassiosira rotula and Pseudo-nitzschia spp.  Centric diatoms dominated the POC pool (Table 4.3) compared to pennate diatom carbon comprising an average of 6% of total POC compared to < 1% for the pennates. Interestingly, most siliceous phytoplankton that were counted at multiple stations and cruises were found in all three regions (near-shelf, transition and HNLC) suggesting that the more numerous species were generally ubiquitous along the whole transect throughout this study.  An interesting exception was the silicoflagellate Dictyocha spp. which was never found at P16 (transition). Although centric diatom abundances were always found in greater numbers compared to pennates (Table 4.4) along Line P (average = 74% of total  140 diatom carbon), pennate diatom cell abundances significantly increased from June to Aug./Sept., especially at the transition and HNLC stations for all years. 4.3.7 Silica production rates Silica production rates in the euphotic zone (Fig. 4.5) for June and Aug./Sept. 1999 and 2000 were very variable. Between June 1999 and Aug./Sept. 2000, ρSi ranged from < 0.01 to 0.14 mmol L-1 d-1 at P12 in Aug./Sept. 2000. Integrated rates of ρSi (Table 4.1) ranged from 0.2 to 4.7 mmol m-2 d-1 with a mean of 1.1 mmol m-2 d-1. Over the four cruises where ρSi rates were measured, maximum integrated ρSi for each cruise occurred at a different station (Table 4.1) indicating that no single station maintains higher ρSi in the spring/summer months of this study. In 1999, ρSi dominated in the HNLC region at P20 in June (2.6 mmol Si m-2 d-1) and P26 in Aug./Sept 1999 (2.7 mmol Si m-2 d-1). In 2000, the near-shelf stations had the highest rates with P04 in June (1.3 mmol Si m-2) and P12 in Aug./Sept. with the highest value for all cruises (4.7 mmol Si m-2 d-1) (Table 4.1). Even though the value at P12 in Aug./Sept 2000 yielded the highest rate, overall ρSi in 1999 was significantly higher in 1999 than 2000. The average integrated Line P ρSi for both June cruises (1999-2000) was similar (1.1 m-2 d-1) to Aug./Sept. (Table 4.2). HNLC stations were generally higher in June and switched to the near-shelf stations (specifically P12) in Aug./Sept. Although the majority of high ρSi rates corresponded well with biogenic silica maxima as well as > 20 µm chl a  biomass, there were some instances of high ρSi rates without a corresponding increase in diatom biomass (measured as >20 mm Chl a and bSi). 4.4 Discussion 4.4.1 Siliceous biomass and community structure The major component of the chl a biomass consists of the 0.2-5 µm autotrophic flagellates which on average made up 64% of the total chl a along Line P during this study (Chapter 2). This agrees with earlier findings from the CJGOFS during the 1990’s by Boyd and Harrison (1999). The 5-20 µm fraction was typically the next largest, making up 22% of the total chl a and was generally composed of dinoflagellates and some small diatoms. The >20 µm size fraction was primarily composed of diatoms, and contributed on average only 14% of the total  141 chl a, but the proportion reached as high as 57% (24 m in June 1998 at P20), emphasizing the sporadic importance of the diatoms to the total phytoplankton biomass. Growth of the larger phytoplankton species, specifically diatoms, is thought to be controlled by persistent low concentration of DFe in the HNLC region of Line P (Martin and Fitzwater, 1988; Martin and Gordon, 1988b; Boyd et al., 1996; Boyd et al., 2004) and a combination of Fe, NO3-, Si(OH)4 and light at the near-shelf stations (Boyd and Harrison, 1999). Although it has been suggested that grazing may also help control the large phytoplankton species such as diatoms (Heinrich, 1962; Goldblatt et al., 1999), investigations of mesozooplankton grazing along Line P suggest that the copepods do not graze much on the larger phytoplankton (Boyd et al., 1999a; Goldblatt et al., 1999; Vezina and Savenkoff, 1999). Silicoflagellates were ubiquitous for all years and cruises and were found at all stations except P16.  They averaged about 3% (Table 4.3) of the total siliceous phytoplankton carbon and rarely made up >15% of the total siliceous phytoplankton (Feb. 1998, at P04 and Aug./Sept. 1998, at P12). Consequently, compared to diatoms, silicoflagellates represented a small fraction of the total siliceous component of the phytoplankton community. Takahashi (1997) found significant seasonal and yearly variation in silicoflagellate flux into sediment traps at P26, with peak fluxes occurring in the late fall and winter. Our data showed similar trends for silicoflagellates with maximum cell abundance occurring in Feb. (mean 3.3 cells ml-1) and Aug./Sept. (2.3 cells ml-1) (data not shown). Significant differences in silicoflagellate abundances occurred between years with maximum cells abundance measured in June and Aug./Sept. 2000 (3.3 cells ml-1) followed by 1998 (1.7 cells ml-1). Spatially, they tended to be found in much higher abundances at the near-shelf stations followed by P26. At P20 cell abundances and silicoflagellate carbon were very low (Table 4.4). The contribution of silicoflagellate silica production compared to diatoms was not determined. However, silicoflagellate cell numbers were low enough that their contribution to overall silica production would be minimal compared to diatoms. Other protozoan siliceous plankton are also known to be present in the NE subarctic Pacific. Radiolarians (Takahashi, 1997) and choanoflagellates (Booth et al., 1980; Booth, 1990) have previously been enumerated at P26, but were seen infrequently in this study (unpubl data). However, due to the significant difference in siliceous phytoplankton abundance and silica production (diatoms and silicoflagellates) compared with siliceous zooplankton (radiolarians and  142 choanoflagellates), the siliceous phytoplankton proportion of bSi flux should be large. This was previously demonstrated by the 3 orders of magnitude difference between diatom and radiolarian flux at P26 (Takahashi, 1997). Silicoflagellate flux was 2 orders of magnitude smaller than diatoms during the same study. 4.4.2 Variations in diatom biomass and carbon production Although total chl a biomass remained relatively constant seasonally and spatially along Line P, there were distinct variations in >20 µm chl a, >20 um POC production, bSi and diatom carbon. As expected, there were significant correlations between centric and pennate carbon and the >20 chl a size fraction as well as bSi. This occurred when all stations were compared, not just the near-shelf station or the HNLC stations (Table 4.6, 4.7 and 4.8), indicating that >20 chl a size fraction and bSi are good proxies for measuring diatom biomass along Line P. Interestingly, only pennate carbon was significantly correlated to >20 µm POC production when you compare all the stations, or just the near-shelf stations (Table 4.6 and 4.7) but not the HNLC stations (Table 4.8). This may be due to the inclusion of larger phytoplankton cells (e.g. dinoflagellates) other than diatoms in the Line P samples. Interestingly, there was no significant correlation between any of the diatom proxies (>20 chl a, >20 POC production, bSi, diatom carbon and ρSi) with nutrient levels (Si(OH)4, NO3- and Fe) under any circumstances probably because of the dominance of small non-diatom cells in the community. There was high diatom abundances at P26 in June 1998 (32.5 cells ml-1). Diatom abundances at P12 in Aug./Sept. 2000 (127 cells ml-1) were the highest and  approached the diatom abundances achieved at the end of 10 days of the SERIES Fe enrichment experiment (Marchetti et al., 2006c) and were concurrent with a very high proportion of  >20 chl a to total chl a (43%) and >20 um POC production to total production (48%) (Table 4.3) and the highest abundance of pennates seen in the study. Interestingly, in all cases where diatom carbon was >500 mg m-3 (Table 4.4), centric species made up the majority of the carbon. Average seasonal bSi concentrations (Table 4.2) were highest in June for all stations except P16. This agrees with Wong et al. (1999) who showed maximum monthly average bSi flux to occur between May and July in the 1000 m sediment trap at P26 (averaged data from 1982-1993). The high values for June also coincided with elevated integrated diatom carbon >20 chl a, and >20 POC production (Table 4.2).  143 4.4.3 Diatom biomass and production: El Niño, La Niña and 2000 Nutrient supply (Si(OH)4 and NO3-) along Line P was low in 1998 compared to 1999 due to the effects of the strong El Niño. Shallower mixed layer depths and increased stratification in 1998 reduced the nutrient supply from below which resulted in the depleted nutrients in summer at the near shore stations (Whitney and Welch, 2002).  A shallow mixed layer will also increase the average MLD irradiance and lead to an increase in surface production which also decreases nutrient concentrations. Conversely, during the 1999 La Niña, mixed layers were deeper and stratification was reduced, resulting in increased nutrients to the mixed layer. Year 2000 was similar to 1999 with higher nutrient levels in the mixed layer and a deeper mixed layer depth. Total averaged (June and Aug./Sept.) integrated chl a and POC production in the euphotic zone (Table 4.1) was highest in 2000 (21 mg chl a m-2 and 531 mg C m-2). Tot chl a was lowest in 1998 (14 mg chl a m-2), but total POC production was slightly lower in 1999 (298 mg C m-2) than 1998 (338 mg C m-2). Interestingly, while the >20 µm averaged integrated POC production was highest in 2000 (97 mg C m-2) followed by 1998, and then 1999 (44 and 35 mg C m-2), averaged integrated >20 µm chl a was highest in 1998 (2.9 mg chl a m-2) followed by 1999 and 2000 (2.2 and 1.7 mg chl a m-2). Only the >20 µm averaged integrated POC production value in 2000 was significantly different than 1999. Whitney and Welch (2002) also demonstrated lower total chl a values in 1999 and postulated that POC production would also be lower as a result of the lower nutrient availability. Even though the integrated tot chl a was lower in 1998 compared to 1999, total and >20 µm integrated chl a and integrated POC production were actually higher in 1998. This was accompanied by significantly higher diatom average cell abundance (9.3 cells ml-1) and average integrated diatom carbon (636 mg C m-2) in 1998 (Table 4.1) compared to 1999 (2.9 cells ml-1 and 162 mg C m-2). In 2000, diatom cell abundance was highest and diatom carbon was intermediate between 1998 and 2000 (17.1 cells ml-1 and 324 mg C m-2). Significant differences in diatom carbon occurred primarily in Feb. and June 1998 compared to 1999 and especially at P12 and P16. While Whitney and Welch (2002) found phytoplankton biomass to be low in 1998, they only refer to total phytoplankton biomass. Additionally, the conditions they described applies predominantly to the near shore and transition stations, and not to the HNLC waters of P26. During the 1998 El Niño, conditions favored an increase in diatom biomass as well as a noticeable spike in bSi flux in the 1000 m sediment trap in 1998 compared to 1999, providing  144 evidence of an increase in diatom production in the spring and early summer (C.S. Wong, unpub. data). This agrees with the high diatom flux observed during the strong 1982-1983 El Niño (Takahashi, 1987), when conditions were similar to the 1998 El Niño in this study. There was much lower diatom production in 1984 (Takahashi 1987), similar to our results for the 1999 La Niña which followed the 1998 El Niño. One of the possible explanations for the higher diatom biomass in June 1998 may be aeolian Fe input from a dust storm (Fig. 4.8) that crossed the Pacific in May (Lam et al., 2006). An anomalous input of Fe would favor an increase in diatom production in the Fe-limited waters of the HNLC region of Line P and would stimulate diatom growth specifically in areas where NO3- and Si(OH)4 may still be available (June vs. Aug./Sept.) and Fe may be low due to spring production at the transitional areas of P16 and perhaps P12. This would result in higher diatom biomass and increased bSi export out of the mixed layer (Wong and Matear, 1999; Whitney et al., 2005a). Alternatively, Wong et al. (1998) found that increased production (using NO3- utilization as a proxy) correlated with the North Pacific Index (NPI) events as well as  increased irradiance.  Therefore, the increased irradiance and shallowing of the mixed layer that occurs during NPI and El Niño events could be driving increased productivity. 4.4.4 Diatom community structure Phytoplankton community studies in the NE subarctic Pacific (Parsons, 1972; Semina and Tarkhova, 1972; Booth et al., 1982; Taylor and Waters, 1982; Booth et al., 1993; Boyd et al., 1995a; Semina, 1997; Varela and Harrison, 1999b; Marchetti et al., 2006c) demonstrate that the community is dominated by small cells.   The diatom community structure found along Line P tended to be dominated by larger centric species in most cases (Table 4.4). There are no diatom taxonomic studies for stations along Line P. However, there are several studies that list either species found in the water column at OSP (P26) (Taylor and Waters, 1982; Clemons and Miller, 1984; Harrison et al., 1991; Booth et al., 1993; Marchetti et al., 2006c), or in sediment traps (Takahashi, 1986, 1987; Mochizuki et al., 2002). All studies suggest a clear presence of the larger centric diatoms at all times of the year. Although there was much seasonal and interannual variability in the diatom community structure in this study, common diatom species found at P26 were consistent with the species found in other studies over a 20 year period (Table 4.9).  145 4.4.5 Dissolved nitrate (NO3-) and silicate [Si(OH)4] utilization Mixed layer NO3- and Si(OH)4 varied seasonally and spatially along Line P. Maximum values tended to occur in the early spring due to strong storm mixing and low nutrient utilization (Whitney and Freeland, 1999; Peña and Varela, 2007). At P26, decadal averages showed maximum NO3- concentrations in March (~15.5 µM) followed by a draw-down through the summer until mid-September (~9 µM). Si(OH)4, on the other hand,  reached a maximum in February-March (~23 µM) and remained high until late May, when a much quicker draw-down occurred, resulting in a minimum (~12.5) in late July (Whitney and Freeland, 1999). Near-shelf stations can become depleted in NO3-  in the late spring through summer. Interestingly, NO3- depletion was so pervasive in 1998 that it occurred as far out as P16 in Aug./Sept. (Table 4.1). However, in most cases, NO3- is rarely <3 µM at the offshore stations (Whitney and Freeland, 1999; Peña and Varela, 2007). Even though Si(OH)4 appeared to have a more rapid drawdown along all of Line P in the late spring, it rarely became depleted along the transect, especially in the HNLC region. However, during this study, there was a surface Si(OH)4 of 2.0 µM at P26 which may have been an indicator of a diatom event previous to our arrival in Aug./Sept. 2000. Concentrations of Si(OH)4 < 2 µM are thought to be limiting to diatom production (Allen et al., 2005; Whitney et al., 2005b) This low Si(OH)4 did coincide with an increased bSi flux in the 1000 m sediment trap at P26 during the summer of 2000 (C.S. Wong, unpub. data.) as well as a lower euphotic zone bSi concentration (Table 4.1) Additionally, the surface Si(OH)4:NO3- ratio at P26 in Aug./Sept. 2000 was 0.36 (Table 4.1), much lower than any ratio encountered during our 1998-2000 study and is a ratio where diatom blooms have been reported to sink out of the photic zone (Kristiansen et al., 2000). Although rare, depletion of surface Si(OH)4 (<1 µM) has been observed at P26 (Wong and Matear, 1999; Wong et al., 2002a) and may be related to atmospheric Fe input (Bishop et al., 2002) or the remnants of coastal eddies (Johnson et al., 2005). NO3-  and Si(OH)4 drawdown are positively correlated, but Si(OH)4 has higher interannual variability, suggesting high variation in seasonal and interannual diatom production, abundance and species composition (Peña and Varela, 2007). This appears to be demonstrated by the large variation measured in >20 µm chl a and POC production, ρSi, diatom carbon, and species composition over this three years study.  146 4.4.6 Seasonal and spatial variations in silica production Silica production rates were generally low (average ~0.02 µmol Si L-1) along the whole of Line P and the observed variability suggests that no single region along the transect is better suited for diatom growth. However, the high integrated values (Table 4.1) measured at P12 in Aug./Sept. 2000 (4.7 mmol Si m-2 d-1) were consistent with the rates found in a diatom bloom (Shipe and Brzezinski, 2001) and corresponded to the highest values measured in this study for integrated > 20 µm chl a (11.7 mg chl a m-2) and POC production (320 mg C m-2 d-1). Silica production was significantly higher in 2000 compared to 1999 for all the June and Aug./Sept. cruises combined. The strongest differences occurred at P12, P20 and P26 where they were significantly higher in 2000 compared to 1999. As may be expected, there was a very strong positive linear regression (Fig. 4.7) between ρSi and >20 µm  POC production (>20 µm  POC prod = 48.807 x ρSi + 0.409; r2 = 0.39), >20 µm  chl a (>20 µm  Chl a = 1.518 x ρSi + 0.016; r2 = 0.49), total siliceous carbon (tot sil C = 210.29 x ρSi + 0.587; r2 = 0.47), and bSi (bSi = 0.0427 x ρSi + 0.006; r2 = 0.28) (p<0.01 for all four regressions). These significant relationships infer that siliceous phytoplankton do make up the bulk of the >20 µm size fraction along Line P and this was confirmed by phytoplankton cell counts (Table 4.4). Additionally, the magnitude of diatom biomass in the form of siliceous carbon or bSi acts as a good proxy for determining ρSi and suggests that most diatoms do not remain in the mixed layer and are most likely lost to export (Boyd et al., 1998b; Kemp et al., 2000; Sarthou et al., 2005). When silica production was compared to total POC production (Fig. 4.6), an average Si:C uptake ratio (0.23 ± 0.23 SD) was found for June and Aug./Sept. 1999 and 2000. The average Si:C uptake ratio was highest at the HNLC stations (0.15 ± 0.24 SD) where average DFe was 0.03 nM (± 0.03 SD) (Nishioka et al., 2001and see Chapter 3) compared to a lower Si:C uptake ratio at the near-shelf stations (0.06 ± 0.14 SD) where average DFe was 0.17 nM (± 0.22 SD). The Si:C uptake ratio also increased with depth at many of the stations. The maximum Si:C uptake ratio was 1.38 at P16 in June 1999 where DFe was very low at 0.02 nM. Low DFe and low light may be the primary reason for the increase in Si:C uptake ratios (Hutchins and Bruland, 1998; Takeda, 1998; Brzezinski et al., 2003a). Concentrations of DFe generally ranged from not detectable to 0.99 nM. (Nishioka et al., 2001 and C. S. Wong pers. comm.) and averaged 0.20 nM (± 0.15 SD), which is known to limit phytoplankton growth rates  147 (Brzezinski et al., 2003a). Indeed, the half-saturation constant (Km) for DFe can range from 0.05 to 0.45 nM in HNLC regions (Coale et al., 1996; Blain et al., 2002) and experimental evidence has also shown that [DFe] below 0.5 can increase the Si:C uptake ratio significantly (Franck et al., 2000). 4.4.7 Fe, light and diatom production Many studies have shown that the availability of Fe controls phytoplankton production in the HNLC regions of Line P (Martin and Fitzwater, 1988; Boyd et al., 1996; Boyd et al., 1998b; Schmidt and Hutchins, 1999; Lam et al., 2001; Nishioka et al., 2001; Bishop et al., 2002; Lam et al., 2006). Low [Fe] causes diatoms to increase their Si(OH)4:NO3- uptake ratios to >2 from an average of  0.9 (Brzezinski, 1985) in the Southern Ocean (Franck et al., 2000; Brzezinski et al., 2003a), the Atlantic (Pondaven et al., 2000) and the Pacific (Smith et al., 2000). This allows the “silicate pump” (Dugdale et al., 1995) to more efficiently recycle N back to the phytoplankton while preferentially exporting silica. Low [Fe] increases the demand for silicic acid per cell from diatoms compared to nitrate (Hutchins and Bruland, 1998; De La Rocha et al., 2000; Brzezinski et al., 2003a). Diatoms are at a disadvantage in low [Fe] systems where the consumption ratio of Si(OH)4 to NO3- increases as does the Si(OH)4 to carbon ratio (Franck et al., 2005), resulting in an increased ratio of export of particulate silicon compared to nitrogen (Takeda, 1998) and carbon. Additionally, it appears that diatoms are only capable of utilizing dissolved forms of Fe as opposed to flagellates which can utilize colloid forms (Nodwell and Price, 2001). This further limits diatom growth in consistently Fe-limited environments such at P20 and P26. Some large diatoms seem to be able to control their buoyancy-regulated vertical migration to access the higher nutrient waters below the mixed layer (Villareal, 1992; Villareal et al., 1993; Moore and Villareal, 1996; Villareal et al., 1999; McKay et al., 2000; Sarthou et al., 2005). They may also be well adapted to growth under low light conditions (Goldman and McGillicuddy, 2003) thus allowing for long term survival in HNLC conditions. This also seems to suggest that these larger diatoms may play a larger part in carbon uptake and export production (Kemp et al., 2000; Goldman and McGillicuddy, 2003; Sarthou et al., 2005) Therefore, the persistence of larger diatoms in the low [Fe] areas of the euphotic zone of Line P may play an important long term role in annual production and export and may explain the presence of larger diatoms below the mixed layer in this study (Fig. 4.1, 4.2 and 4.4).  148 The sources of Fe in the water column of Line P are not well understood. Elevated chl a (average ~0.3 mg chl a m-3) of >2 mg chl a m-3 had been recorded between 1964 – 1976 (Parslow, 1981; Boyd et al., 1998b) that was most likely caused by an increased input of Fe. Boyd et al. (1998b) have suggested that an atmospheric source from dust storms that cross the Pacific from Asia and Alaska. Mineral dust records from the IMPROVE network of aerosol monitoring stations (Eldred et al., 1990) showed only a single large peak in May 1998 (Fig. 4.8). This coincided with an increase in bSi flux in a 1000 m sediment trap at P26 (C.S. Wong, unpub. data.) in May and early June 2000.  Other studies have suggested that the source of DFe is coming off the continental margin off the Aleutian Islands and may have stimulated a bloom of diatoms at P26 in 1996 (Lam et al., 2006). Field observations of dust enhancement only increased POC production for 2 weeks (Bishop et al., 2002). Suggesting that the bioavailable fraction of iron from dust is used up quickly, and making it difficult to achieve full drawdown of the available Si(OH)4. Finally, it has also been suggested that DFe may be increased as a result of anticyclonic mesoscale eddies that form on the western edge of the Gulf of Alaska and can bring waters with a coastal signature into the HNLC area of Line P (Whitney et al., 2005b). During the 1998 Aug./Sept. cruise, an anti-cyclonic eddie that formed off the Queen Charlotte Islands was located just east of P16 (Whitney and Robert, 2002) and may explain the anomalously lower nutrient values found at that station (Table 4.1). 4.4.8 Comparison of Line P POC, PIC and silica production Values of euphotic zone depth integrated PIC production (ρPIC) (Chapter 3), POC (ρPOC) and silica production (ρSi) along Line P have been combined from 4 cruises (June and Aug./Sept. 1999 and 2000) (Fig. 4.9). As expected, ρPOC always remained higher than ρSi or ρPIC. However, neither ρSi nor ρPIC was found to be consistently higher than the other one. There were some periods of high PIC coccolithophore productivity and carbon biomass along Line P (Chapter 3). In 1999, ρSi was either higher or similar to ρPIC. In 2000, ρPIC was clearly higher and this further emphasizes the importance of coccolithophores in the Line P region. Bloom concentrations of coccolithophores were found during June (P26) and Aug./Sept 2000 (P12) (Chapter 3). The extremely high coccolithophore abundances recorded at P12 in Aug./Sept. 2000 coincided with the largest diatom biomass and ρSi found in this study. Interestingly, the high abundances of coccolithophores found at P12 did not correspond to an  149 equally high rate of ρPIC. Combined integrated carbon of the coccolithophores and diatoms made up >95% of the total integrated POC measured at that station. Coccolithophores made up over 5 times more POC than the diatoms at that station, even during a period of the highest diatom production and carbon recorded in this study. 4.4.9 Comparison of silica production with other oceanic provinces Our integrated ρSi rates were generally lower than those of other non-oligotrophic regions, and they were definitely lower than the estimates from other regions in the subarctic Pacific (Table 4.10).  (Banahan and Goering, 1986; Nelson et al., 1995; Wong and Matear, 1999). Our near-shelf values (average 1.1 mmol Si m-2 d-1) were much lower than the near coast studies of the Santa Barbara Channel (17.5 mmol m-2 d-1) and Monterey Bay (42.8 mmol m-3 d-1) (Shipe and Brzezinski, 2001; Brzezinski et al., 2003b) as well as the mean for the Bering Sea (18.0 mmol m-2 d-1), although our range does fall at the low end of their study (Banahan and Goering, 1986). Our HNLC mean (1.1 mmol m-2 d-1) was higher than the oligotrophic areas of the Sargasso Sea (0.5 mmol m-2 d-1) (Banahan and Goering, 1986; Brzezinski and Nelson, 1995; Brzezinski and Kosman, 1996) and the Indian sector of the Indian Ocean (0.5 mmol m-2 d-1) (Leblanc et al., 2005) and fall into the lower end of the range of other oceanic areas. Interestingly, our mean ρSi rate was about 4 times lower than the estimate of average Si(OH)4 utilization for P26 by Wong and Matear (1999) and over 5 times lower than the average May-July ρSi rate of Whitney et al. (2005b). This is not surprising as our measurements were only made during two time periods (June and Aug./Sept.) and appears to have missed the increase in diatom production that usually occurs at P26 in May/early June (Peña and Varela, 2007). Additionally, the inclusion of the 1999 La Niña period of low phytoplankton production and diatom carbon may also skew our averages towards the low scale. In order to provide a more reasonable estimate of average ρSi, increased measurements are needed, especially during the earlier May/early June period of increased phytoplankton production and silica export (Wong et al., 1995; Boyd and Harrison, 1999; Wong et al., 1999). It also would have been helpful to have ρSi measurements during the period between June and Aug./Sept. 2000 where surface Si(OH)4 dropped from 19.9 µM to 2.0 µM, a probable window of high diatom production. This may also explain why the average ρSi for the HNLC stations was slightly higher (not significant) than the near-shelf stations (Table 4.10) due to the increased spring production of the near shore stations  150 that occur much earlier than the more westward stations. It is also likely the values also vary due to differing methodologies. While our ρSi rates are derived from short term (24 h) isotope fixation, nutrient utilization values are derived from longer term nutrient changes and include losses due to dissolution, grazing, sinking, etc. 4.5 Conclusion Both 1998 (June) and 2000 (Aug./Sept.) represent two periods of high diatom biomass, diatom carbon, diatom POC and silica production during the three year period of this study. Periods of  El Niño seem to support increased diatom production and export, especially in the HNLC region of Line P. Diatoms rarely dominated the phytoplankton biomass or production, but there were isolated examples of anomalously high diatom biomass (abundance and carbon) as well as >20 µm POC production. Diatoms appear to be fairly ubiquitous, with the major species appearing at most stations during the course of the 3 year study. Biogenic silica remained relatively constant while ρSi varied between the years of 1999 and 2000, with a maximum influence of diatom parameters occurring at P12 in Aug./Sept. 2000. Evidence is accumulating that increased Si(OH)4 utilization due to the direct role of diatom growth and export does play an important role in the recycling and export of nutrients along Line P. Interestingly, evidence is also becoming clearer that the HNLC stations, specifically P26 (OSP) can experience periods of higher ρSi and actually has a higher average ƒ- ratio (0.29) than near-shelf stations (P04 = 0.18)  (Varela and Harrison, 1999b), suggesting that diatoms may play more of a role in the oceanic regions of the subarctic Pacific than previously thought. Indeed, during this 3 year study, there were measured periods where diatom carbon production, ρSi and biomass were higher at the HNLC region of Line P than at the near-shelf stations. Therefore,  Si(OH)4 availability can occasionally control diatom growth and export along Line P (Whitney et al., 2005a) instead of just Fe and light (Maldonado et al., 1999) and becomes an important control in the effectiveness of carbon acquisition during iron enrichment (Boyd et al., 2001; Boyd et al., 2004).  151 4.6 Tables Table 4.1. Dates of cruises, depth (m) of the euphotic zone (Zeu) as defined by 1% of surface irradiance, mixed layer depth (MLD) as determined by Freeland et al. (1997), surface nitrate and integrated chlorophyll a and POC production. Surface nitrate and silicic acid concentrations were obtained from the Fisheries and Ocean Canada Line P Oceanic Data web site (http://www- sci.pac.dfo-mpo.gc.ca/osap/data/linep/linepselectdata_e.htm). Average biogenic silica (bSi) represents a depth-weighted average in the euphotic zone. Sampling for silica production (ρSi) did not start until June 1999. ND = not detectable.  See (Chapter 3) for more values. LS = lost sample.  Date Station Zeu (m) MLD (m) Int. >20 µm chl a (mg m-2) Int. Chl a (mg m-2) Int. >20 µm POC prod. (mg C m-2 d-1) Int. POC prod. (mg C m-2 d-1) Surface Nitrate (µM) Surface Silicic Acid (µM) Avg. bSi (µM) Int. POC (mmol m-2) Int. ρSi (mmol Si m-2 d-1) 19-Feb-98 P04 40 175 1.5 18.3 7 72 3.5 5.3 0.24 194 21-Feb-98 P12 50 76 2.9 16.8 35 166 5.8 6.8 0.30 247 23-Feb-98 P16 60 81 2.3 26.8 29 195 8.4 11.4 0.24 239 24-Feb-98 P20 80 81 2.0 26.7 6 144 10.3 14.0 0.19 491 26-Feb-98 P26 80 94 3.0 18.9 16 162 13 20.5 0.23 315 5-Jun-98 P04 33 24 2.0 9.5 10 100 ND 2.9 0.80 352 6-Jun-98 P12 40 17 2.5 16.9 20 84 0.1 0.2 0.74 456 8-Jun-98 P16 52 22 1.9 20.0 50 312 4.1 7.6 0.21 449 9-Jun-98 P20 58 15 6.8 15.1 87 143 6.6 10.4 0.90 624 12-Jun-98 P26 50 22 5.1 18.5 48 189 9.9 16.4 0.90 509 27-Aug-98 P04 33 21 0.4 14.9 80 566 ND 4.1 0.19 430 28-Aug-98 P12 45 17 0.4 10.1 35 324 ND 4.5 0.18 468 30-Aug-98 P16 55 27 0.5 12.4 45 460 ND 0.9 0.18 236 31-Aug-98 P20 60 31 0.3 7.5 21 405 5 9.3 0.15 261 5-Sep-98 P26 55 42 1.5 12.6 40 798 5.7 9.1 0.20 516 10-Feb-99 P04 40 78 2.0 18.4 LS LS 8.9 14.4 0.15 222 14-Feb-99 P12 80 102 3.0 27.6 22 123 9.1 14.0 0.14 248 23-Feb-99 P16 75 102 3.5 20.5 36 123 9.2 13.5 0.29 251 20-Feb-99 P20 75 104 3.8 36.8 62 265 10.9 16.1 0.46 392 18-Feb-99 P26 60 114 2.8 22.4 27 131 14.3 19.6 0.28 437 23-Jun-99 P04 35 12 4.0 34.6 60 358 ND 1.6 0.82 370 0.2 21-Jun-99 P12 60 21 1.7 34.0 38 426 6.9 11.7 0.16 367 1.4 19-Jun-99 P16 52 19 1.7 9.0 14 80 8.1 11.4 0.26 203 1.0 18-Jun-99 P20 65 60 3.2 18.3 32 225 9.4 13.5 0.44 338 2.6 12-Jun-99 P26 65 28 3.7 23.4 32 167 13.2 18.7 0.74 569 1.9 29-Aug-99 P04 35 16 1.4 16.0 68 447 ND 8.9 0.35 429 0.3 27-Aug-99 P12 45 19 0.4 14.5 19 365 0.6 7.2 0.14 412 0.4 29-Aug-99 P16 55 31 0.9 13.5 25 304 3.1 9.0 0.11 603 0.5 30-Aug-99 P20 60 26 1.0 7.1 18 181 7.6 12.7 0.39 731 1.2 2-Sep-99 P26 60 35 1.9 14.1 42 432 11.3 19.7 0.35 887 2.7 1-Jun-00 P04 50 11 1.4 21.7 171 1386 ND 6.4 0.13 438 1.3 3-Jun-00 P12 71 36 1.7 19.0 55 458 6.9 13.2 0.17 505 0.6 4-Jun-00 P16 80 32 1.6 17.7 59 483 8.4 13.1 0.15 447 0.6 6-Jun-00 P20 80 29 3.9 13.4 91 416 9.3 14.1 0.25 353 0.6 8-Jun-00 P26 80 27 5.7 18.5 38 152 13.2 19.9 0.47 522 0.6 6-Sep-00 P04 50 21 2.2 22.9 62 653 ND 5.6 0.24 344 0.2 8-Sep-00 P12 50 27 11.7 31.6 320 581 0.9 6.1 0.57 392 4.7 9-Sep-00 P16 66 40 2.1 22.7 78 295 1.8 6.6 0.11 440 0.3 11-Sep-00 P20 75 38 1.8 16.9 34 407 8.2 10.8 0.31 279 0.7 13-Sep-00 P26 50 29 2.6 24.5 58 480 5.5 2.0 0.12 322 0.4   152 Table 4.2. Average integrated diatom and siliceous (diatoms plus silicoflagellates) carbon, silica production (ρSi) biogenic silica (bSi), Chl a and POC productivity (PP). Chl a and POC productivity are divided into the > 20 µm size fraction and the total (Tot.) values (0- 20 plus >20 µm size fractions). Eight cruises were conducted in 3 seasons. Feb. encompasses only 2 cruises (1998 and 1999). June and Aug./Sept. includes 3 cruises. Silica production was not measured in Feb. for any cruise. SD equals ±1 standard deviation. Months Station Int. Diatom Carbon (mg m-2) SD Int. Siliceous Phyto C (mg m-2) SD  Int. ρSi  (mmol Si m-2 d-1) SD Int. bSi (mmol m-2) SD  Int > 20 µm Chl (mg m-2) SD  Int. Chl total (mg m-2) SD Int. >20 µm PP (mg C  m-2 d-1) SD  Int. Tot PP (mg C m-2 d-1) SD ALL P04 79 90 111 164 0.5 0.5 12.8 9.2 1.9 0.9 19.5 7.4 63 53 512 443 Seasons P12 485 666 489 666 1.8 2.0 21.5 19.9 3.6 4.3 21.3 8.6 62 88 316 177  P16 312 668 312 668 0.6 0.3 13.8 4.5 1.9 1.0 17.8 5.9 39 15 282 145  P20 360 464 360 464 1.3 0.9 26.0 15.2 2.8 1.9 17.7 9.9 46 39 273 119  P26 403 312 404 311 1.4 1.1 26.9 14.6 3.2 1.3 19.1 4.3 36 11 314 238  Average all 328 440 335 455 1.1 1.0 20.2 12.7 2.7 1.9 19.1 7.2 49 41 339 224                   Feb. P04 138 172 255 333   8.0 1.1 1.8 0.5 18.4 0.0 7 5 72  P12 323 108 333 97   13.4 0.4 2.6 0.1 22.2 7.6 30 5 145 31  P16 118 59 118 59   17.5 4.4 3.1 0.8 23.7 4.5 37 3 159 50  P20 90 26 90 26   23.5 11.8 3.4 1.6 31.7 7.1 34 42 205 86  P26 274 221 277 217   18.1 0.3 2.9 0.1 20.6 2.5 22 4 147 22  Average all 189 117 215 147   16.1 3.6 2.8 0.6 23.3 4.3 26 12 146 47  June P04 28 29 28 29 0.8 0.8 17.4 14.6 2.3 1.2 21.9 12. 5 81 78 615 681  P12 606 919 606 919 1.0 0.6 26.2 23.9 3.0 2.3 23.3 9.3 36 15 322 207  P16 679 1110 679 1110 0.8 0.3 16.1 1.8 1.8 0.0 15.5 5.8 43 26 292 203  P20 871 352 871 352 1.6 1.4 40.2 13.5 4.3 1.4 15.6 2.5 75 49 261 140  P26 669 349 670 349 1.2 0.9 41.8 10.6 4.5 1.0 20.2 2.8 38 10 170 18  Average all 571 552 571 552 1.1 0.8 28.4 12.9 3.2 1.2 19.3 6.6 54 36 332 250                   Aug./ P04 92 71 99 82 0.3 0.1 11.3 4.7 1.5 1.0 17.9 4.4 64 11 555 103 Sept. P12 473 808 475 811 2.5 3.0 22.2 26.7 4.8 7.5 18.7 11. 4 108 148 423 138  P16 73 19 73 19 0.4 0.1 8.9 0.6 1.1 0.8 16.2 5.6 36 10 353 93  P20 29 36 29 36 1.0 0.3 13.5 3.8 0.9 0.6 10.5 5.5 25 8 331 129  P26 222 147 223 146 1.5 1.6 17.7 9.9 2.0 0.6 17.0 6.5 43 7 570 199   Average all 178 216 180 219 1.1 1.0 14.7 9.1 2.1 2.1 16.1 6.7 55 37 446 133  153 Table 4.3. Proportion of the contribution of siliceous phytoplankton (centric and pennate diatoms) and >20 µm size fraction to total POC, chlorophyll a, and POC production and the proportion of silicoflagellate carbon to total siliceous (diatom plus silicoflagellate) carbon. Proportions derived from integrated values in the euphotic zone. LS=lost sample. Average is the mean for all samples per station or for the whole study (all). Cruise Station Centric C to total POC Pennate C to total POC Tot diatom C to tot POC > 20 µm Chl to tot chl > 20 µm POC prod. to tot POC prod. Silicoflagellate C to tot Siliceous phytoplankton 9803 P04 0.05 0.07 0.11 0.08 0.10 0.47 9803 P12 0.06 0.02 0.08 0.15 0.20 0.07 9803 P16 0.04 0.01 0.06 0.09 0.20 0.00 9803 P20 0.01 0.00 0.01 0.08 0.03 0.01 9803 P26 0.02 0.00 0.11 0.16 0.12 0.00 9815 P04 0.01 0.00 0.01 0.17 0.14 0.00 9815 P12 0.31 0.00 0.31 0.34 0.27 0.00 9815 P16 0.33 0.00 0.33 0.09 0.16 0.00 9815 P20 0.16 0.01 0.17 0.39 0.49 0.00 9815 P26 0.15 0.02 0.18 0.27 0.23 0.00 9829 P04 0.00 0.00 0.00 0.03 0.13 0.00 9829 P12 0.00 0.00 0.00 0.04 0.09 0.26 9829 P16 0.02 0.00 0.02 0.04 0.08 0.00 9829 P20 0.00 0.00 0.00 0.04 0.06 0.00 9829 P26 0.08 0.00 0.08 0.12 0.05 0.00 9901 P04 0.01 0.00 0.01 0.12 LS 0.13 9901 P12 0.11 0.02 0.13 0.10 0.22 0.01 9901 P16 0.03 0.00 0.03 0.18 0.28 0.00 9901 P20 0.01 0.01 0.02 0.12 0.24 0.00 9901 P26 0.02 0.01 0.02 0.13 0.19 0.05 9910 P04 0.00 0.00 0.00 0.10 0.18 0.00 9910 P12 0.03 0.00 0.03 0.05 0.08 0.00 9910 P16 0.01 0.00 0.01 0.21 0.18 0.00 9910 P20 0.18 0.00 0.18 0.17 0.12 0.00 9910 P26 0.04 0.00 0.04 0.14 0.16 0.00 9921 P04 0.02 0.00 0.02 0.11 0.15 0.00 9921 P12 0.00 0.00 0.00 0.03 0.05 0.00 9921 P16 0.01 0.00 0.01 0.06 0.08 0.00 9921 P20 0.01 0.00 0.01 0.12 0.10 0.00 9921 P26 0.01 0.00 0.02 0.13 0.09 0.01 2000-10 P04 0.00 0.00 0.00 0.07 0.12 0.00 2000-10 P12 0.00 0.00 0.00 0.09 0.11 0.00 2000-10 P16 0.01 0.00 0.01 0.11 0.13 0.00 2000-10 P20 0.13 0.00 0.13 0.30 0.30 0.00 2000-10 P26 0.05 0.05 0.10 0.27 0.29 0.00 2000-25 P04 0.02 0.01 0.03 0.11 0.08 0.13 2000-25 P12 0.21 0.09 0.30 0.43 0.48 0.00 2000-25 P16 0.01 0.00 0.01 0.09 0.16 0.00 2000-25 P20 0.00 0.00 0.00 0.10 0.08 0.00 2000-25 P26 0.02 0.00 0.02 0.11 0.10 0.00 Average P04 0.01 0.01 0.02 0.09 0.11 0.08  P12 0.08 0.01 0.10 0.14 0.17 0.04  P16 0.05 0.00 0.05 0.10 0.14 0.00  P20 0.06 0.00 0.06 0.15 0.16 0.00  P26 0.04 0.01 0.06 0.15 0.14 0.01  all 0.06 0.01 0.07 0.14 0.16 0.03  154 Table 4.4. Cell abundance (weighted average) of siliceous phytoplankton (silicoflagellates, pennate and centric diatoms) and carbon concentrations of centric and pennate diatoms for all stations and cruises. Cell abundance and integrated carbon concentrations are from the four light depths (100, 55, 10, 1%). See Chapter 2 for dates and depths of the euphotic zone.   Siliceous phytoplankton average abundance  (cells ml-1) Integrated diatom phytoplankton carbon (mg m-2) Cruise Station Silico-flagellates Centric Pennate Total centric & pennate % Centric Centric Pennate Total % Centric 1998 P04 1.5 2.7 8.2 10.9 24 112 149 261 43 Feb. P12 0.6 4.8 3.9 8.6 55 183 64 247 74  P16 0.0 8.2 3.2 11.4 72 118 42 160 74  P20 0.0 0.8 0.2 1.1 78 70 1 71 99  P26 0.0 1.1 0.3 1.4 78 74 1 75 99 1998 P04 0.0 1.2 0.1 1.3 95 57 3 60 95 June P12 0.0 27.6 0.0 27.6 100 1670 0 1670 100  P16 0.0 7.4 0.1 7.5 99 1960 1 1961 100  P20 0.0 14.4 4.6 19.0 76 1200 73 1270 94  P26 0.3 32.2 0.4 32.5 99 801 123 924 87 1998 P04 0.0 1.7 0.0 1.8 99 16 0 16 100 Aug./Sept. P12 0.1 0.2 0.0 0.2 100 1 0 1 100  P16 0.0 1.0 0.0 1.0 98 76 1 77 99  P20 0.0 0.1 0.0 0.1 91 2 0 2 100  P26 0.0 1.6 0.5 2.1 76 381 3 384 99 1999 P04 0.2 1.3 0.0 1.3 97 16 1 17 94 Feb. P12 0.0 2.3 4.6 6.9 34 337 63 400 84  P16 0.0 1.3 0.0 1.3 100 76 0 76 100  P20 0.0 1.8 0.3 2.0 87 66 42 108 61  P26 0.2 5.2 0.8 6.0 87 90 27 117 77 1999 P04 0.0 1.0 0.3 1.3 77 13 3 16 81 June P12 0.0 0.9 0.0 0.9 100 130 0 130 100  P16 0.0 0.9 0.4 1.4 68 14 1 15 93  P20 0.0 4.8 0.0 4.8 100 735 0 735 100  P26 0.0 0.8 0.4 1.2 70 267 5 272 98 1999 P04 0.0 11.6 1.1 12.6 92 98 4 102 96 Aug./Sept. P12 0.0 0.3 0.1 0.3 81 11 0 11 100  P16 0.0 0.1 0.1 0.2 54 86 4 90 96  P20 0.0 0.2 0.6 0.8 22 67 3 70 96  P26 0.2 1.1 4.1 5.2 21 140 45 185 76 2000 P04 0.0 0.1 0.0 0.2 85 7 1 8 88 June P12 0.0 1.6 0.3 1.9 84 23 0 23 100  P16 0.0 0.6 0.0 0.6 96 61 1 62 98  P20 0.0 4.1 0.1 4.2 98 608 0 608 100  P26 0.0 9.7 6.5 16.2 60 418 394 812 51 2000 P04 1.5 2.7 5.5 8.3 33 109 48 157 69 Aug./Sept. P12 0.7 59.1 68.3 127 46 978 427 1400 70  P16 0.0 2.7 6.3 9.0 30 27 26 53 51  P20 0.0 0.1 2.6 2.7 6 3 14 17 18  P26 0.0 0.8 0.1 1.0 87 97 0 97 100 Average P04 0.4 2.8 1.9 4.7 75 54 26 80 83  P12 0.2 12.1 9.6 21.7 75 416 69 485 91  P16 0.0 2.8 1.3 4.0 77 302 10 312 89  P20 0.0 3.3 1.0 4.3 70 344 17 360 83  P26 0.1 6.6 1.6 8.2 72 284 75 358 86  all 0.1 5.5 3.1 8.6 74 280 39 319 86   155 Table 4.5. List of diatoms identified from samples collected along Line P from 1998 to 2000. ‘S’ in the column indicates that the species was found in the area designated as ‘near-shelf’ (P04 and/or P12). ‘T’ indicates the species was found at the transition station (P16).  ‘H’ indicates the species was found in the HNLC region (P20 and/or P26). There was no cruise for Feb. 2000. Species with the highest diatom abundances (measured by carbon) are marked with an asterisk (*).      1998 1999 2000 Bacillariophyceae Species Feb. June Aug./ Sept. Feb. June Aug./ Sept. June Aug./ Sept. Centric Diatoms Asteromphalus spp. S, T  S T  Chaetoceros atlanticus S, T, H S, H  S  S, H  S  Chaetoceros concavicornis S, T S  S, H H   S  Chaetoceros decipiens        S  Chaetoceros socialis      S  Chaetoceros spp.  H S     S  Corethron hystrix* S, H S, T, H S, T, H S, T, H S, T S S, T, H  Coscinodiscus spp. (>20 µm)* S, T T S, H S, H S, H T, H T, H  Coscinodiscus spp. (8-20 µm) T, H T S, H S, H S, H S, H S, T, H S, H  Ditylum brightwellii    S   S  Planktoniella spp. S  Proboscia alata* S, T, H S, H T, H H H S H S, T  Rhizosolenia spp. S S, T, H S  Rhizosolenia stolterfothii        S  Rhizosolenia styliformis  S, T, H   H  H S  Thalassiosira gravida S     S  Thalassiosira rotula* S H  T, H  S  Thalassiosira subtilis S  Other S, T, H S, H S, T S, T, H S, T, H S, H H S, H Pennate Diatoms Asterionella glacialis S  Cylindrotheca closterium    S  Cylindrotheca spp.  H  Fragilaria spp.  H   H  Navicula distans S, T, H S    T  Navicula spp. T H  S T H S, T S, H  Neodenticula seminae S, T, H  Nitzschia longissima  S  Nitzschia spp. T H T, H S  S H S, T  Pleurosigma normanii     S  Pseudo-nitzschia spp.* S, T H S, T, H H H S, H H S, T, H  Thalassionema nitzschioides T T, H  S  S  S  Thalassiothrix longissima S, T S, H  H  S, H H S, T  Thalassiothrix sp.  T  Tropidoneis spp. S H     H  Other S       S Dictyophyceae  Dictyocha spp. S H S S, H    S   156 Table 4.6. Pearson’s correlation matrix for diatoms (centric and pennate) and other selected parameters in the euphotic zone for all five stations from all 8 cruises during 1998-2000 (n=40).  Integrated values from the mixed layer were used for diatom carbon (centric, pennate and total), biogenic silica (bSi) chlorophyll (Chl 5-20, >20 µm size-fractionated and Chl total) and POC production (PP 5-20, >20 µm size-fractionated and PP total) and nutrients (NO3-, Si(OH)4 and Fe). Si/N was tested as a ratio of the integrated values of Si(OH)4 and NO3- in the mixed layer. See Table 4.1 and Chapter 2 for values. All  Centric carbon Pennate carbon Diatom carbon POC NO3 - Si(OH)4 Si/N Fe bSi Chl 5-20 µm Chl >20 µm Chl total PP 5-20 µm PP >20 µm PP total Centric carbon - Pennate carbon 0.25 - Diatom carbon 0.98** 0.42* - POC 0.23 0.11 0.23 - NO3- -0.08 0.21 -0.03 0.02 - Si(OH)4 -0.09 0.26 -0.03 0.13 0.97** - Si/N -0.15 -0.09 -0.16 0.14 -0.59* -0.46** - Fe -0.05 0.03 -0.04 -0.27 0.17 0.13 -0.08 - bSi 0.62** 0.59** 0.69** 0.27 0.22 0.22 -0.21 -0.12 - Chl 5-20 µm -0.26 0.15 -0.22 -0.14 0.09 0.05 -0.17 0.04 0.12 - Chl >20 µm 0.50** 0.76** 0.61** 0.08 0.13 0.14 -0.16 0.01 0.83** 0.31 - Chl total 0.02 0.25 0.06 -0.15 0.18 0.15 -0.22 0.25 0.20 0.70** 0.43* - PP 5-20 µm -0.28 -0.07 -0.28 0.09 -0.35* -0.28 0.38* -0.15 -0.32* 0.23 -0.21 -0.18 - PP >20 µm 0.22 0.55** 0.31 0.08 -0.12 0.04 0.21 -0.06 0.40* 0.27 0.70** 0.32* 0.28 - PP total -0.15 -0.03 -0.15 0.10 -0.30 -0.21 0.40* -0.13 -0.24 0.09 -0.06 0.06 0.71** 0.57** -   *Denotes coefficients that were significant (α<0.05). **Denotes α<0.005.   157 Table 4.7. Pearson’s correlation matrix for diatoms and other selected parameters in the euphotic zone for stations located near the shelf (P04 and P12) from all 8 cruises (n=16).  See Table 4.6 for details.  Near-shelf  Centric carbon Pennate carbon Diatom carbon POC NO3 - Si(OH)4 Si/N Fe bSi Chl 5-20 µm Chl >20 µm Chl total PP 5-20 µm PP >20 µm PP total Centric carbon - Pennate carbon 0.42 - Diatom carbon 0.98** 0.58* - POC 0.11 -0.10 0.08 - NO3- -0.10 0.09 -0.07 -0.28 - Si(OH)4 -0.21 0.11 -0.16 -0.04 0.94** - Si/N -0.28 -0.19 -0.29 0.48 -0.61* -0.41 - Fe 0.01 0.04 0.02 -0.52* 0.66* 0.55* -0.30 - bSi 0.86** 0.57* 0.88** 0.18 -0.17 -0.24 -0.26 -0.15 - Chl 5-20 µm -0.09 0.39 0.00 0.03 0.10 0.15 -0.17 0.00 0.38 - Chl >20 µm 0.69** 0.91** 0.81** 0.04 0.02 -0.02 -0.24 -0.04 0.85** 0.44 - Chl total 0.11 0.39 0.18 -0.17 0.42 0.41 -0.51* 0.23 0.37 0.80** 0.46 - PP 5-20 µm -0.26 0.10 -0.21 0.50* -0.33 -0.05 0.70** -0.21 -0.17 0.17 0.00 -0.07 - PP >20 µm 0.25 0.80** 0.39 0.24 -0.09 0.08 0.14 -0.13 0.46 0.46 0.77** 0.43 0.54* - PP total -0.23 0.12 -0.18 0.41 -0.16 0.10 0.44 -0.20 -0.17 0.13 0.05 0.17 0.77** 0.63* -   *Denotes coefficients that were significant (α<0.05). **Denotes α<0.005.   158 Table 4.8. Pearson’s correlation matrix for diatoms and other selected parameters in the euphotic zone for HNLC stations (P20 and P26) from all 8 cruises (n=16).  See Table 4.6 for details.  HNLC  Centric carbon Pennate carbon Diatom carbon POC NO3 - Si(OH)4 Si/N Fe bSi Chl 5-20 µm Chl >20 µm Chl total PP 5-20 µm PP >20 µm PP total Centric carbon - Pennate carbon 0.24 - Diatom carbon 0.97** 0.48 - POC 0.30 0.26 0.34 - NO3- -0.17 0.45 -0.04 -0.17 - Si(OH)4 -0.07 0.49 0.06 -0.07 0.97** - Si/N 0.28 0.15 0.29 0.34 0.07 0.31 - Fe -0.38 -0.16 -0.39 -0.05 0.33 0.28 -0.05 - bSi 0.79** 0.62* 0.87** 0.35 0.21 0.28 0.28 -0.13 - Chl 5-20 µm -0.40 -0.16 -0.40 -0.42 -0.07 -0.23 -0.61* 0.48 -0.19 - Chl >20 µm 0.71** 0.55* 0.79** 0.21 0.28 0.29 0.01 0.09 0.92** 0.07 - Chl total -0.19 0.07 -0.15 -0.21 0.35 0.20 -0.49 0.67** 0.09 0.75** 0.41 - PP 5-20 µm -0.35 -0.26 -0.39 -0.28 -0.56* -0.54* 0.02 -0.15 -0.49 0.29 -0.55* -0.26 - PP >20 µm 0.44 0.06 0.41 -0.07 0.08 0.07 -0.06 -0.07 0.55* 0.06 0.54* 0.02 -0.07 - PP total -0.19 -0.34 -0.26 -0.27 -0.45 -0.49 -0.19 -0.25 -0.41 0.21 -0.43 -0.24 0.83** 0.23 -   *Denotes coefficients that were significant (α<0.05). **Denotes α<0.005.   159 Table 4.9. Major diatom species found at P26 (OSP) and P20 (this study). The nomenclature used by the authors has been retained. Note that for this study, winter refers to Feb., spring refers to June and Summer/Fall refers to Aug./Sept. Adapted from Harrison et al (2004).  Season 1980-81a 1984 & 1988b,c Sediment Trapsd,e 1997-1998f Present Study 1998-200 July 2002 SERIESg Winter Chaetoceros atlanticus Chaetoceros concavicornis Rhizosolenia hebetata Thalassiothrix longissima Denticulopsis seminae Proboscia alata  Rhizosolenia alata Coscinodiscus marginatus Neodenticula seminae  Thalassiosira rotula Thalassiosira spp. Proboscia alata Chaetoceros concavicornis  Thalassiosira rotula Proboscia alata Corethron hystrix Chaetoceros atlanticus Chaetoceros concavicornis Thalassiothrix longissima Neodenticula seminae Navicula distans Pseudo-nitzschia spp.  Spring Denticulopsis seminae Nitzschia cylindroformis Thalassiothrix longissima Chaetoceros atlanticus  Thalassiosira rotula Chaetoceros atlanticus Chaetoceros concavicornis Corethron sp. Neodenticula seminae Proboscia alata Pseudo-nitzschia spp.  Thalassiosira rotula Rhizosolenia styliformis Proboscia alata Corethron hystrix Chaetoceros atlanticus Chaetoceros concavicornis Lauderia borealis Leptocylindrus danicus Fragillaria spp. Fragilariopsis spp. Thalassiothrix longissima Pseudo-nitzschia spp. Thalassionema nitzschioides Tropidoneis sp.   Summer/ Fall Corethron criophilum Corethron hystrix Rhizosolenia alata Neodenticula seminae  Rhizosolenia setigera Asteromphalus sp. Pseudo-nitzschia spp.  Proboscia alata Corethron hystrix Chaetoceros atlanticus Thalassiothrix longissima Pseudo-nitzschia spp.   Rhizosolenia hebetata Chaetoceros atlanticus Chaetoceros concavicornis Chaetoceros convolutus Chaetoceros sp. Thalassiosira spp. Proboscia alata Pseudo-nitzschia spp. Neodenticula seminae Thalassiothrix longissima Cylindrotheca closterium a Clemons and Miller (1984); b Booth et al.(1993); c Taylor and Waters (1982); d Mochizuki et al.(2002); e Takahashi (1986; 1987);      f Putland (unpubl. results); g Marchetti et al.(2006c) (before Fe enrichment).   160 Table 4.10. Some regional biogenic ρSi estimates (adapted from (Shipe and Brzezinski, 2001)). Annual production rates were not calculated for Line P due to a lack of any measurements in the winter and early spring.   Silica Production Rates Region Range (mmol Si m-2 d-1) Mean (mmol Si m-2 d-1) Annual Production (mol Si m-2 yr-1) Reference  Sargasso Sea 0.2 - 1.6 0.5 0.2 Brzezinski  and Nelson (1995) and Brzezinski and Kosman (1996) Gulf Stream warm core rings 2.0 – 11.7 6.4  Brzezinski and Nelson (1989) Bering Sea 1.8 – 51 18.0 2.2 Banahan and Goering (1986) Ross Sea, Antarctica 0.9 – 93 9.5 2.0 Nelson et al. (1996) Southern Ocean, Atlantic 2.6 – 38  0.2 – 3.5 Nelson et al. (1995) Santa Barbara Channel 2.4 – 57.3 17.5 5.5 Shipe and Brzezinski (2001) Southern Ocean, Indian sector 0.3 – 0.9 ~ 0.5  (Leblanc et al., 2005) Coastal upwelling areas 2.3 - 1140  8.3 Nelson et al. (1996) and Shipe and Brzezinski (2001) Monterey Bay, CA 4.8-108 42.8  Brzezinski  et al.(2003b) Subarctic Pacific  18a 2.2 Banahan and Goering (1986) and Nelson et al. (1995) Ocean Station Papa (P26)  6.9b  Whitney et al. (2005b) Ocean Station Papa (P26)  5.1c  Wong and Matear (1999) Near-shelf Line P 0.2 – 4.7 1.1  This study HNLC Line P (P20 and P26) 0.3 – 2.7 1.3  This study  a Extrapolated from data collected from the eastern Bering Sea (from Nelson et al., 1995). b From surface Si(OH)4 data estimated for the May-July period from Whitney and Freeland (1999) c Calculated mean Si(OH)4 utilization derived from surface Si(OH)4 concentrations from 31 March to 15 August.   161 4.7 Figures D e p t h  ( m ) 19991998 2000 80 60 40 20 0 80 60 40 20 0 1500 1000 500 80 60 40 20 0 1500 1000 5001500 1000 500 Distance along Line P (km) P26 P20 P16 P12 P4 P26 P20 P16 P12 P4 P26 P20 P16 P12 P4 Feb 98 Jun 98 Aug/Sep 98 Feb 99 Jun 99 Aug/Sep 99 Jun 00 Aug/Sep 00   Fig. 4.1. Vertical contour plots of biogenic silica concentrations (bSi – µmol L-1). Dots represent the 4 sampling depths (100, 55, 10 and 1% of I0) for each of the 5 stations along Line P for 8 cruises. The dark dashed line corresponds to the mixed layer depth. Solid grey line indicates area below 1% I0 and therefore contains no measured data.   162 D e p t h  ( m ) 0 20 40 60 80 mg chl a m-3 0.0 0.1 0.2 0.3 0.4 mg chl a m-3 0.0 0.1 0.2 0.3 0.4 mg chl a m-3 0.0 0.1 0.2 0.3 0.4 0 20 40 60 80 P4 P12 P16 P20 P26 (OSP) 0 20 40 60 80 1999 Feb. 1999 Aug./Sept. 1998 Feb. 1998 Aug./Sept. 1999 June 2000 June 2000 Aug./Sept 1998 June   Fig. 4.2. Chl a > 20 µm (mg chl a m-3) for all 5 stations and all 3 years along Line P. Depths represent the 6 light depths (100, 55, 30, 10, 5 and 1% I0). Deepest sample represents the bottom of the photic zone (Zeu).   163 D e p t h  ( m ) 0 20 40 60 80 mg C m-3d-1 0 2 4 6 8 10 mg C m-3d-1 0 2 4 6 8 10 mg C m-3d-1 0 2 4 6 8 10 0 20 40 60 80 P04 P12 P16 P20 P26 (OSP) 0 20 40 60 80 1999 Feb. 1999 Aug./Sept. 1998 Feb. 1998 Aug./Sept. 1999 June 2000 June 2000 Aug./Sept 1998 June   Fig. 4.3. POC production > 20 µm (mg C m-3 d-1) for all 5 stations and all 3 years along Line P. Depths represent the 6 light depths (100, 55, 30, 10, 5 and 1% I0). Deepest sample represents the bottom of the photic zone (Zeu).    164 D e p t h  ( m ) 19991998 2000 80 60 40 20 0 80 60 40 20 0 1500 1000 500 80 60 40 20 0 1500 1000 5001500 1000 500 Distance along Line P (km) P26 P20 P16 P12 P4 P26 P20 P16 P12 P4 P26 P20 P16 P12 P4 Feb 98 Jun 98 Aug/Sep 98 Feb 99 Jun 99 Aug/Sep 99 Jun 00 Aug/Sep 00   Fig. 4.4. Contour plots of total diatom carbon (pennate plus centric) for all 5 stations and all 3 years (1998-2000) along Line P (mg m- 3). Carbon was sampled at four depths (100, 55, 10 and 1% I0) for each station. The darkest dashed line corresponds to the mixed layer depth. The deepest sample represents the base of the photic zone.    165 μmol L-1 d-1 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 D e p t h  ( m ) 0 20 40 60 80 μmol L-1 d-1 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 D e p t h  ( m ) 0 20 40 60 80 P04 P12 P16 P20 P26 2000 June 1999 June 1999 Aug./Sept. 2000 Aug./Sept.   Fig. 4.5. Silica production rates (ρSi – µmol Si L-1 d-1) for the June and Aug./Sept. cruises (1999 and 2000). ρSi was sampled at four depths (100, 55, 10 and 1% I0) for each station. The deepest sample represents the base of the photic zone. Production rates were not measured in 1998 or Feb. 1999.    166 Si:C 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D e p t h  ( m ) 0 20 40 60 80 Si:C 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 P04 P12 P16 P20 P26 2000 June 1999 June 1999 Aug./Sept. 2000 Aug./Sept.   Fig. 4.6. Gross silicon:carbon (Si:C) uptake ratios (mole to mole) for June and Aug./Sept. 1999 and 2000. Average ratio for all cruises and depths was 0.11 (± 0.23 S.D.). Silica production was only measured in June and Aug./Sept. 1999 and 2000.  167 ρSi (μmol L-1) 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 bS i 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 To ta l s ili ce ou s ca rb on  ( μg  L -1 ) 10 20 30 40 50 > 20  μm  P O C  p ro du ct io n (m g C  m -3  d -1 ) 2 4 6 8 10 12 > 20  μm  c hl  a  (m g ch l a  m -3 ) 0.1 0.2 0.3 0.4 y = 48.807x + 0.4087 r2 = 0.3888 y = 1.5181x + 0.0155 r2 = 0.4921 y = 210.29x - 0.5865 r2 = 0.4666 y = 0.0427x + 0.006 r2 = 0.2798  Fig. 4.7. Linear regressions of silica production rate ρSi (µmol Si L-1 d-1) vs. the > 20 µm size fraction POC production (mg C m-3 d-1), > 20 µm size fraction chl a (mg chl a m-3), total siliceous (diatom plus silicoflagellate) carbon (mg C L-1) and bSi (µmol Si L-1). All 4 regressions are significant (p<0.01).   168 M in er al  D us t ( μg  m -3 ) 0 1 2 Month Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec  Jan 0 1 2 0 1 2 3 4 5 6 7 8 9 2000 1998 1999  Fig. 4.8. Atmospheric mineral dust recorded at Mount Rainier National Park. Data are plotted for 1998-2000. Only one major dust event occurred during this study (May 1998). Data are from the Interagency Program for Visual Environments (IMPROVE). Note that 1999 and 2000 are the same scale as 1998.    169 1999 June U p t a k e  R a t e s  ( m m o l  m - 2  d - 1 ) 0.1 1 10 100 1000 ρPOC ρPIC ρSi 1999 Aug./Sept. P04P12P16P20P26 U p t a k e  R a t e s  ( m m o l  m - 2  d - 1 ) 0.1 1 10 100 1000 2000 June 2000 Aug./Sept. P04P12P16P20P26  Fig. 4.9. Relative magnitudes of POC, PIC and silica integrated production (ρPOC, ρPIC, ρSi mmol m-2 d-1) for the June and Aug./Sept. cruises in 1999 and 2000. See Chapter 3 for more data on PIC production.  170 4.8 References Allen, J.T., Brown, L., Sanders, R., Moore, C.M., Mustard, A., Fielding, S., Lucas, M., Rixen, M., Savidge, G., Henson, S., Mayor, D., 2005. Diatom carbon export enhanced by silicate upwelling in the northeast Atlantic. 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Seasonal and interannual variability in the distribution of surface nutrients and dissolved inorganic carbon in the northern North Pacific: Influence of El Niño. Journal of Oceanography 58 (2), 227-243.  178 Wong, C.S., Waser, N.A.D., Whitney, F.A., Johnson, W.K., Page, J.S., 2002b. Time-series study of the biogeochemistry of the north east subarctic Pacific: reconciliation of the Corg/N remineralization and uptake ratios with the Redfield ratios. Deep Sea Research Part II: Topical Studies in Oceanography 49 (24-25), 5717-5738   179 Chapter 5 : General Conclusions 5.1 Introduction Up to 1992, studies on the phytoplankton assembledge and processes in the subarctic NE Pacific concentrated mainly on Ocean Station Papa (OSP/P26) (Tabata, 1985; Welschmeyer et al., 1993; Wong et al., 1995; Boyd et al., 1999). From 1992-1997, the Canadian Joint Ocean Global Flux Study (JGOFS) focused on the physical, chemical and biological components along Line P and their results acted as a springboard for my research. Despite the numerous studies conducted at P26 and the vicinity, there are very few detailed studies on the response of nutrients and phytoplankton processes to the El Niño/La Niña cycle. Coccolithophore and diatoms are two important components of the phytoplankton community which contribute to C flux to depth, and yet their temporal and spatial dynamics are relatively poorly understood. The focus of this study was to compare nutrient and phytoplankton dynamics during the 1998/99 El Niño/La Niña cycle and also year 2000. In addition, this study investigated the contribution of coccolithophores and diatoms to the phytoplankton ecology of waters along Line P and documented more variability in nutrient and phytoplankton dynamics than expected.  5.2 Line P from present to the future It has been suggested that Line P and the surrounding Gulf of Alaska (GOA) is in the process of warming as well as freshening (Royer and Grosch, 2006; Crawford et al., 2007; Whitney et al., 2007). At present, it is not clear whether these changes are linked to global climate change. The surface warming along Line P has resulted in a shallower, more stratified mixed layer and it has been suggested that this general trend will likely continue (Whitney et al., 2007). More importantly, the shallowing of the mixed layer coupled with increased thermal stratification should result in a decrease in nutrients in the surface water due to reduced vertical mixing and thus further reduce primary production along Line P. This was demonstrated by the shallower mixed layer (especially in June) as well as diminished nutrient concentrations which resulted on a reduction in phytoplankton biomass and production during the 1998 El Niño compared to the 1999 La Niña (Chapter 2).  180 Conversely, an increase in the global atmospheric temperature due to an increase in CO2 may also result in an increase in atmospheric iron (Gaspari et al., 2006). Although the actual impact of atmospheric iron supply on phytoplankton in subarctic Pacific waters is not clear (Boyd et al., 1998; Johnson et al., 2005; Lam et al., 2006), an increase of iron availability due to increased atmospheric input could result in an enhancement in phytoplankton biomass and production along Line P. This could possibly offset the decreased biomass and production due to the shallowing of the mixed layer. Currently, it is thought that the impact of atmospheric iron on phytoplankton of the NE subarctic Pacific is minimal and any increase in atmospheric iron may have little to no consequence since a significant amount of the surface iron may come from vertically transported or horizontally advected waters (F. Whitney pers. comm.).  5.3 Fate of phytoplankton along a warmer Line P If the waters in the NE subarctic Pacific continue to warm (Masson and Cummins, 2007; Whitney et al., 2007), there could be gradual change in the phytoplankton assemblage. Using the 1998 El Niño as a proxy for warmer waters with a shallower mixed layer, there would probably be an increase in diatom and coccolithophores abundances, possibly due to an increase of light because of the shallower mixed layer and an increase in iron availability. If there is an additional input of iron into the GOA due to atmospheric inputs (Boyd et al., 1998), or from additional eddy activity (Whitney and Robert, 2002), or other inputs (Lam et al., 2006), it could have an effect on the seasonal abundance of phytoplankton in the HNLC portion of the subarctic Pacific. Evidence from this study has shown that although there was not a significant seasonal difference in total chlorophyll a concentrations at the HNLC stations P20 and P26 (Chapter 2), there was an increase in POC production in the spring as well as an increase in diatom biomass in June 1998 compared to Aug/Sept. Additionally, there was also an increase in the average POC and bSi flux (Wong et al., 1999) in May and June between 1982 and 1993. The difference that occurs between phytoplankton biomass and production can be mainly attributed to variations in C:Chl a between seasons as well as a phytoplankton assembledge composed of small cells that are reliant on regenerated nitrogen (Varela and Harrison, 1999). However, if the input of iron increases due to an increase in dust input (Mahowald et al., 1999), this could result in a shift from small cells that utilize regenerated nutrients to a stronger  181 spring signal of phytoplankton biomass (more faster growing diatoms) that utilizes nitrate when iron is more available, leading to an increase in new production. This scenario would resemble the more pronounce diatom spring bloom that occurs in the western Pacific gyre where iron concentrations are higher than in the eastern Pacific gyre(Harrison et al., 2004). This increase in diatoms would result in an increased drawdown of silicic acid in the surface mixed layer similar to observations during the warmer 1998 period of this study (Chapter 4). These changes may already occur sporadically at P26 as shown by Wong and Matear (1999) who recorded sporadic silicic acid limitation at P26 between 1970-1980. Such an increase should result in an increased flux of biogenic particles, including POC and bSi into the sediments and thus an increase in the silicate pump (Dugdale et al., 1995). Additionally, a sporadic increase in iron input from atmospheric dust coupled with a shallowing of the mixed layer could also play a role in climate feedback in the NE subarctic region. Such a switch would increase new production and hence the ƒ-ratio, favoring large cells such as diatoms and larger autotrophic dinoflagellates. A shallowing of the mixed layer would also favor coccolithophores that are good competitors at higher light (Putland et al., 2004). Such a combination could result in an increase in DMS production due to higher production. Recent lab studies have shown that E. huxleyi and diatoms increase their DMS activity per cell under nitrogen limitation (Sunda et al., 2007), possibly resulting in a negative atmospheric feedback in the region. Indeed, during the 1998 El Niño, where there was a shallowing of the mixed layer coupled with increased oceanic temperatures, the concentration of diatoms and coccolithophores were higher compared to the colder 1999 La Niña. Interestingly, using samples from the same cruises in 1998 and 1999, Wong et al. (2006) did find dramatically increased concentrations of DMS in June 1998 at P26 compared to 1999. 5.4 Increasing acidification scenario along Line P Recently, evidence indicates that the oceans are becoming more acidic due to an increase in atmospheric CO2 due to anthropogenic inputs. The hydrolysis of CO2 in seawater will increase the hydrogen ion concentration, [H+]. and therefore gradually decrease the pH of the ocean (Haugan and Drange, 1996; Orr et al., 2005). This reduction in pH will also reduce carbonate ion (CO32+) concentrations which will in turn affect calcium carbonate saturation. This gradual ‘acidification’ of the ocean will specifically have an effect on plankton (as well as  182 corals) that produce calcium carbonate structures. In particular, the ability of coccolithophores to divide and form coccoliths will decrease, resulting in a reduction in their capacity to produce calcium carbonate (Tyrrell, 2008). Studies have shown that a small reduction of seawater pH will lower the overall rate of calcification in coccolithophores (Raven et al., 2005). Additionally, such a reduction will also reduce the PIC production per cell resulting in smaller and thinner coccoliths and these cells may be potentially less competitive compared to non-calcifying phytoplankton (Riebesell et al., 2000; Zondervan et al., 2002; Tyrrell, 2008). As demonstrated in Chapter 3, coccolithophores, specifically Emiliania huxleyi, are found in nearly every sample at every station along Line P. They have the ability to reach bloom concentrations at both near shelf and HNLC stations and they are the primary group affecting PIC production and flux below the mixed layer. They are also an important DMSP producer in the NE subarctic Pacific (Wong et al., 2006). Thus, any change in their abundance, growth rate and ability to produce calcium carbonate could have an effect on phytoplankton population dynamics and PIC flux, as well as have an effect on climate feedback in the NE subarctic Pacific. Therefore, increasing acidification in the subarctic Pacific could have two impacts on coccolithophores along Line P, a lower abundance of coccolithophores and a reduction in PIC fixation per cell. This lower rate of total PIC fixation along Line P would likely reduce the abundance of calcifying primary producers and the PIC export from the surface to the deeper ocean As well as having an impact on carbonate chemistry, the acidification of the ocean will also affect other facets of marine chemistry (Raven et al., 2005). A change in ocean acidification also impacts trace metal speciation. Such a change would have an effect on iron chemistry, altering its availability to marine phytoplankton. This would influence the normally replete areas of Line P (P04-P12) as well as the iron depleted HNLC regions (P20-P26). Presently, little is understood about the specific in situ impact of such a change (Tyrrell, 2008). Interestingly, two impacts of climate change, increased CO2 leading to increased acidification and the shallowing of the mixed layer could have the opposite effects. Increased acidification could reduce POC fixation, while the shallower mixed layer could increase it.  183 5.5 Summary The NE subarctic Pacific is a region of low POC production and autotrophic biomass. Generally, autotrophic cells <5 m dominate most of Line P throughout the year and mainly utilize regenerated nitrogen. Episodic occurrences of diatom production were observed, in agreement with previous reports of occasional high carbon export fluxes determined from materials collected from sediment trap material (e.g. Takahashi, 1986, 1987; Takahashi et al., 1990). However, it appears from my study that certain phytoplankton groups (e.g. coccolithophores and diatoms) can play an important long term and seasonal role in production and export, both at the near-shelf stations as well as the HNLC region. Interestingly, this study as well as others (Lam et al., 2006) suggests that winter may also play an important role in the plankton biology of the region. The winter period has been relatively ignored in most of the early studies and it certainly warrants further investigation. The results of this study underscore the importance of maintaining and expanding the Line P program. Due to the long term data set from the weathership program as well as studies including the Subarctic Pacific Ecosystem Research (SUPER) and VERTical Exchange (VERTEX) programs at Ocean Station Papa (P26) as well as the extensive research along Line from the Canadian JGOFS program, a greater understanding of phytoplankton dynamics has been obtained. This study has provided evidence of the dynamic nature of phytoplankton production and the importance of coccolithophores and diatoms to the Line P ecosystem. More research including remote sensing, moorings, and sediment trap analysis is necessary to help understand the actual occurrence of coccolithophore and diatom blooms and their importance in exporting both inorganic and organic forms of carbon to the sea floor. 5.6 Limits of this work This study covers the 5 major stations along Line P over a 3 year period (1998-2000) for a total of 8 cruises and did not cover the winter period (February) in 2000. This research was a continuation of the Canadian JGOFS program (Boyd et al., 1999) which was also a continuation of the Institute of Ocean Sciences Line P program (Wong et al., 1995; Peña and Varela, 2007). Therefore, the program and sampling regime had already been established and did not allow for variation of time frame or sampling locations.  184 Any study that tries to ascertain the temporal and spatial dynamics of something as dynamic as a phytoplankton ecosystem immediately comes under distinct limitations. Ideally, it is best to maximize the sampling frequency and regional coverage to increase the precision of the analysis undertaken in this study. Increasing the station numbers as well as adopting a grid pattern would allow for better coverage of such a vast and dynamic ecosystem as the NE subarctic Pacific. Previous studies have shown that parameters along Line P are surprisingly patchy due to anomalies as eddies and episodic phytoplankton ‘blooms’ (Wong et al., 1995; Whitney and Robert, 2002; Putland et al., 2004; Lam et al., 2006). Even though each separate cruise totaled three to four weeks in duration, this work can not in any way be interpreted as a truly comprehensive treatise of the area of the NE subarctic Pacific or even Line P. Every effort was made to uniformly sample each station at the same time and in the same manner so as to minimize errors when making comparisons among stations. However, this means that even during the more prolific cruise years (1998 and 1999; Feb, June and Aug/Sept), each station was at best only sampled 3 times over a whole year. Therefore, seasonal variation is truly difficult to ascertain with such a small sample size. Even though there are clear limitations inherent in the experimental design of this study, there were several advantages. The first advantage was the timing of the research itself. The period of 1997-1999 encompassed one of the strongest El Niño / La Niña cycles recorded in the region, allowing additional insight into the dynamics of the autotrophic phytoplankton during that time period. An additional strength of this research was the large amount of historical data available from Ocean Station Papa (P26) and the more recent Line P program (Boyd et al., 1999; Wong et al., 2002; Peña and Bograd, 2007). The long established base line sampling program that is still active along Line P (http://www.pac.dfo- mpo.gc.ca/SCI/osap/projects/linepdata/default_e.htm) allowed the incorporation of essential physical and chemical data in tandem with this study. There have also been studies that have occurred after this one, such as the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES) in 2002 that gives insights into the effects of Fe addition to the in situ phytoplankton population. Therefore, even though this study is an incomplete analysis of the phytoplankton dynamics along Line P, it provides a strong contribution to the extensive research that has already occurred in the region as well as a good stepping stone to future work.  185 5.7 Future Studies  This thesis leads to a number of additional studies that would complement the result obtained from this research. Interesting future research may include: 1. A further continuation of measurements of size-fractioned chlorophyll, POC production as well as bacterial production, nutrients and POC. It is clear that the research benefits most when all the parameters that effect phytoplankton dynamics can be inter-compared. 2. Samples collected from sediment traps (both past and future) need to be analyzed for phytoplankton species with a special emphasis on the well preserved structures of coccoliths, diatom frustules and thecal plates of dinoflagellates. This would allow a greater understanding of the seasonality of the differing phytoplankton assemblages through the course of a whole year as opposed to single point sampling. 3. A better understanding of the effects of low inputs (either constant or pulsed) of Fe in the waters of the NE subarctic Pacific, both in the lab and on a larger scale in the field. We have already tested the effects of a large scale Fe fertilization experiment at P26 in the summer. However, we need to test more realistic input conditions such as real atmospheric dust that are similar to the effects of continental or atmospheric inputs. 4. The connection between coccolithophore plate production and PIC production needs to be greater scrutinized in the lab with single clone experiments. This would help to understand the disconnect between coccolithophore abundance and PIC production that we found in this study. 5. More studies are needed on the effects of chemical and physical parameters on the abundance and growth rates of coccolithophores, with a special emphasis on Emiliania huxleyi. This would help to further understand what factors affect the production of this important phytoplankton group that has been shown to bloom at different seasons and locations along Line P. This is important because it would help determine if an increasing abundance of coccolithophores is occurring along  186 Line P and if they are representing sources or sinks of CO2 to the mixed layer and the atmosphere. 6. There is a need to determine diatom silica dissolution rates, especially during periods of higher diatom production. This would allow for a more precise understanding of gross and net silica production that may be an important missing component to the silica pump in the NE subarctic Pacific. 7. Lab analysis on the growth and dormancy characteristics of the larger, slow growing, typical centric diatom that are found persistently at all stations and seasons (especially winter) along Line P. This would help elucidate their importance to the year long production and phytoplankton dynamics at Line P. 8. This study has demonstrated that winter is unexpectedly productive. It has been largely ignored until recently, mainly due to the challenging sea state working conditions. 9. A large amount of the phytoplankton biomass is often composed of the <5 um size fraction, yet we know very little about the species that dominate this size fraction.  187 5.8 References  Boyd, P.W., Wong, C.S., Merrill, J., Whitney, F., Snow, J., Harrison, P.J., Gower, J., 1998. Atmospheric iron supply and enhanced vertical carbon flux in the NE subarctic Pacific: Is there a connection? Global Biogeochemical Cycles 12 (3), 429-441. Boyd, P.W., Harrison, P.J., Johnson, B.D., 1999. The Joint Global Ocean Flux Study (Canada) in the NE subarctic Pacific. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2345-2350. Crawford, W., Galbraith, J., Bolingbroke, N., 2007. Line P ocean temperature and salinity, 1956- 2005. Progress in Oceanography 75 (2), 161-178. Dugdale, R.C., Wilkerson, F.P., Minas, H.J., 1995. The role of a silicate pump in driving new production. Deep Sea Research 42 (5), 697-719. Gaspari, V., Barbante, C., Cozzi, G., Cescon, P., Boutron, C.F., Gabrielli, P., Capodaglio, G., Ferrari, C., Petit, J.R., Delmonte, B., 2006. Atmospheric iron fluxes over the last deglaciation: Climatic implications. Geophysical Research Letters 33 (3). Harrison, P.J., Whitney, F.A., Tsuda, A., Saito, H., Tadokoro, K., 2004. Nutrient and plankton dynamics in the NE and NW gyres of the subarctic Pacific Ocean. Journal of Oceanography 60 (1), 93-117. Haugan, P.M., Drange, H., 1996. Effects of CO2 on the ocean environment. Energy Conversion and Management 37 (6-8), 1019-1022. Johnson, W.K., Miller, L.A., Sutherland, N.E., Wong, C.S., 2005. Iron transport by mesoscale Haida eddies in the Gulf of Alaska. Deep Sea Research Part II: Topical Studies in Oceanography 52 (7-8), 933-953. Lam, P.J., Bishop, J.K.B., Henning, C.C., Marcus, M.A., Waychunas, G.A., Fung, I.Y., 2006. Wintertime phytoplankton bloom in the subarctic Pacific supported by continental margin iron. Global Biogeochemical Cycles 20 (1), Gb1006, doi:1029/2005GB002557. Mahowald, N., Kohfeld, K., Hansson, M., Balkanski, Y., Harrison, S.P., Prentice, I.C., Schulz, M., Rodhe, H., 1999. Dust sources and deposition during the last glacial maximum and current climate: A comparison of model results with paleodata from ice cores and marine sediments. Journal of Geophysical Research-Atmospheres 104 (D13), 15895-15916. Masson, D., Cummins, P.F., 2007. Temperature trends and interannual variability in the Strait of Georgia, British Columbia. Continental Shelf Research 27 (5), 634-649. Orr, J.C., Fabry, V.J., Aumont, O., Bopp, L., Doney, S.C., Feely, R.A., Gnanadesikan, A., Gruber, N., Ishida, A., Joos, F., Key, R.M., Lindsay, K., Maier-Reimer, E., Matear, R., Monfray, P., Mouchet, A., Najjar, R.G., Plattner, G.K., Rodgers, K.B., Sabine, C.L.,  188 Sarmiento, J.L., Schlitzer, R., Slater, R.D., Totterdell, I.J., Weirig, M.F., Yamanaka, Y., Yool, A., 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437 (7059), 681-686. Peña, M.A., Bograd, S.J., 2007. Time series of the northeast Pacific. Progress in Oceanography 75 (2), 115-119. Peña, M.A., Varela, D.E., 2007. Seasonal and interannual variability in phytoplankton and nutrient dynamics along Line P in the NE subarctic Pacific. Progress in Oceanography 75 (2), 200-222. Putland, J.N., Whitney, F.A., Crawford, D.W., 2004. Survey of bottom-up controls of Emiliania huxleyi in the northeast subarctic Pacific. Deep Sea Research Part I: Oceanographic Research Papers 51 (12), 1793-1802. Raven, J.A., Caldeira, K., Elderfield, H., 2005. Ocean Acidification due to Increasing Atmospheric Carbon Dioxide. Royal Society, London. Riebesell, U., Zondervan, I., Rost, B., Tortell, P.D., Zeebe, R.E., Morel, F.M.M., 2000. Reduced calcification of marine plankton in response to increased atmospheric CO2. Nature 407 (6802), 364-367. Royer, T.C., Grosch, C.E., 2006. Ocean warming and freshening in the northern Gulf of Alaska. Geophysical Research Letters 33 (16). Sunda, W.G., Hardison, R., Kiene, R.P., Bucciarelli, E., Harada, H., 2007. The effect of nitrogen limitation on cellular DMSP and DMS release in marine phytoplankton: climate feedback implications. Aquatic Sciences 69 (3), 341-351. Tabata, S., 1985. Statistics of oceanographic data based on hydrographic/STD casts made at Ocean Station P during August 1956 through June 1981. Canadian Data Report of Hydrography and Ocean Sciences 31. Takahashi, K., 1986. Seasonal fluxes of pelagic diatoms in the subarctic Pacific, 1982-1983. Deep-Sea Research Part a-Oceanographic Research Papers 33 (9), 1225-1251. Takahashi, K., 1987. Response of subarctic Pacific diatom fluxes to the 1982-1983 El Niño disturbance. Journal of Geophysical Research-Oceans 92 (C13), 14387-14392. Takahashi, K., Billings, J.D., Morgan, J.K., 1990. Oceanic province: Assessment from the time- series diatom fluxes in the northeastern Pacific. Limnology and Oceanography 35 (1), 154-165. Tyrrell, T., 2008. Calcium carbonate cycling in future oceans and its influence on future climates. Journal of Plankton Research 30 (2), 141-156.  189 Varela, D.E., Harrison, P.J., 1999. Seasonal variability in nitrogenous nutrition of phytoplankton assemblages in the northeastern subarctic Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 46, 2505-2538. Welschmeyer, N.A., Strom, S., Goericke, R., DiTullio, G.R., Belvin, M., Peterson, W., 1993. Primary production in the subarctic Pacific Ocean: Project SUPER. Progress in Oceanography 32 (1-4), 101-135. Whitney, F., Robert, M., 2002. Structure of Haida eddies and their transport of nutrient from coastal margins into the NE Pacific Ocean. Journal of Oceanography 58 (5), 715-723. Whitney, F.A., Freeland, H.J., Robert, M., 2007. Persistently declining oxygen levels in the interior waters of the eastern subarctic Pacific. Progress in Oceanography 75 (2), 179- 199. Wong, C.S., Whitney, F.A., Iseki, K., Page, J.S., Zeng, J., 1995. Analysis of trends in primary productivity and chlorophyll a over two decades at Ocean Station P (50°N 145°W) in the subarctic northeast Pacific Ocean. Canadian Journal Fisheries Aquatic Sciences 121, 107- 117. Wong, C.S., Matear, R.J., 1999. Sporadic silicate limitation of phytoplankton productivity in the subarctic NE Pacific. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2539-2555. Wong, C.S., Whitney, F.A., Crawford, D.W., Iseki, K., Matear, R.J., Johnson, W.K., Page, J.S., 1999. Seasonal and interannual variability in particle fluxes of carbon, nitrogen and silicon from time series of sediment traps at Ocean Station P, 1982-1993: relationship to changes in subarctic primary productivity. Deep Sea Research Part II: Topical Studies in Oceanography 46 (11-12), 2735-2760. Wong, C.S., Waser, N.A.D., Whitney, F.A., Johnson, W.K., Page, J.S., 2002. Time-series study of the biogeochemistry of the north east subarctic Pacific: reconciliation of the Corg/N remineralization and uptake ratios with the Redfield ratios. Deep Sea Research Part II: Topical Studies in Oceanography 49 (24-25), 5717-5738. Wong, C.S., Wong, S.E., Peña, M.A., Levasseur, M., 2006. Climatic effect on DMS producers in the NE subarctic Pacific: ENSO on the upper ocean. Tellus B 58 (4), 319-326. Zondervan, I., Rost, B., Riebesell, U., 2002. Effect of CO2 concentration on the PIC/POC ratio in the coccolithophore Emiliania huxleyi grown under light-limiting conditions and different daylengths. Journal of Experimental Marine Biology and Ecology 272 (1), 55- 70.  190 Appendix A: Publications arising from this thesis  Lipsen, M.S., Crawford, D.W., Gower, J., Harrison, P.J., 2007. Spatial and temporal variability in coccolithophore abundance and production of PIC and POC in the NE subarctic Pacific during El Nino (1998), La Nina (1999) and 2000. Progress in Oceanography 75 (2), 304-325.  Other relevant publications:  Crawford, D.W., Lipsen, M.S., Purdie, D.A., Lohan, M.C., Statham, P.J., Whitney, F.A., Putland, J.N., Johnson, W.K., Sutherland, N., Peterson, T.D., Harrison, P.J., Wong, C.S., 2003. Influence of zinc and iron enrichments on phytoplankton growth in the northeastern subarctic Pacific. Limnology and Oceanography 48 (4), 1583-1600.  191 Appendix B: Line P Size-Fractionated Chlorophyll a Table A.1. Size fractionated chlorophyll a along Line P.          Irradiance Chlorophyll a (mg chl a m-3)    Depth μmol photons Cruise Station % Io m m-2 d-1 0.2-5.0 um 5.0-20 um >20 um Total 9803 P04 100 2 12.6 0.24 0.08 0.01 0.34 9803 P04 55 5 6.9 0.30 0.03 0.03 0.36 9803 P04 30 10 3.8 0.32 0.05 0.01 0.38 9803 P04 10 15 1.3 0.33 0.04 0.04 0.42 9803 P04 3.5 30 0.4 0.46 0.05 0.05 0.55 9803 P04 1 40 0.1 0.46 0.04 0.04 0.54 9803 P12 100 5 10.6 0.20 0.05 0.06 0.31 9803 P12 55 10 5.8 0.24 0.04 0.06 0.34 9803 P12 30 15 3.2 0.18 0.04 0.05 0.27 9803 P12 10 25 1.1 0.24 0.04 0.06 0.33 9803 P12 3.5 35 0.4 0.27 0.05 0.04 0.36 9803 P12 1 50 0.1 0.28 0.05 0.06 0.39 9803 P16 100 5 7.7 0.43 0.05 0.02 0.50 9803 P16 55 15 4.2 0.35 0.07 0.03 0.45 9803 P16 30 20 2.3 0.32 0.06 0.04 0.42 9803 P16 10 35 0.8 0.31 0.07 0.05 0.43 9803 P16 3.5 45 0.3 0.35 0.09 0.06 0.50 9803 P16 1 60 0.1 0.26 0.06 0.04 0.36 9803 P20 100 2 12.5 0.25 0.06 0.03 0.33 9803 P20 55 10 6.9 0.26 0.06 0.03 0.34 9803 P20 30 20 3.8 0.24 0.04 0.04 0.32 9803 P20 10 30 1.3 0.24 0.05 0.02 0.31 9803 P20 3.5 50 0.4 0.26 0.06 0.03 0.34 9803 P20 1 80 0.1 0.26 0.06 0.03 0.35 9803 P26 100 5 14.7 0.18 0.05 0.04 0.27 9803 P26 55 10 8.1 0.17 0.04 0.03 0.24 9803 P26 30 20 4.4 0.16 0.04 0.03 0.23 9803 P26 10 35 1.5 0.14 0.05 0.04 0.23 9803 P26 3.5 50 0.5 0.20 0.04 0.04 0.28 9803 P26 1 80 0.1 0.09 0.03 0.04 0.16 9815 P04 100 2 39.1 0.19 0.05 0.09 0.33 9815 P04 55 3 21.5 0.07 0.05 0.05 0.17 9815 P04 30 5 11.7 0.17 0.04 0.05 0.25 9815 P04 10 13 3.9 0.16 0.03 0.02 0.21 9815 P04 3.5 24 1.4 0.20 0.04 0.02 0.27 9815 P04 1 33 0.4 0.33 0.05 0.11 0.50 9815 P12 100 2 22.8 0.08 0.01 0.06 0.16 9815 P12 55 3 35.7 0.07 0.01 0.05 0.13 9815 P12 30 5 12.1 0.09 0.02 0.04 0.15 9815 P12 10 17 13.5 0.08 0.01 0.04 0.14 9815 P12 3.5 27 4.6 0.43 0.05 0.35 0.83  192         Irradiance Chlorophyll a (mg chl a m-3)    Depth μmol photons Cruise Station % Io m m-2 d-1 0.2-5.0 um 5.0-20 um >20 um Total 9815 P12 1 40 1.6 0.53 0.03 0.10 0.66 9815 P16 100 3 27.8 0.48 0.03 0.06 0.57 9815 P16 55 6 15.3 0.11 0.03 0.05 0.19 9815 P16 30 12 8.3 0.43 0.02 0.06 0.50 9815 P16 10 26 2.8 0.45 0.02 0.03 0.50 9815 P16 3.5 38 1.0 0.19 0.02 0.01 0.22 9815 P16 1 52 0.3 0.26 0.03 0.02 0.31 9815 P20 100 2 46.3 0.10 0.04 0.09 0.23 9815 P20 55 5 25.5 0.05 0.05 0.08 0.18 9815 P20 30 10 13.9 0.08 0.06 0.11 0.25 9815 P20 10 24 4.6 0.08 0.04 0.17 0.29 9815 P20 3.5 39 1.6 0.12 0.06 0.07 0.25 9815 P20 1 58 0.5 0.12 0.10 0.07 0.29 9815 P26 100 2 18.0 0.14 0.11 0.08 0.33 9815 P26 55 5 9.9 0.18 0.09 0.09 0.35 9815 P26 30 9 5.4 0.14 0.11 0.09 0.35 9815 P26 10 21 1.8 0.28 0.08 0.12 0.49 9815 P26 3.5 33 0.6 0.22 0.08 0.10 0.40 9815 P26 1 50 0.2 0.10 0.03 0.09 0.22 9829 P04 100 2 44.2 0.35 0.05 0.01 0.41 9829 P04 55 3 24.3 0.17 0.03 0.01 0.21 9829 P04 30 5 13.3 0.14 0.04 0.01 0.19 9829 P04 10 13 4.4 0.25 0.04 0.01 0.30 9829 P04 3.5 24 1.5 0.61 0.11 0.01 0.74 9829 P04 1 33 0.4 0.40 0.13 0.01 0.54 9829 P12 100 2 24.9 0.08 0.04 0.00 0.12 9829 P12 55 3 13.7 0.06 0.03 0.01 0.10 9829 P12 30 5 7.5 0.06 0.02 0.00 0.09 9829 P12 10 20 2.5 0.07 0.04 0.01 0.12 9829 P12 3.5 31 0.9 0.20 0.09 0.01 0.30 9829 P12 1 45 0.2 0.37 0.14 0.01 0.51 9829 P16 100 3 28.2 0.07 0.03 0.01 0.10 9829 P16 55 6 15.5 0.06 0.03 0.00 0.10 9829 P16 30 15 8.5 0.07 0.03 0.01 0.10 9829 P16 10 30 2.8 0.12 0.05 0.01 0.19 9829 P16 3.5 45 1.0 0.31 0.11 0.01 0.43 9829 P16 1 55 0.3 0.24 0.07 0.01 0.32 9829 P20 100 2 24.5 0.03 0.08 0.01 0.12 9829 P20 55 5 13.5 0.01 0.07 0.01 0.09 9829 P20 30 10 7.4 0.04 0.04 0.01 0.09 9829 P20 10 25 2.5 0.03 0.07 0.01 0.11 9829 P20 3.5 40 0.9 0.07 0.13 0.00 0.20 9829 P20 1 60 0.2 0.06 0.02 0.01 0.08 9829 P26 100 2 34.1 0.14 0.11 0.03 0.29 9829 P26 55 4 18.8 0.16 0.09 0.05 0.29 9829 P26 30 6 10.2 0.11 0.07 0.03 0.21  193         Irradiance Chlorophyll a (mg chl a m-3)    Depth μmol photons Cruise Station % Io m m-2 d-1 0.2-5.0 um 5.0-20 um >20 um Total 9829 P26 10 20 3.4 0.17 0.08 0.03 0.28 9829 P26 3.5 35 1.2 0.14 0.10 0.03 0.26 9829 P26 1 55 0.3 0.10 0.02 0.01 0.13 9901 P04 100 2 13.3 0.30 0.12 0.07 0.48 9901 P04 55 5 7.3 0.34 0.10 0.05 0.49 9901 P04 30 10 4.0 0.35 0.13 0.06 0.53 9901 P04 10 15 1.3 0.24 0.10 0.05 0.38 9901 P04 3.5 30 0.5 0.33 0.13 0.05 0.52 9901 P04 1 40 0.1 0.18 0.12 0.05 0.36 9901 P12 100 2 15.7 0.33 0.09 0.04 0.46 9901 P12 55 10 8.6 0.29 0.09 0.05 0.43 9901 P12 30 20 4.7 0.29 0.08 0.04 0.41 9901 P12 10 30 1.6 0.33 0.06 0.05 0.44 9901 P12 3.5 50 0.5 0.30 0.05 0.03 0.38 9901 P12 1 80 0.2 0.03 0.01 0.01 0.05 9901 P16 100 2 4.8 0.16 0.07 0.05 0.28 9901 P16 55 10 2.7 0.12 0.06 0.06 0.24 9901 P16 30 20 1.4 0.16 0.06 0.05 0.28 9901 P16 10 35 0.5 0.11 0.05 0.04 0.20 9901 P16 3.5 50 0.2 0.16 0.18 0.05 0.38 9901 P16 1 75 0.0 0.08 0.07 0.05 0.20 9901 P20 100 2 18.1 0.32 0.15 0.06 0.53 9901 P20 55 10 10.0 0.22 0.15 0.07 0.44 9901 P20 30 20 5.4 0.24 0.15 0.07 0.46 9901 P20 10 30 1.8 0.34 0.13 0.03 0.50 9901 P20 3.5 50 0.6 0.28 0.16 0.07 0.52 9901 P20 1 75 0.2 0.28 0.12 0.07 0.47 9901 P26 100 5 7.7 0.27 0.09 0.05 0.41 9901 P26 55 15 4.2 0.25 0.07 0.05 0.37 9901 P26 30 20 2.3 0.23 0.07 0.04 0.35 9901 P26 10 35 0.8 0.25 0.08 0.04 0.36 9901 P26 3.5 45 0.3 0.25 0.08 0.05 0.37 9901 P26 1 60 0.1 0.26 0.07 0.05 0.38 9910 P04 100 2 30.3 0.37 0.18 0.10 0.65 9910 P04 55 5 16.7 0.36 0.28 0.10 0.74 9910 P04 30 9 9.1 0.38 0.33 0.07 0.78 9910 P04 10 16 3.0 0.94 0.39 0.16 1.49 9910 P04 3.5 24 1.1 0.64 0.43 0.11 1.18 9910 P04 1 35 0.3 0.31 0.19 0.05 0.56 9910 P12 100 2 32.1 0.13 0.17 0.04 0.33 9910 P12 55 8 17.7 0.32 0.10 0.04 0.45 9910 P12 30 18 9.6 0.32 0.06 0.04 0.41 9910 P12 10 40 3.2 0.79 0.13 0.03 0.94 9910 P12 3.5 53 1.1 0.34 0.05 0.01 0.40 9910 P12 1 60 0.3 0.37 0.07 0.02 0.46 9910 P16 100 3 22.9 0.08 0.03 0.02 0.13  194         Irradiance Chlorophyll a (mg chl a m-3)    Depth μmol photons Cruise Station % Io m m-2 d-1 0.2-5.0 um 5.0-20 um >20 um Total 9910 P16 55 6 12.6 0.06 0.03 0.05 0.14 9910 P16 30 12 6.9 0.09 0.03 0.05 0.17 9910 P16 10 26 2.3 0.08 0.03 0.03 0.13 9910 P16 3.5 38 0.8 0.11 0.05 0.03 0.19 9910 P16 1 52 0.2 0.19 0.05 0.03 0.27 9910 P20 100 2 42.1 0.16 0.04 0.03 0.23 9910 P20 55 5 23.2 0.16 0.05 0.07 0.28 9910 P20 30 20 12.6 0.13 0.03 0.04 0.21 9910 P20 10 35 4.2 0.18 0.07 0.03 0.29 9910 P20 3.5 50 1.5 0.25 0.05 0.06 0.37 9910 P20 1 65 0.4 0.18 0.04 0.06 0.28 9910 P26 100 2 20.9 0.15 0.13 0.08 0.36 9910 P26 55 5 11.5 0.20 0.08 0.04 0.33 9910 P26 30 15 6.3 0.23 0.09 0.06 0.37 9910 P26 10 30 2.1 0.26 0.06 0.03 0.35 9910 P26 3.5 50 0.7 0.26 0.07 0.04 0.37 9910 P26 1 65 0.2 0.14 0.13 0.11 0.37 9921 P04 100 2 32.7 0.31 0.12 0.05 0.47 9921 P04 55 6 18.0 0.23 0.11 0.03 0.38 9921 P04 30 9 9.8 0.19 0.11 0.05 0.35 9921 P04 10 16 3.3 0.33 0.15 0.04 0.51 9921 P04 3.5 23 1.1 0.31 0.07 0.08 0.46 9921 P04 1 35 0.3 0.24 0.24 0.04 0.52 9921 P12 100 2 43.8 0.21 0.11 0.01 0.32 9921 P12 55 6 24.1 0.36 0.10 0.01 0.47 9921 P12 30 10 13.1 0.27 0.11 0.01 0.39 9921 P12 10 20 4.4 0.25 0.06 0.01 0.33 9921 P12 3.5 31 1.5 0.22 0.04 0.01 0.27 9921 P12 1 45 0.4 0.22 0.04 0.01 0.26 9921 P16 100 3 64.0 0.20 0.05 0.03 0.27 9921 P16 55 6 35.2 0.20 0.04 0.02 0.26 9921 P16 30 15 19.2 0.17 0.05 0.02 0.24 9921 P16 10 30 6.4 0.23 0.05 0.02 0.29 9921 P16 3.5 40 2.2 0.15 0.11 0.01 0.27 9921 P16 1 55 0.6 0.09 0.01 0.01 0.11 9921 P20 100 2 23.3 0.07 0.03 0.01 0.11 9921 P20 55 5 12.8 0.07 0.02 0.01 0.11 9921 P20 30 10 7.0 0.09 0.02 0.02 0.12 9921 P20 10 25 2.3 0.09 0.02 0.02 0.12 9921 P20 3.5 40 0.8 0.11 0.03 0.01 0.15 9921 P20 1 60 0.2 0.08 0.03 0.02 0.13 9921 P26 100 2 22.0 0.16 0.07 0.05 0.28 9921 P26 55 10 12.1 0.11 0.06 0.04 0.21 9921 P26 30 15 6.6 0.12 0.09 0.04 0.24 9921 P26 10 30 2.2 0.19 0.05 0.03 0.28 9921 P26 3.5 40 0.8 0.15 0.05 0.02 0.23  195         Irradiance Chlorophyll a (mg chl a m-3)    Depth μmol photons Cruise Station % Io m m-2 d-1 0.2-5.0 um 5.0-20 um >20 um Total 9921 P26 1 60 0.2 0.11 0.05 0.02 0.17 2000-10 P04 100 2 61.2 0.48 0.10 0.05 0.62 2000-10 P04 55 8 33.6 0.53 0.09 0.04 0.67 2000-10 P04 30 14 18.4 0.46 0.09 0.04 0.60 2000-10 P04 10 25 6.1 0.25 0.03 0.02 0.30 2000-10 P04 3.5 38 2.1 0.23 0.05 0.03 0.31 2000-10 P04 1 50 0.6 0.26 0.05 0.02 0.33 2000-10 P12 100 2 21.5 0.18 0.05 0.04 0.26 2000-10 P12 55 8 11.8 0.18 0.02 0.02 0.22 2000-10 P12 30 17 6.5 0.15 0.03 0.03 0.22 2000-10 P12 10 33 2.2 0.23 0.06 0.03 0.31 2000-10 P12 3.5 51 0.8 0.22 0.04 0.02 0.28 2000-10 P12 1 71 0.2 0.21 0.05 0.01 0.27 2000-10 P16 100 2 28.0 0.18 0.02 0.02 0.22 2000-10 P16 55 9 15.4 0.18 0.03 0.03 0.23 2000-10 P16 30 20 8.4 0.18 0.03 0.02 0.23 2000-10 P16 10 40 2.8 0.21 0.03 0.02 0.25 2000-10 P16 3.5 50 1.0 0.16 0.02 0.03 0.22 2000-10 P16 1 80 0.3 0.15 0.01 0.02 0.18 2000-10 P20 100 2 37.4 0.08 0.02 0.03 0.13 2000-10 P20 55 10 20.6 0.08 0.02 0.04 0.13 2000-10 P20 30 20 11.2 0.07 0.02 0.06 0.16 2000-10 P20 10 40 3.7 0.08 0.04 0.08 0.20 2000-10 P20 3.5 50 1.3 0.08 0.04 0.06 0.17 2000-10 P20 1 80 0.4 0.15 0.01 0.02 0.18 2000-10 P26 100 2 26.4 0.11 0.06 0.06 0.23 2000-10 P26 55 9 14.5 0.11 0.05 0.09 0.25 2000-10 P26 30 20 7.9 0.11 0.06 0.06 0.23 2000-10 P26 10 34 2.6 0.16 0.05 0.10 0.31 2000-10 P26 3.5 50 0.9 0.15 0.03 0.06 0.23 2000-10 P26 1 80 0.3 0.11 0.01 0.02 0.14 2000-25 P04 100 2 40.8 0.38 0.07 0.03 0.48 2000-25 P04 55 6 22.4 0.44 0.05 0.03 0.52 2000-25 P04 30 10 12.2 0.44 0.07 0.03 0.53 2000-25 P04 10 20 4.1 0.38 0.08 0.07 0.52 2000-25 P04 3.5 30 1.4 0.38 0.13 0.07 0.59 2000-25 P04 1 50 0.4 0.06 0.03 0.02 0.11 2000-25 P12 100 2 37.6 0.20 0.19 0.31 0.70 2000-25 P12 55 6 20.7 0.23 0.17 0.28 0.68 2000-25 P12 30 10 11.3 0.22 0.18 0.31 0.71 2000-25 P12 10 20 3.8 0.22 0.18 0.33 0.74 2000-25 P12 3.5 30 1.3 0.20 0.18 0.35 0.72 2000-25 P12 1 50 0.4 0.15 0.10 0.04 0.29 2000-25 P16 100 2 18.1 0.16 0.15 0.08 0.38 2000-25 P16 55 5 9.9 0.20 0.15 0.03 0.38 2000-25 P16 30 10 5.4 0.20 0.15 0.04 0.38  196         Irradiance Chlorophyll a (mg chl a m-3)    Depth μmol photons Cruise Station % Io m m-2 d-1 0.2-5.0 um 5.0-20 um >20 um Total 2000-25 P16 10 20 1.8 0.17 0.17 0.04 0.38 2000-25 P16 3.5 40 0.6 0.22 0.17 0.02 0.41 2000-25 P16 1 66 0.2 0.08 0.05 0.02 0.14 2000-25 P20 100 2 37.7 0.11 0.09 0.03 0.22 2000-25 P20 55 10 20.7 0.10 0.10 0.02 0.22 2000-25 P20 30 18 11.3 0.12 0.08 0.01 0.20 2000-25 P20 10 33 3.8 0.13 0.11 0.03 0.26 2000-25 P20 3.5 48 1.3 0.12 0.07 0.02 0.22 2000-25 P20 1 75 0.4 0.14 0.06 0.02 0.22 2000-25 P26 100 2 28.4 0.25 0.21 0.05 0.51 2000-25 P26 55 8 15.6 0.27 0.20 0.06 0.53 2000-25 P26 30 15 8.5 0.23 0.20 0.06 0.49 2000-25 P26 10 35 2.8 0.29 0.20 0.05 0.53 2000-25 P26 3.5 44 1.0 0.24 0.11 0.04 0.40 2000-25 P26 1 50 0.3 0.22 0.13 0.04 0.39  197 Appendix C: Size-Fractionated POC and PIC Production Table B.1. Size fractionated POC and PIC production along line P.        Productivity (mgC/m3/d)    0.2-5.0 um 5-20 um >20 um Total Cruise Station % Io POC PIC POC PIC POC PIC POC PIC  9803 P04 100 3.71 -0.01 0.62 0.00 0.52 0.02 4.85 0.01 9803 P04 55 2.82 0.05 0.90 0.04 0.49 0.03 4.20 0.12 9803 P04 30 3.03 0.05 0.51 0.02 0.28 0.02 3.82 0.08 9803 P04 10 0.94 0.03 0.09 -0.01 0.10 0.01 1.13 0.03 9803 P04 3.5 0.40 0.00 0.02 0.00 0.05 0.01 0.47 0.01 9803 P04 1 0.31 0.00 0.10 0.00 0.02 -0.01 0.43 -0.01 9803 P12 100 0.73 0.04 0.15 0.06 0.29 -0.01 1.17 0.08 9803 P12 55 3.10 0.02 0.60 0.01 1.05 0.08 4.75 0.10 9803 P12 30 3.70 -0.01 0.50 0.03 1.09 0.06 5.30 0.08 9803 P12 10 3.04 0.05 0.37 0.02 0.83 0.04 4.24 0.11 9803 P12 3.5 2.49 0.03 0.35 0.09 0.50 0.01 3.34 0.13 9803 P12 1 0.64 0.37 0.22 0.06 0.47 0.03 1.33 0.46 9803 P16 100 1.54 0.31 0.26 0.00 0.78 -0.19 2.58 0.12 9803 P16 55 3.37 0.00 1.08 0.32 0.68 -0.19 5.12 0.13 9803 P16 30 4.09 0.14 0.69 -0.11 1.20 -0.19 5.97 -0.16 9803 P16 10 1.85 0.27 0.36 0.09 0.19 -0.12 2.39 0.24 9803 P16 3.5 1.23 -0.16 0.55 -0.02 0.62 -0.22 2.40 -0.40 9803 P16 1 0.75 -0.06 0.17 0.10 0.58 0.54 1.50 0.59 9803 P20 100 0.04 0.07 0.55 0.00 0.03 0.12 0.62 0.19 9803 P20 55 1.46 0.01 0.36 0.33 0.25 0.09 2.07 0.43 9803 P20 30 2.54 -0.03 0.21 0.00 0.12 0.42 2.87 0.39 9803 P20 10 2.38 -0.02 0.50 0.25 0.08 -0.04 2.96 0.19 9803 P20 3.5 1.42 0.16 0.30 0.50 0.01 -0.07 1.73 0.59 9803 P20 1 0.34 0.02 0.07 0.04 -0.01 -0.04 0.40 0.02 9803 P26 100 0.73 0.10 0.36 0.29 0.43 0.00 1.52 0.39 9803 P26 55 2.49 -0.05 0.49 -0.06 0.24 0.21 3.22 0.10 9803 P26 30 2.92 -0.02 0.54 0.01 0.61 0.82 4.07 0.81 9803 P26 10 2.22 -0.01 0.33 -0.02 0.23 0.03 2.78 0.00 9803 P26 3.5 1.31 0.09 0.22 0.17 0.10 0.00 1.64 0.26 9803 P26 1 -0.24 0.18 0.03 -0.03 0.04 0.39 -0.17 0.54 9815 P04 100 4.39 2.77 1.08 1.89 1.02 0.71 6.49 5.37 9815 P04 55 1.80 1.89 0.90 2.71 0.71 -0.49 3.41 4.12 9815 P04 30 4.37 1.25 0.70 2.91 0.82 2.03 5.89 6.19 9815 P04 10 1.76 1.36 0.73 1.08 0.19 -0.39 2.69 2.05 9815 P04 3.5 0.63 0.79 0.48 0.83 0.30 1.89 1.41 3.51 9815 P04 1 0.98 0.12 0.13 0.41 0.05 -0.46 1.16 0.07 9815 P12 100 1.86 0.70 0.41 0.72 0.82 0.61 3.09 2.02 9815 P12 55 2.50 1.75 0.20 -0.01 0.73 0.90 3.42 2.63 9815 P12 30 1.11 1.23 0.26 2.17 0.60 0.45 1.98 3.85 9815 P12 10 1.03 2.16 0.14 0.14 0.57 1.84 1.73 4.14 9815 P12 3.5 1.98 0.36 0.06 -0.13 0.70 0.36 2.74 0.59  198       Productivity (mgC/m3/d)    0.2-5.0 um 5-20 um >20 um Total Cruise Station % Io POC PIC POC PIC POC PIC POC PIC 9815 P12 1 0.83 1.94 0.06 0.02 0.15 1.23 1.04 3.19 9815 P16 100 6.13 5.44 1.01 2.55 1.94 3.16 9.08 11.16 9815 P16 55 6.80 0.03 0.51 1.14 1.93 0.32 9.24 1.49 9815 P16 30 6.67 2.88 1.15 0.03 1.35 1.57 9.16 4.47 9815 P16 10 6.09 0.10 0.49 1.41 0.58 0.02 7.15 1.54 9815 P16 3.5 1.69 1.03 0.43 1.23 0.56 0.22 2.68 2.48 9815 P16 1 0.88 0.37 0.14 0.85 0.44 0.22 1.46 1.43 9815 P20 100 0.71 1.38 0.67 0.55 1.81 2.59 3.19 4.51 9815 P20 55 1.15 1.35 0.69 1.06 2.14 2.13 3.99 4.54 9815 P20 30 1.61 1.66 0.75 2.38 1.57 2.16 3.93 6.20 9815 P20 10 1.86 1.05 0.45 1.70 2.02 2.56 4.33 5.31 9815 P20 3.5 0.42 0.08 0.00 0.16 0.55 2.89 0.97 3.12 9815 P20 1 -0.25 0.56 -0.07 0.65 0.24 1.49 -0.08 2.70 9815 P26 100 6.07 4.98 2.45 1.42 2.18 1.06 10.70 7.45 9815 P26 55 6.38 2.98 3.22 0.16 2.20 -0.18 11.80 2.95 9815 P26 30 4.04 -0.19 1.42 1.07 1.72 3.30 7.18 4.17 9815 P26 10 0.89 2.30 0.64 -0.03 0.72 -1.05 2.25 1.21 9815 P26 3.5 0.34 0.28 0.45 1.58 0.21 -1.77 1.00 0.09 9815 P26 1 0.88 -0.28 0.34 0.93 0.25 0.74 1.46 1.38 9829 P04 100 13.63 0.78 2.08 0.10 2.06 0.04 17.77 0.92 9829 P04 55 15.66 0.04 3.18 0.29 1.87 -0.01 20.71 0.33 9829 P04 30 12.24 0.11 2.82 0.31 3.98 0.02 19.04 0.44 9829 P04 10 9.81 -0.05 2.80 0.10 4.12 0.07 16.73 0.11 9829 P04 3.5 14.45 0.12 4.70 0.26 0.54 -0.01 19.68 0.37 9829 P04 1 6.42 0.08 1.78 0.09 0.27 -0.01 8.47 0.16 9829 P12 100 6.31 0.20 4.02 0.00 0.62 0.03 10.96 0.24 9829 P12 55 7.27 0.41 4.72 0.38 0.69 -0.02 12.68 0.78 9829 P12 30 6.08 0.07 4.08 0.20 0.58 0.05 10.74 0.32 9829 P12 10 3.45 -0.03 2.62 0.09 1.22 0.03 7.29 0.09 9829 P12 3.5 3.33 -0.05 1.96 0.36 0.35 0.13 5.64 0.44 9829 P12 1 2.12 0.17 0.74 0.20 0.12 0.05 2.97 0.42 9829 P16 100 5.64 0.16 3.70 0.24 0.85 0.04 10.19 0.44 9829 P16 55 5.56 0.14 4.23 0.21 0.87 -0.02 10.66 0.32 9829 P16 30 4.68 0.11 3.39 0.46 0.71 -0.06 8.78 0.51 9829 P16 10 4.52 0.05 3.40 0.61 1.21 -0.04 9.13 0.62 9829 P16 3.5 4.45 -0.04 2.92 1.22 0.33 -0.07 7.70 1.11 9829 P16 1 3.61 -0.04 0.92 1.18 0.03 -0.08 4.56 1.07 9829 P20 100 4.61 0.22 5.02 0.59 0.59 0.03 10.21 0.85 9829 P20 55 2.95 0.03 6.01 0.01 0.87 0.00 9.83 0.04 9829 P20 30 2.94 0.03 6.47 0.28 0.56 0.16 9.97 0.47 9829 P20 10 3.07 0.37 3.46 0.23 0.32 0.03 6.86 0.63 9829 P20 3.5 1.74 0.16 4.03 0.59 0.40 -0.02 6.18 0.73 9829 P20 1 1.39 0.06 0.51 0.05 -0.01 0.01 1.89 0.13 9829 P26 100 16.38 0.15 8.56 0.46 2.05 0.49 27.00 1.11 9829 P26 55 17.36 0.22 7.79 0.41 1.50 -0.27 26.64 0.35 9829 P26 30 16.53 0.27 7.58 0.44 0.88 -0.26 24.99 0.46 9829 P26 10 13.67 0.27 5.22 0.28 0.87 0.20 19.77 0.75  199       Productivity (mgC/m3/d)    0.2-5.0 um 5-20 um >20 um Total Cruise Station % Io POC PIC POC PIC POC PIC POC PIC 9829 P26 3.5 5.84 0.01 3.74 0.28 0.64 -0.31 10.22 -0.02 9829 P26 1 1.31 -0.08 0.36 -0.06 -0.04 -0.36 1.63 -0.49 9901 P04 100 9901 P04 55 9901 P04 30 Data lost due to weather. 9901 P04 10 9901 P04 3.5 9901 P04 1 9901 P12 100 2.54 0.15 0.99 0.14 1.25 0.08 4.78 0.38 9901 P12 55 2.37 0.14 0.89 0.10 0.53 0.08 3.79 0.32 9901 P12 30 1.34 0.07 0.59 0.15 0.59 0.17 2.51 0.39 9901 P12 10 0.53 0.05 0.26 0.11 0.21 0.00 1.00 0.16 9901 P12 3.5 0.37 0.02 0.14 0.03 0.22 0.02 0.72 0.07 9901 P12 1 0.10 0.01 0.03 0.00 0.00 0.00 0.13 0.02 9901 P16 100 1.16 0.01 1.07 0.11 1.41 0.01 3.64 0.14 9901 P16 55 1.73 0.02 1.08 0.11 1.11 0.02 3.92 0.15 9901 P16 30 1.25 0.01 0.88 0.25 0.79 0.03 2.93 0.30 9901 P16 10 0.56 0.11 0.28 0.05 0.26 0.02 1.11 0.18 9901 P16 3.5 0.32 0.00 0.16 0.02 0.10 0.06 0.58 0.08 9901 P16 1 0.04 0.02 0.06 0.03 0.02 0.00 0.12 0.05 9901 P20 100 0.43 0.03 0.49 0.06 0.47 0.00 1.39 0.10 9901 P20 55 2.00 0.05 1.66 0.20 0.96 -0.01 4.62 0.25 9901 P20 30 1.56 0.05 1.67 0.12 1.35 0.08 4.59 0.24 9901 P20 10 1.57 0.05 1.64 0.11 1.32 0.00 4.54 0.16 9901 P20 3.5 1.69 0.06 1.64 0.16 0.80 0.01 4.13 0.23 9901 P20 1 0.49 0.02 0.28 0.05 0.10 0.00 0.87 0.07 9901 P26 100 2.42 0.05 0.59 0.08 0.76 0.12 3.77 0.25 9901 P26 55 2.02 0.03 0.56 0.22 0.67 0.07 3.25 0.32 9901 P26 30 1.33 0.02 0.68 0.14 0.62 0.09 2.63 0.25 9901 P26 10 1.56 0.04 0.47 0.18 0.37 0.05 2.40 0.27 9901 P26 3.5 0.47 0.02 0.16 0.06 0.11 0.01 0.74 0.09 9901 P26 1 0.31 0.02 0.08 0.02 0.07 -0.01 0.45 0.03 9910 P04 100 12.31 0.01 3.04 0.10 4.55 -0.03 19.90 0.09 9910 P04 55 11.23 0.01 2.98 -0.02 3.80 0.01 18.01 0.00 9910 P04 30 12.16 0.03 3.01 0.03 3.16 0.01 3.72 0.07 9910 P04 10 6.03 0.03 1.08 0.07 1.01 0.02 8.12 0.12 9910 P04 3.5 3.84 0.01 1.52 0.01 0.80 0.03 6.16 0.04 9910 P04 1 0.50 -0.01 0.19 0.00 0.21 0.01 0.91 0.00 9910 P12 100 8.91 0.01 0.89 -0.01 1.03 0.07 10.84 0.07 9910 P12 55 8.74 0.03 0.76 -0.02 1.43 -0.03 10.93 -0.02 9910 P12 30 6.78 0.05 0.72 -0.02 0.74 0.09 3.72 0.12 9910 P12 10 6.69 0.00 0.46 0.02 0.18 0.02 7.33 0.04 9910 P12 3.5 1.92 0.00 0.20 -0.03 0.05 0.03 2.17 0.00 9910 P12 1 0.50 0.04 0.13 -0.04 0.06 -0.02 0.68 -0.02 9910 P16 100 1.61 0.02 0.52 0.01 0.66 0.16 2.79 0.18 9910 P16 55 2.17 0.06 0.69 -0.01 0.42 -0.03 3.27 0.03 9910 P16 30 1.94 0.01 0.85 0.00 0.56 0.00 3.72 0.02  200       Productivity (mgC/m3/d)    0.2-5.0 um 5-20 um >20 um Total Cruise Station % Io POC PIC POC PIC POC PIC POC PIC 9910 P16 10 0.54 -0.03 0.21 -0.01 0.28 0.23 1.04 0.19 9910 P16 3.5 0.29 -0.01 0.03 0.00 0.02 -0.01 0.35 -0.02 9910 P16 1 0.16 -0.03 -0.01 -0.01 0.00 0.09 0.15 0.05 9910 P20 100 2.16 -0.01 0.77 0.07 0.60 0.01 3.52 0.06 9910 P20 55 4.53 0.02 0.93 0.01 0.56 0.07 6.01 0.10 9910 P20 30 3.68 0.00 0.89 0.05 0.46 0.03 3.72 0.08 9910 P20 10 2.38 -0.01 0.63 0.06 0.67 0.00 3.68 0.05 9910 P20 3.5 1.29 -0.02 0.25 0.02 0.22 -0.04 1.76 -0.04 9910 P20 1 0.64 0.00 0.08 0.04 0.06 0.00 0.79 0.04 9910 P26 100 7.03 0.09 1.74 0.17 1.42 0.03 10.19 0.29 9910 P26 55 2.91 -0.07 0.80 0.03 0.91 0.07 4.62 0.04 9910 P26 30 1.73 0.01 0.61 0.06 0.51 0.05 2.85 0.12 9910 P26 10 1.76 0.01 0.64 0.11 0.42 0.08 2.82 0.20 9910 P26 3.5 0.35 -0.05 0.19 0.02 0.07 -0.01 0.61 -0.05 9910 P26 1 0.57 0.03 0.17 0.21 0.08 0.04 0.82 0.27 9921 P04 100 9.29 0.03 9.63 0.34 4.45 0.00 23.37 0.37 9921 P04 55 7.72 0.00 7.91 0.18 3.26 -0.02 18.89 0.15 9921 P04 30 8.81 0.06 8.66 0.28 3.51 -0.02 20.98 0.33 9921 P04 10 5.36 0.04 4.77 0.16 1.84 -0.01 11.97 0.19 9921 P04 3.5 4.54 0.05 4.90 0.45 0.84 -0.04 10.28 0.46 9921 P04 1 0.13 -0.03 0.02 -0.05 0.03 -0.03 0.18 -0.11 9921 P12 100 8.17 0.00 5.22 0.05 0.64 0.01 14.03 0.05 9921 P12 55 8.14 0.06 5.07 -0.01 0.83 -0.02 14.04 0.03 9921 P12 30 6.77 0.03 5.90 0.18 0.94 0.07 13.61 0.28 9921 P12 10 6.44 0.01 2.95 0.04 0.40 0.00 9.80 0.05 9921 P12 3.5 2.54 -0.03 0.71 0.05 0.03 0.00 3.28 0.02 9921 P12 1 1.63 -0.03 0.18 0.00 0.09 0.00 1.90 -0.02 9921 P16 100 3.21 0.03 3.93 0.18 0.57 0.03 7.71 0.24 9921 P16 55 3.78 0.02 4.31 0.12 0.73 0.03 8.82 0.18 9921 P16 30 2.58 0.01 4.24 0.14 0.87 0.12 7.69 0.26 9921 P16 10 3.21 0.03 3.53 0.09 0.48 0.03 7.22 0.15 9921 P16 3.5 1.40 0.02 0.80 0.00 0.12 0.00 2.32 0.01 9921 P16 1 0.46 0.01 0.26 -0.01 0.07 0.02 0.79 0.02 9921 P20 100 3.03 0.00 1.92 0.16 2.08 0.03 7.03 0.19 9921 P20 55 4.28 0.04 1.96 0.14 0.50 -0.02 6.74 0.16 9921 P20 30 3.92 0.03 1.74 0.14 0.53 -0.02 6.18 0.15 9921 P20 10 2.05 0.04 0.69 0.05 0.16 -0.02 2.89 0.07 9921 P20 3.5 1.02 0.00 0.29 0.01 0.07 -0.01 1.38 0.00 9921 P20 1 0.42 0.01 0.05 0.07 0.06 0.00 0.53 0.07 9921 P26 100 7.98 0.21 4.54 0.44 1.69 -0.02 14.21 0.63 9921 P26 55 8.77 0.36 4.99 0.51 1.56 0.02 15.32 0.89 9921 P26 30 7.48 0.15 3.92 0.19 1.17 -0.08 12.57 0.27 9921 P26 10 5.46 0.02 1.37 0.07 0.41 -0.02 7.24 0.06 9921 P26 3.5 1.48 0.10 0.14 0.02 0.10 0.03 1.71 0.15 9921 P26 1 0.49 0.04 0.07 0.06 0.00 0.03 0.56 0.12 2000-10 P04 100 32.68 0.16 8.33 0.29 5.09 0.01 46.09 0.46 2000-10 P04 55 35.15 0.06 8.57 0.34 6.89 0.04 50.61 0.43  201       Productivity (mgC/m3/d)    0.2-5.0 um 5-20 um >20 um Total Cruise Station % Io POC PIC POC PIC POC PIC POC PIC 2000-10 P04 30 45.65 0.19 8.79 0.33 5.90 0.03 60.34 0.55 2000-10 P04 10 8.10 3.69 3.27 0.18 3.14 -0.01 14.51 3.86 2000-10 P04 3.5 9.86 0.08 0.97 0.10 0.91 0.03 11.74 0.21 2000-10 P04 1 2.49 0.00 0.36 -0.01 0.05 -0.06 2.91 -0.07 2000-10 P12 100 7.90 0.32 2.08 0.33 1.89 0.14 11.87 0.79 2000-10 P12 55 7.53 0.00 1.10 0.25 1.22 -0.01 9.85 0.24 2000-10 P12 30 7.02 -0.02 1.00 1.61 1.34 0.50 9.35 2.09 2000-10 P12 10 7.10 -0.02 0.54 0.83 0.83 0.09 8.47 0.90 2000-10 P12 3.5 2.38 0.03 0.43 0.35 0.13 1.03 2.95 1.40 2000-10 P12 1 0.59 0.09 0.13 0.08 0.04 0.02 0.76 0.20 2000-10 P16 100 7.06 0.00 1.11 0.03 1.54 -0.01 9.71 0.02 2000-10 P16 55 9.17 0.83 1.09 1.32 1.54 0.07 11.80 2.23 2000-10 P16 30 4.30 0.00 0.85 0.79 1.08 0.16 6.22 0.94 2000-10 P16 10 4.73 0.11 0.49 -0.02 0.57 -0.01 5.78 0.08 2000-10 P16 3.5 5.21 0.43 0.32 0.01 0.83 -0.10 6.37 0.34 2000-10 P16 1 0.61 0.20 0.22 0.28 0.04 0.16 0.87 0.64 2000-10 P20 100 4.26 0.01 0.52 0.36 1.84 0.02 6.62 0.39 2000-10 P20 55 5.25 -0.07 1.75 0.24 1.60 -0.08 8.60 0.09 2000-10 P20 30 6.42 -0.03 0.81 0.13 4.86 0.01 12.09 0.11 2000-10 P20 10 3.05 -0.25 0.67 0.07 1.47 0.56 5.18 0.38 2000-10 P20 3.5 1.35 -0.25 0.23 -0.08 0.30 0.56 1.88 0.23 2000-10 P20 1 0.29 -0.25 -0.04 0.35 -0.08 -0.08 0.17 0.02 2000-10 P26 100 0.76 0.17 0.85 0.79 0.78 0.02 2.39 0.98 2000-10 P26 55 1.31 0.39 0.67 0.79 0.86 0.02 2.84 1.20 2000-10 P26 30 1.36 0.36 0.97 0.55 0.83 0.01 3.17 0.92 2000-10 P26 10 0.98 0.14 0.92 0.17 0.55 0.01 2.46 0.32 2000-10 P26 3.5 0.85 0.02 0.12 0.04 0.59 0.26 1.57 0.32 2000-10 P26 1 0.08 0.00 -0.03 0.01 0.03 -0.01 0.08 0.00 2000-25 P04 100 17.23 0.58 1.54 0.24 1.88 0.59 20.64 1.41 2000-25 P04 55 20.11 1.71 1.26 0.28 2.16 0.62 23.54 2.61 2000-25 P04 30 20.86 1.15 2.15 0.22 1.51 0.38 24.52 1.75 2000-25 P04 10 17.34 1.39 1.51 0.36 1.51 0.26 20.37 2.01 2000-25 P04 3.5 4.87 0.57 0.92 0.28 0.55 0.31 6.33 1.16 2000-25 P04 1 0.52 0.04 -0.01 0.04 0.08 0.05 0.60 0.13 2000-25 P12 100 8.16 6.51 3.46 0.55 10.79 1.75 22.41 8.81 2000-25 P12 55 6.54 0.80 4.35 0.60 9.67 0.17 20.56 1.57 2000-25 P12 30 5.53 0.35 4.20 0.45 8.73 0.08 18.46 0.88 2000-25 P12 10 4.85 0.40 2.15 0.51 8.39 1.69 15.39 2.61 2000-25 P12 3.5 1.81 0.02 1.78 0.22 3.25 0.05 6.84 0.30 2000-25 P12 1 1.06 0.11 0.97 0.07 0.35 0.01 2.37 0.18 2000-25 P16 100 4.96 0.60 4.33 0.68 1.14 11.08 10.42 12.37 2000-25 P16 55 4.40 0.14 4.07 0.31 1.39 6.54 9.86 6.98 2000-25 P16 30 4.82 0.83 3.56 1.64 0.78 4.61 9.16 7.07 2000-25 P16 10 2.77 0.10 2.14 0.43 0.43 3.38 5.34 3.91 2000-25 P16 3.5 0.64 0.32 0.83 0.29 -0.13 -0.01 1.33 0.60 2000-25 P16 1 0.74 0.11 0.25 0.33 2.09 0.31 3.08 0.75 2000-25 P20 100 5.98 0.23 2.00 0.69 4.93 18.56 12.91 19.48  202       Productivity (mgC/m3/d)    0.2-5.0 um 5-20 um >20 um Total Cruise Station % Io POC PIC POC PIC POC PIC POC PIC 2000-25 P20 55 6.61 0.05 2.13 0.24 0.30 11.70 9.05 11.99 2000-25 P20 30 6.59 0.40 1.91 0.26 0.68 7.06 9.17 7.72 2000-25 P20 10 5.46 0.21 0.88 -0.05 0.22 0.44 6.55 0.59 2000-25 P20 3.5 1.59 0.24 0.72 0.20 -0.24 9.58 2.07 10.03 2000-25 P20 1 0.68 0.09 0.27 0.84 -0.33 2.52 0.61 3.46 2000-25 P26 100 10.28 0.03 5.10 -0.08 2.22 19.68 17.59 19.63 2000-25 P26 55 9.22 -0.03 4.59 -0.06 1.81 0.10 15.61 0.01 2000-25 P26 30 6.77 1.04 2.31 -0.09 1.06 0.11 10.14 1.06 2000-25 P26 10 5.56 -0.23 2.59 0.10 0.79 3.39 8.94 3.27 2000-25 P26 3.5 1.98 0.14 0.74 -0.12 0.18 4.88 2.90 4.90 2000-25 P26 1 0.50 0.40 0.21 -0.19 0.11 -0.03 0.83 0.18  203 Appendix D: IOS Website Data Table C.1. Physical data obtained from the Fisheries and Ocean Canada Line P Oceanic Data web site (http://www-sci.pac.dfo-mpo.gc.ca/osap/data/linep/linepselectdata_e.htm). Note that the depths (see Pressure) included were closest to the depths used for this study and were taken <24 h.. Nutrients were measured by the Institute of Ocean Sciences (Sydney, British Columbia, Canada) following Barwell-Clarke and Whitney (1996). The detection limit for nitrate is 0.05 µM, and 0.2 µM for silicic acid (Frank Whitney pers. comm.).     Pressure Temp Salinity Oxygen Nitrate +nitrite Phosphate Silicic Acid Cruise Station dbar °C   umol/kg μΜ μΜ μΜ 9803 P04 2.5 11.4 32.7 265.8 3.5 0.63 5.3 9803 P04 6.0 11.3 32.7 265.5 3.5 0.58 5.5 9803 P04 11.0 11.3 32.7 265.4 3.5 0.59 5.3 9803 P04 20.5 11.3 32.7 265.4 3.5 0.58 5.5 9803 P04 30.7 11.3 32.7 265.7 3.5 0.65 5.5 9803 P04 39.7 11.3 32.7 263.9 3.6 0.59 5.3 9803 P12 2.4 8.6 32.6 285.6 5.8 0.77 6.8 9803 P12 11.0 8.6 32.6 284.1 5.8 0.77 6.8 9803 P12 20.7 8.6 32.6 283.9 5.8 0.76 6.7 9803 P12 25.5 8.5 32.6 284.4 6.0 0.78 6.9 9803 P12 35.8 8.5 32.6 285.1 6.3 0.80 7.1 9803 P12 51.6 8.4 32.6 284.4 6.6 0.80 7.4 9803 P16 2.4 7.5 32.6 288.5 8.4 0.93 11.4 9803 P16 9.4 7.5 32.6 288.0 8.4 0.92 11.6 9803 P16 21.3 7.5 32.6 288.9 8.4 0.92 11.6 9803 P16 40.2 7.5 32.6 288.4 8.4 0.93 11.6 9803 P16 49.0 7.5 32.6 287.4 8.4 0.93 11.6 9803 P16 61.0 7.5 32.6 287.8 8.4 0.92 11.8 9803 P20 1.3 6.6 32.7 292.0 10.3 1.02 14.0 9803 P20 9.7 6.6 32.7 291.8 10.3 1.03 14.0 9803 P20 19.7 6.6 32.7 291.2 10.3 1.02 14.0 9803 P20 41.6 6.6 32.7 291.5 10.3 1.03 14.1 9803 P20 49.5 6.6 32.7 291.5 10.2 1.03 14.1 9803 P20 80.4 6.6 32.7 286.1 11.0 1.07 15.2 9803 P26 1.5 5.4 32.7 302.8 13.0 1.23 20.5 9803 P26 10.3 5.4 32.7 300.7 13.0 1.23 20.6 9803 P26 20.0 5.4 32.7 301.4 13.0 1.23 20.3 9803 P26 29.7 5.4 32.7 301.5 13.0 1.23 20.1 9803 P26 51.1 5.4 32.7 301.5 13.1 1.24 20.6 9803 P26 79.2 5.4 32.7 299.8 13.3 1.24 20.6 9815 P04 1.4 12.6 32.0 281.4 0.0 0.32 2.9 9815 P04 1.4 12.6 32.0 281.4 0.0 0.32 2.9 9815 P04 10.8 12.3 32.0 282.6 0.0 0.33 2.4 9815 P04 10.8 12.3 32.0 282.6 0.0 0.33 2.4 9815 P04 25.5 10.8 32.3 294.8 0.3 0.43 2.6  204    Pressure Temp Salinity Oxygen Nitrate +nitrite Phosphate Silicic Acid Cruise Station dbar °C   umol/kg μΜ μΜ μΜ 9815 P04 37.8 10.0 32.4 284.8 3.0 0.60 4.4 9815 P12 3.6 12.1 32.4 285.3 0.0 0.36 0.2 9815 P12 11.3 11.7 32.4 287.5 0.0 0.36 0.4 9815 P12 11.3 11.7 32.4 287.5 0.0 0.36 0.4 9815 P12 11.3 11.7 32.4 287.5 0.0 0.36 0.4 9815 P12 24.0 11.4 32.4 289.6 0.0 0.36 0.7 9815 P12 37.1 10.4 32.5 284.4 2.6 0.54 3.3 9815 P16 2.7 10.9 32.7 289.2 4.1 0.66 7.6 9815 P16 4.4 10.9 32.7 290.0 4.1 0.66 7.5 9815 P16 9.8 10.9 32.7 289.3 4.1 0.66 7.6 9815 P16 19.4 10.9 32.7 289.2 4.1 0.66 7.6 9815 P16 31.8 10.6 32.7 291.8 4.3 0.67 7.8 9815 P16 50.8 8.7 32.7 299.4 5.9 0.77 10.3 9815 P20 1.9 10.0 32.7 299.7 6.6 0.81 10.4 9815 P20 4.8 10.0 32.7 300.0 6.9 0.81 10.4 9815 P20 10.0 10.0 32.7 301.0 7.0 0.81 10.5 9815 P20 21.0 8.7 32.7 310.4 6.8 0.81 9.8 9815 P20 40.0 8.1 32.7 308.4 6.9 0.86 13.4 9815 P20 60.2 7.0 32.7 304.2 9.6 1.00 14.8 9815 P26 1.9 9.1 32.7 310.1 9.9 1.03 16.4 9815 P26 5.6 9.1 32.7 309.6 9.9 1.03 16.1 9815 P26 10.6 9.1 32.7 309.4 9.8 1.03 16.1 9815 P26 20.5 8.1 32.7 324.1 9.4 1.01 15.2 9815 P26 30.0 7.0 32.7 325.7 10.0 1.05 15.7 9815 P26 49.8 6.7 32.7 309.0 11.9 1.21 19.0 9829 P04 1.6 16.6 32.0 254.2 0.0 0.27 4.1 9829 P04 4.9 16.5 32.0 254.2 0.0 0.27 3.9 9829 P04 4.9 16.5 32.0 254.2 0.0 0.27 3.9 9829 P04 15.6 16.4 32.0 254.9 0.0 0.27 4.1 9829 P04 20.1 16.4 32.0 254.5 0.0 0.26 3.9 9829 P04 30.8 13.4 32.1 267.7 0.0 0.33 2.8 9829 P12 1.9 16.7 32.1 254.4 0.0 0.31 4.5 9829 P12 5.0 16.7 32.1 254.2 0.0 0.31 4.3 9829 P12 5.0 16.7 32.1 254.2 0.0 0.31 4.3 9829 P12 19.8 15.6 32.3 265.7 0.0 0.34 3.1 9829 P12 30.2 13.1 32.4 286.9 0.0 0.38 3.3 9829 P12 45.1 11.4 32.6 297.9 0.1 0.43 2.7 9829 P16 10.8 16.0 32.3 255.7 0.0 0.34 0.9 9829 P16 6.0 16.0 32.3 256.3 0.0 0.33 0.9 9829 P16 15.8 16.0 32.3 256.5 0.0 0.33 0.9 9829 P16 30.8 12.2 32.3 291.3 0.0 0.36 0.2 9829 P16 41.2 10.8 32.4 296.0 0.0 0.44 1.1 9829 P16 55.8 9.7 32.4 274.6 4.5 0.72 4.2 9829 P20 2.5 14.0 32.6 267.3 5.1 0.75 9.3 9829 P20 4.5 14.0 32.6 267.2 5.0 0.75 9.3 9829 P20 9.5 14.0 32.6 267.5 5.0 0.75 9.5 9829 P20 19.8 14.0 32.7 274.5 5.2 0.76 10.0  205    Pressure Temp Salinity Oxygen Nitrate +nitrite Phosphate Silicic Acid Cruise Station dbar °C   umol/kg μΜ μΜ μΜ 9829 P20 43.2 8.6 32.8 314.5 7.7 0.92 12.9 9829 P20 59.7 7.5 32.8 309.8 9.7 1.08 16.5 9829 P26 3.4 12.1 32.6 275.3 5.7 0.79 9.1 9829 P26 3.8 12.1 32.6 275.3 5.7 0.79 9.1 9829 P26 5.5 12.1 32.6 274.3 5.7 0.79 9.1 9829 P26 19.4 12.1 32.6 274.6 5.6 0.78 8.9 9829 P26 39.4 12.1 32.6 274.8 5.7 0.79 8.9 9829 P26 55.1 8.1 32.7 302.4 9.3 1.07 15.6 9901 P04 2.7 8.3 31.8 283.6 8.9 0.94 14.4 9901 P04 9.9 8.4 31.8 283.7 8.6 0.92 14.2 9901 P04 9.9 8.4 31.8 283.7 8.6 0.92 14.2 9901 P04 15.2 8.4 31.9 283.8 7.9 0.88 12.3 9901 P04 31.2 8.9 32.3 276.0 7.1 0.83 9.4 9901 P04 40.2 8.9 32.4 275.7 6.8 0.82 9.1 9901 P12 2.3 7.5 32.3 290.2 9.1 0.96 14.0 9901 P12 9.4 7.5 32.3 290.0 9.0 0.95 14.0 9901 P12 19.6 7.6 32.5 288.7 8.3 0.91 12.2 9901 P12 30.2 7.8 32.6 285.9 8.3 0.92 11.5 9901 P12 50.5 7.8 32.7 279.8 8.8 0.95 11.8 9901 P12 80.6 7.8 33.1 228.5 15.6 1.37 20.0 9901 P16 1.9 6.6 32.8 296.7 9.2 0.97 13.5 9901 P16 8.9 6.6 32.8 296.4 9.4 0.98 13.7 9901 P16 19.3 6.7 32.8 296.1 9.4 0.99 13.7 9901 P16 39.0 6.6 32.8 296.7 9.5 1.00 13.6 9901 P16 50.6 6.6 32.8 295.9 9.4 0.99 13.6 9901 P16 80.4 6.6 32.8 296.3 9.4 1.00 13.9 9901 P20 3.2 6.2 32.8 297.3 10.7 1.11 16.1 9901 P20 9.5 6.2 32.8 297.2 10.7 1.09 15.9 9901 P20 19.1 6.2 32.8 297.8 10.7 1.09 15.6 9901 P20 29.7 6.2 32.8 298.0 10.8 1.09 15.6 9901 P20 49.7 6.2 32.8 303.6 10.7 1.07 15.3 9901 P20 80.1 6.2 32.8 299.8 10.7 1.07 15.1 9901 P26 3.0 5.2 32.8 302.7 14.3 1.30 19.6 9901 P26 15.4 5.2 32.8 302.7 14.3 1.30 19.3 9901 P26 20.3 5.2 32.8 302.5 14.3 1.31 21.4 9901 P26 29.9 5.2 32.8 302.4 14.4 1.30 21.5 9901 P26 50.3 5.2 32.8 303.2 14.4 1.31 21.1 9901 P26 60.5 5.2 32.8 302.3 14.5 1.30 20.9 9910 P04 1.8 12.1 31.6 292.9 0.0 0.17 1.6 9910 P04 5.6 12.1 31.6 293.7 0.0 0.17 1.4 9910 P04 9.9 11.8 31.6 295.8 0.0 0.18 1.6 9910 P04 14.9 11.1 31.7 294.6 0.4 0.29 2.3 9910 P04 19.8 10.0 31.9 278.3 2.0 0.52 4.3 9910 P04 39.4 8.7 32.5 252.5 8.1 1.14 14.3 9910 P12 4.7 10.1 32.8 291.8 6.9 0.73 11.7 9910 P12 9.8 9.9 32.8 296.5 6.7 0.73 11.5 9910 P12 19.8 9.8 32.8 294.2 6.8 0.76 11.3  206    Pressure Temp Salinity Oxygen Nitrate +nitrite Phosphate Silicic Acid Cruise Station dbar °C   umol/kg μΜ μΜ μΜ 9910 P12 40.6 8.7 32.8 300.8 7.3 0.78 11.5 9910 P12 50.6 7.7 32.9 303.9 8.2 0.84 12.4 9910 P12 59.7 7.1 32.9 299.6 9.3 0.91 12.9 9910 P16 1.7 8.8 32.7 300.1 8.1 0.88 11.4 9910 P16 5.6 8.8 32.7 299.5 8.0 0.87 11.6 9910 P16 15.6 8.7 32.7 301.9 8.0 0.88 11.4 9910 P16 20.6 8.4 32.7 309.7 8.2 0.88 12.0 9910 P16 41.4 8.1 32.7 307.1 8.3 0.90 12.0 9910 P16 50.2 8.0 32.7 308.1 8.3 0.90 12.2 9910 P20 3.3 8.1 32.7  9.4 1.01 13.5 9910 P20 5.3 8.1 32.7  9.4 1.01 13.2 9910 P20 20.6 8.0 32.7  9.4 1.01 13.6 9910 P20 30.6 8.0 32.7  9.3 1.01 13.6 9910 P20 50.0 7.7 32.7  9.3 1.01 13.4 9910 P20 58.9 7.6 32.7  9.4 1.02 13.6 9910 P26 1.4 7.0 32.8 310.5 13.2 1.23 18.7 9910 P26 5.6 8.8 32.7 299.5 8.0 0.87 11.6 9910 P26 15.6 8.7 32.7 301.9 8.0 0.88 11.4 9910 P26 30.3 8.2 32.7 306.3 8.1 0.89 12.0 9910 P26 50.2 8.0 32.7 308.1 8.3 0.90 12.2 9910 P26 67.8 6.2 32.8 312.1 12.2 1.17 17.5 9921 P04 1.9 15.7 31.9 274.2 0.0 0.29 8.9 9921 P04 9.8 15.3 31.9 277.6 0.0 0.29 9.5 9921 P04 10.4 15.3 31.9 277.9 0.0 0.28 9.5 9921 P04 17.3 13.5 32.1 282.7 1.0 0.45 9.5 9921 P04 24.1 11.6 32.4 287.9 2.0 0.60 9.5 9921 P04 37.5 9.9 32.6 284.9 5.7 0.79 10.9 9921 P12 2.0 14.6 32.4 272.9 0.6 0.42 7.2 9921 P12 8.8 14.6 32.4 270.2 0.6 0.42 7.2 9921 P12 8.8 14.6 32.4 270.2 0.6 0.42 7.2 9921 P12 26.2 12.2 32.7 292.4 3.5 0.62 9.1 9921 P12 37.8 10.6 32.7 300.2 4.8 0.73 9.8 9921 P12 49.3 9.0 32.8 308.0 6.1 0.84 10.5 9921 P16 1.7 13.1 32.5 274.7 3.1 0.58 9.0 9921 P16 1.7 13.1 32.5 274.7 3.1 0.58 9.0 9921 P16 11.7 13.1 32.5 274.8 3.1 0.59 9.0 9921 P16 25.3 13.1 32.5 274.8 3.1 0.58 9.3 9921 P16 50.2 9.6 32.7 298.1 6.9 0.88 11.3 9921 P16 63.3 8.1 32.8 301.3 8.3 1.00 12.6 9921 P20 1.3 12.4 32.7 282.4 7.6 0.76 12.7 9921 P20 1.3 12.4 32.7 282.4 7.6 0.76 12.7 9921 P20 10.1 12.4 32.7 282.6 7.8 0.79 12.7 9921 P20 19.9 12.3 32.7 283.7 7.6 0.80 12.7 9921 P20 30.0 12.0 32.7 285.9 7.7 0.82 13.1 9921 P20 63.2 7.8 32.8 309.5 10.2 1.05 16.6 9921 P26 1.5 12.8 32.7 280.4 11.3 1.05 19.7 9921 P26 10.1 12.7 32.7 280.6 11.2 1.07 19.5  207    Pressure Temp Salinity Oxygen Nitrate +nitrite Phosphate Silicic Acid Cruise Station dbar °C   umol/kg μΜ μΜ μΜ 9921 P26 10.1 12.7 32.7 280.6 11.2 1.07 19.5 9921 P26 25.1 12.4 32.7 284.1 11.4 1.08 19.7 9921 P26 37.6 9.6 32.8 300.5 12.1 1.17 19.8 9921 P26 62.7 6.1 32.9 315.0 13.7 1.31 20.2 2000-10 P04 0.7 11.8 31.9 293.9 0.0 0.36 6.4 2000-10 P04 5.1 11.5 31.9 294.9 0.0 0.35 6.4 2000-10 P04 15.3 11.4 32.0 295.5 0.0 0.35 6.8 2000-10 P04 25.5 10.8 32.5 295.1 0.4 0.45 7.6 2000-10 P04 40.5 9.0 32.6 295.2 4.0 0.70 9.2 2000-10 P04 49.9 8.8 32.6 291.6 5.0 0.76 9.7 2000-10 P12 0.7 9.8 32.6 300.2 6.9 0.89 13.2 2000-10 P12 5.4 9.6 32.6 361.0 6.8 0.89 13.1 2000-10 P12 15.2 9.6 32.6 301.9 6.7 0.88 13.0 2000-10 P12 30.1 9.5 32.6 301.4 7.0 0.90 13.3 2000-10 P12 50.6 8.4 32.7 308.4 6.8 0.87 12.6 2000-10 P12 79.3 7.9 32.7 304.5 8.0 0.95 13.3 2000-10 P16 1.4 9.2 32.7 301.4 8.4 0.98 13.1 2000-10 P16 9.8 9.1 32.7 302.2 8.4 0.98 13.1 2000-10 P16 24.6 9.0 32.7 303.4 8.4 0.98 13.1 2000-10 P16 50.7 8.1 32.6 309.8 8.7 1.00 13.3 2000-10 P16 50.7 8.1 32.6 309.8 8.7 1.00 13.3 2000-10 P16 75.0 7.1 32.7 303.7 10.0 1.09 15.5 2000-10 P20 1.1 8.7 32.6 304.4 9.8 1.07 14.1 2000-10 P20 10.6 8.5 32.7 304.1 9.8 1.09 14.3 2000-10 P20 20.4 8.3 32.7 306.6 9.9 1.09 14.3 2000-10 P20 40.2 7.3 32.6 313.3 11.5 1.18 17.7 2000-10 P20 50.0 6.9 32.7 312.8 11.7 1.20 17.8 2000-10 P20 80.6 5.8 32.7 313.8 13.7 1.35 21.2 2000-10 P26 1.1 7.7 32.7 309.0 13.2 1.25 19.9 2000-10 P26 10.7 7.7 32.7 309.6 13.2 1.26 20.0 2000-10 P26 18.8 7.6 32.7 310.3 13.2 1.26 20.1 2000-10 P26 39.7 6.7 32.7 319.4 13.9 1.33 21.4 2000-10 P26 49.4 6.2 32.7 319.9 14.3 1.37 21.9 2000-10 P26 79.4 4.7 32.7 315.4 16.2 1.49 24.4 2000-25 P04 1.2 15.1 32.1 269.0 0.0 0.38 5.6 2000-25 P04 4.6 15.0 32.1 263.4 0.0 0.39 5.6 2000-25 P04 10.4 14.9 32.1 265.6 0.0 0.37 5.8 2000-25 P04 19.4 14.9 32.1 265.2 0.0 0.38 5.6 2000-25 P04 28.7 12.4 32.3 270.3 2.9 0.66 8.1 2000-25 P04 50.0 8.8 32.6 279.8 7.3 0.86 11.6 2000-25 P12 1.2 14.8 32.3 266.4 0.9 0.44 6.1 2000-25 P12 4.9 14.8 32.3 264.1 0.9 0.45 6.0 2000-25 P12 10.3 14.7 32.3 265.4 1.0 0.44 6.2 2000-25 P12 19.7 14.7 32.3 264.4 1.0 0.45 6.2 2000-25 P12 34.7 11.0 32.5 292.1 5.0 0.78 9.9 2000-25 P12 55.3 8.2 32.7 289.8 8.5 0.96 13.3 2000-25 P16 1.1 14.6 32.4 263.8 1.8 0.50 6.6  208    Pressure Temp Salinity Oxygen Nitrate +nitrite Phosphate Silicic Acid Cruise Station dbar °C   umol/kg μΜ μΜ μΜ 2000-25 P16 5.2 14.6 32.4 264.7 1.8 0.51 6.4 2000-25 P16 10.2 14.6 32.4 265.3 1.9 0.51 6.6 2000-25 P16 20.0 14.5 32.4 263.7 1.9 0.51 6.8 2000-25 P16 40.6 9.6 32.7 313.9 7.1 0.90 11.7 2000-25 P16 60.6 7.6 32.7 299.7 9.7 1.06 15.0 2000-25 P20 0.6 13.9 32.6 268.1 8.2 0.90 10.8 2000-25 P20 9.9 13.8 32.6 269.3 8.3 0.91 10.8 2000-25 P20 19.6 13.7 32.6 268.5 8.2 0.93 10.5 2000-25 P20 29.6 13.6 32.6 269.6 8.2 0.92 10.6 2000-25 P20 49.0 6.9 32.7 313.6 12.9 1.25 16.6 2000-25 P20 78.7 5.3 32.7 301.1 16.5 1.46 22.6 2000-25 P26 3.4 13.2 32.6 273.0 5.1 0.74 2.0 2000-25 P26 10.6 13.2 32.6 272.5 4.9 0.74 2.3 2000-25 P26 15.0 13.2 32.6 271.9 5.1 0.74 2.3 2000-25 P26 31.2 13.1 32.6 274.5 5.2 0.75 2.3 2000-25 P26 46.4 6.5 32.7 307.5 10.8 1.30 9.9 2000-25 P26 51.3 5.4 32.7 305.7 13.1 1.45 15.0  209 Appendix E: Size Fractionated Chlorophyll a with Depth  9803 P-12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D ep th  (m ) 0 20 40 60 80 9815 P-12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9829 P-12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9803 P-16 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D ep th  (m ) 0 20 40 60 80 9815 P-16 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9829 P-16 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9803 P-20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D ep th  (m ) 0 20 40 60 80 9815 P-20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9829 P-20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9803 P-26 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D ep th  (m ) 0 20 40 60 80 9815 P-26 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9829 P-26 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9803 P-04 mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D ep th  (m ) 0 20 40 60 80 9815 P-04 mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 <0.2 μm 0.2-5.0 μm >20 μm mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9829 P-04  Fig. D.1. Depth profiles of size-fractionated chlorophyll a  for all 1998 stations.  210  9901 P-12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D ep th  (m ) 0 20 40 60 80 9910 P-12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9921 P-12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9901 P-16 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D ep th  (m ) 0 20 40 60 80 9910 P-16 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9921 P-16 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9901 P-20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D ep th  (m ) 0 20 40 60 80 9910 P-20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9921 P-20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9901 P-26 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D ep th  (m ) 0 20 40 60 80 9910 P-26 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9921 P-26 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9901 P-04 mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 D ep th  (m ) 0 20 40 60 80 9910 P-04 mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 <0.2 μm 0.2-5.0 μm >20 μm mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 9921 P-12  Fig. D.2. Depth profiles of size-fractionated chlorophyll a for all 1999 stations.  211 2000-10 P-12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 2000-25 P-12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 2000-10 P-16 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 2000-25 P-16 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 2000-10 P-20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 2000-25 P-20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 2000-10 P-26 0 5 10 15 20 25 30 0 20 40 60 80 2000-25 P-26 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 2000-10 P-04 mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 <0.2 μm 0.2-5.0 μm >20 μm mg chl a m-3 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 2000-25 P-04  Fig. D.3.Depth profiles of size-fractionated chlorophyll a for all 2000 stations.  212 Appendix F: Depth Profiles of size-Fractionated POC Production  9803 P-12 0 5 10 15 20 25 30 D ep th  (m ) 0 20 40 60 80 9815 P-12 0 5 10 15 20 25 30 0 20 40 60 80 9829 P-12 0 5 10 15 20 25 30 0 20 40 60 80 9803 P-16 0 5 10 15 20 25 30 D ep th  (m ) 0 20 40 60 80 9815 P-16 0 5 10 15 20 25 30 0 20 40 60 80 9829 P-16 0 5 10 15 20 25 30 0 20 40 60 80 9803 P-20 0 5 10 15 20 25 30 D ep th  (m ) 0 20 40 60 80 9815 P-20 0 5 10 15 20 25 30 0 20 40 60 80 9829 P-20 0 5 10 15 20 25 30 0 20 40 60 80 9803 P-26 0 5 10 15 20 25 30 D ep th  (m ) 0 20 40 60 80 9815 P-26 0 5 10 15 20 25 30 0 20 40 60 80 9829 P-26 0 5 10 15 20 25 30 0 20 40 60 80 9803 P-04 Production mgC m-3 d-1 0 5 10 15 20 25 30 D ep th  (m ) 0 20 40 60 80 9815 P-04 Production mgC m-3 d-1 0 5 10 15 20 25 30 0 20 40 60 80 <0.2 μm 0.2-5.0 μm >20 μm Production mgC m-3 d-1 0 5 10 15 20 25 30 0 20 40 60 80 9829 P-12  Fig. E.1. Depth profiles of size-fractionated primary productivity for all 1998 stations.   213  9901 P-12 0 5 10 15 20 25 30 D ep th  (m ) 0 20 40 60 80 9910 P-12 0 5 10 15 20 25 30 0 20 40 60 80 9921 P-12 0 5 10 15 20 25 30 0 20 40 60 80 9901 P-16 0 5 10 15 20 25 30 D ep th  (m ) 0 20 40 60 80 9910 P-16 0 5 10 15 20 25 30 0 20 40 60 80 9921 P-16 0 5 10 15 20 25 30 0 20 40 60 80 9901 P-20 0 5 10 15 20 25 30 D ep th  (m ) 0 20 40 60 80 9910 P-20 0 5 10 15 20 25 30 0 20 40 60 80 9921 P-20 0 5 10 15 20 25 30 0 20 40 60 80 9901 P-26 0 5 10 15 20 25 30 D ep th  (m ) 0 20 40 60 80 9910 P-26 0 5 10 15 20 25 30 0 20 40 60 80 9921 P-26 0 5 10 15 20 25 30 0 20 40 60 80 9901 P-04 Production mgC m-3 d-1 0 5 10 15 20 25 30 D ep th  (m ) 0 20 40 60 80 9910 P-04 Production mgC m-3 d-1 0 5 10 15 20 25 30 0 20 40 60 80 <0.2 μm 0.2-5.0 μm >20 μm Production mgC m-3 d-1 0 5 10 15 20 25 30 0 20 40 60 80 9921 P-12 No Data  Fig. E.2. Depth profiles of size-fractionated primary productivity for all 1999 stations.    214 2000-10 P-12 0 5 10 15 20 25 30 0 20 40 60 80 2000-25 P-12 0 5 10 15 20 25 30 0 20 40 60 80 2000-10 P-16 0 5 10 15 20 25 30 0 20 40 60 80 2000-25 P-16 0 5 10 15 20 25 30 0 20 40 60 80 2000-10 P-20 0 5 10 15 20 25 30 0 20 40 60 80 2000-25 P-20 0 5 10 15 20 25 30 0 20 40 60 80 2000-10 P-26 0 5 10 15 20 25 30 0 20 40 60 80 2000-25 P-26 0 5 10 15 20 25 30 0 20 40 60 80 2000-10 P-04 Production mgC m-3 d-1 0 10 20 30 40 50 60 0 20 40 60 80 <0.2 μm 0.2-5.0 μm >20 μm Production mgC m-3 d-1 0 5 10 15 20 25 30 0 20 40 60 80 2000-25 P-04  Fig. E.3. Depth profiles of size-fractionated primary productivity for all 2000 stations.  215 Appendix G: Depth Profiles of Size Fractionated Chl Specific POC production   9803 P-12 0 20 40 60 80 100 120 140 D ep th  (m ) 0 20 40 60 80 9815 P-12 0 20 40 60 80 100 120 140 0 20 40 60 80 9829 P-12 0 100 200 300 400 500 600 0 20 40 60 80 9803 P-16 0 20 40 60 80 100 120 140 D ep th  (m ) 0 20 40 60 80 9815 P-16 0 20 40 60 80 100 120 140 0 20 40 60 80 9829 P-16 0 100 200 300 400 500 600 0 20 40 60 80 9803 P-20 0 20 40 60 80 100 120 140 D ep th  (m ) 0 20 40 60 80 9815 P-20 0 20 40 60 80 100 120 140 0 20 40 60 80 9829 P-20 0 100 200 300 400 500 600 0 20 40 60 80 9803 P-26 0 20 40 60 80 100 120 140 D ep th  (m ) 0 20 40 60 80 9815 P-26 0 20 40 60 80 100 120 140 0 20 40 60 80 9829 P-26 0 100 200 300 400 500 600 0 20 40 60 80 9803 P-04 Production per chl  mgC (mg chl)-1 m -3  d -1 0 20 40 60 80 100 120 140 D ep th  (m ) 0 20 40 60 80 9815 P-04 Production per chl  mgC (mg chl)-1 m -3  d -1 0 20 40 60 80 100 120 140 0 20 40 60 80 <0.2 μm 0.2-5.0 μm >20 μm Production per chl  mgC (mg chl)-1 m -3  d -1 0 100 200 300 400 500 600 0 20 40 60 80 9829 P-12  Fig. F.1. Depth profiles of size-fractionated chlorophyll a specific primary productivity for all 1998 stations.  216   9901 P-12 0 20 40 60 80 100 120 140 D ep th  (m ) 0 20 40 60 80 9910 P-12 0 20 40 60 80 100 120 140 0 20 40 60 80 9921 P-12 0 100 200 300 400 500 600 0 20 40 60 80 9901 P-16 0 20 40 60 80 100 120 140 D ep th  (m ) 0 20 40 60 80 9910 P-16 0 20 40 60 80 100 120 140 0 20 40 60 80 9921 P-16 0 100 200 300 400 500 600 0 20 40 60 80 9901 P-20 0 20 40 60 80 100 120 140 D ep th  (m ) 0 20 40 60 80 9910 P-20 0 20 40 60 80 100 120 140 0 20 40 60 80 9921 P-20 0 100 200 300 400 500 600 0 20 40 60 80 9901 P-26 0 20 40 60 80 100 120 140 D ep th  (m ) 0 20 40 60 80 9910 P-26 0 20 40 60 80 100 120 140 0 20 40 60 80 9921 P-26 0 100 200 300 400 500 600 0 20 40 60 80 9901 P-04 Production per chl  mgC (mg chl)-1 m -3  d -1 0 20 40 60 80 100 120 140 D ep th  (m ) 0 20 40 60 80 9910 P-04 Production per chl  mgC (mg chl)-1 m -3  d -1 0 20 40 60 80 100 120 140 0 20 40 60 80 <0.2 μm 0.2-5.0 μm >20 μm Production per chl  mgC (mg chl)-1 m -3  d -1 0 100 200 300 400 500 600 0 20 40 60 80 9921 P-12 No Data  Fig. F.2. Depth profiles of size-fractionated chlorophyll a specific primary productivity for all 1999 stations.  217  2000-10 P-12 0 100 200 300 400 500 600 0 20 40 60 80 2000-25 P-12 0 100 200 300 400 500 600 0 20 40 60 80 2000-10 P-16 0 100 200 300 400 500 600 0 20 40 60 80 2000-25 P-16 0 100 200 300 400 500 600 0 20 40 60 80 2000-10 P-20 0 100 200 300 400 500 600 0 20 40 60 80 2000-25 P-20 0 100 200 300 400 500 600 0 20 40 60 80 2000-10 P-26 0 100 200 300 400 500 600 0 20 40 60 80 2000-25 P-26 0 100 200 300 400 500 600 0 20 40 60 80 2000-10 P-04 Production per chl  mgC (mg chl)-1 m -3  d -1 0 100 200 300 400 500 600 0 20 40 60 80 <0.2 μm 0.2-5.0 μm >20 μm Production per chl  mgC (mg chl)-1 m -3  d -1 0 100 200 300 400 500 600 0 20 40 60 80 2000-25 P-04  Fig. F.3. Depth profiles of size-fractionated chlorophyll a specific primary productivity for all 2000 stations.   218 Appendix H: Photosynthetron 24 h Incubation Parameters Table G.1. Photosynthetic parameters αB and βB [mg C (mg chl a)-1 h-1 (mol photons m-2 s-1)-1], PBmax (mg C (mg chl a)-1 h-1) and EK (µmol photons m-2 s-1) from photosynthetron incubations during the June (2000-10) and Aug/Sept (2000-25) cruises in 2000. Cruise Station Depth (m) Light Depth (% I0) αB βB PBmax EK 2000-10 P04 2 100% 0.105 0.00009 16.06 153.3 2000-10 P04 8 55% 0.069 0.00165 9.76 141.1 2000-10 P04 25 10% 0.151 0.05000 30.70 203.1 2000-10 P04  1% N.D. 2000-10 P12 2 100% 0.012 0.00038 2.70 229.2 2000-10 P12 8 55% 0.033 0.00033 3.20 97.2 2000-10 P12 33 10% 0.020 0.00032 2.20 111.9 2000-10 P12 71 1% 0.022 0.00112 1.03 46.9 2000-10 P16 2 100% 0.003 0.05463 0.54 167.9 2000-10 P16 9 55% 0.028 0.00129 1.37 48.2 2000-10 P16 40 10% 0.026 0.00015 2.56 96.8 2000-10 P16 80 1% 0.023 0.00169 1.25 54.2 2000-10 P20 2 100% 0.019 0.00039 3.57 187.0 2000-10 P20 10 55% 0.022 0.00041 3.49 158.2 2000-10 P20 40 10% 0.038 0.00036 3.36 88.7 2000-10 P20 80 1% 0.025 0.00054 0.98 40.0 2000-10 P26 2 100% 0.045 0.00037 2.96 65.5 2000-10 P26 9 55% 0.029 0.00040 1.96 66.5 2000-10 P26 34 10% 0.025 0.00022 1.87 75.9 2000-10 P26 80 1% 0.007 0.00444 1.11 168.3 2000-25 P04 2 100% 0.041 0.00042 4.37 107.6 2000-25 P04 6 55% 0.042 0.00003 4.16 99.3 2000-25 P04 20 10% 0.090 0.00038 4.30 47.8 2000-25 P04 50 1% 0.041 0.00088 1.25 30.2 2000-25 P12 2 100% 0.018 0.00003 2.21 122.3 2000-25 P12 6 55% 0.009 0.00044 1.33 145.1 2000-25 P12 20 10% 0.004 0.01658 0.94 215.3 2000-25 P12 50 1% 0.024 0.00010 0.89 36.4 2000-25 P16 2 100% 0.022 0.00001 1.25 56.4 2000-25 P16 5 55% 0.029 0.00015 1.66 56.8 2000-25 P16 20 10% 0.036 0.00026 1.92 53.4 2000-25 P16 66 1% 0.123 0.07500 9.21 75.2 2000-25 P20 2 100% 0.033 0.00008 1.71 52.4 2000-25 P20 10 55% 0.003 0.02534 0.90 284.2 2000-25 P20 33 10% 0.095 0.00077 6.48 68.2 2000-25 P20 75 1% 0.055 0.00045 1.19 21.5 2000-25 P26 2 100% 0.103 0.00040 2.71 26.2 2000-25 P26 8 55% 0.024 0.00075 1.07 44.1 2000-25 P26 35 10% 0.036 0.00017 2.03 56.2 2000-25 P26 50 1% 0.044 0.00077 1.35 30.6 

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