Seasonal and across-shelf trends of the phytoplankton community of the Oregon coastal environment Public Deposited

http://ir.library.oregonstate.edu/concern/defaults/9019s4127

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  • This project, part of the Northeast Pacific GLOBEC Long Term Observation Project (NEPGLOBEC- LTOP), constitutes the first multi-year study of phytoplankton variability in the Oregon coastal environment. The work divides into two studies: analysis of interseasonal change and analysis of detailed changes within the summer upwelling period. In the first study, I found that the majority of variability in phytoplankton biomass in this system is due to changes in the abundance of chain forming diatoms, particularly diatoms of the genera Chaetoceros and Skeletonema. The abundance of nanoflagellates (<10 μm) remains constant across the shelf. They dominate the phytoplankton community in the offshore stations and larger cells, usually diatoms, are added inshore. Cyanobacteria, though numerically abundant, never comprise more than approximately 10% of phytoplankton biomass. Variation within the summer phytoplankton bloom over the shelf was analyzed based on results from the four NEP-GLOBEC-LTOP summer cruises between August 1998 and July 2001. Nutrient concentrations during the summer upwelling blooms show a linear decrease with increasing temperature from 8 to 12° C. Over this range of temperatures, total Chl a and phytoplankton biomass increase, though not significantly, and the % Chl a >10 μm remains high (>50 %). Above 12° C, when inorganic nutrients are depleted or greatly reduced, total Chl a and % Chl a >10 μm decrease. The diatom genera Chaetoceros and Skeletonema are also responsible for the majority of the variability in phytoplankton stock during the summer phytoplankton bloom. Dinoflagellates, although present, are consistently less abundant than diatoms.
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  • NEP-GLOBEC Long-term Observation Program Data Report
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  • Introduction 4 The Oregon Coastal Environment and the California Current System The Importance of Phytoplankton Size and Diversity Northeast Pacific GLOBEC-LTOP Main Questions Considered Methods 6 Sample Collection Physical Oceanographic Data Biological Oceanographic Data Inorganic Nutrients Phytoplankton Identification and Biomass Estimation Calculations and Statistical Analyses Estimation of Euphotic Zone Depth and Integrated Chl a Seasonal Groupings Results 11 Part I- Seasonal and Across-Shelf Environmental Variability Upwelling and Hydrography During the Study Seasonal and Across-Shelf Variation Part II- The Summer Upwelling Phytoplankton Bloom 15 Discussion 17 Seasonal and Across-Shelf Environmental Variability The Summer Upwelling Phytoplankton Bloom Literature Cited 20 Figures 22 Appendix A: Data for all of the cruises, stations and depths used in this study. 49 Appendix B: Numerical abundance of cyanobacteria, flagellates and diatoms. 91 Appendix C: Biomass estimates of cyanobacteria, flagellates and diatoms. 93 Appendix D: Numerical abundance of various sizes of unidentifiable diatoms. 95 Appendix E: Numerical abundance estimates of various diatom genera. 97 Appendix F: Biomass estimates of various sizes of unidentifiable diatom groups. 99 Appendix G: Biomass estimates of various diatom genera. 101 Appendix H: Biovolume estimates of phytoplankton cells. 103 Figures 1 PAR derived estimates of integrated Chl a. 2 Daily average upwelling index at 45°N 125°W. 3 Sea surface temperature and salinity. 4 Euphotic zone depth. 5 Integrated Chl a as a function of distance from shore. 6 % Chl a >10 μm as a function of distance from shore. 7 Integrated nitrate as a function of distance from shore. 8 July 2000 and 2001 across-shelf distribution of phytoplankton biomass. 9 July 2000 and 2001 across-shelf distribution of diatoms. 10 September 2000 across-shelf distribution of phytoplankton biomass. 11 September 2000 across-shelf distribution of diatoms. 12 January 2001 across-shelf distribution of phytoplankton biomass. 13 January 2000 across-shelf distribution of diatoms. 14 April 2000 and March 2001 across-shelf distribution of phytoplankton biomass. 15 April 2000 and March 2001 across-shelf distribution of diatoms. 16 Summer and September % Chl a >10 μm as a function of total Chl a. 17 Nutrient concentrations as a function of temperature. 18 Ammonium concentrations as a function of temperature. 19 Total Chl a and Chl a >10μm vs. temperature and % Chl a >10μm vs. total Chl a 20 Total Chl a as a function of nutrient concentrations. 21 % Chl a >10μm as a function of nutrient concentrations. 22 Chl a as a function of ammonium concentrations. 23 Distribution of biomass for the major groups of phytoplankton. 24 Cross shelf distribution of diatoms. 25 Chl and biomass of diatoms and flagellates vs. temperature Table List of Tables Page 1 List of stations on the NH-Line sampled during this study. 7 2 Means and coefficients of variation (C.V.) for inorganic nutrient samples. 8 3 Shapes with corresponding equations of volume. 9 4 Seasonal delineation of NEP GLOBEC-LTOP cruises used in the study. 11 5 Upwelling index values. 11 6. upwelling index values for first three days of each cruise. 12 7. Euphotic zone depth, integrated Chl a, integrated nitrate and % Chl a > 10μm. 13 8. ANOVA tables of multiple linear regressions analysis. 14 9. Nutrients and Chl grouped by temperature. 16
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