Biological factors impacting macronutrient cycles in the Southern Ocean

Relationships among major nutrients during biological production and recycling in surface ocean waters are a critical aspect in current models of biogeochemical cycling. This thesis reports the results of an effort to test nutrient relationships derived from mid water oxidative ratios against the relationships derived explicitly from surface waters of the Southern Ocean. This inter-nutrient comparison focuses on the Antarctic Circumpolar Current region (ACC), and how changes in biological structure impact geochemical fluxes in the surface ocean.; A surface water mass balance for carbon, nitrogen, phosphorus, and silica was constructed for four different physical regimes across the ACC from seasonal data along 170°W in the Pacific Sector. Frontal positions, mixed layer depths, air-sea gas exchange and horizontal nutrient flux were revised through time to optimize estimates of net community production (NCPi ). The southward migration of the meridional gradient of silica had a significant impact on NCPSi(OH)4. Peak NCPDIN and NCPPO4 preceded NCPDIC and NCPSi(OH)4 and all regimes exhibited NCPDIN/NCPPO4 ratios (11 to 14), well below Redfield values. In addition, phosphorus was more efficiently recycled than the other nutrients.; NCPi was adjusted for changes in particulate material and dissolved organic matter to isolate export (ei) so that the impact of epipelagic variations on ei could be evaluated. Growth of heavily silicified Fragilariopsis spp. south of the Antarctic Polar Front (APF) was associated with a rapid increase in eSi in December when sea ice was receding. However, elevated eC continued as the diatom community declined (particularly in the north) resulting from the appearance of later successional forms such as Chaetoceros spp. and Corethron spp. that likely increased e C due to enhanced particle aggregation. Thus, the seasonal pattern of eC in the ACC was impacted by the nature of the diatom community and was not a simple function of total opal concentration. Pigment concentrations reflected additional environmental associations including dinoflagellates with the APF and Phaeocystis with melt water from retreating ice. Thus, water column structure, temperature, and nutrients play a role in phytoplankton community structure, and these communities in turn are important for determining processes and magnitude of NCPi and efficiency of export.