Physics and Recycling Efficiency as Factors Controlling New (Nitrate) Production in the Southern Ocean

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9530981 Sambrotto This project is part of the U.S. Joint Global Ocean Flux Study (U.S.JGOFS) Southern Ocean Process Study aimed at (1) a better understanding of the fluxes of carbon, both organic and inorganic, in the Southern Ocean, (2) identifying the physical, ecological, and biogeochemical factors and processes regulating the magnitude and variability of these fluxes, and (3) placing these fluxes into the context of the contemporary global carbon cycle. As the fourth U.S.JGOFS study region, the Southern Ocean in potentially the most significant yet examined by this interdisciplinary program. The Southern Ocean's vast size together with its abundance of nutrients has led to extensive speculation about its role in past and present-day exchanges of carbon with the atmosphere as well as how this role may change in response to future climactic perturbation. Thus project will measure nitrate uptake and the uptake and regeneration of nitrogen from ammonium, area, and dissolved amino acid sources in surface water. The light response of nitrate uptake will be measured and the size distribution analyzed to determine how vertical mixing can affect the local rates of new production. Although all of the major physiographic regions of the Southern Ocean will be sampled during this project, the focus will be on the frontal systems at the northern portion of the study area as well as the permanently ice- free region immediately to the south. This extensive region encompasses the largest, uninterrupted biogeochemical province in the world ocean. Thus, the work addresses the JGOFS goal of identifying the factors that regulate the magnitude and variability of biological production and its ultimate export from surface water and will be critical to the success of future models that intend to predict the response of the Southern Ocean to climate change.