Primary Production in the Southern Ocean

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95-30611 MARRA This research project is part of the US Joint Global Ocean Flux Study (JGOFS) Southern Ocean Program 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 which regulate the magnitude and variability of these fluxes, and (3) placing these fluxes into the context of the contemporary global carbon cycle. The Joint Global Ocean Flux Study (JGOFS) has had three successful field efforts (North Atlantic, Equatorial Pacific, Arabian Sea), and the next major field effort will be in the Southern Ocean. The overall objectives of JGOFS are to quantify and understand processes controlling the time-varying fluxes of carbon and associated biogenic elements, and to predict the response of marine biogeochemical processes to climate change. The Southern Ocean is critical to the global carbon cycle, as judged by its size and the physical process which occur there (e.g., deep and intermediate water formation), but its present quantitative role is uncertain. In order to address the objectives of USJGOFS successfully, the measurement of primary production is required for all process cruises planned for the Southern Ocean Study. Three methods will be employed: in situ incubations, deck incubations, and the photosynthesis-irradiance response. The areas of study will be the continental shelf of the Ross Sea, and the Polar Front region to the north of the Ross Sea. The controls on photosynthesis will also be investigated. It is hypothesized that on the continental shelf, irradiance limitation is the major factor controlling phytoplankton productivity, whereas in the Polar Front region, the availability of iron limits phytoplankton growth and influences the size distribution of the populations. The productivity data in conjunction with hydrographic data, will form a large part of the Southern Ocean JGOFS database which bot h at-sea investigators and modelers will use to clarify the role of the Southern Ocean in the global carbon cycle.