Southern Ocean JGOFS: Mesoscale Physical and Biological Processes at the Polar Front

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95-30758 COWLES 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 Southern Ocean is recognized as an important , yet poorly resolved, region of the world ocean. It is thought that this region plays a critical role in global carbon dynamics, as well as strongly influencing the flux of heat and salt between the Atlantic, Pacific, and Indian Oceans. Attempts to improve our understanding of this region and its role in the global carbon budget depend on our ability to adequately assess those processes which control or constrain the rates of carbon fixation and air- sea exchange of CO2. Recent observations in the Southern Ocean suggest that mesoscale variability in physical, chemical and biological properties limits our ability to provide accurate large-scale estimates of important rate processes. Our understanding of carbon flux in the Southern Ocean thus depends upon resolution of connections between mesoscale and large-scale processes. The mesoscale dynamics of the Polar Front region of the Antarctic Circumpolar Current will be investigated using an instrumented towed vehicle (SeaSoar) to resolve the physical and biological fields over horizontal spatial scales of 1-150 km, with 2m vertical resolution within the upper 400m. High resolution surveys of physical and biological properties will be made during three cruises in the Polar Front (Oct `97, Dec-Jan `97/'98, Mar `98). Towed instrumentation will document the physical and biological structure associated with mixing and interleaving of mesoscale features. The high resolution surveys of physical properties will allow the determination of the relationship between lateral processes and local vertical mixing. Resolution of these mesoscale circulation features will be critical for the evaluation of the properties measured at discrete sampling stations, and will provide the regional context for evaluation of carbon flux at given locations. Objectives are: 1) determine the characteristics and spatial scales of the physical and biological fields in the Polar Frontal region of the Antarctic Circumpolar Current system; 2) evaluate the role of mesoscale circulation in mixing heat, salt, and biogeochemical properties into and out of the euphotic zone; 3) determine, using bio-optical indices, the spatial scales of photoadaptation of the autorophic assemblage in the Polar Front region; 4) incorporate mesoscale patterns of physical and biological property distribution into a high resolution regional ocean circulation model.