Deep Ocean Ventilation Through Antarctic Intermediate Layers (DOVETAIL)

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9528806 Smethie The proposed project is part of a multi-institutional integrated study of the outflow of newly formed bottom water from the Weddell Sea and its dispersion into the South Atlantic Ocean. It builds upon earlier successful studies of the inflow of intermediate water masses into the Eastern Weddell Sea, their modification within the Weddell Gyre, and their interaction with bottom water formation processes in the western Weddell Sea. The study is called Deep Ocean Ventilation Through Antarctic Intermediate Layers (DOVETAIL) and includes six components involving hydrographic measurements, natural tracer experiments, and modeling studies. The study will be centered east of the Drake Passage where water masses from the Weddell Sea and the Scotia Sea come together in the Weddell-Scotia Confluence, and will be carried out in cooperation with the national antarctic programs of Germany and Spain. This particular component concerns the measurement of the chlorofluorocarbon concentration as a tracer of residence time and movement of Weddell Gyre water. The study has four related objectives. The first is to assess the quantity and the physical and chemical characteristics of Weddell Sea source waters for the confluence. The second is to describe the dominant processes associated with spreading and sinking of dense antarctic waters within the Weddell-Scotia Confluence. The third is to estimate the ventilation rate of the world ocean, and the fourth is to estimate seasonal fluctuations in the regional ocean transport and hydrographic structure and to assess the likely influence of seasonal to interannual variability on rates of ventilation by Weddell Sea waters. Ventilation of the deep ocean -- the rising of sub-surface water masses to the surface to be recharged with atmospheric gases and to give up heat to the atmosphere -- is a uniquely antarctic phenomenon that has significant consequences for global change by affecting the global reser voir of carbon dioxide, and by modulating the amount and extent of seasonal sea ice in the southern hemisphere. This component will make measurements of three species of chlorofluorocarbons (also known as freons or CFC's): F-11, F-12, and F-113. Since the atmospheric concentration of these anthropogenic gases has been tracked quite precisely for almost fifty years, their oceanic values, and the ratios of their values can be used to provide accurate estimates of the time since a given water sample was last exposed to the atmosphere, and to infer the time scales of water mass modification and mixing processes in the Weddell Sea. ***