VENTILATION OF THE SOUTHERN OCEAN DURING THE PLIOCENE CLIMATIC OPTIMUM

We examine early Pliocene (~4.7-4.3 Ma) Southern Ocean circulation changes by reconstructing sedimentary redox and paleoproductivity at Integrated Ocean Drilling Program (IODP) Site U1359 on the Wilkes Land continental rise. The Southern Ocean plays a significant role in the formation of deep water and is an important conveyor in the exchange of heat and dissolved gases to the atmosphere. At 4.6 Ma, Mn/Al maxima indicate a shift from suboxic to oxic conditions resulting from the enhanced production of Antarctic bottom water. The interval of high Mn/Al at 4.5 Ma is overlain by an interval of extremely high Ba-excess values exceeding 40,000 ppm, in the presence of sedimentary barite. Elevated levels of Ba-excess are the result of high productivity events in response to an increase in the availability of nutrients supplied by upwelling and terrigenous dust. Ventilation of deepwater during the Pliocene Climatic Optimum allows for a role for the Southern Ocean in carbon cycle feedbacks during previous warm periods.