Paleocirculation and Ventilation History of Southern Ocean Sourced Deep Water Masses During the Last 800,000 Years

Most conceptual models of ocean circulation during past glacial periods invoke a shallowed North Atlantic-sourced water mass overlying an expanded, poorly ventilated Southern Ocean (SO)-sourced deep water mass (Southern Component Water or SCW), rich in remineralized carbon, within the Atlantic basin. However, the ventilation state, carbon inventory, and circulation pathway of SCW sourced in the Pacific sector of the SO (Pacific SO) during glacial periods are less well understood. Here we present multiproxy data-including delta O-18 and delta C-13 measured on the benthic and planktic foraminifera Cibicidoides wuellerstorfi, and Neogloboquadrina pachyderma, and productivity proxies including percent CaCO3, total organic carbon, and Ba/Ti-from a sediment core located in the high-latitude (71 degrees S) Pacific SO spanning the last 800 kyr. Typical glacial delta C-13 values of SCW at this core site are similar to 0%o. We find no evidence for SCW with extremely low delta C-13 values during glacials in the high-latitude Pacific SO. This leads to a spatial gradient in the stable carbon isotope composition of SCW from the high-latitude SO, suggesting that there are different processes of deep- and bottom-water formation around Antarctica. A reduced imprint of air-sea gas exchange is evident in the SCW formed in the Atlantic SO compared with the Pacific SO. A spatial delta C-13 gradient in SCW is apparent throughout much of the last 800,000 years, including interglacials. A SO-wide depletion in benthic delta C-13 is observed in early MIS 16, coinciding with the lowest atmospheric pCO(2) recorded in Antarctic ice cores.