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 remineralised 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 multi‐proxy data – including δ18O and δ13C measured on the benthic and planktic foraminifera Cibicidoides wuellerstorfi, and Neogloboquadrina pachyderma, and productivity proxies including percent CaCO3, total organic carbon (TOC) and Ba/Ti – from a sediment core located in the high latitude (71°S) Pacific SO spanning the last 800 kyr. Typical glacial δ13C values of SCW at this core site are ~0 ‰. We find no evidence for SCW with extremely low δ13C 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 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 δ13C gradient in SCW is apparent throughout much of the last 800,000 years, including interglacials. A SO‐wide depletion in benthic δ13C is observed is early MIS 16, coinciding with the lowest atmospheric pCO2 recorded in Antarctic ice cores.

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