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Southern Ocean, sea ice, and ice sheet interactions play an important role in the formation and export of deep water into the adjacent ocean basins. This process of deep ocean circulation has an important consequence on Earth’s meridional distribution and transport of heat, salts, and gases. Ocean Drilling Program (ODP) Site 1123 sits in the path of the southwest Pacific Deep Western Boundary Current (DWBC), where the largest inflow of deep Southern Ocean water enters into any of the ocean basins. Here we present a multi-proxy mid-Pliocene to early Pleistocene (3.5-2.5 Ma) study examining how changes in the inflow of deepwater coincided with Late Pliocene Southern Ocean cooling at 3.3 Ma. Our benthic δ18O record is consistent with the globally integrated stack, LR04. Our benthic δ13C data covaries with X-ray diffraction (XRD) redox proxies (e.g., Mn/Fe and Mn/Al), indicating changes in deep ocean ventilation over glacial-interglacial cycles. Initial grain size data examining the size sorting of silt (sortable silt) implies a potential increase in deep water inflow into the Pacific after 3.3 Ma, as a consequence of sea ice development around the Antarctic margin that is characterized by relatively low δ13C composition, reflecting the enhanced contribution of Circumpolar Deep Water (CDW) with a relatively strong southern sourced signature. Future research will focus on the development of a complement 3.5 to 2.5 Ma grain size record in order to examine the relationship between changes in sediment supply, size sorting of sediment and deep ocean ventilation changes.



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Grain Analysis of Pliocene-Pleistocene Sediments from the Chatham Rise