PLIO-PLEISTOCENE PALEOCEANOGRAPHY OF THE ROSS SEA SHELF BREAK, ANTARCTICA BASED ON FORAMINIFERA: IODP SITE U1523

International Ocean Discovery Program (IODP) Expedition 374 sailed to the Ross Sea in early 2018 to study the history of the West Antarctic Ice Sheet (WAIS) and Ross Ice Shelf over the last 20 million years. WAIS collapse during past warm periods may be connected to an intensification of ocean-cryosphere interactions (Naish et al., 2009; Pollard and DeConto, 2009), and present day upwelling of Circumpolar Deep Water (CDW) is causing ice melting in the Ross Sea (Pritchard et al., 2012).

Site U1523 is located on the outermost continental shelf with a water depth of 828 m. A primary objective at this site is to investigate past changes in the Antarctic Slope Current and use the cores to correlate records of ice sheet advance and retreat. The purpose of this study is to explore if foraminiferal abundance data show warming events that created open water conditions in the Ross Sea during the Plio-Pleistocene, or evidence of CDW incursion.

Both planktic and benthic foraminiferal assemblage data reflect the changes from glacial times, with low abundance and poorly preserved and fragmented shells, to interglacial times when relatively abundant assemblages of foraminifera occur. Based on a preliminary age model, especially high abundances of planktic and benthic foraminifera are associated with interglacial MIS 5e, MIS 11, and before and after MIS 31. The interval of abundant forams around MIS 31 (MIS 37 to 21) suggests multiple warmer interglacials during the Mid-Pleistocene Transition (MPT). After the MPT, percent foram fragmentation increases (except for MIS 5e and 11) while forams per gram of sediment is greatly reduced which could indicate a major advance of the Ross Ice Shelf (e.g., Elderfield et al., 2012). Multiple incursions of warmer water taxa occurred prior to ~1.5 Ma (Globigerina falconensis, G. bulloides, Globoconella inflata, Globigerinoides ruber and Turborotalita quinqueloba); total benthics and planktics, and forams per gram of sediment increase during these warm water incursions. An interval of abundant planktics, including G. falconensis (~2.0-1.8 Ma), may correlate with low amplitude cyclicity and warmer than present conditions; not identified previously as a warm interval.