Analyses of lithology, stratigraphy, and tephra from marine sediment cores collected from the western Ross Sea during cruises Eltanin 32 and 52 and Deep Freeze 80 and 87 indicate that subglacial till does not extend to the continental shelf edge. Subglacial till occurs as the lowest unit in most cores landward (south) of approximately 74°S, while seaward of approximately 74°S, the lowest diamicton units are glacial marine diamictons. Glacial marine diamictons are distinguished from subglacial tills by the presence of higher and more variable total organic carbon content downcore, distinct tephra layers, stratification, higher diatom and foraminifera abundances, higher sand content, and radiocarbon dates in chronological order downcore. Sand-sized tephra layers from two cores on the outer continental shelf are interpreted as single eruptive events, one likely to have been derived from the Mount Melbourne volcano and the other from the Pleiades volcano. Radiocarbon dates from sediment above and below the tephra layer in one of these cores (Df87-32) show that deposition indicative of open-water conditions occurred between 22 and 26 ka in the western Ross Sea.

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