Lithologic data from marine sedimentary cores and accelerator mass spectrometer (AMS) radiocarbon dates indicate that grounded ice did not advance to the western Ross Sea continental shelf edge during the last glacial maximum (LGM). A chronology of the timing of ice retreat was provided by 26 AMS dates, obtained from 12 cores. Dates ranging from 20 to 29 ka suggest that the outer continental shelf (beyond ca. lat 74°S) was not covered by grounded glacial ice prior to and during the early stages of the LGM. 14C dates just above transitions from subglacial diamictons to marine muds indicate that the area around the Drygalski ice tongue was deglaciated by at least 11.5 ka. The Ross Ice Shelf reached its present-day position near Ross Island by about 7 ka. A hiatus of about 15 ka is apparent in radiocarbon dates in cores from the outer continental shelf. The hiatus is interpreted to represent an absence of sedimentation caused by the presence of an ice shelf.

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