GSA QUATERNARY GEOLOGY AND GEOMORPHOLOGY DIVISION MARIE MORISAWA AWARD: RECONSTRUCTION OF KOETTLITZ GLACIER, SOUTHERN MCMURDO SOUND, ANTARCTICA, DURING THE LAST GLACIAL MAXIMUM AND TERMINATION

Accurate reconstructions of the Antarctic Ice Sheet are important for evaluating past, present, and future sea-level change. During the last glacial maximum (LGM), ice grounded in the Ross Sea, reaching close to the continental shelf edge. A traditional hypothesis is that this event was caused largely by changing sea level that led to grounding of floating portions of West Antarctic ice streams and East Antarctic outlet glaciers. This grounding buttressed the inflowing ice and caused thickening on the lower reaches of these glaciers; interior ice remained the same or even thinned because of reduced accumulation. Following deglaciation of the Ross Embayment at 8-13 ka, some data suggest thickening of interior ice and growth of local glaciers in response to Holocene accumulation increase. In contrast, other studies have proposed that expanded local glaciers contributed to Ross Sea ice at the LGM. These glaciers are thought to have receded to their present positions in the Holocene despite relatively high accumulation, and thus may be largely insensitive to accumulation changes.

Koettlitz Glacier, a large local glacier, flows from the Royal Society Range into McMurdo Sound (78°S, 163°E). Competing hypotheses as to how this glacier behaved during the LGM range from minor recession to significant expansion and contribution to grounded Ross Sea ice. Our preliminary data suggest only a minor expansion at the LGM. There is no evidence that the glacier spilled over into adjacent Pyramid Trough, something that would have occurred had the glacier expanded to fill McMurdo Sound. Radiocarbon dates of subfossil algae in glaciolacustrine deposits in Pyramid Trough range from 10.3-21.9 ka, suggesting a lake, not ice, occupied the valley during the LGM. Algae within a moraine adjacent to present-day Koettlitz Glacier date to 3.3 ka and afford a maximum age for both the moraine and the advance of the glacier to its current position. Altogether, existing data suggest that Koettlitz Glacier, and by inference other local glaciers in the region, did not expand significantly at the LGM, likely because of a reduction in local accumulation.