History of the Antarctic Ice Sheet in the McMurdo Sound region at and since the Last Glacial Maximum: Evidence from Miers Valley

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Reconstructions of past Antarctic Ice Sheet (AIS) behavior can afford key information about likely ice-sheet response to future climate change. Here, we examine the history of a marine-based ice mass grounded in McMurdo Sound of the western Ross Embayment during the Last Glacial Maximum and termination. Geomorphological mapping and interpretation of stratigraphic sections, as well as 67 radiocarbon dates of algal mats and 16 234U/230Th ages of carbonate and gypsum in glaciolacustrine sediments, indicate that ice from the broader Ross Embayment entered McMurdo Sound by approximately 24,000 yr BP and blocked the seaward mouth of Miers Valley. Maximum thickness of the McMurdo Sound ice was maintained from ∼19,000 yr BP, with fluctuations, until ∼12,600 yr BP. A lake-ice conveyor operated on a large ice-dammed lake that accompanied this advance until dessication at 10,000–7900 yr BP concurrent with ice recession. In contrast to the expansion of grounded marine-based ice in McMurdo Sound, alpine glaciers at the valley head did not advance at the Last Glacial Maximum. This out-of-phase behavior of the marine-based ice sheet vs. independent terrestrial glaciers is consistent with previous studies suggesting that local glaciers respond primarily to accumulation, which rises during warm periods. The long and late maximum of the McMurdo Sound ice (corresponding largely to Termination I) and delayed recession until after the Antarctic Cold Reversal (∼14,700–12,900 yr BP) lends support to the hypothesis that the AIS in the Ross Sea sector is controlled by the competing effects of marine (sea level, ocean temperatures) and accumulation forcing.