Date of Award

5-2013

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Brenda Hall

Second Committee Member

George Denton

Third Committee Member

Peter Koons

Abstract

The Ross Sea Ice Sheet (RSIS) filled much of the Ross Sea embayment with grounded ice during the global Last Glacial Maximum (LGM). However, the precise chronology and duration of the maximum ice-sheet extent remains unresolved. This uncertainty propagates into estimates of the contribution of Antarctic ice to the sea-level lowstand of the LGM and to the sea-level rise of the last termination. Most of the LGM RSIS terminus was marine-based. A unique exception is that the RSIS terminated on land on the western shore of McMurdo Sound and constructed terminal moraines on the coastal headlands. These headland moraines descend into Miers Valley, where the RSIS dammed a proglacial lake during the LGM. The moraine geometry and the occurence of kenyte erratics from western Ross Island both indicate that grounded ice flowed from the Ross Sea embayment westward and southwestward across McMurdo Sound and into Miers Valley.

Here, I present a chronology for the maximum extent of the RSIS near and in Miers Valley, based on forty-three radiocarbon dates of algae samples from the headland moraines and from lacustrine deposits on the valley floor. Construction of the headland moraines during the local LGM occurred between 18,800 and 13,000 cal yr BP. Lacustrine sediments deposited in an ice-dammed lake in Miers Valley indicate that thick, grounded ice blocked McMurdo Sound between 24,000 and 11,500 cal yr BP. The Ross Sea ice that impinged on the Miers headlands reached its maximum extent by 18,800 cal yr BP, just after the global LGM, and did not begin to thin until after 13,000 cal yr BP, at the end of the Antarctic Cold Reversal. Retreat of ice from the mouth of Miers Valley was delayed by at least 5000 years with respect to the onset of global sea- level rise, as well as to the retreat of mountain glaciers and New Zealand and Patagonia.

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