Date of Award

8-2012

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Brenda L. Hall

Second Committee Member

George H. Denton

Third Committee Member

Daniel F. Belknap

Abstract

Understanding the history of the Ross Sea ice sheet bears on questions concerning the stability of the West Antarctic ice sheet, as well as the contribution of Antarctic ice to global sea-level rise following the terminations of ice ages. Deposits in Marshall Valley in the Royal Society Range record the history of the Ross Sea ice sheet, which dammed the valley mouth during at least the last two glacial cycles. Radiocarbon ages of algae from prominent moraines on the coastal headlands adjacent to Marshall Valley show that Ross Sea ice was near its maximum from ~17,000 to ~13,000 yr BP and reached elevations of 319 m above sea level. Grounded Ross Sea ice blocked the valley mouth until at least ~11,000 yr BP.

My results do not support a Ross Sea source for mwp 1A. Instead, my data, when combined with other glacial records from the Transantarctic Mountains, support the presence of a modest-sized ice sheet. The retreat occurred after ~13,000 yr BP and continued through the Holocene. If mwp 1A came from Antarctica, it must have come from another region of the continent, something for which there is no evidence at present.

My data also bear on the Ross Sea ice sheet during the penultimate glaciation. Stratigraphic sections in Marshall Valley show interbedded glacial diamictons and lake beds that contain carbonate and gypsum. As all lakes in Marshall Valley must be ice-dammed, the presence of the lacustrine sediments, as well as the diamictons, indicates that Ross Sea ice occupied the valley mouth. Uranium-thorium dates of carbonates suggest that this occurred between at least ~154,000 and 137,000 yr BP. The youngest dated lake bed at ~137,000 yr BP may correspond to the onset of Termination II and retreat of Ross Sea ice from the mouth of Marshall Valley.

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