Date of Award

2010

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor

Brenda Hall

Second Committee Member

George Denton

Third Committee Member

Terence Hughes

Abstract

This thesis described the distribution of glacial deposits at two sites in the Southern Hemisphere: Nevado Coropuna, in the Peruvian Andes, and Scott Glacier, Antarctica. At each site, glacial-geologic mapping forms the basis for reconstructing former ice extent and for resolving the chronology of glaciation with cosmogenic nuclide surface-exposure dating. Together, these data provide answers to fundamental questions about the timing and magnitude of key climate events, such as the Last Glacial Maximum (LGM), in the Southern Hemisphere. On Coropuna (15°S), deposits attest to several glacial episodes during which ice was more extensive than today. Snowline reconstructions and 3He surface-exposure dating show that glaciers last reached their maxima during the LGM in response to an ELA lowering of approximately 750 m. Subsequent deglaciation was interrupted by a major advance between 12 and 14 ka, during which glaciers maintained terminal positions midway between the LGM and modern glacier margins. In contrast to several recently published datasets, my Coropuna record reveals a broad synchrony in the structure of late-Pleistocene climate variability between at least parts of the tropics and higher latitudes. In the southern Transantarctic Mountains, the distribution of glacial deposits at Scott Glacier indicates that the most recent advance was synchronous with the LGM. A longitudinal- surface profile of the glacier based on these LGM deposits indicates that the West Antarctic Ice Sheet (WAIS), at the mouth of Scott Glacier, maintained a surface elevation of ~1100 m. In conjunction with the Ross Sea geologic record and grounding-line chronology, my reconstruction of the former WAIS casts doubt on Antarctica's contribution to Meltwater Pulse 1A at 14.6 ka.

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