A GLACIAL-GEOLOGIC APPROACH TO STUDYING LATE QUATERNARY CLIMATE AND ICE FLUCTUATION IN THE SOUTHERN HEMISPHERE

A GLACIAL-GEOLOGIC APPROACH TO STUDYING LATE QUATERNARY CLIMATE AND ICE FLUCTUATION IN THE SOUTHERN HEMISPHERE

By Gordon Bromley

Thesis Advisor: Dr. Brenda Hall

A Lay abstract of the Thesis Presented

in Partial fulfilment of the Requirements for the

Degree of Doctor of Philosophy

(in Earth Sciences)

December, 2010

This thesis describes the distribution of landforms deposited by glaciers at two sites in the Southern Hemisphere: Nevado Coropuna, in the Peruvian Andes, and Scott Glacier, Antarctica. At each site, I mapped glacial deposits in order to determine how large glaciers had become in the past. In addition, I collected samples for cosmogenic surface-exposure dating – a relatively new geologic-chronologic tool – to resolve the timing of past glacial events. Together, these data provide answers to outstanding climatologic questions concerning the timing and magnitude of key climate events, such as the last ice age (“Last Glacial Maximum” or “LGM”), in the Southern Hemisphere.

On Nevado Coropuna (15˚S), glacial deposits attest to several ice-age episodes during which glaciers were more extensive than today. My reconstructions show that glaciers there last reached their maxima during the LGM in response to an atmospheric cooling of approximately 5˚C. Subsequent glacier retreat was interrupted by a major cold event between 12,000 and 14,000 years ago, during which glaciers on Coropuna advanced to positions midway between the LGM and modern glacier margins. In contrast to several recently published datasets, my Coropuna record reveals that the tropical climate responded to the last ice age in much the same way as did higher latitudes.

In the southern Transantarctic Mountains, Antarctica, the distribution of landforms at Scott Glacier indicates that the most recent glacial advance also occurred during the LGM. My geologic reconstruction of Scott glacier indicates that the West Antarctic Ice Sheet was smaller than suggested by several published computer-model datasets. In conjunction with the existing geologic record and glacial chronology from the Transantarctic Mountains, my data cast doubt on Antarctica’s contribution to large jumps in global sea-level reported to have occurred following the end of the last ice age.