Date of Award

5-2013

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

The extent and volume of the Antarctic ice sheet at the Last Glacial Maximum (LGM), as well as the timing of subsequent deglaciation, remains poorly known. However, this information is important for understanding the dynamics of the ice sheet and therefore the potential for catastrophic ice-sheet collapse and future sea-level rise. I focus here on the ice sheet that filled the Ross Sea Embayment during the LGM and during other Quaternary ice ages. Drifts alongside outlet glaciers that extend through the Transantarctic Mountains (TAM) from the East Antarctic Ice Sheet (EAIS) to the Ross Sea Embayment record former changes in ice elevation and can be used to improve our understanding of ice-sheet history. Fieldwork in the southern TAM at one of these outlets, Shackleton Glacier, involved mapping and dating of Late Quaternary ice extents. This work revealed that ice midway up-glacier was close to its LGM limit at about 10,500 to 8500 cal yr BP, after which time it thinned to present-day levels. These ages suggest that most ice thinning occurred during the Holocene, a result consistent with information from other TAM outlet glaciers. These results also support reconstructions of Ross Sea ice sheet grounding-line retreat that indicate recession through the Holocene.

This work not only addresses the timing of the LGM, but also bears on the question of the amount of excess ice in the Ross Sea Embayment (RSE) at this time. Reconstructed minimum surface elevations, based on surficial mapping of drift limits, indicate that ice at locations midway up Shackleton Glacier reached approximately 280 to 330 m above the present-day levels during the LGM. Extrapolation of these surface elevations to locations near the mouth of the glacier suggests that Shackleton Glacier reached roughly 1100 m near its confluence with the Ross Sea ice sheet. This elevation is similar to that obtained from other outlet glaciers within the southern TAM. However, these results are in contrast with both glaciological and conceptual models that place more extensive ice in the southern Ross Sea Embayment during the LGM and with limited data indicating little or no LGM ice expansion. The modest ice elevations reconstructed in this study cast doubt on the possibility of ice in the Ross Sea Embayment contributing any significant amount to large meltwater fluxes during the last deglaciation.

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