Date of Award

Summer 8-17-2018

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Brenda Hall

Second Committee Member

George Denton

Third Committee Member

Aaron Putnam

Additional Committee Members

Gordon Bromley

Abstract

The Antarctic Ice Sheet contains ~58 m of global sea-level equivalent and thus its future behavior under global warming is of pressing concern. Examination of past ice-sheet behavior during periods of warming climate can afford insight useful for predicting future sea-level rise. This study focuses on a major unanswered question - namely, the cause of Antarctic Ice Sheet retreat following the last glaciation. Documenting the timing and nature of this deglaciation is crucial to understand the mechanisms behind ice-sheet behavior. Here, I examine how the marine portions of the ice sheet responded to the major warming that occurred at the end of the last ice age. I carried out fieldwork at Amundsen and Liv Glaciers, outlet glaciers of the East Antarctic Ice Sheet that drain through the Transantarctic Mountains to the Ross Ice Shelf. Thinning during the last deglaciation left drift on nunataks along the Ross Sea coast. My goal was to document these deposits and produce a chronology for the last stages of the most recent ice retreat. This chronology comes from radiocarbon dates of algae that lived in former ice-marginal ponds dammed by the ice sheet.

My results indicate that the Ross Sea grounding line retreated southeastward past Liv Glacier by ~4,200 yrs BP and past Amundsen Glacier by 2,900 yrs BP. Prior studies show that the deglaciation was marked by an initial period of rapid retreat, indicative of instability in this sector of the AIS. My data show that this was followed by a more gradual period of retreat in the late Holocene, with possible stabilization of the grounding line shortly after ~3000 yrs BP when it retreated to near its current position on the Siple Coast in the vicinity of Mercer Ice Stream. The timing of grounding-line retreat does not correspond closely with the largest post-LGM changes in global sea level or ocean temperature. Rather, recession was delayed significantly relative to the global deglaciation. Slowing of grounding-line retreat in the late Holocene may have been due to the effects of increased accumulation and falling local sea level, suggesting that these factors may be important in controlling the extent of the Antarctic Ice Sheet.

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