| Summary: | Ph.D. Ice sheets play a critical role in Earth’s climate system; their presence can substantially alter atmospheric and oceanic circulation, Earth’s surface albedo, and sea level. Ice sheets also respond to changes in climate, and projected increases in global temperatures over the next centuries have as-yet-unknown consequences for the stability of modern-day ice sheets in Greenland and Antarctica. Despite the urgency of climate change and its associated impacts, the sensitivity of ice sheets to centennial- to millennial-scale temperature oscillations remains poorly understood. In this dissertation, I use 10Be surface exposure dating and 14C dating to reconstruct the late Pleistocene to Holocene retreat of two northern hemisphere ice sheets. In Southeast Alaska, I date the latest Pleistocene recession of a marine-terminating margin of the Cordilleran Ice Sheet (CIS). In Southwest Greenland, I reconstruct the Holocene history of a land-terminating region of the Greenland Ice Sheet (GrIS). In doing so, I provide a key perspective on ice sheet history that places recently observed cryosphere changes into a longer-term context.The records of ice sheet change presented here reveal the rapid response of both land- and marine-terminating ice sheet margins to climate oscillations. In Southeast Alaska, retreat of CIS margins between ~17,000 and 15,000 years ago was concurrent with ocean warming and rising sea levels along the Pacific coast, suggesting that changes in deglacial oceanic conditions were an important factor in driving marine-terminating CIS retreat. In addition, retreat of the CIS in the early deglacial period opened up a potentially habitable corridor that may have been used by early humans to migrate to the Americas. Ice sheet margins across western Greenland reversed their overall pattern of retreat multiple times early Holocene, depositing extensive moraine systems between Disko Bugt and Kangersuneq fjord. These results suggest that the western GrIS was highly responsive to short-term climate fluctuations. A continuous reconstruction of Southwest GrIS retreat rates over the entire Holocene demonstrates that the ice margin recession was fastest between 10,400 and 9,100 years ago, providing support for an early Holocene Thermal Maximum in western Greenland.This dissertation presents new data that add to the growing body of work on Pleistocene to Holocene ice sheet history, contributing to a better understanding of ice sheet change in both space and time. Importantly, this dissertation has demonstrated that continental-scale ice sheets can respond rapidly to short-term climate change. These results can be used to assess the performance of ice sheet and climate models over long timescales, and may ultimately help to reduce uncertainties in estimates of future sea level rise.
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