The Sensitivity of the Greenland Ice Sheet to Climate Change: Reconstructing the Response of the Jakobshavn Isbrae During the Little Ice Age and Holocene Thermal Maximum

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The response of the cryosphere to global warming has significant ramifications for society. The ability to predict rates of global climatic change, glacier melt, and sea-level rise through the next century requires an accurate understanding of glacier and ice sheet response to climatic change. Although a negative mass balance of the Greenland Ice Sheet and recent rapid acceleration of many of its outlet glaciers has been documented, forecasts of the pattern and rate of future ice sheet retreat are extremely uncertain. This project will link the paleo-record with historical data on the behavior of the Greenland Ice Sheet's fastest and most dynamic outlet glacier, Jakobshavn Isbræ, to quantify its sensitivity to temperature change. Specifically, this project will: 1) determine the rate of retreat of the Jakobshavn margin during the early and middle Holocene, a time period that was warmer than today; and 2) determine the timing of advance/retreat of the Jakobshavn ice margin during the Little Ice Age, quantify associated volumetric changes, and estimate the sensitivity of the margin to temperature change. The findings will constrain the sensitivity of the Greenland Ice Sheet to temperature change, knowledge that is urgent in the face of rapid contemporary changes in the ice sheet, by using four state-of-the-art approaches: 1) Beryllium-isotope exposure dating of ice-sculpted bedrock surfaces, 2) radiocarbon dating of lake sediments, 3) fossil insect (chironomid)-based paleothermometry, and 4) 3D mapping of past ice sheet margins.This project can help explain the nature of current changes in ice cover in a part of the world sensitive to shifts in climate. This research is important because it will: 1) provide a longer-term context (decades to centuries) for rapid ongoing changes along the Greenland Ice Sheet margin, which have been monitored for only years or decades, 2) provide empirical constraints on ice-sheet behavior that can be used to improve numerical ice sheet models, and 3) advance tools and approaches used to combine paleo data with historical and observational data. In addition, the anticipated findings are designed to complement numerous ongoing NSF and NASA projects focused on contemporary dynamics of the Jakobshavn Isbræ.