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

冰冻圈对全球变暖的反应对社会具有重大影响。要预测下个世纪全球气候变化、冰川融化和海平面上升的速度，就需要准确地了解冰川和冰盖对气候变化的反应。尽管格陵兰冰盖的负质量平衡以及最近许多出口冰川的快速加速已被记录在案，但对未来冰盖消退的模式和速度的预测极不确定。该项目将把古记录与格陵兰冰盖最快、最具活力的出口冰川Jakobshavn Isbræ的行为历史数据联系起来，以量化其对温度变化的敏感性。具体地说，该项目将：1)确定雅各布港边缘在全新世早期和中期的退缩速度，这段时间比今天温暖；以及2)确定小冰期雅各布港冰缘进退的时间，量化相关的体积变化，并估计边缘对温度变化的敏感性。这些发现将限制格陵兰冰盖对温度变化的敏感性，这一知识在面对当代冰盖快速变化的情况下是迫切的，通过使用四种最先进的方法：1)冰雕基岩表面的铍同位素暴露测年，2)湖泊沉积物的放射性碳测年，3)基于昆虫化石(摇摆虫)的古温度测定，以及4)过去冰盖边缘的3D绘制。这个项目可以帮助解释世界上对气候变化敏感的部分地区当前冰盖变化的本质。这项研究之所以重要，是因为它将：1)提供格陵兰冰盖边缘持续快速变化的较长期背景(数十年至数百年)，这些变化仅被监测数年或数十年；2)提供有关冰盖行为的经验约束，可用于改进数值冰盖模型；3)先进的工具和方法，用于将古数据与历史和观测数据结合起来。此外，预期的发现旨在补充国家科学基金会和美国国家航空航天局正在进行的许多项目，这些项目侧重于雅各布港伊斯布雷的当代动态。

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.