Doctoral Dissertation Research: Cosmogenic Surface Exposure Dating of Late Holocene Spatial and Temporal Variability of the Southern Greenland Ice Sheet

这一博士论文研究项目将研究格陵兰南部冰盖边缘在全新世晚期的行为，这一时间段涵盖了过去数千年。这位博士生将试图确定该地区的冰缘行为是否同步，以及它们是否在大约1300年至1900年被称为小冰期之前或期间达到了最大程度。更准确地确定格陵兰南部冰盖何时达到最大范围，将为更广泛的半球气候动态提供新的信息和见解。如果格陵兰南部的冰缘在小冰期与欧洲和北美的冰川边缘同时达到最大程度，那么格陵兰南部冰盖的行为很可能与半球范围的气候信号一致。这一发现表明，目前格陵兰南部冰盖的消退可能是对近几个世纪来全球变暖趋势的回应，这些趋势正在影响欧洲和北美的冰川消退。然而，如果格陵兰南部冰盖在小冰期之前达到最大值，就需要一套更复杂的解释，解释为什么北半球不同地区的冰缘在不同的时间段达到最大值。确定一个更早的最大值还需要重新考虑影响格陵兰南部冰盖本身的动态，因为它的边缘可能在未来稳定下来，因为气候模型预测，下个世纪格陵兰这一部分的变暖幅度最小。项目成果将通过教育和博物馆项目与学校团体和公众更广泛地分享。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生能够建立强大的独立研究生涯。博士生将使用来自冰原的巨石的宇宙表面暴露年龄来测定格陵兰南部两个冰盖出口冰川的消退，这些巨石的年代被测得超过300年。“这些结果将与试点研究的现有数据和这些地点以北的新数据进行比较。”最后，将确定格陵兰南部四个不同冰缘的年代，从而能够测试格陵兰南部冰盖的空间和时间变异性。学生将回答两个基本的研究问题。(1)格陵兰南部冰盖的晚全新世最大值是什么时候？关于这个问题，学生将检验一种假设，即晚全新世最大值经历了一次比小冰期更广泛的晚全新世推进，以响应显著的早期冷却。(2)在百年时间尺度上，区域气候是否控制着格陵兰南部冰盖的可变性？这名学生将通过测试以下假设来解决这个问题：格陵兰南部冰盖对百年来的气候变化做出同步反应，例如在全新世晚期观察到的气候变化。检验这些假说将有助于揭示最近的冰盖-气候相互作用，这对于模拟格陵兰冰盖对空间变化的温度变化的响应很重要。项目结果将决定南部地理信息系统边缘是否在与人类相关的时间尺度上对小于几度的气候变化做出了响应？S预测，在短期内，这是一个潜在的变革性结果，特别是对于预测下一个世纪海平面上升。

This doctoral dissertation research project will examine the behavior of the margins of the southern Greenland ice sheet during the late Holocene epoch, a time period covering the last several thousand years. The doctoral student will seek to determine whether ice margins behaved synchronously in the region and whether they reached their maximum extent before or during the time known as the Little Ice Age from about 1300 to 1900. A more precise determination of when the southern Greenland ice sheet reached its maximum extent will provide new information and insights regarding broader hemispheric climate dynamics. If the southern Greenland ice margins reached their maximum extent during the Little Ice Age at the same time as glacial margins in Europe and North America, then the southern Greenland ice sheet likely behaved in concert with a hemispheric wide climate signal. This finding would suggest that current southern Greenland ice sheet retreat might be in response to warming trends around the globe in recent centuries that are influencing ice retreat in Europe and North America. If the southern Greenland ice sheet reached its maximum before the Little Ice Age, however, a more complex set of explanations for why ice margins in different parts of the Northern Hemisphere reached their maxima during different time periods will be required. Identification of an earlier maximum also would require reconsideration of dynamics affecting the southern Greenland ice sheet itself, because its margins may stabilize in the future as climate models predict minimal warming over this part of Greenland in the coming century. Project findings will be shared more broadly with school groups and the public through education and museum programs. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.The doctoral student will date the retreat of two southern Greenland ice sheet outlet glaciers using cosmogenic surface exposure ages on boulders from moraines that are dated as being more than 300 years in age. `These results will be compared with existing data from a pilot study and new data to the north of these locations. In the end, four different ice margins in southern Greenland will be dated, thereby allowing the testing of spatial and temporal variability in the southern Greenland ice sheet. The student will address two fundamental research questions. (1) When was the late-Holocene maximum of the southern Greenland ice sheet? Regarding this question, the student will test the hypothesis that the late-Holocene maximum underwent a late-Holocene advance more extensive than its Little Ice Age advance in response to significant early cooling. (2) Does regional climate govern southern Greenland ice sheet variability at centennial timescales? The student will address this question by testing the hypothesis that the southern Greenland ice sheet responds synchronously to centennial climate variations, such as those observed during the late Holocene. Testing these hypotheses will shed light on geologically recent ice sheet-climate interactions important for modeling the Greenland ice sheet response to spatially variable temperature changes. Project results will determine if southern GIS margins have responded to climatic changes of less than several degrees on a timescale relevant to humanity?s near-term future, a potentially transformative result, particularly for predicting sea-level rise over the coming century.