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

这个博士论文研究项目将研究格陵兰岛南部冰盖边缘在全新世晚期的行为，这是一个覆盖过去几千年的时期。这位博士生将试图确定该地区的冰缘是否同步，以及它们是否在1300年至1900年的小冰河期之前或期间达到了最大范围。更精确地确定南格陵兰冰盖何时达到最大范围，将为更广泛的半球气候动力学提供新的信息和见解。如果格陵兰岛南部的冰缘在小冰期与欧洲和北美的冰缘同时达到最大值，那么格陵兰岛南部冰盖的行为可能与半球范围内的气候信号一致。这一发现表明，目前格陵兰岛南部冰盖的退缩可能是对近几个世纪全球变暖趋势的反应，这种趋势正在影响欧洲和北美的冰川退缩。然而，如果南格陵兰冰盖在小冰期之前达到最大值，就需要一套更复杂的解释，来解释为什么北半球不同地区的冰缘在不同的时期达到最大值。要确定一个更早的最大值，还需要重新考虑影响格陵兰岛南部冰盖本身的动力学，因为它的边缘可能在未来稳定下来，因为气候模型预测格陵兰岛这部分地区在下个世纪将出现最小的变暖。项目成果将通过教育和博物馆项目更广泛地与学校团体和公众分享。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。这位博士生将利用冰碛石的宇宙表面暴露年龄来确定格陵兰岛南部两个冰原出口冰川的退缩时间，这些冰碛石的年龄超过300年。“这些结果将与现有的初步研究数据和这些地区北部的新数据进行比较。”最后，将确定南格陵兰岛四个不同冰缘的年代，从而可以测试南格陵兰冰盖的时空变化。学生将解决两个基本的研究问题。(1)格陵兰岛南部冰盖的晚全新世最大值是什么时候？关于这个问题，学生将测试一个假设，即晚全新世极大期经历了一个比小冰河期更广泛的晚全新世推进，以应对早期显著的冷却。(2)区域气候是否在百年尺度上控制着格陵兰岛南部冰盖的变化？该学生将通过验证南格陵兰冰盖对百年气候变化（如在全新世晚期观察到的气候变化）同步响应的假设来解决这个问题。验证这些假设将揭示最近冰盖与气候的相互作用，这对于模拟格陵兰冰盖对空间可变温度变化的响应非常重要。项目结果将确定南方地理信息系统边缘是否对与人类相关的时间尺度上小于几度的气候变化做出了反应？这是一个潜在的变革性结果，特别是对于预测未来一个世纪的海平面上升。

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.