Doctoral Dissertation Research: Late Pleistocene Glaciation in Southeastern Alaska: Assessing the Sensitivity of a Marine-Terminating Ice Sheet to Changing Environmental Conditions

这个博士论文研究项目将整合冰川地质学、详细的冰缘测绘和高分辨率地质年代学，以评估气候和地形对阿拉斯加东南部科迪勒兰冰盖海洋边缘的范围和退缩的影响。这个项目将为控制海洋冰盖边缘稳定性的过程提供新的见解。它将提供西科迪勒冰盖沿海洋边缘退缩的直接年表，从而促进这部分冰盖的重建，并增加关于气候、地形和冰盖范围之间的时空关系的知识。该项目将对控制海洋冰盖边缘稳定性的过程产生新的见解，并为改进冰盖-气候系统的预测模型提供经验约束。此外，该项目将为先前提出的北美环太平洋沿岸无冰地区的无冰状况提供直接证据，这将对人类向美洲迁移的分析产生重要影响。项目成果将纳入与布法罗科学博物馆合作开展的一项外展计划，该计划综合了目前在地理、古气候学、人类学和古生物学方面的研究，以教育公众了解环境条件变化的原因和后果。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。海洋冰盖边缘，包括今天格陵兰岛和南极洲的冰盖边缘，被认为对气候变化高度敏感，但环境变化对海洋冰盖边缘的影响仍然知之甚少。在末次盛冰期（大约26000到19000年前），科迪勒拉冰盖覆盖了北美西部的大部分地区，从阿拉斯加南部一直延伸到美国太平洋西北部。相对而言，人们对科迪勒拉冰盖在这段时间内的行为知之甚少，尤其是在它终止于海洋的西海岸。本项目将集中研究三组关于末次盛冰期期间和之后西科迪勒拉冰盖行为的研究问题：(1)末次盛冰期期间阿拉斯加东南部科迪勒拉冰盖的范围有多大，阿拉斯加东南部是否有任何地区保持无冰状态？这个问题将通过对先前提出的无冰区的铍-10同位素基岩和巨石表面进行宇宙暴露测年来解决。再加上从公开的地形数据和航空图像中获得的古冰缘的详细地图，这些地点的暴露年龄将使博士生能够重建西科迪勒拉冰盖的最大范围。(2)西科迪勒冰盖退缩的时间和速度是什么？沿海岸至内陆样带的岩石表面的宇宙成因铍-10定年将用于解决这个问题，这对了解海洋终端冰盖对气候变化的敏感性具有重要意义。(3)海洋变暖、大气变暖和海平面上升等哪些环境因子影响了冰盖的退缩？本研究开发的退缩年代学将与现有的气候和海平面记录相关联，以验证海洋变暖是影响阿拉斯加东南部海洋冰盖崩塌的主要因素的假设。

This doctoral dissertation research project will integrate glacial geology, detailed ice-margin mapping, and high-resolution geochronology to assess the influence of climate and topography on the extent and retreat of a marine margin of the Cordilleran Ice Sheet is southeastern Alaska. This project will provide new insights into the processes that control the stability of marine ice-sheet margins. It will yield a direct chronology of a western Cordilleran Ice Sheet retreat along a marine margin, thereby facilitating reconstructions of this part of the ice sheet and adding to knowledge about the spatial and temporal relationships among climate, topography, and ice-sheet extent. This project will generate new insights into the processes that control the stability of marine ice sheet margins and provide empirical constraints to improve predictive models of the ice sheet-climate system. In addition, the project will provide direct evidence of ice-free conditions in previously proposed coastal ice-free areas along the Pacific Rim of North America that will have important implications for analyses of human migrations into the Americas. Project results will be incorporated into an outreach program conducted in concert with the Buffalo Museum of Science that synthesizes current research in geography, paleoclimatology, anthropology, and paleontology to educate the public about the causes and consequences of changing environmental conditions. 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.Marine ice-sheet margins, including those in present-day Greenland and Antarctica, are thought to be highly sensitive to climatic variation, but the effects of environmental change on marine ice sheet margins are still poorly understood. During the Last Glacial Maximum (roughly 26,000 to 19,000 years ago), the Cordilleran Ice Sheet covered much of western North America, stretching from southern Alaska to the Pacific Northwest of the U.S. Relatively little is known about Cordilleran Ice Sheet behavior during this time period, particularly along the west coast where it terminated in the ocean. This project will focus on three sets of research questions concerning the behavior of the western Cordilleran Ice Sheet during and following the Last Glacial Maximum: (1) How extensive was the Cordilleran Ice Sheet in southeastern Alaska during the Last Glacial Maximum, and did any areas of southeastern Alaska remain ice-free? This question will be addressed using cosmogenic exposure dating of the beryllium-10 isotope bedrock and boulder surfaces in previously proposed ice-free areas. Together with detailed mapping of the paleo-ice margin from publicly available topographic data and aerial imagery, exposure ages from these locations will allow the doctoral student to reconstruct the maximum extent of the western Cordilleran Ice Sheet. (2) What was the timing and pace of retreat of the western Cordilleran Ice Sheet? Cosmogenic beryllium-10 dating of rock surfaces along coast-to-inland transects will be used to resolve this question, which has implications for basic understanding of the sensitivity of marine-terminating ice sheets to climate change. (3) What environmental factors, such as ocean warming, atmospheric warming, and sea-level rise, influenced ice-sheet retreat? The retreat chronology developed in this study will be correlated with existing climate and sea-level records to test the hypothesis that ocean warming was the primary factor influencing marine ice-sheet collapse in southeastern Alaska.