Unlocking the Glacial History of the McMurdo Dry Valleys, Antarctica by Fingerprinting Glacial Tills with Detrital Zircon U-Pb Age Populations

本研究的目的是识别和区分南极洲麦克默多干谷冰川沉积物的不同来源区域，以确定过去的冰川流动方向。了解冰流对于确定南极冰盖在过去的表现是至关重要的。这种洞见对于科学家预测南极冰盖将如何演变，进而预测海平面可能上升的幅度和速度至关重要。这个项目的研究地点是麦克默多干谷，那里有大量的冰川沉积记录，可以追溯到至少1400万年前。冰川沉积物中岩石的化学成分提供了沉积这些物质的冰的来源的线索。对冰川沉积物的化学分析将有助于绘制以前冰川作用范围的地图，从而更好地了解冰流的历史。在麦克默多干谷绘制过去1400万年以来最大的冰盖扩张地图，引起了全球气候变化界的广泛兴趣。本科生组成了大部分的实地团队，并将负责实验室的样品制备和分析。该项目利用新的地球化学技术来测试关于南极洲麦克默多干谷（MDV）沉积冰川丘的冰川冰的来源、范围和流动模式的假设。MDV包含了一个无与伦比的陆地冰川沉积物档案，它记录了沉积它们的多种冰源。这些变化包括覆盖南极横贯山脉的东北流动冰、南极东部冰盖的向东扩张、代表南极西部冰盖扩张的罗斯冰架的向西延伸，以及当地高山冰川的增长。南极的冰碛和冰碛通常孤立在一块块或不相交的露头模式中，因此很难将冰碛联系起来并确定其来源。该项目将对麦克默多干谷的土丘进行系统研究，利用各种地球化学技术确定其来源，包括用x射线荧光进行主要元素和次要元素分析，重矿物组成，土壤盐浓度，并确定这些土丘中所含锆石砂的铀铅（U-Pb）年龄。主要工具将是冰川漂移中碎屑锆石种群的年龄分布，因为它反映了岩石的来源，并提供了一个独特的地球化学“指纹”，用于区分来源区域，同时将不同地点的单位联系起来。这个项目的成果将是建立一个社区可用的锆石指纹库，用于从极地岩石储存库的存档样本中绘制冰川碛，并在MDV中系统地收集样本。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The goal of this study is to identify and distinguish different source areas of glacial sediment in the McMurdo Dry Valleys, Antarctica to determine past glacial flow direction. Understanding ice flow is critical for determining how the Antarctic Ice Sheets have behaved in the past. Such insight is fundamental for allowing scientists to predict how the Antarctic Ice Sheets will evolve and, in turn, forecast how much and how fast sea level may rise. The project study site, the McMurdo Dry Valleys, contain a tremendous record of glacial deposits on land that extends back at least 14 million years. Chemistry of the rocks within the glacial deposits hold clues to the sources of ice that deposited the material. The chemical analyses of the glacial deposits will allow mapping of the former extent of glaciations providing a better understand of ice flow history. The mapping of the largest ice sheet expansion of the past 14 million years in the McMurdo Dry Valleys is of broad interest to the global climate change community. Undergraduate students comprise the majority of the field teams and will be responsible for sample preparation and analysis in the laboratory. This project utilizes new geochemical techniques to test hypotheses about the source, extent, and flow patterns of the glacier ice that deposited glacial tills in the McMurdo Dry Valleys, Antarctica (MDV). The MDV contain an unparalleled terrestrial archive of glacial deposits, which record multiple sources of ice that deposited them. These include the northeast flowing ice that overrode the Transantarctic Mountains, the eastward expansion of the East Antarctic Ice Sheet, the westward extension of the Ross Ice Shelf representing an expansion of the West Antarctic Ice Sheet, and the growth of local alpine glaciers. The glacial tills and drifts in the Antarctic are typically isolated in patches or disjointed outcrop patterns making it difficult to correlate tills and determine their source. This project will undertake a systematic study of the tills in the McMurdo Dry Valleys to determine their provenance with a variety of geochemical techniques including major and minor element analyses with X-ray fluorescence, heavy mineral composition, soil salt concentration, and determining the uranium-lead (U-Pb) ages of zircon sands contained in these tills. The primary tool will be the age distribution of the population of detrital zircon in a glacial drift because it reflects the source of the tills and provides a unique geochemical "fingerprint" used to distinguish source areas while correlating units across different sites. A deliverable from this project will be a community available library of zircon fingerprints for mapped glacial tills from archived samples at the Polar Rock Repository and the systematic collection of samples in the MDV.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.