Collaborative Research: EAGER: Development of a Method for Paired Potassium/Argon Geochronology and Strontium-Neodymium-Lead Radiogenic Isotope Geochemistry of Dust in Ice Cores

大气尘埃和沉积物是过去地球和海洋过程的宝贵示踪物，因为它们的地球化学成分反映了它们的基岩母质。科学家利用沉积物和尘埃的成分作为“指纹”，将冰芯和沉积物核心等下游地点的物质联系起来，追溯到它们的源头。通过地球化学指纹，科学家们深入了解了气候突然变化的原因和影响，冰盖的稳定性及其对海平面上升的潜在贡献，以及海洋和大气环流模式变化的机制。该项目旨在利用用于确定沉积物来源的两种不同技术的能力。该方法将使该团队能够解决有关南极洲周围过去的风型、不同尘源在向南大洋提供营养物质方面的作用以及西南极冰盖在最后一次间冰期暖期期间的行为等关键问题。此外，该方法有可能应用于外星物质，如火星任务和月球岩石。尘埃和其他沉积物来源的地球化学示踪是帮助重建过去的大气、海洋和冰盖动力学的有效方法。然而，在一些区域，如南半球，即使是使用锶、钕和铅同位素的多变量方法，也会由于源区成分重叠而产生不明确的结果。研究小组发现，铅同位素在区分来源方面有很大的价值，与钾/氩年代学相结合，对沉积物的来源提供了显著的额外限制。这一附加值是由于在随后的地质事件中重置K/Ar年龄相对容易，例如在成岩作用期间新矿物的结晶，或通过加热重置，重置发生在比其他同位素系统更低的温度。该团队将使用岩石和矿物标准以及细粒沉积物来开发和测试拟议的方法，然后将其应用于来自去冰芯的冰芯尘埃样本和关键地点最后一次冰盛期的尘埃。除了这种新方法的更广泛的科学影响，该项目还将为科尔比学院的本科生提供机会，完全沉浸在发现的世界中，他们在科尔比的贝丝·科夫曼博士的地球化学实验室和哥伦比亚大学的拉蒙特-多尔蒂地球天文台工作，在那里他们将与来自全国各地的更广泛的学生进行接触，并获得最先进的分析设施。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Atmospheric dust and sediment serve as valuable tracers of past Earth and ocean processes because their geochemical compositions reflect their bedrock parent material. Scientists use the compositions of sediments and dust as a ‘fingerprint’, linking materials at downstream sites, such as ice and sediment cores, back to their sources. Through geochemical fingerprinting, scientists have gained insight into the causes and impacts of abrupt climate changes, the stability of ice sheets and their potential contributions to sea level rise, and the mechanisms by which ocean and atmospheric circulation patterns change. This project aims to harness the capabilities of two different techniques used to determine sediment provenance. The approach will allow the team to address critical questions regarding past wind patterns around Antarctica, the roles of different dust sources in supplying nutrients to the Southern Ocean, and the behavior of the West Antarctic Ice Sheet during the last interglacial warm period. In addition, the method has the potential to be applied to extraterrestrial materials such as from the Mars Mission and Moon rocks. Geochemical tracing of dust and other sediment sources is a powerful approach that aids in reconstructing past atmosphere, ocean, and ice-sheet dynamics. However, in some regions such as the Southern Hemisphere, even multi-variate approaches such as those using strontium, neodymium, and lead isotopes yield ambiguous results due to overlapping source-area compositions. The team has found that lead isotopes add great value in distinguishing sources and that combining these with potassium/argon geochronology provides significant additional constraints on sediment provenance. The added value is due to the relative ease of resetting potassium/argon ages during subsequent geologic events such as crystallization of new minerals during diagenesis, or by heating, with resetting occurring at lower temperatures than other isotopic systems. The team will develop and test the proposed approach using rock and mineral standards and fine-grained sediments, then apply it to ice-core dust samples from deaccessioned ice cores and dust from the Last Glacial Maximum at key sites. Beyond the broader scientific impact of this new approach, the project will provide opportunities for Colby College undergraduates to experience complete immersion in the world of discovery, working both in Dr. Bess Koffman’s geochemistry lab at Colby and at the Lamont-Doherty Earth Observatory of Columbia University, where they will engage with a wider cohort of students from around the country and have access to state-of-the-art analytical facilities.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.