Collaborative Research: Determining the role of uranium(V) in the global uranium cycle by characterizing burial mechanisms in marine sinks

本研究将探讨铀在贫氧条件下的海底循环，这是铀最重要的汇。提高我们对铀地球化学的理解对于地质应用至关重要，这些应用包括岩石年龄，古环境重建，水质和确保新的关键矿物来源。重建古代海洋的氧气水平有助于将环境的演变与地球上的生命进化联系起来，并可能在系外行星上。随着时间的推移，探测海洋中氧气水平的解释工具，如U和其他对氧气水平敏感的元素，仍然具有挑战性，因为它们在低氧海洋环境中的行为尚不清楚。为了解决这一知识差距，该项目将跟踪一种新的铀物种U（+V）的存在，并研究其在现代和古代海洋中的铀循环中的作用。这些结果将为地球海洋和大气中氧气的重建以及更广泛的全球U循环提供重要的见解。U在海洋环境中的宿主相和形态在很大程度上仍然未知，阻碍了我们重建沉积条件的能力。该项目将调查U埋藏在最重要的海洋汇的特征之间的关系U形态，去除途径，和全岩U地球化学，包括其同位素组成。这一目标将通过以下几个方面来实现：（1）与海洋环境相关的铀相实验;（2）表征富含有机质的页岩和沉积物中铀形态与铀地球化学之间的关系;（3）开发一个解释模型，根据背景信息预测铀地球化学。除了研究生培训，该项目还将促进博物馆收藏和地球与环境科学专业的科学交流，以及宾夕法尼亚州和密歇根州农村地区环境地球科学的K-12推广。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

This study will investigate uranium (U) cycling in oxygen-depleted conditions on the ocean floor, the most important sink of U. Improving our understanding of U geochemistry is critical for geological applications as diverse as dating the age of rocks, paleoenvironmental reconstruction, water quality, and securing new critical mineral sources. Reconstructing the oxygen levels of ancient oceans helps to link the evolution of the environment with evolution of life on Earth and potentially on exoplanets. Interpreting tools to probe oxygen levels in the oceans through time, such as U and other elements sensitive to oxygen level, remain challenging because of the unknowns about how they behave in low-oxygen marine settings. To address this knowledge gap, this project will track the presence of a new U species, U(+V), and investigate its role in the U cycle in modern and ancient oceans. These results will provide important insights for reconstructions of oxygen of Earth’s oceans and atmosphere, as well as the global U cycle more broadly. The host phases and speciation of U in marine settings remain largely unknown, hampering our ability to reconstruct depositional conditions. This project will investigate U burial in the most significant marine sink to characterize the relationship between U speciation, removal pathways, and whole-rock U geochemistry, including its isotope composition. This goal will be accomplished with: (1) experiments of U phases relevant to marine settings; (2) characterizing the relationship between U speciation and U geochemistry in organic-rich shales and sediments; and (3) developing an interpretive model to predict U geochemistry from contextual information. In addition to graduate training, this project will promote museum collections and science communication for Earth and environmental science majors and K-12 outreach in environmental geosciences in rural Pennsylvania and Michigan.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.