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

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.