MCA: Developing geochemical and analytical capabilities for selenium isotope geochemistry in Louisiana

This project will allow a mid-career scientist to learn cutting-edge geochemical methodologies related to Selenium (Se) isotope geochemistry. These methods will be used to investigate the geochemistry of Se in recent sediments and their potential as an archive to reconstruct paleoenvironmental conditions. While most paleo-redox work has focused on organic shales as an archive, carbonate rocks are more common in the geologic record, are often continuous over long time periods, and are widespread in open ocean basins. If successful, the Se technique can be applied to ancient carbonate deposits to better understand the history of oxygenation of the Earth. Broader impacts include strengthening collaborations with local (Louisiana) and international (Granada, Spain) scientists. The project will develop new research directions for the principal investigator and enable new research experiences for students. Selenium geochemistry has attracted significant research interest owing to its geochemical behavior being similar to sulfur (S) yet differing in important ways. Both elements are redox sensitive, having multiple oxidation states and multiple isotopes, yet different Se and S species are stable under different redox potentials and thus have different responses to oxidation under similar Eh and pH conditions. Therefore, selenium isotope signatures can serve as indicators of Se sources and biogeochemical transformations of selenium in the environment. To date, not much is known about Se isotopes in carbonate sediments. The scientific goals of this project are (1) to identify different pools of selenium and their impact on the Se isotopic composition of recent carbonate sediments from the Florida Keys and from laboratory co-precipitation experiments, (2) the speciation of Se in these sediments using a synchrotron facility, and (3) to determine whether carbonate sediments have the potential to capture a paleoredox signal. 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.