CAREER: Calibrating selenium isotopes as tracers of nutrient and redox dynamics in past and present marine environments

About This Grant

Selenium is a common trace element found in seawater and sediments. It has six stable isotopes whose ratios allow it to track oxygen content and biochemical reactions in seawater. So far, Selenium isotopes have proven difficult to measure accurately due to their low concentration. This project will develop new methods to measure Selenium isotopes. Water samples taken along a profile across the Eastern Pacific Ocean and from sediments in the Black Sea will be used. These samples have very low oxygen seawater. This low oxygen seawater provides ideal conditions to calibrate the isotopes of Selenium to oxygenation. The project includes education and training in stable isotope techniques in geosciences. Two graduate-level workshops on state-of-the art elemental isotope analysis will be held. Workshops will introduce advanced hands-on techniques and theory for trace element analysis. Also, middle- and high-school students will visit the research laboratory and learn about Selenium contamination in the local environment. Selenium is a trace element that is both an essential micronutrient and a toxin at relatively low concentrations. It inhabits four oxidation states in surface environments and is comprised of six stable isotopes, the relative abundances of which are fractionated during biogeochemical reactions. Selenium isotope systematics therefore hold great promise for tracking its cycling in nature, including in reconstructions of paleo-environmental conditions using ancient sediments. However, the understanding of Selenium isotope mass balance in the modern ocean remains poor due to a lack of data. This project seeks to develop and refine methods for measuring Selenium isotopes in seawater and marine sediments. The research team will make the first phase-specific Se isotopes along transect through the East Pacific and through recent marine sediment cores with the goal of calibrating modern Selenium isotope mass balance in the oceans for use in reconstructions of paleo-oceanographic oxidation and nutrient dynamics. As part of the project, the team will host workshops for graduate students focused on state-of-the-art mass spectrometry for trace element isotope analysis. The team will also host lab visits for Durham high school students to engage with environmental chemistry research and see how isotopes are used to study coal-ash contamination of North Carolina lakes. 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.