Phytoplankton Controls on Selenium Uptake, Speciation, and Cycling in the Global Ocean

Selenium is a naturally occurring element that is required at low levels by many organisms, including phytoplankton in the ocean. Selenium has a complicated chemistry and exists in both organic and inorganic forms. Currently, cycling of selenium across its different forms is not well-understood in the ocean. Key gaps remain in understanding how these forms affect the uptake of selenium by phytoplankton and other organisms. This research project aims to fill key knowledge gaps that are needed to improve a recently developed global model of selenium in the ocean. The research team will develop new methods for measuring the different forms of selenium in seawater and perform laboratory experiments to investigate how selenium is used by phytoplankton. In addition, they will measure key processes that influence the distribution and cycling of selenium in the ocean. This information will improve understanding of the role of selenium in ocean ecosystem health, human health and nutrition, mercury accumulation in marine food webs and harmful algal blooms. The project will train a postdoctoral researcher and two graduate students and provide research opportunities for undergraduate interns. The research team will also participate in education and outreach activities. This project will improve understanding of marine selenium cycling by quantifying the biological processes that control its uptake, transformation, and retention in the ocean. Using a combination of new analytical methods that measure selenium species by isotope dilution, isotopic tracer experiments, and targeted field observations, this study will determine how microbial communities use inorganic and organic forms of selenium under different environmental conditions. Controlled laboratory experiments will be used to investigate how selenium bioavailability and physiological regulation vary across different phytoplankton groups. In addition, sustained observations at the Scripps Pier and regional measurements in the California Current will link these processes to natural environmental variability. The new data generated by this study will be incorporated into a global ocean model to improve the representation of microbial selenium cycling and to assess how projected changes in ocean temperature, stratification, and supply may alter the distributions and bioavailability of selenium in the future. Overall, this research will provide critical information that is needed to interpret present patterns of selenium in the ocean and predict future change. 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.