OCE-PRF Isotopic and microbial investigations of the iron geochemistry and bioavailability of glaciogenic particles

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Trace element micronutrients such as iron, play important roles in biological processes in the ocean. In surface waters where phytoplankton grow and support the base of the marine food web, iron is often present at vanishingly small concentrations and near the poles, can limit phytoplankton productivity. Motivated by widespread oceanic iron deficiency, microbes have developed specialized strategies for accessing even relatively unavailable mineral forms of iron, such as particulate matter. One source of iron-rich particles is the delivery of glacial meltwater to the ocean, which is expected to increase as the climate continues to warm. The research proposed here seeks to study the relationships between iron supplied from the melting of glaciers and the ability of microbes to take advantage of this new source of iron nutrition. To do this, the growth of microbes will be tested on glacial ice particles from two coastal locations heavily influenced by glaciers: Antarctica and Alaska. This project will support the training of a postdoctoral scholar, and the participation of the PI in education and outreach activities carried out through the Alaskan Native Science & Engineering Program (ANSEP) and Scripps Undergraduate Research Fellowship (SURF) programs, including mentorship of an undergraduate in a research project. Glacial meltwater is expected to fertilize the high-latitude oceans due to its high content of bioavailable iron (Fe). Bioavailability of glacially-derived Fe is typically inferred from size and chemical lability, and previous investigations in biological systems use a limited number of Fe substrates to probe the bioavailability with select phytoplankton species. A mechanistic understanding of glaciogenic Fe acquisition and biological uptake in marine environments is still needed. Mechanistic studies which fully characterize the geochemical and microbial acquisition of glaciogenic iron have the potential to greatly inform our understanding of the coupled interaction between the supply of glacial meltwater and ecosystems productivity. This proposal seeks to assess the bioavailability of glacially-derived Fe-bearing particles by combining examinations of the Fe isotopic composition of chemically treated glaciogenic particles from discrete glacial ice pieces with growth experiments using a genetically-modified marine heterotrophic bacteria. Two hypotheses regarding chemical lability and bioavailability of glaciogenic particles will be examined in the proposed work: 1) The Fe-stable isotopic signatures of glaciogenic particles are linked to chemical lability, and can be used to gauge the fertilization potential of sediment transported to marine environments and its subsequent fate; and 2) Chemical lability can be directly linked to bioavailability via microbial iron acquisition, which in turn affects Fe-stable isotopic signatures. This project stands to contribute to our understanding of which members of the marine microbial community will benefit from glacially-derived Fe, the role of Fe acquisition strategies in Fe isotopic signatures and bioavailability in marine systems, and the fertilization potential of increased cryospheric weathering inputs to the ocean.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.