Collaborative Research: US GEOTRACES GP-17-OCE: Molecular speciation of trace element-ligand complexes in the South Pacific Ocean

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All microscopic life in the ocean requires iron to grow and to thrive. This iron is supplied by dust that is carried from land out across the ocean by strong winds, or by volcanic activity deep within the ocean. However, large areas of the ocean are very remote from both land and deep-sea volcanic activity, and the amount of iron that reaches these areas is quite small. In these regions microscopic life is often limited by the very low concentrations of iron that characterize this environment. To use iron, microbes must first extract it from seawater. To do this, some microbes have the ability to manufacture unique organic compounds called siderophores that are specifically designed to capture iron from seawater and transport it into the cell. The presence of siderophores in seawater acts as a signal to know where in the ocean iron may be limiting microbial productivity.US GEOTRACES program is a cooperative, multi-investigator effort to make high quality, high-resolution measurements of metal concentrations across representative sections of major ocean basins. GEOTRACES data will serve as a benchmark against which future measurements, made as the ocean responds to climate change, can be referenced. Most biologically important metals in the ocean are bound to organic compounds such as siderophores, and the goals of our project are to identity and measure these metal-organic complexes at the molecular level on a section across the South Pacific and Southern Oceans between Tahiti and Antarctica. The section will consist of ~ 30 evenly spaced sites where samples of seawater will be collected from the surface to the bottom of the ocean. Trace-metal organic complexes will be extracted from these samples and analyzed in the laboratory for iron, copper, cobalt, nickel, zinc, manganese, and iodine containing complexes. The molecular identities, concentrations and water column distributions of these complexes will be determined and used to assess how microbes acquire and use trace metals and other nutrients. In parallel, select samples will also be collected and analyzed for microbial genomes to provide information on which classes of microbes manufacture and use siderophores to acquire iron. Data will be archived in national and international databases. The project activities will help train the next generation of marine scientists and inform the public about how science can inform us about 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.