Assessing the impact of global change on the distribution and physicochemical speciation of bioactive trace elements in seawater

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The distribution and bioavailability of essential trace elements can impact marine productivity, ecosystem structure and air-sea exchange of greenhouse gases. An understanding of the response of marine biogeochemical cycles to global change must, therefore, include studies of trace element sources, sinks, and chemical speciation. This is because marine microbes have absolute requirements for trace element nutrients that can help explain temporal-spatial variability in microbial community structure and set upper limits on carbon and nitrogen fixation in the sea. The bioavailability of trace element nutrients to marine microbes is controlled not only by the concentration but the speciation, or chemical form, that essential elements take in seawater. In turn, microorganisms can affect the distribution and speciation of trace elements through biologically mediated uptake/exudation, redox reactions and the production of strong organic ligands that complex dissolved trace elements in the water column. The proposed research program will investigate how changing hydrography and ocean acidification will affect the bioavailability of trace element nutrients in marine surface waters and continue studies of the dominant mechanisms that control interactions between marine microbes and trace metals in coastal and open ocean environments. The long term goals of the program are to provide an understanding of how changes in the distribution and availability of bioactive trace metals to marine microbes affect: 1) the magnitude of C and N fluxes into and out of the surface ocean, and, 2) the elemental and isotopic composition of the sinking flux of particulate matter to the ocean interior.