Determining the distribution and physicochemical speciation of bioactive trace elements in the oceans under a changing climate

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The distribution and bioavailability of essential (e.g. Cu, Fe and Zn) and potentially toxic (e.g. Cu, Ag and Cd) trace elements in the ocean can impact marine productivity, ecosystem structure and therefore the air-sea exchange of climate active 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 or sensitivities to trace element nutrients and toxins 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 elements to marine microbes is controlled not only by the concentration but the speciation, or chemical form, that metals 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 long-term goals of my research program are to understand the processes that control the distribution, chemical speciation and resulting bioavailability of trace metals, and how altered physical and chemical conditions in response to climate change are likely to impact the biogeochemical cycling of metals in the ocean. Recently, my research group has made significant progress towards these goals through the development and application of powerful analytical methods in both the field and the laboratory. We have focused on metals that control primary production and community structure (e.g. Fe, Cu and Zn), serve as paleoceanographic tracers that provide important information regarding the oceans role in past climate change (e.g. Cd, Ag), or potentially toxic heavy metals that might negatively impact ecosystem health and function (Cu, Ag and Cd). Over the next 5 years my research objectives are to: 1) examine how changing temperature, pH and light regimes in high latitude ocean surface waters will impact the cycling of biologically important metals; 2) unravel how trace metal fluxes are modified at the ocean margins with an emphasis on sources and sinks at the continental shelves; and 3) determine how the secular trend of decreasing oxygen levels in the ocean will impact the relative distribution of bioactive metals. The work proposed here will help to elucidate the role that trace metals play in shaping community composition and productivity of marine microbes that represent the base of the ocean food chain. Metals can act as essential nutrients and toxins that can modulate the biological production and consumption of climate active gases. Our data will allow for better parameterization of biogeochemical rate processes in coupled atmosphere-ocean models designed to predict the response of marine systems in the subarctic and Arctic to regional warming, ocean acidification, and changing sea ice and light regimes. In addition, a more thorough understanding of what controls the basin scale distribution of trace metals and their relationships with the major algal nutrients will aide in efforts to verify existing and develop new paleoproxies that are essential for reconstructing the oceans role in past climate variability.