Collaborative Research: GEOTRACES Arctic Section: Marine Cycling of Bioactive Trace Metals in the Arctic Ocean

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In this project, a group of investigators participating in the 2015 U.S.GEOTRACES Arctic expedition will study the chemistry and regional distribution of seven trace metals in the Arctic Ocean: iron, manganese, zinc, cadmium, copper, nickel, and cobalt. These so-called bioactive metals are of special scientific interest because of their role in multiple biogeochemical processes including biological production of the sea and the planetary cycling of carbon and nitrogen. Like other multinational initiatives in the International GEOTRACES Program, the goals of the U.S. Arctic expedition are to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions. This study in particular would contribute to our understanding of the sources and sinks of these seven bioactive metals as well as examine their interaction with biological processes. The project will focus on two major overarching research questions: (1) What are the sources and sinks for micronutrients and macronutrients in the Arctic? And (2) How does bioactive trace element nutrition influence productivity and species composition in the Arctic, and conversely, how do biological processes influence the cycling of these metals? In terms of broader impacts, the PIs on this project will be actively involved in educational outreach efforts, and the research team itself will include two postdoctoral researchers and a graduate student. The team leaders also plan to publish a children's ocean education book based on the expedition with the aim of generating next-generation excitement about modern ocean scienceWIth regard to technical specifics, the research team will measure the dissolved seawater phases of the bioactive metals Fe, Mn, Zn, Cd, Cu, Ni, and Co, the dissolved stable metal isotopes 56Fe, 66Zn, and 114Cd, and the chemical speciation of Co. The recent development of methods for multi-element and multi-isotope analysis methods, in conjunction with the high-resolution sampling of the GEOTRACES program, make it possible to efficiently produce this dense dataset of metals and metal isotopes. This will be a team-based approach to achieve comprehensive duplication for analysis of the key parameters of dissolved metal concentrations. Each investigator will further conduct specialized additional measurements of metal isotopes and dissolved Co (which has unique analytical challenges) and Co speciation. Interpretation of these rich datasets would will be directed toward determination of sources and sinks as well as their ecological stoichiometry, in collaboration with other U.S.GEOTRACES participants measuring synergistic parameters. Together, this Arctic Ocean bioactive trace metal dataset is expected to provide an important contribution to the understanding of micronutrient roles in Arctic biogeochemical processes. These results should also be highly relevant to research studies of the ancient ocean, in which trace-metal analyses are commonly used to trace a wide variety of processes including paleo-ocean circulation and biological productivity. Finally, understanding the sources and sinks for elements in the modern ocean is key to predicting how the concentrations of bioactive elements might vary in a changing future climate.