US GEOTRACES N. Atlantic: Measuring the δ13C-DIC distribution and quantifying the impact of organic matter export on δ13C, nutrients and biologically active trace

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).In this project, researchers at the University of Washington will address two of the overriding goals of the GEOTRACES program: advancing our understanding of the processes that control trace element distributions in the ocean, and understanding the processes that control the concentrations of geochemical species used for proxies of the past ocean environment. The overall goal is to improve our ability to use trace element and del13C proxies as indicators of past changes in ocean circulation and carbon cycling. The research has three components: (1) to measure the 13C/12C of the dissolved inorganic carbon (DIC) during the GEOTRACES cruise in the North Atlantic Ocean; (2) to estimate the rate of organic matter (OM) export from the surface layer; and (3) to quantify the impact that air-sea CO2 gas exchange, OM export, remineralization and circulation have on the modern distributions of bioactive trace elements, del 13C-DIC and nutrients in the Atlantic Ocean. Del13C-DIC will be measured at all stations for a total of ca. 600 samples with particular emphasis on improving the sampling coverage in intermediate waters and deep sea. Additionally, the team will measure the dissolved O2/Ar gas ratio in the surface layer using discrete and underway measurements. The rates of OM export will be determined using two approaches. The first method relies on the air-sea disequilibrium of the ä13C-DIC; the second method relies on the air-sea disequilibrium of the dissolved oxygen gas. Air-sea gas exchange rates will be estimated from satellite-based wind speeds. The goal of this part of the project is to improve our understanding of the impact of OM export on bioactive trace elements. Broader Impacts. This project is part of an international scientific program (GEOTRACES) and, thus, the data and research results will be broadly distributed to the international oceanographic community. Additionally, the results will be incorporated into the principal investigator's teaching curricula, specifically in an undergraduate course entitled Climatic Extremes and graduate course entitled Isotope Biogeochemistry. Third, there will be active undergraduate participation in preparing samples for del13C-DIC analyses during this project. Lastly, there are clear societal benefits from the GEOTRACES program goals that will improve predictions of future climate change under increasing atmospheric CO2 levels.