Radiocarbon as a Tool for Studying Organic Matter Diagenesis in Rapidly Accumulating, Continental Margin Sediments: Linking Bulk Organic Matter and Molecular Level Studies

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ABSTRACTOCE-0526389Organic matter oxidation in sediments plays a central role in a wide range of geochemical cycles. Although recent advances in organic geochemistry and pore water sampling and modeling have led to improvements of our understanding of the process, marine geochemists have not yet achieved a satisfactory description for quantitative models of sedimentary diagenesis.In this project, researchers at the Woods Hole Oceanographic Institution will conduct studies to advance our quantitative understanding of organic matter oxidation in continental margin sediments through the combination of solute and solid composition measurements with determinations of the carbon isotopic composition (stable C and radiocarbon) of dissolved and solid phase C. The project will be carried out in collaboration with Dr. T. Eglinton who is currently undertaking a project to study the concentration and radiocarbon age of specific organic compounds in continental margin sediments. Through their combined efforts, the researchers plan to examine hypotheses arising from the organic geochemical work in ways that would not otherwise be possible. They will focus the effort in 3 areas: (1) The use of radiocarbon as a tracer for investigating organic matter oxidation in margin sediments, (2) Examination of the hypothesis that distributions of radiocarbon-dated, refractory organic compounds can be used to infer post-depositional transport of sediments, (3) Adding measurements of bioturbation mixing rates and mechanisms to the Eglinton group's measurements of downcore profiles of specific organic compounds to calculate a suite of reactivities. The resulting combined inorganic and organic perspective will provide a substantial step beyond the separate organic and inorganic studies that have been the norm in benthic geochemistry. They will also carry out work with detailed solute and solid phase measurements at two locations: Station W, the location of moorings for monitoring physical oceanographic parameters and particle concentrations as well as a set of moored sediment traps, which is located at a depth of 3000m, south of Massachusetts; and a contrasting site at the Mid-Atlantic Bight depocenter off Cape Hatteras.In terms of broader impacts, the development of models to examine the role of marine geochemical cycles in global carbon and nutrient budgets is a key part of efforts to explain past climate changes and forecast future changes. This project will contribute to model development through both the collection of new data and the examination of new ways to interpret the data. It will also provide research opportunities for graduate and undergraduate students. In addition, the PIs will use results from this project in the graduate level Sediment Geochemistry course that they teach.