The Geochemistry of U, Re, Mo in Margin and Coastal Sediments

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ABSTRACTOCE-0220892The accumulation rates of Mo, Re and U in marine sediments can be useful proxies for reconstructing past redox conditions. While an increase in accumulation rates of authigenic Mo, Re and U is often a clear indication of more reducing conditions in sediments, it is more difficult to deduce whether the change is due to a decrease in bottom water oxygen content or an increase in organic carbon flux. Three scientist from Woods Hole Oceanographic Institution plan to develop a means of distinguishing between these two potential causes utilizing porewater samples obtained from the Washington margin and seasonally from sediments in Buzzards Bay (coastal site). The PIs will acquire these samples using benthic flux chambers, centrifugation and in-situ polyacrylamide gel probes. The porewater and solid phase samples will be analyzed for U, Re and Mo as well as the necessary supporting parameters. Results from the profiles obtained at Buzzards Bay will serve to document the seasonal evolution of porewater concentrations and benthic fluxes as a function of bioturbation, bioirrigation and non-steady state O2 penetration into the sediments. Samples from the Washington margin region will be used to assess the influence of water depth, carbon flux and O2 bottom water concentrations on the burial of these redox sensitive metals. Results from this study will be incorporated into a steady-state sediment-pore water model to use the derived parameters to obtain realistic solid phase metal profiles.