Collaborative Research: Tracing the Transformations of Organic Carbon in Marine Sediments using Natural C Isotopes

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Pore-water dissolved organic carbon (DOC) is one of the least characterized pools of organic carbon in the ocean. Thus, its biogeochemical role in the marine carbon cycle remains unclear. Scientists from San Francisco State University and Old Dominion University propose to test the hypothesis that pore water DOC consists not only of material hydrolyzed from labile particulate organic carbon (POC), but also of resistant moieties derived from the solubilization of 14C-depleted, recalcitrant POC. To test their hypothesis, vertical profiles of '13C and '4C signatures of DOC, dissolved inorganic carbon, POC, and carbonates in sediment cores from Santa Monica Basin would be determined. Results from these cores would be analyzed using an isotope mass balance model to determine the component of POC that supplies DOC to pore waters, the component of DOC that is oxidized to dissolved inorganic carbon, and the component that is accumulated in pore water and subsequently released from sediments as a benthic flux. Results of this research would provide new insight into the sources and reactivity of DOC accumulating in, and effluxing from, anoxic continental margin sediments. As regards broader impacts, the outcome of this research would not only impact our understanding of the significance of benthic DOC fluxes on the cycling of DOC in the oceans, but would also further our understanding of the controls on organic carbon mineralization in marine sediments. This research includes funding to support numerous education and training opportunities for graduate and undergraduate students as well as hands on research experiences for high school students through the Project SEED summer programs, an American Chemical Society program created to encourage students from low-income families to pursue a career in the chemical sciences. Findings from this study would also be disseminated beyond the professional scientific community through outreach activities such as teacher workshops and open-house events.