Photochemical Formation of Carbon Dioxide from Dissolved Organic Matter: A New Approach to Constraining a Major Term in Marine Carbon Cycling

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ABSTRACTOCE-0223200Recent discoveries have shown that photoxidation of colored dissolved organic matter (CDOM) also lead to the formation of dissolved inorganic carbon (DIC) or photo-CO2. Fluxes of photo-CO2 are estimated to produce one to several gigatons of CO2-C per year globally. A PI from Woods Hole Oceanographic Institution proposes to constrain photo-CO2 production using the Pool Isotopic Exchange (PIE) method, a technique which does not require perturbing the sample as occurs in currently available methods (i.e., changing pH, removing carbonate system, bubbling of sample). In the PIE method, the DI12C pool in seawater is replaced via exchange with DI13CO2 during incubation of the samples; thus, the DI12C pool which dilutes the newly formed 12CO2 (DI12C) from dissolved organic carbon (DOC) is minimized without major perturbations of the physical and chemical properties of the sample. The rates of formation of DI12C as a result of photoxidation will be measured by isotope ratio mass spectrometry (IRMS). The objectives of the proposal are to develop, test and optimize the PIE approach both in the laboratory and in the field. In addition, the PI will apply the PIE method and compare his results with those obtained by a collaborator from the State University of New York, Stony Brook using the Pool Depletion (PD) technique on the same samples recovered from waters enriched in CDOM. Lastly, the PI plans to resolve any potential discrepancies obtained via the PIE and PD methods.