Carbon burial and benthic fluxes in coastal marine sediments: Model study and sensitivity analysis

The response of calcareous coastal marine sediments to changes in ocean chemistry and productivity is not yet fully understood. The efficiency of seafloor carbon burial is nevertheless important to quantify in the context of ongoing ocean acidification. We developed a one-dimensional reactive transport model to study the effect of changes in particulate inorganic carbon (PIC) and particulate organic carbon (POC) deposition fluxes on carbon burial efficiency in coastal sediments. The model incorporates the transport processes of sediment accumulation, advection, diffusion, bioturbation and bioirrigation with reactions including the redox pathways of organic carbon oxidation, re-oxidation of reduced nitrogen, iron and sulfur compounds, acid-base chemical equilibria, and dissolution of particulate inorganic carbon (calcite, aragonite, and Mg-calcite). The following processes are also included: precipitation of iron sulfide and iron carbonate, sorption of Fe (II), ammonium and phosphate, sulfidization of organic matter, and pyritization.

Model predicted benthic fluxes of dissolved inorganic carbon (DIC) and alkalinity (AT) are estimated to be 100 Tmol C/yr and 90 Tmol AT/yr for the global coastal ocean, respectively. These return fluxes are weakly sensitive to changes in seawater pH, but are very sensitive to Fe (III) deposition fluxes. At least 93% of the labile POC is oxidized via sulfate reduction, which is responsible for )57% of alkalinity generation. PIC dissolution, ammonification, and iron reduction also contribute at least 10% to net alkalinity fluxes. The effect of changes in PIC and POC depositional fluxes up to 2X present-day estimates are simulated. Mg calcite completely dissolves in all simulations, while aragonite dissolves completely when the POC:PIC ratio is greater than 7. Calcite dissolution commences when POC:PIC is greater than 10. The reactive-transport modeling approach proposed here thus provides a means to estimate changes in the magnitude of carbon and nutrients burial and recycling fluxes as a result of changes in ocean productivity.

Krumins, V., van Cappellen, P., & Regnier, P., Carbon burial and benthic fluxes in coastal marine sediments: Model study and sensitivity analysis. Geochimica et Cosmochimica Acta, Goldschmidt 2010: Earth, Energy, and the Environment 74(12; Supplement 1): A542. Abstract.

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