Benthic Mineralization of Organic Matter on the Continental Rise and the Dissolution of CaCo3 at the Deep Seafloor

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During the preceeding grant periods, the instrumentation required to perform in situ benthic flux chamber measurements and to retrieve and maintain sediment cores at in situ temperatures and pressures during shipboard pore water sampling and incubations were developed. This project will utilize these instruments to study two important aspects of the marine carbon cycle, the mineralization of organic matter and the kinetics of CaCO3 dissolution in deep sea surface sediments. Specifically, sites adjacent to the highly productive west African margin (in collaboration with the French-sponsored EUMELI program) and sites above and below the lysocline in the western equatorial Pacific will be studied. At each location, the particulate input of organic matter, opal, and CaCO3, the mineralization and dissolution rate of these phases in surface sediments, and the burial rate will be determined. This information, when coupled through models to environmental parameters such as bottom water CaCO3 saturation state, diffusive boundary layer thickness, etc., will permit the following questions to be addressed: 1. Are organic matter fluxes to the seafloor off Africa important to deep Atlantic carbon budgets? 2. Can organic matter fluxes off Africa be supported by vertical rain rates as measured by sediment traps? 3. Is denitrification at the deep seafloor important off west Africa? 4. What is the CaCO3 dissolution rate constant at the seafloor? 5. To what extent is metabolic CO2 neutralized by the dissolution of sedimentary CaCO3? 6. Does transport across the diffusive sublayer limit the total CaCO3 dissolution rate in the deep sea?