In Situ Measurements of Calcium Carbonate Dissolution Rates

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CaCO3 dissolution is an important component in the global cycling of C02. Various approaches have been used to study carbonate dissolution rates; laboratory experiments, in situ dissolution experiments in the water column and modeling to compare with observed distributions of %CaC03 in sediments. This work provides measurements of in situ dissolution rates using benthic flux chambers. Direct measurements will be made by measuring the flux of calcium into a chamber; indirect measurements will be made by establishing a budget for alkalinity in the chamber, based on measurements of alkalinity, C02, oxygen and nitrate fluxes. A numerical model to simulate pore water carbonate ion concentration and dissolution fluxes will be compared to observed data and used to estimate the bulk carbonate dissolution rate constant. The accuracy of the model and the predicted rate constants will be tested by injecting acid into the chamber water and monitoring the response of alkalinity, C02 and calcium. Measurements of nutrient, radon and oxygen fluxes, augmented by pore water profiles, will be used to constrain the diagenetic reactions occuring at the sites studied. This study will be conducted in two regions that include a range of sediment types, the basins of the California borderland and a transect in the Eastern equatorial Pacific.