Calcite Production Rates in the Arabian Sea

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9311077 Balch This project will address the magnitude of the calcification relative to the organic production in the Arabian Sea as part of the U.S. JGOFS program. Geological and geochemical evidence points to calcite dominating the burial of carbon in this very productive region. However, no direct estimates of calcification exist at time scales compatible with standard photosynthesis measurements. Indirect estimates based on vertical changes in alkalinity and TCO2 suggest that euphotic zone calcification rates will be on the order of 0.3-0.4 gC m-2d-1 during the SE monsoon as compared to primary production of 1-2 gC m-2 d-1. Indirect estimates based on sediments accumulation rates give very similar predictions. In terms of carbon burial, however, the organic carbon is preferentially remineralized such that the regional organic carbon deposition is 2.65x10 5 tonnes C yr-1, less than a tenth of the calcite burial of 3.6x10 6 tonnes C y-1 over the northern Arabian Sea. Such indirect estimates of calcite production require broad assumptions which need to be validated with empirical data. Direct isotope estimates of calcification are essential to understanding the magnitude of the production rate of calcite, measured on time scales compatible with standard primary production measurements. Equally important will be the comparison of the estimates of calcification with geochemical estimates made by others in the program. ***