INFLUENCE OF VARIABLE RATES OF NERITIC CARBONATE DEPOSITION ON ATMOSPHERIC CARBON-DIOXIDE AND PELAGIC SEDIMENTS

Short-term imbalances in the global cycle of shallow water calcium car bonate deposition and dissolution may be responsible for much of the o bserved Pleistocene change in atmospheric carbon dioxide content. Howe ver, any proposed changes in the alkalinity balance of the ocean must be reconciled with the sedimentary record of deep-sea carbonates. The possible magnitude of the effect of shallow water carbonate deposition on the dissolution of pelagic carbonate can be tested using numerical simulations of the global carbon cycle. Boundary conditions can be de fined by using extant shallow water carbonate accumulation data and pe lagic carbonate deposition/dissolution data. On timescales of thousand s of years carbonate deposition versus dissolution is rarely out of eq uilibrium by more than 1.5 x 10(13) mole yr(-1). Results indicate that the carbonate chemistry of the ocean is rarely at equilibrium on time scales less than 10 ka. This disequilibrium is probably due to sea lev el-induced changes in shallow water calcium carbonate deposition/disso lution, an interpretation that does not conflict with pelagic sediment ary data from the central Pacific.