The Role of CaCO3 Reactions in the Contemporary Oceanic CO2 Cycle

The present analysis adjusts previous estimates of global ocean CaCO3 production rates substantially upward, to 133 x 10(12) mol yr(-1) plankton production and 42 x 10(12) mol yr(-1) shelf benthos production. The plankton adjustment is consistent with recent satellite-based estimates; the benthos adjustment includes primarily an upward adjustment of CaCO3 production on so-called carbonate-poor sedimentary shelves and secondarily pays greater attention to high CaCO3 mass (calcimass) and turnover of shelf communities on temperate and polar shelves. Estimated CaCO3 sediment accumulation rates remain about the same as they have been for some years: similar to 20 x 10(12) mol yr(-1) on shelves and 11 x 10(12) mol yr(-1) in the deep ocean. The differences between production and accumulation of calcareous materials call for dissolution of similar to 22 x 10(12) mol yr(-1) (similar to 50 %) of shelf benthonic carbonate production and 122 x 10(12) mol yr(-1) (>90 %) of planktonic production. Most CaCO3 production, whether planktonic or benthonic, is assumed to take place in water depths of <100 m, while most dissolution is assumed to occur below this depth. The molar ratio of CO2 release to CaCO3 precipitation (CO2 up arrow/ CaCO3 down arrow) is <1.0 and varies with depth. This ratio, Psi, is presently about 0.66 in surface seawater and 0.85 in ocean waters deeper than about 1000 m. The net flux of CO2 associated with CaCO3 reactions in the global ocean in late preindustrial time is estimated to be an apparent influx from the atmosphere to the ocean, of +7 x 10(12) mol C yr(-1), at a time scale of 10(2)-10(3) years. The CaCO3-mediated influx of CO2 is approximately offset by CO2 release from organic C oxidation in the water column. Continuing ocean acidification will have effects on CaCO3 and organic C metabolic responses to the oceanic inorganic C cycle, although those responses remain poorly quantified.