Glacial carbonate dissolution cycles and atmospheric pCO2: A view from the ocean bottom

We present a calculation of the global calcium carbonate dissolution response to glacial/interglacial changes in seawater carbonate chemistry inferred from Cd/Ca and carbon isotope ratios in benthic foraminifera. Our model is based on the relationship between the carbonate dissolution flux and the degree of calcite saturation in the three main ocean basins. The rate of carbonate dissolution is derived using mechanisms inferred from studies of surface sediment pore water geochemistry. The model predicts a change in the relative importance of CaCO3 burial among the Atlantic, Indian, and Pacific oceans between glacial and interglacial times. Chemical rearrangement of deep waters appears to be a viable mechanism for driving interocean differences in carbonate accumulation, and observed CaCO3 burial trends constrain alkalinity changes that accompanied deepwater nutrient redistribution. Our model predicts atmospheric pCO2 lowering during glacial times caused by the carbonate dissolution response to be less than 10 ppm suggesting that this mechanism is not a viable candidate for explaining a large fraction of the observed 80 ppm decrease observed in ice cores.