Processes determining the marine alkalinity and calcium carbonate saturation state distributions

Carter, B. R.; Toggweiler, J. R.; Key, R. M.; Sarmiento, J. L.

We introduce a composite tracer for the marine system, Alk *, that has a global distribution primarily determined by CaCO 3 precipitation and dissolution. Alk * is also affected by riverine alkalinity from dissolved terrestrial carbonate minerals. We estimate that the Arctic receives approximately twice the riverine alkalinity per unit area as the Atlantic, and 8 times that of the other oceans. Riverine inputs broadly elevate Alk * in the Arctic surface and particularly near river mouths. Strong net carbonate precipitation results in low Alk * in subtropical gyres, especially in the Indian and Atlantic oceans. Upwelling of dissolved CaCO 3-rich deep water elevates North Pacific and Southern Ocean Alk *. We use the Alk * distribution to estimate the variability of the calcite saturation state resulting from CaCO 3 cycling and other processes. We show that regional differences in surface calcite saturation state are due primarily to the effect of temperature differences on CO 2 solubility and, to a lesser extent, differences in freshwater content and air–sea disequilibria. The variations in net calcium carbonate cycling revealed by Alk * play a comparatively minor role in determining the calcium carbonate saturation state.

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Carter, B. R. / Toggweiler, J. R. / Key, R. M. / et al: Processes determining the marine alkalinity and calcium carbonate saturation state distributions. 2014. Copernicus Publications.

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