Processes determining the marine alkalinity and calcium carbonate saturation state distributions

• Published in: Biogeosciences
• Main Authors: B. R. Carter, J. R. Toggweiler, R. M. Key, J. L. Sarmiento
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2014
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Arctic; Southern Ocean; Pacific; Indian
• Online Access: https://doi.org/10.5194/bg-11-7349-2014; https://doaj.org/article/66f1e177be934ec99dbb9035a35213b2

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.