A Revised Estimate of Calcium Carbonate Dissolution in Coastal and Shelf Sediments Suggests Large Shelf Exports in the Marine CaCO 3 Cycle

Abstract Calcium carbonate (CaCO 3 ) dissolution plays a key role in the marine carbon and alkalinity cycles and the regulation of atmospheric CO 2 levels across geological time scales. Until now, most attention has focused on dissolution in the deep sea, while dissolution in coastal and shelf environments remains poorly constrained. Here, we present a synthesis of CaCO 3 dissolution rates in sediments of coastal and shelf environments and integrate them into an updated global marine CaCO 3 budget. The highest areal dissolution rates occur in coral reefs and lagoons, and in seagrass‐dominated banks and bays, as these sediments combine high amounts of soluble high‐magnesium calcite with deep oxygen penetration and high organic matter input that facilitate dissolution. Nevertheless, carbonate‐poor shelves contribute as much (∼45%) as coral reefs and lagoons to global coastal and shelf carbonate dissolution. Total coastal and shelf dissolution is estimated at 11 ± 9 Tmol yr −1 and thus provides ∼8% of the total CaCO 3 dissolution in the ocean. Combining these dissolution rates with published estimates of production, terrestrial input, and burial, mass balance closure requires an off‐shelf lateral export of ∼15 Tmol CaCO 3 yr −1 . Although this estimate carries large uncertainty (>100%), it suggests that a significant fraction of the CaCO 3 produced on the shelf is transferred from a short‐term climate buffer in the shelf seafloor to a long‐term climate buffer in the deep‐sea seafloor.