Effects of Deep Circulation on CaCO3 Dissolution and Accumulation in the Southwestern Atlantic Ocean

Deep oceanic circulation regulates seafloor calcium carbonate (CaCO3) accumulation by transporting atmospheric carbon dioxide (CO2) to depth and then transferring it, with respired CO2, along the global ocean conveyor belt. This creates the shallowing trend of CaCO3 preservation from the Atlantic to the Pacific Oceans. The thermohaline flow can be, however, complex on a basin‐wide scale; here, we use a state‐of‐the‐art data compilation and a carbonate accumulation/dissolution model to explain the CaCO3 distribution within the basins of the Southwestern Atlantic Ocean. Our results demonstrate that different currents foster systematically dissimilar CaCO3 preservation within these connected ocean basins. The more undersaturated, faster moving, northward‐flowing Antarctic bottom water readily dissolves more CaCO3 than the southward‐flowing North Atlantic deep water. We are able to predict quantitatively these observations, based on benthic carbonate chemistry and mass‐transfer rates. Our model and CaCO3 records in such basins have the potential to provide new understanding about deep‐ocean circulation of the past. Plain Language Summary Biologically produced CaCO3 (calcite) both accumulates and dissolves on the ocean floor, depending on the CaCO3 saturation state of overlying water. This saturation state decreases with depth and can be lowered by the introduction of carbon dioxide (CO2), either from organic matter decomposition or from sinking and circulation of CO2‐enhanced surface waters. Here, we reveal that the distribution of sedimentary CaCO3 with ocean depth within the Southwest Atlantic Ocean is sensitive to and reflects the complexity of benthic ocean currents, the source of these bottom waters, and the nature of the processes that control the dissolution rate on the seafloor. Specifically, we find greater dissolution/lowered accumulation of CaCO3 in sediments beneath waters with Antarctic source, when compared to sediments beneath waters originating from the North Atlantic. We are able to predict quantitatively these differences in CaCO3 preservation using a simple model and available chemical data. Our approach has the potential to provide important insights into basin scale distributions and the sources of bottom currents in the past oceans. Key Points Sedimentary calcium carbonate (CaCO3) distributions, which differ when overlain by Antarctic bottom water and North Atlantic deep water, are predictable using a carbonate dissolution model CaCO3 pre