Natural ocean alkalinization through erosion of glacial till and weathering at the seafloor

Abstract The ocean absorbs about 25% of anthropogenic carbon dioxide emissions, with this uptake regulated by acid-neutralizing anions collectively termed alkalinity. Most seawater alkalinity originates from the weathering of aluminosilicate and carbonate minerals on land, whose dissolved products are transported to the ocean by rivers, a slow process that causes carbon dioxide removal to lag behind emissions. Here we present geochemical evidence showing that fine-grained glacial sediments mobilized by coastal erosion undergo rapid seafloor weathering. While aluminosilicate weathering is largely balanced by secondary clay formation (reverse weathering), carbonate dissolution yields a significant net release of alkalinity to coastal waters. Because more than two-thirds of the global coastline was formerly glaciated, ongoing deglaciation and erosion may enhance alkalinity fluxes, providing a previously unrecognized shortcut in the global carbon cycle. As this enhanced flux is ultimately driven by climate warming, it may act as a negative feedback that helps moderate future increases in atmospheric carbon dioxide.