 mangroves and salt marshes are biogeochemical hotspots that store carbon in sediments and the ocean through lateral carbon export outwelling. Coastal seawater pH is modified by both natural biogeochemical processes and anthropogenic carbon dioxide uptake. Observations from 45 mangroves and 16 salt marshes worldwide revealed that more than 70% of intertidal wetlands export dissolved in organic carbon, DIC, than alkalinity, potentially decreasing the pH of coastal waters. Poor water derived DIC outwelling was the major term in blue carbon budgets, but substantial amounts of fixed carbon remain unaccounted for. Alkalinity outwelling is a significant but often overlooked carbon sequestration mechanism that is similar or higher than sediment carbon burial. This article was authored by Gloria M. S. Reithmeier, Alex Cabral, Ani Bunacand, and others.