The role of marsh‐dominated heterotrophic continental margins in transport of CO2 between the atmosphere, the land‐sea interface and the ocean

Recent air‐to‐sea CO2 flux measurements at several major continental shelves suggest that shelves may act as a one‐way pump and absorb atmospheric CO2 into the ocean. The U.S. South Atlantic Bight (SAB) contrasts these findings in that it acts as a source of CO2 to the atmosphere while simultaneously exporting dissolved inorganic carbon (DIC) to the open ocean. The shelf‐wide heterotrophy and carbon exports in the SAB are subsidized by the export of organic carbon from the abundant intertidal marshes, which are a sink for atmospheric CO2. It is proposed here that the SAB represents a marsh‐dominated heterotrophic ocean margin as opposed to river‐dominated autotrophic margins. Based on this and other studies, DIC export flux from margins to the open ocean must be significant in the overall global ocean carbon budget.