Permeable coral reef sediment dissolution driven by elevated p CO 2 and pore water advection

Ocean acidification (OA) is expected to drive the transition of coral reef ecosystems from net calcium carbonate (CaCO 3 ) precipitating to net dissolving within the next century. Although permeable sediments represent the largest reservoir of CaCO 3 in coral reefs, the dissolution of shallow CaCO 3 sands under future p CO 2 levels has not been measured under natural conditions. In situ, advective chamber incubations under elevated p CO 2 (~800 µatm) shifted the sediments from net precipitating to net dissolving. Pore water advection more than doubled dissolution rates (1.10 g CaCO 3 m −2 d −1 ) when compared to diffusive conditions (0.42 g CaCO 3 m −2 d −1 ). Sediment dissolution could reduce net ecosystem calcification rates of the Heron Island lagoon by 8% within the next century, which is equivalent to a 25% reduction in the global average calcification rate of coral lagoons. The dissolution of CaCO 3 sediments needs to be taken into account in order to address how OA will impact the net accretion of coral reefs under future predicted increases in CO 2 .