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

Ocean acidification (OA) is expected to drive the transition of coral reef ecosystems from net calcium carbonate (CaCO₃) precipitating to net dissolving within the next century. Although permeable sediments represent the largest reservoir of CaCO₃ in coral reefs, the dissolution of shallow CaCO₃ sands under future pCO₂ levels has not been measured under natural conditions. In situ, advective chamber incubations under elevated pCO₂ (~800 μatm) shifted the sediments from net precipitating to net dissolving. Pore water advection more than doubled dissolution rates (1.10 g CaCO₃ m^-2 d^-1) when compared to diffusive conditions (0.42 g CaCO₃ 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 CaCO₃ 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 CO₂.