Effects of lower surface ocean pH upon the stability of shallow water carbonate sediments

It is predicted that surface ocean pH will reach 7.9, possibly 7.8 by the end of this century due to increased carbon dioxide (CO2) in the atmosphere and in the surface ocean. While aragonite-rich sediments don't begin to dissolve until a threshold pH of ~ 7.8 is reached, dissolution from high-Mg calcites is evident with any drop in pH. Indeed, it is high-Mg calcite that dominates the reaction of carbonate sediments with increased CO2, which undergoes a rapid neomorphism process to a more stable, low-Mg calcite. This has major implications for the future of the high-Mg calcite producing organisms within coral reef ecosystems. In order to understand any potential buffering system offered by the dissolution of carbonate sediments under a lower oceanic pH, this process of high-Mg calcite dissolution in the reef environment must be further elucidated.

Research Highlights
► With increased atmospheric CO2, ocean pH is predicted to drop significantly.
► We find that a decrease in ocean pH will lead to dissolution of carbonate reef sediments.
► Aragonite and low-Mg calcite sediments will react when pH reaches 7.8.
► High-Mg calcite reacts with any drop in pH, with reprecipitation of low-Mg calcite.