Proton‐Transfer Reaction Dynamics and Energetics in Calcification and Decalcification

CaCO 3 ‐saturated saline waters at pH values below 8.5 are characterized by two stationary equilibrium states: reversible chemical calcification/decalcification associated with acid dissociation, Ca 2+ +HCO 3 − ⇌CaCO 3 +H + ; and reversible static physical precipitation/dissolution, Ca 2+ +CO 3 2− ⇌CaCO 3 . The former reversible reaction was determined using a strong base and acid titration. The saturation state described by the pH/ P CO2 ‐independent solubility product, [Ca 2+ ][CO 3 2− ], may not be observed at pH below 8.5 because [Ca 2+ ][CO 3 2− ]/([Ca 2+ ][HCO 3 − ]) ≪1. Since proton transfer dynamics controls all reversible acid dissociation reactions in saline waters, the concentrations of calcium ion and dissolved inorganic carbon (DIC) were expressed as a function of dual variables, pH and P CO2 . The negative impact of ocean acidification on marine calcifying organisms was confirmed by applying the experimental culture data of each P CO2 /pH‐dependent coral polyp skeleton weight (Wskel) to the proton transfer idea. The skeleton formation of each coral polyp was performed in microspaces beneath its aboral ectoderm. This resulted in a decalcification of 14 weight %, a normalized CaCO 3 saturation state Λ of 1.3 at P CO2 ≈400 ppm and pH ≈8.0, and serious decalcification of 45 % and Λ 2.5 at P CO2 ≈1000 ppm and pH ≈7.8.