Proton‐Transfer Reaction Dynamics and Energetics in Calcification and Decalcification

CaCO₃‐saturated saline waters at pH values below 8.5 are characterized by two stationary equilibrium states: reversible chemical calcification/decalcification associated with acid dissociation, Ca²⁺+HCO₃^??CaCO₃+H⁺; and reversible static physical precipitation/dissolution, Ca²⁺+CO₃^2??CaCO₃. 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, Ca²⁺]CO₃^2?], may not be observed at pH below 8.5 because Ca²⁺]CO₃^2?]/(Ca²⁺]HCO₃^?]) ?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 CaCO₃ 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.