The effect of increases in the atmospheric carbon dioxide content on the carbonate ion concentration of surface ocean water at 25°C

Equilibrium thermodynamics is used to assess the influence of predicted fossil carbon dioxide injections on the carbonate ion concentration in the oceanic mixed layer at 25°C. The calculations indicate that a tenfold increase is required in the atmospheric partial pressure of carbon dioxide to reduce the carbonate ion concentration to a level where calcite would begin to dissolve. This is at least three times the highest predicted partial pressure for atmospheric carbon dioxide. This result contradicts a number of recent claims that the calcite saturation level would be attained within the next 30 years. Such rapid removal of carbonate ions is only possible if the mixed layer is grossly out of equilibrium with the atmosphere.