The Recommended Dissociation Constants for Carbonic Acid in Seawater

A coherent representation of carbonate dissociation constants and measured inorganic carbon species is essential for a wide range of environmentally important issues such as oceanic uptake of anthropogenic CO ₂ and carbon cycle depictions in ocean circulation models. Previous studies have shown varying degrees of discordance between calculated and measured CO ₂ -system parameters. It is unclear if this is due to errors in thermodynamic models or in measurements. In this work, we address this issue using a large field dataset (15,300 water samples) covering all ocean basins. Our field data, obtained using laboratory-calibrated measurement protocols, are most consistent with calculated parameters using the dissociation constants of Mehrbach et al. [1973] as refit by Dickson and Millero [1987]. Thus, these constants are recommended for use in the synthesis of the inorganic carbon data collected during the global CO ₂ survey during the 1990s and for characterization of the carbonate system in seawater.