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 i mportant issues such as oceanic uptake of anthropogenic CO2 and carbon cycl e depictions in ocean circulation models. Previous studies have shown varyi ng degrees of discordance between calculated and measured CO2-system parame ters. 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 datas et (15,300 water samples) covering all ocean basins. Our field data, obtain ed using laboratory-calibrated measurement protocols, are most consistent w ith calculated parameters using the dissociation constants of Mehrbach et a t. [1973] as refit by Dickson and Millero [1987]. Thus, these constants are recommended for use in the synthesis of the inorganic carbon data collecte d during the global CO2 survey during the 1990s and for characterization of the carbonate system in seawater.