Preliminary assessment of carbonic acid dissociation constants: Insights from observations in China's east coastal oceans

Based on observations in China's east coastal oceans, we conducted a preliminary assessment of 16 sets of carbonic acid dissociation constants (K1* and K2*) by comparing spectrophotometrically measured pH values at 25 degrees C with those calculated from total alkalinity and dissolved inorganic carbon. We obtained that K1* and K2* often performed differently within different salinity ranges, and that the constants of Millero et al. (2002) (M02) demonstrated the best performance for the salinity range of 24-35. In contrast, the often recommended constants of Mehrbach et al. (1973) refit by Dickson and Millero (1987) (DM87-M) and Lucker et al. (2000) (L00) would underestimate pH at salinities of 24-30. This was mainly associated with the higher product of K1* and K2* by DM87-M and L00 than by M02 at this salinity range. Also, we found almost no differences between pH values calculated with DM87-M and L00.