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 °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.

Wang P., Meng Q., Xue L., Zhao Y., Qiao H., Hu H., Wei Q., Xin M., Ran X., Han C., Zhou F. & Liu C., 2023. Preliminary assessment of carbonic acid dissociation constants: Insights from observations in China’s east coastal oceans. Marine Environmental Research: 106219. doi: 10.1016/j.marenvres.2023.106219. Article.

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