CO2SYS does not allow the determination of DIC concentrations by use of pH and AT (or CO32−). Thus, DIC was calculated as done previously (15) by using the measured CO32− concentrations, pH, and the dissociation constants of carbonic acid in seawater K1 and K2 (52) according to the following equation [derivation of Eq. 1 given in note S1]Embedded Image(1)

For this, we used the average values for CO32− and pH and propagated their individual SD into a compound SD (see below).

Using the measured Ca2+ and CO32− data, Ωarag was calculated according to Eq. 2Embedded Image(2)where Ksp = 7.184, as derived by linear regression for salinity 38 from the given salinities from Mucci (53) (solubility constants for aragonite at 25°C; table 4). The calculations of the compound SD for DIC and Ωarag are described in note S2.