869 compact sample changer

Total alkalinity was measured with an open cell potentiometric titration following Dickson et al. [21 (link)], using a Metrohm Titrino Plus 848 equipped with an 869 Compact Sample Changer and corrected with certified reference material supplied by A. Dickson (batch 128). The pH_t was determined via two methods: (1) through a glass electrode (WTW, pH 340i), which was calibrated with a TRIS seawater buffer, supplied by A. Dickson and; (2) colorimetrically by adding known amounts of m-cresol purple [22 (link),23 (link)].
The carbonate system was manipulated by the addition of specific amounts of NaHCO₃ and HCl in a closed system following [24 (link)]. All carbonate chemistry parameters were calculated from measured salinity, temperature, phosphate concentrations and pH and TA using CO2sys [25 ], with the equilibrium constants determined by Mehrbach et al. [26 (link)] as refitted by Dickson and Millero [27 ] (Tables S1 and S2).

The carbonate system was manipulated by adding calculated amounts of NaHCO₃ and HCl in a closed system following Schulz et al. [21] . Alkalinity was measured by potentiometric titration following Dickson et al. [22] , using a Metrohm Titrino Plus 848 equipped with a 869 Compact Sample Changer, and calibrated with certified reference material supplied by A. Dickson. The pH was measured using a glass electrode (WTW, pH 340i) and calibrated with a TRIS seawater buffer, supplied by A. Dickson.
Carbonate chemistry was calculated from measured temperature, salinity, silicate and phosphate concentrations, and pH and TA using CO2sys [23] , with the equilibrium constants determined by Mehrbach et al. [24] as refitted by Dickson and Millero [25] .