TALK Measurements

TALK measurements were collected in 500 mL bottles for 665 samples from 26 stations with the same precautions as for TCO₂. The bottles were stored in the dark at 4°C and analyzed within 24 hours. The samples were transferred into a closed titration cell with a volume of approximately 120 mL and titrated at 25 ± 0.1°C with 0.1 M HCl containing 0.6 M NaCl. The titration cell was based on the systems described by Bradshaw and Brewer (1988) and Millero et al. (1993). The potential was followed with an electrode pair consisting of a ROSS (Orion Inc.) glass pH electrode and a ROSS AgCl reference electrode connected to a high precision digital voltmeter. The titration was controlled by a computer that waited for stable emf-readings before adding the next acid increment. The titration curve was analyzed through a modified GRAN-plot method described by Stoll et al. (1993) that used the carbonic acid constants of Goyet and Poisson (1989) and that takes into account the silicate and phosphate concentrations of the sample to obtain the titration alkalinity. The precision of the method was ±2.0 µmol/kg as determined by replicate analyses of samples. Standardization was accomplished with NaCO₃ standards in NaCl solutions corrected for the blank arising from impurities in the salt. No reference materials were analyzed for alkalinity during this cruise.