Improvements in potentiometric determinations of the CO2 oceanic system using seawater sub-standards and CO2 reference materials

During the Cither 3 cruise along WOCE section A14, where 107 full-water col umn stations were surveyed, pH and alkalinity were measured potentiometrica lly. Corrections carried out on the raw data set have allowed us to improve the data quality. The correction procedure was focused on monitoring: (i) calibrations, (ii) liquid junction potential and (iii) seawater sub-standar ds; CO2 reference material (CRM) has been used to check this procedure. Acc uracy of pH(15) measurements (NBS scale) and alkalinity was 0.004 and 1.4 m u mol.kg(-1), respectively. Certified total inorganic carbon on CRM, batch 24, is 1987.55 mu mol.kg.(-1). A value of 1987.8 +/- 2.2 mu mol.kg(-1) was obtained following the correction procedure. This improvement was independe ntly verified by means of the covariances between nitrate and pH, and betwe en silicate and normalized alkalinity in North Atlantic Deep Water.