Assessment of the quality of the shipboard measurements of total alkalinity on the WOCE Hydrographic Program Indian Ocean CO2 survey cruises 1994-1996

In 1995, we participated in a number of WOCE Hydrographic Program cruises in the Indian Ocean as part of the Joint Global Ocean flux Study (JGOFS) CO, Survey sponsored by the Department of Energy (DOE). Two titration systems were used throughout this study to determine the pH, total alkalinity (TA) and total inorganic carbon dioxide (TCO2) of the samples collected during these cruises. The performance of these systems was monitored by making closed cell titration measurements on Certified Reference Materials (CRMs). A total of 962 titrations were made on six batches of CRMs during the cruises. The reproducibility calculated from these titrations was +/-0.007 in pH, +/-4.2 mu mol kg(-1) in TA, and +/-4.1 mu mol kg(-1) in TCO2. The at-sea measurements on the CRMs were in reasonable agreement with laboratory measurements made on the same batches. These results demonstrate that the CRMs can be used as a reference standard for TA and to monitor the performance of titration systems at sea. Measurements made on the various legs of the cruise agreed to within 6 mu mol kg(-1) at the 15 crossover points. The overall mean and standard deviation of the differences at all the crossovers are 2.1 +/- 2.1 mu mol kg(-1). These crossover results are quite consistent with the overall reproducibility of the CRM analyses for TA (+/-4 mu mol kg(-1)) over the duration of the entire survey, The TA results for the Indian Ocean cruises provide a reliable data set that when combined with TCO2 data can completely characterize the carbonate system. (C) 1998 Elsevier Science B.V. All rights reserved.