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 i n 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 t hese cruises. The performance of these systems was monitored by making clos ed cell titration measurements on Certified Reference Materials (CRMs). A t otal 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 mea surements on the CRMs were in reasonable agreement with laboratory measurem ents 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 ti tration 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 m ean 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 t he 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.