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

Frank J. Millero, Andrew G. Dickson, Greg Eischeid, Catherine Goyet, Peter Guenther, Kenneth M. Johnson, Robert M. Key, Kitack Lee, Dave Purkerson, Christopher L. Sabine, Rolf G. Schottle, Douglas W.R. Wallace, Ernie Lewis, Christopher D. Winn

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


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) CO2 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 μmol kg-1 in TA, and ±4.1 μmol 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 μmol 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 μmol kg-1. These crossover results are quite consistent with the overall reproducibility of the CRM analyses for TA (±4 μmol 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.

Original languageEnglish (US)
Pages (from-to)9-20
Number of pages12
JournalMarine Chemistry
Issue number1-2
StatePublished - Dec 1998


  • Alkalinity
  • CO
  • WOCE Hydrographic Program

ASJC Scopus subject areas

  • Oceanography
  • Chemistry(all)
  • Environmental Chemistry
  • Water Science and Technology


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