Abstract

This report discusses the procedures and methods used to obtain measurements of total carbon dioxide (TCO₂), total alkalinity (TALK), and radiocarbon (Δ¹⁴C), as well as hydrographic and chemical data, during the Research Vessel Thomas Washington Expedition TUNES-1 in the Equatorial Pacific Ocean (Section P17C). Conducted as part of the World Ocean Circulation Experiment (WOCE), the cruise began in San Diego, California, on May 31, 1991, and ended in Papeete, Tahiti, on July 11, 1991. WOCE Meridional Section P17C, along 135° W and between ~5° S and 36° N, was completed during the 42-day expedition. All 123 hydrographic stations (including 9 large-volume stations) were completed to the full water-column depth. Spacing between stations was 30 nautical miles, except between 3° N and 3° S, where it was 10 nautical miles. At 30 stations, CO₂ measurements were provided for the U.S. Department of Energy's Carbon Dioxide Program. Hydrographic and chemical measurements made along WOCE Section P17C included pressure, temperature, salinity, and oxygen (measured by conductivity, temperature, and depth sensor), as well as bottle measurements of salinity, oxygen, phosphate, nitrate, nitrite, silicate, chlorofluorocarbon (CFC)-11, CFC-12, Δ¹⁴C, TCO₂, and TALK. In addition, potential temperatures were calculated from the measured variables.

The TCO₂ concentration in 1022 seawater samples was determined by semiautomated coulometry using an improved version of the instrument earlier described by Johnson et al. (1985, 1987). The precision of these measurements was estimated to be better than 0.01%. The desired accuracy was better than 4 µmol/kg.

The TALK concentration in 323 seawater samples was determined by an automated potentiometric acid titration system that was described by Bradshaw and Brewer (1988). The precision of the measurements was estimated to be better than 0.1%.

Fifty replicate samples were also collected for later shore-based reference analyses of TCO₂ and TALK by vacuum extraction and manometry in the laboratory of C. D. Keeling of Scripps Institution of Oceanography.

The data set is available, free of charge, as a numeric data package (NDP) from the Carbon Dioxide Information Analysis Center. The NDP consists of two oceanographic data files; two FORTRAN 77 data-retrieval-routine files; a documentation file; and a printed report, which describes the contents and format of all files and the procedures and methods used to obtain the data.

Reference

• Goyet, Catherine, Robert M. Key, Kevin F. Sullivan, and Mizuki Tsuchiya. 1997. Carbon Dioxide, Hydrographic, and Chemical Data Obtained During the R/V Thomas Washington Cruise TUNES-1 in the Equatorial Pacific Ocean (WOCE Section P17C). ORNL/CDIAC-99, NDP-062. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee. doi: 10.3334/CDIAC/otg.ndp062.