CO2, Hydrographic, and Chemical Data Obtained During the R/V Thomas Washington Cruise TUNES-3 in the Equatorial Pacific Ocean (WOCE section P16C)

This data documentation discusses the procedures and methods used to obtain total carbon dioxide (TCO2), total alkalinity (TALK), hydrographic, and chemical data during the Research Vessel Thomas Washington Expedition TUNES-3 in the Equatorial Pacific Ocean (Section P16C). Conducted as a part of the World Ocean Circulation Experiment (WOCE), the cruise began in Papeete, Tahiti, on August 31, 1991, and finished in Honolulu, Hawaii, on October 1, 1991. WOCE Meridional Section P16C along 150 degrees W and between 18 degrees S and 19 degrees N was completed during the 31-day expedition. All 105 hydrographic and 8 large-volume stations were completed to the full water column depth. Station spacing was 30 nautical miles (nm), except between 3 degrees N and 3 degrees S where it was 10 nm. Twenty-five bio-optics stations were sampled for the Joint Global Ocean Flux Study, and at 21 stations carbon dioxide measurements were provided for the U.S. Department of Energy's CO2 program. Hydrographic and chemical measurements made along WOCE Section P16C included pressure, temperature, salinity, and oxygen measured by conductivity, temperature, and depth sensor; and bottle salinity, oxygen, phosphate, nitrate, nitrite, silicate, chlorofluorocarbon (CFC)-11, CFC-12, TCO2, and TALK. In addition, potential temperatures were calculated from the measured variables. The TCO2 concentration in 652 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 micro-mol/kg. The TALK concentration in 539 seawater samples was determined by a potentiometric acid titration system that was designed and constructed at the Scripps Institution of Oceanography (SIO) by David Moss and Timothy Lueker (Guenther et al. 1994a).