Carbon Measurements

To measure the TCO₂ concentration in seawater, a coulometric analysis system was used during the cruise. This system has been described by Chipman et al. (1993) and consists of a coulometer (Model 5011), manufactured by the UIC, Inc. (Jolliet, IL), and a sample introduction/CO₂ extraction system of the LDEO design. A total of 1290 water samples was analyzed for TCO₂ concentration. In addition, 172 determinations were made at sea for 62 bottles of the Certified Reference Material (batch no. 7) yielding an average value of 1927.5±1.8 µmol/kg. This compares with the SIO manometric value of 1926.6±0.7 µmol/kg (6 determinations) (Fig. 2). The mean values for each set of measurements agree with each other within respective standard deviations.

To measure the pCO₂ in seawater a fully-automated equilibrator-gas chromatograph system was used during the cruise. This system has been described by Chipman et al. (1993). A total of 1273 water samples was analyzed for pCO₂. Since pCO₂ is strongly affected by temperature changes, the equilibration flasks were kept in a constant-temperature water bath of 4.0°C throughout the expedition. The precision of the pCO₂ measurements has been estimated to be ~±0.12% for a single station based on the reproducibility of replicate equilibrations. However, the station-to-station reproducibility was about ±0.5%.

A full description of the methods and instrumentation used to perform the TCO₂ and pCO₂ measurements during the R/V Akademik Ioffe cruise in the South Pacific Ocean (WOCE Section S4P) is provided in hard copy of NDP-063 (now available from CDIAC) or Chipman et al. (1996).

Figure 3 shows the sampling density and depth along the WOCE Section S4P.