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.

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