Participating Discrete fCO₂ System

The only discrete fCO₂ system ("H") involved in this intercomparison exercise is based on a batch-equilibration, static-headspace technique that requires a small sample volume of 60 mL and has an average analysis time of only 2 min per sample. It includes closed-system equilibration of a headspace in a shaking water bath, followed by analysis of the CO₂ mole fraction in the water-saturated equilibrated headspace by gas chromatography with flame-ionization detection (GC-FID). The method has been described in detail by Neill et al. (1997). This paper is also reprinted in Appendix B at the end of hard copy report. It should be noted that this method is not specifically designed for work in surface seawater but for full-depth profiling. The equilibration temperature (i.e., the water bath temperature) was changed two times during the exercise, from 17°C (June 10) to 20°C (June 11-13, first sample) and, finally, to 25°C (from June 13, second sample). The magnitude of the correction of fCO₂ from the temperature of equilibration to the in situ temperature was 44-133 µatm (mean: 89 µatm) for the samples presented here.