Table 1.
Summary table of methods used in this study.
Sample measurement time refers to measurements made during this study, with the upper end of the time range allowing for machine warm-up.
Fig 1.
Diagram of the portable NDIR CO2 equilibrator.
The portable CO2 equilibrator consists of a commercially available non-dispersive infrared (NDIR) CO2 gas analyser and data logger display interface, in-line air pump, impermeable-walled tubing and a section of gas-permeable membrane that is submerged in water. Air is pumped in a closed loop around the system and equilibrates with CO2 in seawater.
Table 2.
Estimated measurement uncertainties associated with each method determined from CT and AT-derived reference values.
Fig 2.
Seawater pCO2 calculated from CT and AT, compared with three other methods: 1) spectrophotometric pHT and AT (n = 25), 2) electrode pHNBS and AT (n = 25), and 3) the direct measurement of seawater CO2 with a NDIR CO2 equilibrator (n = 23); a) for pCO2 data and b) for the difference in pCO2 compared to pCO2 derived from CT and AT (delta pCO2).
Fig 3.
Relationship of seawater pCO2 and aragonite saturation state (Ωar) determined by four different methods: 1) CT and AT (n = 25), 2) spectrophotometric pHT and AT (n = 45), 3) electrode pHNBS and AT (n = 49), and 4) the direct measurement of seawater CO2 with a NDIR CO2 equilibrator (n = 46).