Development of a gas-liquid equilibrator for estimating CO₂ flux at the ocean surface

A system for measuring partial pressure of CO₂ in seawater (pCO₂) has been developed as a part of a missing-sink elucidation study. The most important part of this system is the multistage bubbling gas-liquid equilibrator. This equilibrator has four independent equilibrate cells in parallel. Seawater flows into each cell in parallel, while the bubbled carrier gas stream passes through every cell in series. The carrier gas circuit of a nondispersive infrared gas analyzer is opened to the atmosphere to keep the pressure of carrier gas at a barometric pressure. The present system can measure pCO₂ continuity with sample water of 24 L min^-1. Furthermore, a performance test was carried out to examine the degree of equilibrium achieved. The results showed an 83% equilibrium per cell. This indicates that the uncertainty of this equilibrator is 1 μatm. The correlation coefficient between the deviation of pH and that of pCO₂ observed with this system was -0.96.