Underway pCO2 System

An underway pCO2 system continuously measures the partial pressure of carbon dioxide in surface seawater from a moving ship. Seawater from the clean intake passes through a showerhead or membrane equilibrator, and a non-dispersive infrared analyzer reads the CO2 mole fraction of the equilibrated air, calibrated against reference gases on each cycle. The result, with sea surface temperature and salinity, gives the ocean-atmosphere CO2 gradient that drives the air-sea carbon flux. Volunteer ships and research vessels feed the Surface Ocean CO2 Atlas, the dataset behind global estimates of the ocean carbon sink, near 2.5 to 3 petagrams of carbon per year.