Distribution and variations of oceanic carbon dioxide in the western North Pacific, eastern Indian, and Southern Ocean south of Australia

The partial pressure of carbon dioxide (pCO₂) in surface seawater was measured to clarify its time and space variation in the western North Pacific, eastern Indian and Southern Ocean south of Australia during the Southern Cross Cruise in 1968/69, the BIOMASS Cruise in 1983/84 and the Ryofu-maru Cruises in 1984 and 1987. The pCO₂ in surface seawater was high in high latitudes, coastal and equatorial regions and low in the subtropics. The spatial variation of pCO₂ clearly reflects the general circulation of seawater, i.e., vertical mixing of seawater plays an important rijle in determining the pCO₂ in surface seawater.

Two kinds of periodicities during the annual cycle, which are caused by the variations in seawater temperature, vertical mixing and biological activities, were found off Japan’s coast. The pCO₂ in surface seawater obtained in the boreal winters of 1969 and 1984 suggests an increase due to the enhancement of CO₂ flux from air to sea. The apparent increase was 20.0 ± 10.6 ppm in the western North Pacific, and 24.4 ± 8.3 ppm in the Southern Ocean, south of Australia.