Carbon dioxide concentrations in the surface seawater have been determined in the Japanese ocean time series program at station KNOT (155°E, 44°N). The seasonal amplitude of dissolved inorganic carbon was more than 100 µmol/kg (Figure), mainly due to biological uptake in summer and strong vertical mixing in winter. As a result of these large changes, surface fugacity of carbon dioxide was lower than the atmospheric value in summer and autumn, and oceanic absorption of carbon dioxide was largest in autumn when the wind velocity started to increase. The increase rate of carbon dioxide in the surface seawater was estimated at about 1 µmol/kg/year.