Persistently strong oceanic CO 2 sink in the western subtropical North Pacific

The long‐term trend of the partial pressure of CO 2 in surface seawater ( p CO 2 sea ) in late‐January to early‐February during the past two decades was examined in the western North Pacific along the repeat line at 137°E from 3°N to 34°N. The growth rate of p CO 2 sea at each 1° in latitude ranged from +1.3 ± 0.2 to +2.1 ± 0.3 μatm yr −1 , and the average was +1.7 ± 0.2 μatm yr −1 . The growth of p CO 2 sea is attributable mainly to the uptake of anthropogenic CO 2 in surface water and, to a small extent, to the regional changes in sea surface temperature (SST). The net air‐to‐sea CO 2 flux in January–February that accounts for 40 to 60% of the annual flux remained at a similar level in the subtropical regions (7°N to 34°N). In the equatorial region (3°N to 6°N), however, a slight increase in the CO 2 efflux was seen.