Recent increase of the CO2 efflux in the western subtropical North Pacific

We found relatively high surface values (> 440 µatm) of partial pressure of carbon dioxide (pCO2) in the western subtropical North Pacific where the Subtropical Mode Water forms in August 2015. The NOAA Kuroshio Extension Observatory moored buoy located at this region also showed very high CO2 values, up to 530 µatm during this summer. Regionally, these high pCO2 values are explained by much higher total dissolved inorganic carbon and slightly higher total alkalinity concentrations compared to those in the equatorial Pacific. The differences in pCO2 values between surface seawater and air observed in this region are much higher than the climatological values, indicating the recent increase in CO2 efflux. To support this, we present changes in sea-air CO2 fluxes and increase rates of surface pCO2 in this area using a large amount of surface pCO2 data from the SOCAT (Surface Ocean CO2 Atlas) database. Drivers for the changes are also presented.