• sea-air CO2 flux;
  • pCO2;
  • interannual variability;
  • biogeochemical processes;
  • shelf and basin

[1] We investigated seasonality and interannual variability of the surface water pCO2 (pCO2sw) and sea-air CO2 fluxes in the upwelling region of the southern Bering Sea (53°N to 55°N, 174°E to 194°E). Data of surface water and atmospheric pCO2, sea surface temperature and salinity were based on automated measurements on board cargo ships for 6 years (1995–2001). We observed a significant interannual trend towards more CO2 supersaturated surface water relative to the atmosphere. From linear regression of seasonally detrended data we obtained an annual pCO2sw increase of 6.5 ± 1.4 μatm yr−1 and 11 ± 1.9 μatm yr−1 in the basin and shelf slope, respectively. This was higher than the observed pCO2air increase (between 0.47 ± 0.28 and 0.96 ± 0.62 μatm yr−1), indicating the importance of other processes than oceanic CO2 uptake from the atmosphere to explain the pCO2sw increase. Sea surface temperature and salinity showed a trend towards cooler and more saline conditions. We estimated large interannual variability of net annual oceanic CO2 outgassing, with low CO2 outgassing in years before 1998 (<1 mol m−2 yr−1), increasing to a maximum of 4.5 mol m−2 yr−1 in 2000. Highest net CO2 outgassing was observed in the relatively cold years of 1999 and 2000, whereas the exceedingly warm year 1997 showed four times lower CO2 flux to the atmosphere. Interestingly, we found close coupling between the net CO2 outgassing and biological production; years with less net CO2 outgassing coincided with high biological CO2 drawdown, especially evident in 1997.