Reconstructing the time history of the air-sea CO2 disequilibrium and its rate of change in the eastern subpolar North Atlantic, 1972–1989



[1] This study determines the temporal changes of wintertime surface ocean partial pressure of CO2 (pCO2SW) in the eastern subpolar North Atlantic (esNA) (50–64°N; 32–10°W) by using data of carbon-system parameters and chlorofluorocarbon-12 acquired in 1993. Wintertime pCO2SW and its temporal trend from early 1970s through to the late 1980s were reconstructed through the application of a back-calculation method that isolates surface variations which have been transmitted to the ocean interior during the formation of Subpolar Mode Water. Our computations suggest a pCO2SW growth rate (3 μatm/yr) which is twice as large as that of atmospheric pCO2, 1.47 μatm/yr. The sensitivity of the estimated pCO2SW growth rate to remineralization ratios as well as to the CFC-12-derived ages is discussed. Cooling and northward advection of surface water equilibrated with the increasing atmospheric CO2 is suggested as the process responsible for the excessive pCO2SW growth rate.