Reconstructing the time history of the air‐sea CO 2 disequilibrium and its rate of change in the eastern subpolar North Atlantic, 1972–1989

This study determines the temporal changes of wintertime surface ocean partial pressure of CO 2 (pCO 2 SW ) 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 pCO 2 SW 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 pCO 2 SW growth rate (3 μatm/yr) which is twice as large as that of atmospheric pCO 2 , 1.47 μatm/yr. The sensitivity of the estimated pCO 2 SW 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 CO 2 is suggested as the process responsible for the excessive pCO 2 SW growth rate.