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

Abstract

This study determines the temporal changes of wintertime surface ocean partial pressure of CO2 (pCO2 SW) in the eastern subpolar North Atlantic (esNA) (50–64ºN; 32–10ºW) by using data of carbon-system parameters and chlorofluorocarbon-12 acquired in 1993. Wintertime pCO2 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 pCO2 SW growth rate (3 matm/yr) which is twice as large as that of atmospheric pCO2, 1.47 matm/yr. The sensitivity of the estimated pCO2 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 CO2 is suggested as the process responsible for the excessive pCO2 SW growth rate.