Wintertime fCO₂ Variability in the Subpolar North Atlantic Since 2004

Winter data of surface ocean temperature (SST), salinity (SSS) and CO 2 fugacity ( f CO 2 ) collected on the VOS M/V Nuka Arctica in the subpolar North Atlantic between 2004 and 2017 are used to establish trends, drivers, and interannual variability. Over the period, waters cooled and freshened, and the f CO 2 increased at a rate similar to the atmospheric CO 2 growth rate. When accounting for the freshening, the inferred increase in dissolved inorganic carbon (DIC) was found to be approximately twice that expected from atmospheric CO 2 alone. This is attributed to the cooling. In the Irminger Sea, f CO 2 exhibited additional interannual variations driven by atmospheric forcing through winter mixing. As winter f CO 2 in the region is close to the atmospheric, the subpolar North Atlantic has varied between being slightly supersaturated and slightly undersaturated over the investigated period.