Sea-surface CO₂ fugacity in the subpolar North Atlantic

Abstract. We present the first year-long subpolar trans-Atlantic set of surface seawater CO₂ fugacity (fCO₂^sw) data. The data were obtained aboard the MV Nuka Arctica in 2005 and provide a quasi-continuous picture of the fCO₂^sw variability between Denmark and Greenland. Complementary real-time high-resolution data of surface chlorophyll-a (chl-a) concentrations and mixed layer depth (MLD) estimates have been collocated with the fCO₂^sw data. Off-shelf fCO₂^sw data exhibit a pronounced seasonal cycle. In winter, surface waters are saturated to slightly supersaturated over a wide range of temperatures. Through spring and summer, fCO₂^sw decreases by approximately 60 μatm, due to biological carbon consumption, which is not fully counteracted by the fCO₂^sw increase due to summer warming. The changes are synchronous with changes in chl-a concentrations and MLD, both of which are exponentially correlated with fCO₂^sw in off-shelf regions.