Acceleration of ocean warming, salinification, deoxygenation and acidification in the surface subtropical North Atlantic Ocean

Ocean chemical and physical conditions are changing. Here we show decadal variability and recent acceleration of surface warming, salinification, deoxygenation, carbon dioxide (CO 2 ) and acidification in the subtropical North Atlantic Ocean (Bermuda Atlantic Time-series Study site; 1980s to present). Surface temperatures and salinity exhibited interdecadal variability, increased by ~0.85 °C (with recent warming of 1.2 °C) and 0.12, respectively, while dissolved oxygen levels decreased by ~8% (~2% per decade). Concurrently, seawater DIC, f CO 2 (fugacity of CO 2 ) and anthropogenic CO 2 increased by ~8%, 22%, and 72% respectively. The winter versus summer f CO 2 difference increased by 4 to 8 µatm decade −1 due to seasonally divergent thermal and alkalinity changes. Ocean pH declined by 0.07 (~17% increase in acidity) and other acidification indicators by ~10%. Over the past nearly forty years, the highest increase in ocean CO 2 and ocean acidification occurred during decades of weakest atmospheric CO 2 growth and vice versa. Carbon dioxide concentrations and ocean acidification in the subtropical surface Atlantic Ocean increased fastest during the two decades of weakest atmospheric carbon dioxide level increases, according to an analysis of observations at two open-ocean hydrographic stations.