Detecting anthropogenic carbon dioxide uptake and ocean acidification in the North Atlantic Ocean

Fossil fuel use, cement manufacture and land-use changes are the primary sources of anthropogenic carbon dioxide (CO2) to the atmosphere, with the ocean absorbing approximately 30% (Sabine et al., 2004). Ocean uptake and chemical equilibration of anthropogenic CO2 with seawater results in a gradual reduction in seawater pH and saturation states (Omega) for calcium carbonate (CaCO3) minerals in a process termed ocean acidification. Assessing the present and future impact of ocean acidification on marine ecosystems requires detection of the multi-decadal rate of change across ocean basins and at ocean time-series sites. Here, we show the longest continuous record of ocean CO2 changes and ocean acidification in the North Atlantic subtropical gyre near Bermuda from 1983-2011. Dissolved inorganic carbon (DIC) and partial pressure of CO2 (pCO(2)) increased in surface seawater by similar to 40 mu mol kg(-1) and similar to 50 mu atm (similar to 20%), respectively. Increasing Revelle factor (beta) values imply that the capacity of North Atlantic surface waters to absorb CO2 has also diminished. As indicators of ocean acidification, seawater pH decreased by similar to 0.05 (0.0017 yr(-1)) and omega values by similar to 7-8%. Such data provide critically needed multi-decadal information for assessing the North Atlantic Ocean CO2 sink and the pH changes that determine marine ecosystem responses to ocean acidification.