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

Abstract

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 (Ω) 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 ( p CO2) increased in surface seawater by ∼40 I1/4mol kgĝ̂'1 and ∼50 I1/4atm (∼20%), respectively. Increasing Revelle factor ( I2) 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 ∼0.05 (0.0017 yr−1) and ω values by ∼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.