Glob. Biogeochem. Cycles http://doi.org/m6n (2013)

Ocean uptake of CO2 slows the rate of increase in atmospheric CO2 concentrations. How this carbon sink will respond to climate change remains unknown, but understanding the changes that have occurred over recent decades will help to improve future projections.

Amanda Fay and Galen McKinley of the University of Wisconsin-Madison, USA, investigate trends in observed surface ocean CO2 concentration over various timescales between 1981 and 2010. The global ocean was divided into 16 biomes. Over the full 30-year period, they find that CO2 concentrations in the surface ocean have generally increased at a rate consistent with, or slightly lower than, that of the atmosphere.

On shorter timescales, climate variability forces ocean concentrations to increase more sharply than atmospheric CO2 in some regions, and more slowly in others. For example in the Southern Ocean, the positive Southern Annular Mode has weakened and the carbon sink strengthened since the early 2000s. Of more concern is the impact of North Atlantic surface warming. This reduces CO2 solubility and thus decreases the magnitude of the sink, constituting a potential negative feedback that reinforces increasing atmospheric CO2 concentrations.