The Antarctic Ocean has been absorbing increasing levels of carbon dioxide over the past decade, a new study has found, dispelling fears that the ocean's carbon sink might have begun to "saturate".
The Antarctic Ocean, also known as the Southern Ocean, seasonally absorbs vast amounts of carbon dioxide from the atmosphere and releases it back later in the year.
On an annual average the seas surrounding Antarctica absorb significantly more CO2 than they release. These seas remove a large part of the CO2 that human activities emit into the atmosphere, thereby slowing down the growth of this greenhouse gas in the atmosphere, lessening the rate of climate change.
The Southern Ocean accounts for 40 per cent of the global oceanic uptake of that man-made carbon dioxide.
From the year 2005, however, scientists pointed out that the Southern Ocean carbon sink might have begun to "saturate." Based on model results, they suggested that it had not increased since the late 1980s.
This was unexpected as it was assumed that a direct relationship existed between the magnitude of the carbon sink and the concentration of atmospheric CO2: the higher the concentration of CO2 in the air, the greater the amount of CO2 absorbed by the sea.
But researchers found that since the beginning of the millennium the Southern Ocean carbon sink has become much stronger, thereby regaining its expected strength.
In a new study by an international research team led by Nicolas Gruber, a professor at ETH Zurich, and his postdoc Peter Landschutzer the scientists analysed measurements of the concentration of carbon dioxide in the surface waters of the Southern Ocean.
They also compared the resulting fluxes with estimates based on measurements of atmospheric carbon dioxide.
The interpolated surface ocean carbon dioxide data and the estimates based on atmospheric carbon dioxide data show that the Southern Ocean carbon sink began to revive around 2002.
By 2010, its carbon uptake was once again comparable to the level expected on the basis of atmospheric CO2 increase alone.
Gruber concluded that the strength of the Southern Ocean carbon sink fluctuates strongly, possibly in periodic cycles, rather than increasing monotonically in response to the growth in atmospheric carbon dioxide.
The study was published in the journal Science.
