A decade ago scientists feared that the ability of the Southern Ocean to absorb additional atmospheric CO2 would soon be stalled. But the analysis of more recent observations show that this carbon sink reinvigorated during the past decade.

A research vessel breaks through waves of the Roaring Forties while measuring dissolved CO2. This region is known for its violent wind systems. Picture: Nicolas Metzl, LOCEAN/IPSL Laboratory
A research vessel breaks through waves of the Roaring Forties while measuring dissolved CO2. This region is known for its violent wind systems. Picture: Nicolas Metzl, LOCEAN/IPSL Laboratory

Like a giant lung, the Southern Ocean seasonally absorbs vast amounts of carbon dioxide (CO2) from the atmosphere and releases it back later in the year. But on an annual average the seas surrounding Antarctica absorb significantly more CO2 than they release – they act as a carbon sink.

Based on model results, scientists suggested that the carbon sink had not increased since the late 1980s. This was unexpected as one had 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.

Now the tables have turned. Since the beginning of the millennium the Southern Ocean carbon sink has become much stronger, thereby regaining its expected strength. This is demonstrated by an international research team led by researchers from ETH Zurich in a study recently published in Science. Dr Mario Hoppema is climatologist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, and co-author of the study. He has provided CO2 data from expeditions with RV Polarstern to the ice-covered Antarctic Ocean. Only a small number of research icebreakers is able to reach this sea area, which makes these region’s data extremely valuable for climate models.

Further information can be found in this press release of the ETH Zürich

Source: AWI, Bremerhaven