Southern Ocean ‘breathing in’ more CO2

Recent analysis shows that the South Ocean is absorbing carbon dioxide again. Just ten years ago scientists had feared that this vital carbon sink would soon stall.

Although the Southern Ocean represents no more than a quarter of the total surface of the world’s oceans, it accounts for 40 per cent of the global oceanic uptake of that man-made CO2. But beginning in 2005, scientists feared that the Southern Ocean carbon sink might have begun to ‘saturate’ based on models that suggested the carbon sink had not increased since the late 1980s.

Now the tables have turned. Since the beginning of the millennium the Southern Ocean carbon sink has actually become much stronger, regaining its expected strength. This is demonstrated by an international team of researchers led by Nicolas Gruber, a professor of environmental physics at ETH Zurich, and his postdoc Peter Landschützer in a recently published study.

The researchers used a newly developed method based on neural networks to create a statistical model of the oceanic CO2 concentrations and then used this model to fill in the gaps. Their data clearly demonstrates 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.

The researchers concluded that the ability of the Southern Ocean carbon sink is influenced by weather patterns. In the 1990s winds were stronger over much of the Southern Ocean, causing more water to be upwelled to the surface from the depth. As deeper waters contain higher concentrations of C02, this upwelling led to higher amounts of C02 being released into the atmosphere. Wind and temperature changes since the turn of the millennium have weakened this upwelling and reinvigorated the carbon sink.

 

Photo credit: Reeve Jolliffe, flickr/Creative Commons

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