Determining what share of the man-made CO₂ the oceans absorb has long been a priority for climate researchers. An international team of scientists led by Nicolas Gruber, Professor for Environmental Physics at ETH Zurich, has now determined this oceanic sink over a period of 13 years. As reported in the latest issue of Science, the researchers have found that the ocean has taken up from the atmosphere as much as 34 gigatonnes (billions of metric tonnes) of man-made carbon between 1994 and 2007. This figure corresponds to 31 per cent of all anthropogenic CO₂ emitted during that time.

This percentage of CO₂ taken up by the oceans has remained relatively stable compared to the preceding 200 years, but the absolute quantity has increased substantially. This is because as long as the atmospheric concentration of CO₂ rises, the oceanic sink strengthens more or less proportionally: the more CO₂ is in the atmosphere, the more is absorbed by the oceans – until it becomes eventually saturated.

The results are based on a global survey of CO₂ and other chemical and physical properties in the various oceans, measured from the surface down to depths of up to 6 kilometres. Scientists from 7 countries participated in the internationally coordinated programme that started in 2003. Globally they carried out more than 50 research cruises up to 2013, which were then synthesized into a global data product.

You'll find more information and the original press release on the website of the ETH Zurich