Double edged sword as Southern Ocean “regains” its capacity to absorb atmospheric CO2

The Guardian reports, 11th September 2015: The Southern Ocean has started to absorb more greenhouse gases after a period when the vast ocean’s uptake had slumped by about a half, a study has found.

The ocean’s role as a crucial carbon “sink” appeared to be waning throughout the 1990s, but after 2002 it began to rebound to its previous level, absorbing 1.2bn tonnes of carbon in 2011.

This enormous uptake, double that of its lowest point in the 1990s, is roughly equivalent to the European Union’s annual carbon output.

The huge Southern Ocean, which encircles Antarctica, accounts for 40% of all the carbon soaked up by the world’s oceans. In turn, all the oceans suck up a quarter of all the carbon emitted through human activity, including burning fuels such as coal, gas and oil.

Research by scientists based in Switzerland, France, the US and Australia, published in Science, found the Southern Ocean had “regained its expected strength”. Changes in winds and temperatures were given as a reason.

Its gargantuan carbon intake is due to its pattern of seawater circulation, which effectively takes carbon from the surface and buries it deep underwater.

“The evidence that the sink efficiency was decreasing was a concern, because it means that carbon dioxide accumulates more heavily in the atmosphere,” said a co-author, Bronte Tilbrook, who is a research scientist at CSIRO and the Antarctic and Climate Systems CRC. “That sink has now re-established itself due to a change in weather patterns around an Antarctica. Long term, we don’t know how the sink will respond but we are getting an idea that its variability is much greater than we previously thought. It’s possible it may reduce again.”

A Swiss scientist, Nicolas Gruber, who led the research, said: “We were surprised to see such large variations in this ocean’s net carbon uptake.”

While the world’s oceans are considered a crucial “handbrake” on the escalating amount of greenhouse gases spewed out by power stations and vehicles, the absorption of large quantities of carbon is changing the make-up of oceans.

While heat-trapping gases are causing the oceans to warm and expand, causing sea levels to rise, carbon is also making the oceans more acidic. The oceans are about 30% more acidic than they were a century ago.

This has severe implications for a variety of marine creatures, including corals and shellfish, which are likely to shrink as they struggle to form carbonate shells in acidic water.

A recent study found that acidifying oceans were to blame for a mass extinction event 250m years ago that killed 90% of all marine species.

“We are likely to see a big impact on marine species, which is a concern,” Tilbrook said.  “We are potentially tinkering with these ecosystems and the end result isn’t something we fully understand at the moment. The rate of acidification is quite fast at the moment and the increased absorption of carbon will increase that.”
Source: The Guardian, 11th September 2015. For the full details, see

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