Southern Ocean carbon sink weakens

Scientists have observed the first evidence that the Southern Ocean’s ability to absorb carbon dioxide, the major greenhouse gas, has weakened by about 15 per cent per decade since 1981. The Southern Ocean normally cycles about 15% of the world's carbon dioxide, but can no longer keep up. Researchers had predicted this weakening would occur somewhere in the second half of this century, not this soon. The Southern Ocean's efficiency at cycling vast amounts of carbon dioxide is due to its cool waters.

Now a four-year study by scientists from Germany's Max-Planck Institute for Biogeochemistry, the University of East Anglia (UEA) and the British Antarctic Survey (BAS) reveals that an increase in winds over the Southern Ocean, caused by greenhouse gases and ozone depletion, has led to a release of stored CO2 into the atmosphere and is now preventing further absorption of the greenhouse gas.

The study [*abstract] published in Science today shows that this weakening of one of the Earth’s major carbon dioxide sinks will lead to higher levels of atmospheric carbon dioxide in the long-term, in what is called a 'positive feedback'.

"This is the first time that we've been able to say that climate change itself is responsible for the saturation of the Southern Ocean sink. This is serious. All climate models predict that this kind of 'feedback' will continue and intensify during this century. The Earth's carbon sinks - of which the Southern Ocean accounts for 15% � absorb about half of all human carbon emissions. With the Southern Ocean reaching its saturation point more CO2 will stay in our atmosphere." - Lead author Dr Corinne Le Quéré, UEA and BAS.

The new research suggests that stabilisation of atmospheric CO2 is even more difficult to achieve than previously thought. Additionally, acidification in the Southern Ocean is likely to reach dangerous levels earlier than the projected date of 2050.

The Biopact thinks these findings once again strengthen the case of those who say we may already be facing a 'dangerous climate change' scenario that warrants radical interventions and the uncompromising implementation of the precautionary principle. Likewise, the case for the massive introduction of carbon negative bioenergy systems ('BECS') that take historic CO2 emissions out of the atmosphere is becoming ever stronger:
biofuels :: energy :: sustainability :: climate change :: carbon dioxide :: carbon sink :: Southern Ocean :: abrupt climate change :: Bio-energy with Carbon Storage :: carbon negative :: biomass :: bioenergy ::

Professor Chris Rapley, Director of British Antarctic Survey makes the point on the need to limit our reliance on fossil fuels: "Since the beginning of the industrial revolution the world's oceans have absorbed about a quarter of the 500 gigatons of carbon emitted into the atmosphere by humans. The possibility that in a warmer world the Southern Ocean - the strongest ocean sink - is weakening is a cause for concern."

The saturation of the Southern Ocean was revealed by scrutinising observations of atmospheric CO2 from 40 stations around the world. Since 1981 the Southern Ocean sink ceased to increase, whereas CO2 emissions increased by 40%.

Dr Paul Fraser, who leads research into atmospheric greenhouse gases at Australia's CSIRO Marine and Atmospheric Research, says the international team’s four-year study concludes that the weakening is due to human activities.

“The researchers found that the Southern Ocean is becoming less efficient at absorbing carbon dioxide due to an increase in wind strength over the Ocean, resulting from human-induced climate change,” Dr Fraser says.

“The increase in wind strength is due to a combination of higher levels of greenhouse gases in the atmosphere and long-term ozone depletion in the stratosphere, which previous CSIRO research has shown intensifies storms over the Southern Ocean.”

The increased winds influence the processes of mixing and upwelling in the ocean, which in turn cause an increased release of carbon dioxide into the atmosphere, reducing the net absorption of carbon dioxide into the ocean.

More information:
Corinne Le Quéré, et al., Saturation of the Southern Ocean CO2 Sink Due to Recent Climate Change, Science, Published Online May 17, 2007, Science DOI: 10.1126/science.1136188

Eurekalert: Climate change affects Southern Ocean carbon sink - May 18, 2007.

CSIRO: Southern ocean carbon sink weakened - May 18, 2007.