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Antarctic Ocean Losing Ability to Absorb Carbon Dioxide

NORWICH, UK, May 18, 2007 (ENS) - Recent climate change brought on by human activities has weakened one the Earth's natural defenses against global warming. Atmospheric carbon dioxide is not being absorbed by the Southern Ocean as quickly as it once was, an international research team has found.

Scientists have observed the first evidence that the Southern Ocean’s ability to absorb the major greenhouse gas carbon dioxide, CO2, has weakened by about 15 percent per decade since 1981. The study was published today in the journal "Science."

"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," said lead author Dr. Corinne Le Quere of the University of East Anglia and the British Antarctic Survey.

Le Quere

Dr. Corinne Le Quere is on the faculty of the School of Environmental Sciences, University of East Anglia and is a strategic alliance senior fellow at the British Antarctic Survey. (Photo courtesy University of East Anglia)
"All climate models predict that this kind of feedback will continue and intensify during this century," said Dr. Le Quere.

"The Earth’s carbon sinks – of which the Southern Ocean accounts for 15 percent – absorb about half of all human carbon emissions. With the Southern Ocean reaching its saturation point more CO2 will stay in our atmosphere," she said.

Such weakening of one of the Earth’s major carbon dioxide sinks will lead to higher levels of atmospheric carbon dioxide in the long term.

And the study suggests that stabilization of atmospheric carbon dioxide 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 scientists said.

ocean

Research vessel makes its way across the Southern Ocean. (Photo courtesy University of East Anglia)
The international team included researchers from CSIRO in Australia, the Max-Planck Institute in Germany, the University of East Anglia and British Antarctic Survey in England, the Climate Monitoring and Diagnostics Laboratory in the United States, New Zealand's National Institute of Water and Atmospheric Research, the South African Weather Service, LSCE/IPSL and CNRS in France, and the Centre for Atmospheric and Oceanic Studies in Japan.

Professor Chris Rapley, director of British Antarctic Survey said, "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 scrutinizing observations of atmospheric carbon dioxide from 40 stations around the world.

The data show that since 1981 the Southern Ocean sink ceased to increase, whereas CO2 emissions increased by 40 percent.

Dr. Paul Fraser, who leads research into atmospheric greenhouse gases at CSIRO Marine and Atmospheric Research, says the 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.

station

Data from the monitoring station at Cape Grim, Tasmania, Australia was used in the Southern Ocean carbon sink study. (Photo courtesy CSIRO)
"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," he said.

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, he explained.

Dr. Fraser points to one piece of good news - ozone levels in the stratosphere have stopped declining and should recover slowly in coming decades.

"Thus the impact of ozone depletion on the Southern Ocean carbon dioxide sink will lessen in the future," he said, "but the impact of increasing levels of greenhouse gases will continue unabated."



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