|The Southern Ocean. Source: CIA Factbook 2007|
Scientists have observed the first evidence that the Southern Ocean’s ability to absorb carbon dioxide has weakened by about 15% per decade since 1981.
In research published in the journal Science, an international research team concludes that the Southern Ocean carbon dioxide sink has weakened between 1981 and 2004 by 0.08 PgC/y per decade relative to the trend expected from the large increase in atmospheric CO2. The consequences of this include a reduction in the efficiency of the sink in the short term (about 25 years) and possibly a higher level of stabilization of atmospheric CO2 on a multicentury time scale.
The Southern Ocean is the circumpolar body of water around the continent of Antarctica and extending up to 60 degrees south latitude. The Southern Ocean is the fourth largest of the world’s five oceans (after the Pacific Ocean, Atlantic Ocean, and Indian Ocean, but larger than the Arctic Ocean).
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. 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.—Dr Paul Fraser, CSIRO Marine and Atmospheric Research
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.
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.—Dr Corinne Le Quéré, University of East Anglia and British Antarctic Survey
The international team comprised 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 US, NIWA in New Zealand, the South African Weather Service, LSCE/IPSL and CNRS in France, and the Centre for Atmospheric and Oceanic Studies in Japan.
The team used observations from 40 stations around the world, including Cape Grim in north-west Tasmania. The Cape Grim station, operated by the Australian Bureau of Meteorology, monitors and studies changes in global atmospheric composition in a program led by CSIRO and the Bureau.
“Saturation of the Southern Ocean CO2 Sink Due to Recent Climate Change”; Corinne Le Quéré, Christian Rödenbeck, Erik T. Buitenhuis, Thomas J. Conway, Ray Langenfelds, Antony Gomez, Casper Labuschagne, Michel Ramonet, Takakiyo Nakazawa, Nicolas Metzl, Nathan Gillett, Martin Heimann; Science Express DOI: 10.1126/science.1136188