An ice-free arctic may not be large carbon sink

The Arctic Ocean has recently soaked up substantial amounts of carbon dioxide and may already be well on its way to reaching its limit as a carbon sink.

These findings are reported by Wei-Jun Cai and colleagues, who measured carbon dioxide levels in water samples taken from across the Arctic Ocean's Canada Basin. As the ocean warms and its sea ice continues to melt, more of the ocean's surface will be exposed. Because these waters are cold and home to large amounts of photosynthesizing microbes, researchers have noted the Arctic's important potential for taking up atmospheric carbon dioxide.

Exactly how carbon dioxide levels in Arctic surface waters may change in response to sea-ice melt has not been clear, however.

Cai and colleagues now report that the amount of carbon dioxide in these surface waters has increased markedly since previous observations in 1994 and 1999, except for in heavily ice-covered areas. This increase appears to be caused largely by rapid carbon dioxide influx from the atmosphere and a low level of biological "drawdown," due to the fact that the surface waters are relatively poor in nutrients.

More information:
This paper will be published online by the journal Science, at the Science Express website, on Thursday, 22 July. See www.sciencexpress.org

Provided by AAAS