"Overturning" oceans keeps C[O.sub.2] under waves.

• Position: Climate Change

With the ocean absorbing more carbon dioxide over the past decade, less of the greenhouse gas is reaching the Earth's atmosphere. That is decidedly good news, according to researchers at the University of California, Santa Barbara, but it comes with a catch: rising levels of C[O.sub.2] in the ocean promote acidification, which breaks down the calcium carbonate shells of some marine organisms.

The cause of this recent increase in oceanic C[O.sub.2] uptake, which has implications for climate change, has been a mystery, but research from geographer Timothy DeVries and colleagues demonstrates that a slowdown of the ocean's overturning circulation is the likely catalyst.

"Such a slowdown is consistent with the projected effects of anthropogenic climate change, where warming and freshening of the surface ocean from melting ice caps leads to weaker overturning circulation, but over the time periods we studied, it's not possible to say whether the slowdown is related to natural climate variability or to climate change caused by human activity," explains DeVries.

DeVries and fellow researchers Mark Holzer of Australia's University of New South Wales, Sydney, and Francois Primeau of the University of California, Irvine, compiled existing oceanographic tracer data--measurements of temperature, salinity, chloroflurocarbons, and carbon-14--and separated it into three decade-long time periods: the 1980s, 1990s, and 2000s.

Subsequent computer analysis of that data enabled...