Ian Sample, science correspondent
The Guardian, Tuesday November 25 2008
Goose barnacles, which are likely to decline dramatically as acid levels rise. Photograph: Science Photo Library
The world's oceans are becoming acidic more quickly than climate change models predict, according to scientists who claim it will have a dramatic impact on marine ecosystems.
Water samples collected around an island in the eastern Pacific over the past eight years showed seawater had acidified more than 20 times faster than scientists expected. The effect could be devastating for shellfish and other crustaceans, because acidic waters dissolve calcium carbonate used by the organisms to make their protective shells.
Oceans absorb about a third of the carbon dioxide released into the atmosphere by human activities. When the gas dissolves in water, it forms carbonic acid, which alters the ocean's delicate chemical balance.
The increasing acidification of the oceans is likely to have impacts that run throughout the marine ecosystem, because the organisms most affected are at the bottom of the foodchain.
Timothy Wootton, a biologist at the University of Chicago, led a team of researchers who analysed the acidity, salinity and temperature of water around Tatoosh Island off the northwestern coast of Washington state.
Over eight years, the pH level of the water fell by 0.36 to about 8.1, more than 23 times more than the predicted fall of just 0.015 points. Water is neutral if its pH is seven, and becomes more acidic as the pH falls below that.
Writing in the US journal Proceedings of the National Academy of Sciences, the scientists raise concerns at how rapidly the process is happening and the impact it could have. "Acidification may be a more urgent issue than previously predicted, at least in some areas of the ocean," the authors write.
According to computer models of the local marine life, the rise in acidity is likely to cause substantial falls in the numbers of mussels and large goose barnacles, while algae and populations of smaller barnacles may increase. In turn, the changing distribution of these organisms will have effects on marine life that feed on them.
Last month, researchers warned that a new global deal on climate change would come too late to save many of the world's corals. A report from the Carnegie Institution at Stanford University in California found that carbon dioxide emissions are likely to acidify seawater enough to cause widespread damage to major reefs, including the Great Barrier Reef in Australia. Even stringent cuts designed to stabilise greenhouse gas levels still put more than 90% of the world's reefs in jeopardy.
"Declines in seawater pH were expected to happen very slowly, so we've been lax in dealing with the problem, but our study shows ocean acidification may be happening much quicker," said Wootton.