Ocean Acidity Rising at Surprising Pace

Nov. 25, 2008 -- Measurements of ocean acidification in the U.S. Pacific Northwest show acidity is rising more than ten times faster than climate models have predicted.

The researchers can't yet say how widespread this trend is. But as the waters acidified over the eight years the team measured, the numbers of barnacles, mussels and algae inhabiting the area also changed.

Ocean acidity rises as sea water absorbs more carbon dioxide released into the atmosphere from power plants and automobiles. Lead author Timothy Wootton of the University of Chicago did not intend to measure the effects of ocean acidification when he installed his ocean monitor in the waters near Tatoosh Island off the northwest tip of Washington state in 2000.

But as global concern over ocean acidification grew, "I realized we'd been sitting on all this data that we could use to determine whether it was happening," Wootton said. His instruments recorded changes in pH -- a measure of acidity that lowers as acidity rises.

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"The expectation was that the pH would change so slowly that it would be hard to see a change. Almost to our surprise we found the signal that it was going on," Wootton said. "We were sort of surprised to find in general just how much it was changing over time."

From there, Wooton looked at his biological observations to try to assess how much these pH changes matter to the ecosystem of the area. His team published their findings in the Proceedings of the National Academy of Sciences.

He found certain species that would be expected to be the most pH-sensitive did indeed show the worst performance. These included mussels and certain barnacles -- large species with calcified shells. Scientists believe acidification interferes with the formation of such shells.

But the trend was not entirely predictable.

The acorn barnacle increased in abundance, along with several types of noncalciferous algae. Wootton suggests that the acorn barnacle may also suffer from low pH conditions, but not as much as the other types of barnacles, which normally outcompete it. With the other species taking a bigger hit, the acorn barnacle can move in.

Another possibility, Wootten added, is that these species are easy prey for shelled predators like snails, which may also be less abundant in a more acidic environment.