Jessica Marshall, Discovery News
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.
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.
"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.
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.
Such complicated interactions would not have emerged from studies of individual organisms, said Christopher Harley of the University of British Columbia in Vancouver, "That's the stroke of genius of this paper."
"I think the ecological observations are quite important, also for future projections," agreed Peter Brewer of the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., who was not involved in the study. "For example, the study indicates which species may be most affected in a low-pH/high-CO2 world."
But how does Wootton explain why his measured pH changes are so much larger than what models have predicted?
"That's something that, frankly, is a big mystery and presumably will spark some thought or explanation of what might be going on," said Brewer.
Richard Zeebe of the University of Hawaii at Manoa pointed out that Wootten's study was on a coastal site, not in the open ocean, so "one needs to be cautious about extrapolating the pH findings to other locations."
The part of the ocean that Wootton studied also experiences a great deal of upwelling, so it's not completely suprising to find changes in acidity. But, Brewer said, "I think the changes are bigger than we expected."
The unexpected scale of the pH changes suggest that scientists may be in for more surprises as global warming continues to alter ocean environments.
"If I look at how the wider scale of impacts may occur," Brewer added, "it is clear that we are in for big changes that are not yet well understood."
"I think the ecological observations are quite important, also for future projections," agreed Peter Brewer of the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., who was not involved in the study. "For example, the study indicates which species may be most affected in a low-pH/high-CO2 world."
But how does Wootton explain why his measured pH changes are so much larger than what models have predicted?
"That's something that, frankly, is a big mystery and presumably will spark some thought or explanation of what might be going on," said Brewer.
Richard Zeebe of the University of Hawaii at Manoa pointed out that Wootten's study was on a coastal site, not in the open ocean, so "one needs to be cautious about extrapolating the pH findings to other locations."
The part of the ocean that Wootton studied also experiences a great deal of upwelling, so it's not completely suprising to find changes in acidity. But, Brewer said, "I think the changes are bigger than we expected."
The unexpected scale of the pH changes suggest that scientists may be in for more surprises as global warming continues to alter ocean environments.
"If I look at how the wider scale of impacts may occur," Brewer added, "it is clear that we are in for big changes that are not yet well understood."
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