Thursday, December 4, 2008

Oceans acidifying 10 times faster than thought

Our island state and the world are even more severely threatened by the acidification of the ocean than previously known.

(Image: Washington State waters, where researchers measured dramatic increases in acidification.)

Scientists are already measuring declines in populations of creatures as a result of acidification—and notably the replacement of certain shellfish by acid-tolerant seaweeds.

Ocean acidification is perhaps the most under-reported feature of the steady advance of the amount of carbon dioxide in the atmosphere.

“For a potential environmental problem that is receiving increasing attention, there is surprisingly little published data in the scientific literature on how pH in the ocean is actually changing over time, and none that we know of outside of the tropics,” said Tim Wootton, of the Department of Ecology and Evolution at the University of Chicago.

Some of the seminal research on sea acidification was performed in Hawaiian waters just within the past couple of years. But new research is adding breadth and depth to that data—and it is finding that the oceans are growing acid alarmingly faster than anyone thought.

Wootton's team, including colleagues Catherine Pfister and James Forester, conducted a multi-year study of ocean acidity off Washington State. One of their findings was that there is considerable variability in the pH level of the ocean, based largely in changes in ocean biology. But the other finding was that acidity is rising very fast.

Their paper, “Dynamic patterns and ecological impacts of declining ocean pH in a high-resolution multi-year dataset,” was published in the Proceedings of the National Academy of Sciences.

The fundamental process is this: As carbon dioxide increases in the air, it mixes with the water, forming carbonic acid. The result is that the pH of the ocean—the measure of water acidity or alkalinity—is decreasing. That means the ocean is growing more acid.

“An alarming surprise is how rapidly pH has declined over the study period at our site--about 10 times faster than expected,” Wootton said in an email to RaisingIslands.

He said his studies showed that acidity of the oceans varies with changes in biological activity in the ocean, but that the overall direction is toward greater acidity.

Some of the creatures that most obviously are affected by the pH changes are ones that develop shells made of calcium carbonate or have skeletons that are weakened in a less alkaline environment.

“Although we have some idea about the chemical processes affecting pH in seawater, know that pH affects integrity of the calcium carbonate shells and skeletons that many marine animals have, and can demonstrate that plants and animals respond to reduced pH in the lab, we also know that we cannot easily extrapolate laboratory studies to ecosystem in nature,” Wootton said.

His team's work out in the real world shows that the laboratory results do reflect what happens in nature, but not necessarily entirely accurately.

“Our analyses reveal generally reduced performance of calcifying organisms, as expected, but this does not uniformly hold true. Because of the extensive experimental studies we have carried out at our site, we know that these exceptions are readily explained by the web of interactions among species,” he said.

Among those species most significantly affected, according to the study, were large calcifying mussels and goose barnacles. Since these animals are in the food chain for other species, it suggests a larger impact that is not yet readily apparent.

In the paper, the authors write about the challenge:

“The results of our analysis of ecological dynamics follow the general prediction that declining pH will negatively affect calcareous species, but the web of species interactions complicates the response,”
For instance, while the mussels and gooseneck barnacles did more poorly, acorn barnacles and certain fleshy seaweeds actually did better.

The essence: things are changing, changing fast, and we don't know exactly where they'll end up.

This blog has covered acidification aggressively in several previous posts:

© 2007 Jan W. TenBruggencate

No comments: