Ocean acidification is happening at 10 to 20 times the rate predicted by existing climate models, according to an eight-year study. The rapid acidification of the oceans is linked to global warming and may be a sign that the oceans, the largest absorber of atmospheric carbon dioxide, may not be as hardy as presumed. The changes threaten disaster for marine life with shells that are easily corroded by acid. Marine biologist Nancy Knowlton said, “This is typical of so many climate studies—almost without exception things are turning out to be worse than we originally thought.” [National Geographic News].
The study was done around Takoosh Island off the coast of Washington state and represents the first detailed dataset on variations of coastal pH at a temperate latitude, where the world’s most productive fisheries are found [Times of India]. The researchers took over 24,000 measurements of ocean pH over an 8-year period. During that time, the pH of the seawater was predicted to decrease by only 0.015 points. Instead, the data showed that seawater pH dropped by 0.36 to about 8.1. “The increase in acidity we saw during our study was about the same magnitude as we expect over the course of the next century,” said study co-author Timothy Wootton [National Geographic News].
The researchers found that atmospheric carbon dioxide exhibited a corresponding steady change, with current levels as high as they’ve ever been in the last 650,000 years. About one-third of man-made carbon dioxide is dissolved into the oceans and removed from the atmosphere. But once in seawater, carbon dioxide forms carbonic acid, lowering seawater pH. “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 [The Guardian].
The study noted a significant decline in large mussels, which normally dominate their niches but have calcium carbonate shells that are weakened or corroded by acid. 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 [The Guardian]. The changing balance in the ecosystem may be felt throughout the food chain and may speed up as it goes along, as large populations of certain species begin to die off.
Last year, the Intergovernmental Panel on Climate Change predicted that rising ocean temperatures and acidification would cause the extinction of many coral species by the end of the century. The new study, published in the Proceedings of the National Academy of Sciences [subscription required], paints an even grimmer picture. The researchers would like to collect more data to determine if the situation around Takoosh Island is representative of a global pattern. “It’s been thought pH in the open oceans is well buffered, so it’s surprising to see these fluctuations,” [Wootton] said [BBC News].
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Image: flickr / Shayan (USA)