Monday, February 23, 2009

Acidification from absorbing atmospheric CO2 is changing the ocean's chemistry

Chemical & Engineering News: People can't walk on water, but scientists say the carbon dioxide emitted by humans into the atmosphere has started to leave noticeable footprints on the ocean.

Scientists have been concerned for years that lower ocean pH caused by absorption of CO2 emissions could decrease calcification processes underlying the growth of shells and corals' hard exteriors. Besides studying that phenomenon, they are investigating how acidification alters the concentration and behavior of the ocean's trace metals, some of which are nutrients for marine life. They are also looking into some unexpected consequences of ocean acidification, such as disruptions to sound propagation and transmission of chemical cues. Some scientists believe the net effect of these and other yet undiscovered changes may threaten the survival of a wide variety of marine organisms.

Increased use of fossil fuels has caused the levels of CO2 in the atmosphere to nearly double since the Industrial Revolution. "Over the past 200 years, the oceans have absorbed approximately 550 billion tons of CO2 from the atmosphere, or about a third of the total amount of anthropogenic emissions over that period," says Richard A. Feely, a senior scientist with the National Oceanographic & Atmospheric Administration's Pacific Marine Environmental Laboratory, in Seattle. That means the ocean currently absorbs about 22 million tons of CO2 per day, he adds.

Marine scientists who have measured the pH of the ocean's surface waters for decades see that it has been dropping. They say that the pH is currently about 8.1, down from about 8.2 in the 18th century. If CO2 emissions continue at current rates, they expect the pH to fall by approximately 0.3 more units in the next 50–100 years. And as the ocean becomes more acidic, scientists anticipate myriad changes to the ocean's chemistry….

Sea urchins off the coast of Madagascar. Their spines get truncated as the surrounding seawater becomes more acidic. Shot by Mila Zinkova, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 2.5, Attribution ShareAlike 2.0 and Attribution ShareAlike 1.0 License

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