As worried as many researchers are about carbon dioxide’s effects on global climate change, a cadre of oceanographers and marine biologists are most concerned about what the greenhouse gas is doing to the oceans. Since the industrial revolution, the oceans have absorbed 142 billion metric tons of carbon dioxide, enough to increase the water’s acidity by 30% and to threaten coral and other organisms that depend on dissolved carbonate to build their skeletons, according to a U.S. government report released today.
Analyses of ice cores have shown that the ocean’s chemistry has been stable for about 650,000 years. But in the past 150 years, excess carbon dioxide dissolving into the water has caused the average ocean pH to drop from 8.2 to 7.9. This change has decreased the concentration of carbonate ions, which corals, planktonic marine snails called pteropods, and other marine organisms need to make calcium carbonate shells and skeletons. Laboratory studies have shown that the fewer the number of carbonate ions, the slower these organisms grow. And if the pH gets too low, these shells may start to dissolve, says Joan Kleypas a marine ecologist from the National Center for Atmospheric Research in Boulder, Colorado, and a co-author of the report. Eventually, reefs could shrink, and pteropods–a key food for juvenile salmon and other fish–could disappear, she warns.