Human-generated carbon dioxide in the atmosphere is slowly acidifying the ocean, threatening a catastrophic impact on marine life. And just as scientists are starting to grasp the magnitude of the problem, researchers have delivered more bad news: Acid rain is making things worse.
Scientists estimate that one-third of the world’s acid rain falls near the coasts, carrying some 100 million tons of nitrogen oxide, ammonia, and sulfur dioxide into the ocean each year. Using direct measurements and computer models, oceanographer Scott Doney of Woods Hole Oceanographic Institution and his colleagues calculated that acid rain causes as much as 50 percent of the acidification of coastal waters, where the pH can be as low as 7.6. (The open ocean’s pH is 8.1.)
The findings increase the urgency of confronting the crisis of ocean acidity, says Richard Feely, a collaborator at the National Oceanic and Atmospheric Administration. In the laboratory, researchers have seen some effect on just about every ocean creature that forms a calcium carbonate shell, says Feely, including algae—the tiny creatures at the crucial bottom of the deepwater food chain—and coral, whose skeletons grow more slowly in water with a pH even slightly lower than normal. Soon-to-be-released field experiment findings “seem to be showing the same kind of thing,” Feely says. That’s bad news, he adds, since a third of the world’s fish species depend in part on coral reefs for their ecosystems.
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