Some corals buffered from warming

Some western Pacific corals seem to be weathering global warming. Despite a warming ocean, reefs off Micronesia, Polynesia, and Melanesia suffered relatively little bleaching in the past 25 years, new research suggests.

Bleaching occurs when symbiotic algae living inside corals die, robbing the reefs of nutrients, color, and life. Seawater temperatures just a degree above normal can spur bleaching.

A team led by Joan Kleypas of the National Center for Atmospheric Research in Boulder, Colo., tracked changes in tropical-ocean temperatures and instances of notable coral bleaching around the world. The already balmy waters of the western Pacific warm pool (WPWP)—a swath the size of Australia—have heated little since 1950, and the corals living there have stayed healthy, the team reports in the Feb. 9 Geophysical Research Letters.

Even as atmospheric carbon dioxide levels climb, the reefs in the slow-warming waters of WPWP might continue to escape bleaching, says Kleypas. With warming effects blunted, efforts to reduce other stresses on the corals could make a dent there, she says.

The study jibes with other research suggesting that oceans have a built-in upper limit, or thermostat, keeping areas like the WPWP from warming much further. One proposal for an ocean thermostat claims that upwelling from the deep ocean keeps sea-surface temperatures in check, says Raymond Pierrehumbert of the University of Chicago. Unfortunately, continued increases in carbon dioxide levels would eventually quell the thermostat’s effects, he says.

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