Ocean Thermostat May Shield Reefs

Feb. 13, 2008 -- Some coral reefs may be protected from global warming by a natural thermostat that regulates sea-surface temperatures in the open ocean, researchers said Wednesday.

The research team led by reef specialist Joan Kleypas studied a region of ocean northeast of Australia where surface temperatures have risen little since 1980.

Reefs there suffered fewer episodes of bleaching, which is when corals expel the colorful, microscopic algae that provide them with nutrition. Bleaching episodes, triggered by warming water, can be deadly for the coral and have damaged nearly half the reefs worldwide.

"Global warming is damaging many corals, but it appears to be bypassing certain reefs that support some of the greatest diversity of life on the planet," said Kleypas, who works at Australia's National Center for Atmospheric Research.

"In essence, reefs that are already in hot water may be more protected from warming than reefs that are not. This is some rare hopeful news for these important ecosystems."

Kleypas said the study, which appeared last week in the journal Geophysical Research Letters, lent support to a much-debated theory that a natural ocean thermostat prevents sea-surface temperatures from exceeding about 88 degrees Fahrenheit in open oceans.

The theory says that as surface waters warm, more water evaporates, which can increase cloud cover and winds that cool the surface.