Natural Ocean Thermostat May Protect Some Coral Reefs

Sea Technology, Mar 2008

Natural processes may prevent oceans from warming beyond a certain point, helping protect some coral reefs from the impacts of climate change, new research finds. The study, by scientists at the National Center for Atmospheric Research (NCAR) and Australian Institute of Marine Science, shows evidence that an ocean "thermostat" appears to be helping to regulate sea-surface temperatures in a biologically diverse region of the Pacific Ocean.

The research team looked at the Western Pacific Warm Pool, a region northeast of Australia where naturally warm sea-surface temperatures have risen little in recent decades.

The study lends support to a much debated theory that a natural ocean thermostat prevents sea-surface temperatures from exceeding about 88° F in open oceans. If so, this thermostat would protect reefs that have evolved in naturally warm waters that will not warm much further, as opposed to reefs that live in slightly cooler waters that face more significant warming.

Between 1980 and 2005, only four episodes of coral bleaching, a phenomenon that can be caused by warming oceans and damages corals, have been reported on reefs in the Western Pacific Warm Pool. This is a lower rate than any other reef region. Sea-surface temperatures in the Warm Pool naturally average about 84° F, which is close to the proposed thermostat limit, and they have warmed up about half as much as cooler areas of the oceans.

Researchers have speculated about several processes that could regulate ocean temperatures. As surface waters warm, more water evaporates, which can increase cloud cover and winds that cool the surface. In some areas, warming alters ocean currents in ways that bring in cooler waters. In addition, the very process of evaporation removes heat.

Lead author Joan Kleypas, of NCAR, and her coauthors say more research needs to be conducted on the thermostat. In particular, scientists are uncertain whether global warming may alter it, raising the upper limit for sea-surface temperatures.