Antarctic Melting as Deep Ocean Heat Rises

Global warming is sneaky. For more than a century it has been hiding large amounts of excess heat in the world's deep seas. Now that heat is coming to the surface again in one of the worst possible places: Antarctica. This trend means that Earth is already locked into long term melting and sea level rise.

New analyses of the heat content of the waters off Western Antarctic Peninsula are now showing a clear and exponential increase in warming waters undermining the sea ice, raising air temperatures, melting glaciers (melting iceberg at right) and wiping out entire penguin colonies.

"In the area I work there is the highest increase in temperatures of anywhere on Earth," said physical oceanographer Doug Martinson of the Lamont-Doherty Earth Observatory. Martinson has been collecting ocean water heat content data for more than 18 years at Palmer Island, on the western side of the Antarctic Peninsula.

"Eighty-seven percent of the alpine glaciers are in retreat," said Martinson of the Western Antarctic Peninsula. "Some of the Adele penguin colonies have already gone extinct."

Martinson and his colleagues looked not only at their very detailed and mapped water heat data from the last two decades, but compared them with sketchier data from the past and deep ocean heat content measurements worldwide. All show the same rising trend that is being seen in Antarctica.

"When I saw that my jaw just dropped," said Martinson. The most dramatic rise has happened since 1960, he said.

What the rising water heat means, he said, is that even if humanity got organized and soon stopped emitting greenhouse gases, there is already too much heat in the oceans to stop a lot of impacts -- like the melting of a huge amount of Antarctic ice.

"There's the potential that we're locked into long term sea level rise for a long time," Martinson told Discovery News. Martinson presented his latest ocean heat results on Monday at the meeting of the American Geophysical Union in San Francisco.

As for how fast the ice will melt and in what locations, that depends largely on whether the upwelling warm water comes in contact with the thick ice shelf that crowds the coast and holds the block the glaciers from reaching the sea.

That, in turn, depends on the winds which drive away the surface waters and make it possible for the deeper waters to rise to the surface, said senior researcher Robert Bindschadler of NASA's Goddard Earth Science and Technology Center and the University of Maryland-Baltimore County.

"It can destroy the ice shelf if that heat can get to it," said Bindschadler, who at the same meeting presented his work from the melting Pine Island Ice Shelf (right) in Antarctica.

Now that the upwelling deep sea water is the clear cause of the melting ice shelf, rather than summer melt water, as had been thought in the past, it's a question of how winds will change in a warming world and whether they will drive more warm water into the ice shelves.

"So we have thrown the problem back over the fence to the climate modelers," said Bindschadler.

Source:
Discovery News, "Antarctic Melting as Deep Ocean Heat Rises", accessed December 16, 2010