A yellow submarine has helped solve a puzzle about one of Antarctica's fastest-melting glaciers, adding to concerns about how climate change may push up world sea levels, scientists said Sunday.
The robot submarine, deployed under the ice shelf floating on the sea at the end of the Pine Island Glacier, found that the ice was no longer resting on a subsea ridge that had slowed the glacier's slide until the early 1970s.
Antarctica is key to predicting the rise in sea levels caused by global warming — it has enough ice to raise sea levels by nearly 200 feet if it ever all melted. Even a tiny thaw at the fringes could swamp coasts from Bangladesh to Florida.
The finding from the 2009 mission indicates that the glacier is key to the much larger West Antarctic Ice Sheet, Stan Jacobs, a study co-author who works at Columbia University's Lamont-Doherty Earth Observatory, said in a statement.
"Since our first measurements in the Amundsen Sea, estimates of Antarctica’s recent contributions to sea level rise have changed from near-zero to significant and increasing," he added. "Now finding that the PIG’s grounding line has recently retreated more than 30 kilometers from a shallow ridge into deeper water, where it is pursued by a warming ocean, only adds to our concern that this region is indeed the ‘weak underbelly’ of the West Antarctic Ice Sheet. Increased melting of continental ice also appears to be the primary cause of persistent ocean freshening and other impacts, both locally and downstream in the Ross Sea."
West Antarctica's thaw accounts for 10 percent of a recently observed rise in sea levels, with melting of the Pine Island glacier quickening, especially in recent decades, according to the study led by the British Antarctic Survey and published in the journal Nature Geoscience.
Loss of contact with the subsea ridge meant that ice was flowing faster and also thawing more as relatively warmer sea water flowed into an ever bigger cavity.
Satellite photographs in the early 1970s had shown a bump on the surface of the ice shelf, indicating the subsea ridge. That bump has vanished and the submarine found the ridge was now up to 300 feet below the ice shelf.
Adrian Jenkins, the study's lead author and a BAS scientist, said the study raised "new questions about whether the current loss of ice from Pine Island Glacier is caused by recent climate change or is a continuation of a longer-term process that began when the glacier disconnected from the ridge."
Pierre Dutrieux, also at BAS, said the ice may have started thinning because of some as yet-unknown mechanism linked to climate change, blamed mainly on mankind's use of fossil fuels.
"It could be a shift in the wind, due to a change in climate, that pushed more warm water under the shelf," he told Reuters.
The U.N. panel of climate scientists projected in 2007 that world sea levels could rise by 7-24 inches by 2100, excluding risks of faster melting in Antarctica and Greenland.
U.N. Secretary-General Ban Ki-moon has said the 21st century rise might be six feet in the worst case.
