Big chunk of Antarctic ice shelf falling apart
By Jean-Louis Santini
Agence France-Presse
First Posted 04:47:00 03/27/2008
WASHINGTON—Antarctica's massive Wilkins Ice Shelf has begun disintegrating under the effects of global warming, satellite images by the University of Colorado's National Snow and Ice Data Center showed.
The collapse of a substantial section of the shelf was triggered February 28 when an iceberg measuring 41 by 2.4 kilometers (25.5 by 1.5 miles) broke off its southwestern front.
That movement led to disintegration of the shelf's interior, of which 414 square kilometers (160 square miles) have already disappeared, scientists say.
The Wilkins Ice Shelf is a broad plate of permanent floating ice 1,609 kilometers (1,000 miles) south of South America, on the southwest Antarctic Peninsula.
Now, as a result of recent losses, a large part of the 12,950-square-kilometer (5,000-square-mile) shelf is supported by a narrow 5.6-kilometer (3.5-mile) strip of ice between two islands, scientists said.
"If there is a little bit more retreat, this last 'ice buttress' could collapse and we'd likely lose about half the total ice shelf area in the next few years," NSIDC lead scientist Ted Scambos said in a statement.
"Wilkins is the largest ice shelf on West Antarctica yet to be threatened. This shelf is hanging by a thread," echoed David Vaughan of the British Antarctic Survey, which contributed data on the break-up.
Jim Elliott, who was onboard a British Antarctic Survey Twin Otter aircraft sent to video the extent of the damage, said the scene looked like a bomb site.
"I've never seen anything like this before -- it was awesome," he said in a BAS statement.
"We flew along the main crack and observed the sheer scale of movement from the breakage.
"Big hefty chunks of ice, the size of small houses, look as though they've been thrown around like rubble -- it's like an explosion."
Antarctica has suffered unprecedented warming in the last 50 years -- with several ice shelves retreating and six of them collapsing since the 1970s.
"Climate warming in the Antarctic Peninsula has pushed the limit of viability for ice shelves further south, setting some of them that used to be stable on a course of retreat and eventual loss," Vaughan said.
Vaughan said the Wilkins breakout would not affect sea levels because it was already floating when it broke off.
"But it is another indication of the impact that climate change is having on the region."
Over the past half century, the western Antarctic Peninsula has experienced the steepest temperature increase on Earth, 0.5 degrees Celsius (0.9 Fahrenheit) per decade.
"We believe the Wilkins has been in place for at least a few hundred years, but warm air and exposure to ocean waves are causing a breakup," said Scambos, who first spotted the disintegration in March.
With the Antarctic summer drawing to a close, scientists do not expect the ice shelf to further disintegrate in the next several months.
"This unusual show is over for this season," said Scambos. "But come January, we'll be watching to see if the Wilkins continues to fall apart."
Ultimately, ice shelf breakup in the Antarctic -- more than 13,000 square kilometers (5,000 square miles) have been lost over the past 50 years -- could significantly increase ocean levels around the world.
In 1995 the Larsen A Ice Shelf -- 75 kilometers (47 miles) long and 35 kilometers (22 miles) wide -- disintegrated, fragmenting into icebergs in the Weddell Sea.
In March 2002, a NASA satellite captured the collapse of Larsen B, which had a surface area of 3,850 square kilometers (1,486 square miles), was 200 meters (656 feet) high, and packed in 720 billion tons of ice. It took just 30 days to break apart.
According to some calculations based on the present sea level rise of three millimeters per year (0.11 inches), ocean levels could rise by 1.4 meters (4.6 feet) by the end of the century.
|
