ICE SHELF ABOUT TO BREAK AWAY FROM ANTARCTICA
** New rifts' appeared this week along Wilkins; shelf holds back ice on land **
April 4, 2009
PARIS -- A massive ice shelf anchored to the Antarctic coast by a narrow and quickly deteriorating ice bridge could break away soon, the European Space Agency warned Friday.
The Paris-based agency said satellite images show the bridge that connects the Wilkins Ice Shelf to Charcot and Latady Islands "looks set to collapse."
"The beginning of what appears to be the demise of the ice bridge began this week when new rifts" appeared and a large block of ice broke away, it said.
The Wilkins Ice Shelf -- which like the rest of Antarctic's ice sheet "was formed by thousands of years of accumulated and compacted snow" -- had been stable for most of the last century before it began retreating in the 1990s, the statement said.
The shelf, which was originally [the size] of Jamaica or the U.S. state of Connecticut, is located on the western side of the Antarctic Peninsula, which thrusts up from the continent toward the southern tip of South America.
Originally covering about 5,000 square miles, the ice shelf lost 14 percent of its mass last year alone, the statement quotes a scientist Angelika Humbert of Germany's Munster University as saying.
In two 2008 incidents, large chunks of the ice bridge fell away, shaving it down to just 985 yards across at its narrowest, the statement said.
As a result, "in the past months, we have observed the ice bridge deforming and its narrowest location acting as a kind of hinge," Humbert is quoted as saying.
Scientist are examining whether global warming is behind the shelf's breakup, the statement said. Average temperatures in the Antarctic Peninsula have risen by 3.8 degrees Fahrenheit over the past half century, the statement said -- higher than the average global rise.
HUGE ICE CHUNKS BREAK AWAY FROM ANTARCTIC ICE SHELF
By David Rising
April 29, 2009
BERLIN -- Massive ice chunks are crumbling away from a shelf in the western Antarctic Peninsula, researchers said Wednesday, warning that 1,300 square miles of ice -- an area larger than Rhode Island -- was in danger of breaking off in coming weeks.
The Wilkins Ice Shelf had been stable for most of the last century, but began retreating in the 1990s. Researchers believe it was held in place by an ice bridge linking Charcot Island to the Antarctic mainland.
But the 127-square-mile (330-square-kilometer) bridge lost two large chunks last year and then shattered completely on April 5.
"As a consequence of the collapse, the rifts, which had already featured along the northern ice front, widened, and new cracks formed as the ice adjusted," the European Space Agency said in a statement Wednesday on its Web site, citing new satellite images.
The first icebergs broke away on Friday, and since then some 270 square miles (700 square kilometers) of ice have dropped into the sea, according to the satellite data.
"There is little doubt that these changes are the result of atmospheric warming," said David Vaughan of the British Antarctic Survey.
The falling away of Antarctic ice shelves does not, in itself, raise sea levels, since the ice was already floating in the sea. But such coastal tables of ice usually hold back glaciers, and when they disintegrate that land ice will often flow more quickly into the sea, contributing to sea-level rise.
Researchers said the quality and frequency of the ESA satellite images have allowed them to analyze the Wilkins shelf breakup far more effectively than any previous event.
"For the first time, I think, we can really begin to see the processes that have brought about the demise of the ice shelf," Vaughan said.
He said eight ice shelves along the Antarctic Peninsula have shown signs of retreat over the last few decades.
"The retreat of Wilkins Ice Shelf is the latest and the largest of its kind," he said.
The Wilkins shelf, which is the size of Jamaica, lost 14 percent of its mass last year, according to scientists who are looking at whether global warming is the cause of its breakup.
Average temperatures in the Antarctic Peninsula have risen by 3.8 degrees Fahrenheit (2.5 Celsius) over the past 50 years -- higher than the average global rise, according to studies.
Over the next several weeks, scientists estimate the Wilkins shelf will lose some 1,300 square miles (3,370 square kilometers) -- a piece larger than the state of Rhode Island, or two-thirds the size of Luxembourg.
One researcher said, however, that it was unclear how the situation would evolve.
"We are not sure if a new stable ice front will now form between Latady Island, Petrie Ice Rises, and Dorsey Island," said Angelika Humbert of Germany's Muenster University Institute of Geophysics.
But even more ice could break off "if the connection to Latady Island is lost," she said, "though we have no indication that this will happen in the near future."
On the Net:
* ESA's 'Webcam' from Space: http://www.esa.int/esaEO/SEMWZS5DHNF_index_0.html
NEW YORK-SIZED ICE SHELF COLLAPSES OFF ANTARCTICA
April 28, 2009
An area of an Antarctic ice shelf almost the size of New York City has broken into icebergs this month after the collapse of an ice bridge widely blamed on global warming, a scientist said today.
"The northern ice front of the Wilkins Ice Shelf has become unstable and the first icebergs have been released," Angelika Humbert, glaciologist at the University of Muenster in Germany, said of European Space Agency satellite images of the shelf.
Humbert told Reuters about 700 sq km of ice -- bigger than Singapore or Bahrain and almost the size of New York -- has broken off the Wilkins this month and shattered into a mass of icebergs.
She said 370 sq kms of ice had cracked up in recent days from the Shelf, the latest of about 10 shelves on the Antarctic Peninsula to retreat in a trend linked by the U.N. Climate Panel to global warming.
The new icebergs added to 330 sq kms of ice that broke up earlier this month with the shattering of an ice bridge apparently pinning the Wilkins in place between Charcot island and the Antarctic Peninsula.
Nine other shelves -- ice floating on the sea and linked to the coast -- have receded or collapsed around the Antarctic peninsula in the past 50 years, often abruptly like the Larsen A in 1995 or the Larsen B in 2002.
The trend is widely blamed on climate change caused by heat-trapping gases from burning fossil fuels, according to David Vaughan, a British Antarctic Survey scientist who landed by plane on the Wilkins ice bridge with two Reuters reporters in January.
Humbert said by telephone her estimates were that the Wilkins could lose a total of 800 to 3,000 sq kms of area after the ice bridge shattered.
The Wilkins shelf has already shrunk by about a third from its original 16,000 sq kms when first spotted decades ago, its ice so thick would take at least hundreds of years to form.
Temperatures on the Antarctic Peninsula have warmed by up to 3 Celsius this century, Vaughan said, a trend climate scientists blame on global warming from burning fossil fuels in cars, factories and power plants.
The loss of ice shelves does not raise sea levels significantly because the ice is floating and already mostly submerged by the ocean.
But the big worry is that their loss will allow ice sheets on land to move faster, adding extra water to the seas.
Wilkins has almost no pent-up glaciers behind it, but ice shelves further south hold back vast volumes of ice.
The Arctic Council, grouping nations with territory in the Arctic, is due to meet in Tromsoe, north Norway, today to debate the impact of melting ice in the north.
NORTHERN ICE FRONT OF WILKINS ICE SHELF IS BECOMING UNSTABLE
German Aerospace Center
April 28, 2009
Following the loss of an ice bridge on the Antarctic Wilkins Ice Shelf, the northern ice front is now becoming unstable. The first icebergs broke off at this point on 20 April 2009. This was observed by scientists using the TerraSAR-X Earth observation satellite operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). "We anticipate that, over the next days and weeks, an area of 570 to 3370 square kilometers will break away before -- hopefully -- a new and more stable northern ice front will form," states Dr. Angelika Humbert, a glaciologist at the University of Münster's Geophysics Institute.
The TerraSAR-X images from 23 and 25 April 2009 show these 'calved' icebergs. These icebergs are breaking away at the failure zones which have gradually formed over the past 15 years. "The high resolution of TerraSAR-X satellites enables us to observe deformations in the Wilkins Ice Shelf, down to the range of approximately 100 metres," says Dr. Humbert, and she goes on to add: "This information enables we glaciologists to describe distortion more precisely with the help of models."
Newly formed cracks are very narrow during their initial stages and are therefore not visible on images taken at a lower resolution, such as those supplied by the older generation of satellites. To reconstruct the chronological sequence of events, the kind of high-resolution images supplied by TerraSAR-X are necessary. Through an analysis of the chronological development leading to the point where cracks start to appear, an insight into the 'stress conditions' at work in the ice can be gained. Since it started work in 2007, the German Earth observation satellite TerraSAR-X has been supplying scientists with a range of images of the Wilkins Ice Shelf. "It is in particular the combination of high-resolution TerraSAR-X images and the more frequent, lower-resolution images taken by the European Earth observation satellite ENVISAT (ENVIronmental SATellite) which has provided such a substantial step forward for science, enabling us to gain unique insights into the process of disintegration of an ice shelf," states Dr. Humbert.
The Wilkins Ice Shelf is a focal point of the 'Antarctic Background Mission' set up by DLR. The aim of this is to observe changes in the Antarctic ice shelves and to seek to classify the root causes on the basis of all the collated information.
The spectacular break-up events on the Wilkins Ice Shelf in 2008 caused the ice bridge between Charcot and Latady Island, measuring some 40 to 50 kilometers in length, to be cut to a width of just 900 meters at its narrowest point. This plate of ice, only 250 meters thick, finally broke off on 5 April 2008. Ice shelves are stabilized by the islands adjacent to them, which to a certain extent hold them in check. The loss of this link to Charcot Island will inevitably give rise to instability in the northern ice front of the Wilkins Ice Shelf.
Ice shelves are the floating masses of ice that surround the continent of Antarctica. Some 90 percent of inland ice flows down ice streams and glaciers into these ice shelves. Scientists are of the view that these ice shelves hold back the ice streams and glaciers. However, the precise role played by ice shelves has not yet been fully explained. The disintegration of the ice shelves reduces this restraining force, causing the movement of ice masses lying behind them to accelerate. This in turn causes more ice to flow into the ocean, causing sea levels to rise. Over the last 30 years, seven ice shelves have retreated across large areas or have completely broken away, causing a loss in surface area amounting to 25,000 square kilometres. All these ice shelves were located on the Antarctic Peninsula, a region in which temperatures have risen by 2.5 degrees Celsius over the last 50 years -- a significantly higher increase than the global average. The Wilkins Ice Shelf, also located on the Antarctic Peninsula, reduced in size during the course of 2008 by some 1800 square kilometers (which equates to about 14 percent of its total area). In March 2009 -- which was prior to the loss of the ice bridge and the current breakup -- its area measured 11,200 square kilometers. However, due to the fact that the catchment area further inland is comparably small, this reduction in the size of the Wilkins Ice Shelf will have only a marginal impact on sea level.
THE TerraSAR-X MISSION
TerraSAR-X is the first German satellite that has been manufactured under what is known as a Public-Private Partnership (PPP) between DLR and EADS Astrium GmbH in Friedrichshafen. The satellite travels around the Earth in a polar orbit and records unique, high-quality X-band radar data about the entire planet using its active antenna. TerraSAR-X works regardless of weather conditions, cloud cover or absence of daylight, and is able to provide radar data with a resolution of down to one metre per pixel.
DLR is responsible for using TerraSAR-X data for scientific purposes. It is also responsible for planning and implementing the mission as well as controlling the satellite. Astrium built the satellite and shares the costs of developing and using it. Infoterra GmbH, a subsidiary company founded specifically for this purpose by Astrium, is responsible for marketing the data commercially.
German Aerospace Center (DLR)
Tel.: +49 2203 601-2164
Fax: +49 2203 601-3249
Deutsches Zentrum für Luft- und Raumfahrt (DLR) - German Aerospace Center
Communication Department, Spokesman
Tel.: +49 2203 601-2474
Mobile: +49 171 3126466
Fax: +49 2203 601-3249
Dr. Angelika Humbert
University of Muenster
Tel.: +49 251 83 33590
Dr. Stefan Buckreuß
DLR-Institut für Hochfrequenztechnik und Radarsysteme
Mission Manager TerraSAR-X