Satellite imagery shows fragile Wilkins Ice Shelf destabilized

The figure displays the Envisat Advanced Synthetic Aperture Radar image from April 27, 2009, superimposed on an image from April 24, 2009. The margins of the collapsed ice bridge that formerly connected Charcot and Latady Islands are outlined in white. The demise of the ice bridge led to a destabilization of the northern ice front of the Wilkins Ice Shelf, where the first icebergs calved off on 20 April 2009 (area denoted in red). -  ESA (Annotations by A. Humbert, Münster University)
The figure displays the Envisat Advanced Synthetic Aperture Radar image from April 27, 2009, superimposed on an image from April 24, 2009. The margins of the collapsed ice bridge that formerly connected Charcot and Latady Islands are outlined in white. The demise of the ice bridge led to a destabilization of the northern ice front of the Wilkins Ice Shelf, where the first icebergs calved off on 20 April 2009 (area denoted in red). – ESA (Annotations by A. Humbert, Münster University)

Satellite images show that icebergs have begun to calve from the northern front of the Wilkins Ice Shelf – indicating that the huge shelf has become unstable. This follows the collapse three weeks ago of the ice bridge that had previously linked the Antarctic mainland to Charcot Island.

The ice bridge, which effectively formed a barrier pinning back the northern ice front of the central Wilkins Ice Shelf, collapsed on 5 April removing about 330 sq km of ice. 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 in the days that followed.

Dr Angelika Humbert from the Institute of Geophysics, Münster University and Dr Matthias Braun from the Center for Remote Sensing, University of Bonn have been monitoring the ice shelf using a combination of radar images from ESA’s Envisat satellite and the German Aerospace Centre’s TerraSAR-X satellite.

On 24 April, the satellite data showed that the first icebergs had started to break away from the fragile ice shelf. A very rough estimate suggests that, so far, about 700 sq km of ice has been lost from the Wilkins Ice Shelf.

In contrast to the ice bridge, which shattered very quickly, it is expected that the discharge of ice will continue for some weeks. The icebergs are calving as a result of fracture zones that have formed over the last 15 years and which turned Wilkins into a fragile and vulnerable ice shelf.

“The retreat of Wilkins Ice Shelf is the latest and the largest of its kind. Eight separate ice shelves along the Antarctic Peninsula have shown signs of retreat over the last few decades. There is little doubt that these changes are the result of atmospheric warming on the Antarctic Peninsula, which has been the most rapid in the Southern Hemisphere,” explained David Vaughan from the British Antarctic Survey.

“The changes to Wilkins Ice Shelf provide a fabulous natural laboratory that will allow us to understand how ice shelves respond to climate change and what the future will hold for the rest of Antarctica,” Vaughan commented. “The quality and frequency of images acquired by ESA satellites mean that the break-up of Wilkins Ice Shelf can be analysed 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.”

However, it is still unclear how the situation will evolve. Humbert noted that, “We are not sure if a new stable ice front will now form between Latady Island, Petrie Ice Rises and Dorsey Island. If the connection to Latady Island is lost, the projected loss of 3370 sq km of ice might be greater – though we have no indication that this will happen in the near future.”

The combination of high resolution TerraSAR-X images and the more frequently acquired Envisat images, increases the understanding of ice shelf break-up more than ever before.

ESA’s Webcam from Space is available to the public and features the latest Envisat images, documenting the break-up of Antarctica’s Wilkins Ice Shelf.

Wilkins Ice Shelf hanging by its last thread





Annotated image of Wilkins Ice Shelf acquired on 9 July 2008 by Envisat's ASAR instrument, showing the ice bridge connecting to Charcot Island and Latady Island (bottom left). A new fracture that could open the ice bridge is visible at the bottom of the ice bridge. - Credits: ESA
Annotated image of Wilkins Ice Shelf acquired on 9 July 2008 by Envisat’s ASAR instrument, showing the ice bridge connecting to Charcot Island and Latady Island (bottom left). A new fracture that could open the ice bridge is visible at the bottom of the ice bridge. – Credits: ESA

The Wilkins Ice Shelf is experiencing further disintegration that is threatening the collapse of the ice bridge connecting the shelf to Charcot Island. Since the connection to the island in the image centre helps to stabilise the ice shelf, it is likely the break-up of the bridge will put the remainder of the ice shelf at risk.



This animation, comprised of images acquired by Envisat’s Advanced Synthetic Aperture Radar (ASAR) between 30 May and 9 July 2008, shows the break-up event which began on the east (right) rather than the on west (left) like the previous event that occurred last month. By 8 July, a fracture that could open the ice bridge was visible.



According to the image acquired on 7 July 2008, Dr Matthias Braun from the Center for Remote Sensing of Land Surfaces at Bonn University estimates the area lost on the Wilkins Ice Shelf during this break-up event is about 1350 km² with a rough estimate of 500 to 700 km² in addition being lost if the bridge to Charcot Island collapses.



This break-up is puzzling to scientists because it has occurred in the Southern Hemispheric winter and does not have characteristics similar to two earlier events that occurred in 2008, which were comparable to the break-up of the Larsen-A and -B ice shelves.



“The scale of rifting in the newly-removed areas seems larger, and the pieces are moving out as large bergs and not toppled, finely-divided ice melange,” said Ted Scambos from the National Snow and Ice Data Center who uses ASAR images to track the area.



“The persistently low sea ice cover in the area and data from some interesting sources, electronic seal hats [caps worn by seals that provide temperature, depth and position data] seems to suggest that warm water beneath the halocline may be reaching the underside of the Wilkins Ice Shelf and thinning it rapidly – and perhaps reaching the surface, or at least mixing with surface waters.”



Prof. David Vaughan of the British Antarctic Survey (BAS) said: “Wilkins Ice Shelf is the most recent in a long, and growing, list of ice shelves on the Antarctic Peninsula that are responding to the rapid warming that has occurred in this area over the last fifty years.



“Current events are showing that we were being too conservative, when we made the prediction in the early 1990s that Wilkins Ice Shelf would be lost within thirty years – the truth is it is going more quickly than we guessed.”


The Wilkins Ice Shelf, a broad plate of floating ice south of South America on the Antarctic Peninsula that is connected to Charcot and Latady Islands, had been stable for most of the last century before it began retreating in the 1990s.



By studying ESA ERS SAR satellite images since the 1990s, Braun and his colleague Dr Angelika Humbert from the Institute of Geophysics, Münster University, have found the Wilkins Ice Shelf has break-up events with loss of large areas rather than underlying ordinary, continuous calving.



For instance, in February 2008 an area of about 400 km² broke off from the Wilkins Ice Shelf, narrowing the ice bridge that connects it to Charcot and Latady Islands down to a 6 km strip. From 30 to 31 May 2008 it experienced further break-up with an area of about 160 km² breaking off, reducing the ice bridge to just 2.7 km.



Braun and Humbert are monitoring the ice sheet daily via Envisat acquisitions as part of their contribution to the International Polar Year (IPY) 2007-2008, a large worldwide science programme focused on the Arctic and Antarctic.



Satellite data are essential for observing polar regions. Envisat’s ASAR instrument is able to produce high-quality images, even through clouds and darkness. Therefore, it is particularly suited to acquire images over Antarctica during the local winter period where hours of daylight are limited and cloud cover is quite frequent.



“ESA provides daily ASAR images that are easily accessible to scientists. It is particularly rewarding for us to see that the Envisat data are essential for scientists to quickly and easily observe these ice-shelf phenomena — a luxury that was not available to the scientific community a few years ago,” ESA Envisat Mission Manager Henri Laur said.



“ESA is committed to continue monitoring the polar areas with Envisat and in the future with the GMES Sentinel-1 satellite.”



In an effort to ensure as much SAR data as possible is made available to scientists and polar region projects during IPY, ESA is coordinating with other space agencies worldwide, such as Japan’s JAXA, the Canadian Space Agency and the German and Italian space agencies, to acquire additional SAR data over these areas with their own satellites.

Even the Antarctic winter cannot protect Wilkins Ice Shelf





<IMG SRC="/Images/Wilkins_Ice_Shelf.jpg" WIDTH="350" HEIGHT="339" BORDER="0" ALT="Wilkins Ice Shelf has experienced further break-up with an area of about 160 km2 breaking off. “>
Wilkins Ice Shelf has experienced further break-up with an area of about 160 km2 breaking off.

Wilkins Ice Shelf has experienced further break-up with an area of about 160 km² breaking off from 30 May to 31 May 2008. ESA’s Envisat satellite captured the event – the first ever-documented episode to occur in winter.



Wilkins Ice Shelf, a broad plate of floating ice south of South America on the Antarctic Peninsula, is connected to two islands, Charcot and Latady. In February 2008, an area of about 400 km² broke off from the ice shelf, narrowing the connection down to a 6 km strip; this latest event in May has further reduced the strip to just 2.7 km.



This animation, comprised of images acquired by Envisat’s Advanced Synthetic Aperture Radar (ASAR) between 30 May and 9 June, highlights the rapidly dwindling strip of ice that is protecting thousands of kilometres of the ice shelf from further break-up.



According to Dr Matthias Braun from the Center for Remote Sensing of Land Surfaces, Bonn University, and Dr Angelika Humbert from the Institute of Geophysics, Münster University, who have been investigating the dynamics of Wilkins Ice Shelf for months, this break-up has not yet finished.



“The remaining plate has an arched fracture at its narrowest position, making it very likely that the connection will break completely in the coming days,” Braun and Humbert said.




<IMG SRC="http://www.esa.int/images/asa_imm_geo_sub_L,0.gif" BORDER="0" ALT="Wilkins Ice Shelf has experienced further break-up with an area of about 160 km2 breaking off. “>

Braun and Humbert are monitoring the ice sheet daily via Envisat acquisitions as part of their contribution to the International Polar Year (IPY) 2007-2008, a large worldwide science programme focused on the Arctic and Antarctic.



The ASAR images used to compile these animations were acquired as part of ESA’s support to IPY. ESA is helping scientists during IPY to collect an increasing amount of satellite information, particularly to understand recent and current distributions and variations in snow and ice and changes in the global ice sheets.



ESA is also co-leading a large IPY project – the Global Interagency IPY Polar Snapshot Year (GIIPSY) – with the Byrd Polar Research Centre. The goal of GIIPSY is to make the most efficient use of Earth-observing satellites to capture essential snapshots that will serve as benchmarks for gauging past and future changes in the environment of the polar regions.



ASAR is extremely useful for tracking changes in ice sheets because it is able to see through clouds and darkness – conditions often found in polar regions.



Long-term satellite monitoring over Antarctica is important because it provides authoritative evidence of trends and allows scientists to make predictions. Ice shelves on the Antarctic Peninsula are important indicators for on-going climate change because they are sandwiched by extraordinarily raising surface air temperatures and a warming ocean.



The Antarctic Peninsula has experienced extraordinary warming in the past 50 years of 2.5°C, Braun and Humbert explained. In the past 20 years, seven ice shelves along the peninsula have retreated or disintegrated, including the most spectacular break-up of the Larsen B Ice Shelf in 2002, which Envisat captured within days of its launch.

Antarctic Ice Shelf Disintegrating As Result Of Climate Change, Scientists Say





This series of satellite images shows the Wilkins Ice Shelf as it begins to break up. The large image is from March 6. The images at right, from top to bottom, are from Feb. 28, Feb. 29 and March 8. The images were processed from the MODIS satellite sensor flying on NASA's Earth Observing System Aqua and Terra satellites. Images courtesy NSIDC, NASA, University of Colorado.
This series of satellite images shows the Wilkins Ice Shelf as it begins to break up. The large image is from March 6. The images at right, from top to bottom, are from Feb. 28, Feb. 29 and March 8. The images were processed from the MODIS satellite sensor flying on NASA’s Earth Observing System Aqua and Terra satellites. Images courtesy NSIDC, NASA, University of Colorado.

Satellite imagery from the University of Colorado at Boulder’s National Snow and Ice Data Center shows a portion of Antarctica’s massive Wilkins Ice Shelf has begun to collapse because of rapid climate change in a fast-warming region of the continent.



While the area of collapse involves 160 square miles at present, a large part of the 5,000-square-mile Wilkins Ice Shelf is now supported only by a narrow strip of ice between two islands, said CU-Boulder’s Ted Scambos, lead scientist at NSIDC. “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.”



In the past 50 years, the western Antarctic Peninsula has experienced the biggest temperature increase on Earth, rising by 0.9 degree F 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 activity in March.



Satellite images indicate the Wilkins began its collapse on Feb. 28. Data revealed that a large iceberg, measuring 25.5 by 1.5 miles, fell away from the ice shelf’s southwestern front, triggering a runaway disintegration of 220 square miles of the shelf interior. The Wilkins Ice Shelf is a broad sheet of permanent floating ice on the southwest Antarctic Peninsula roughly 1,000 miles south of South America.



The edge of the shelf crumbled into the sky-blue pattern of exposed deep glacial ice that has become characteristic of climate-induced ice shelf breakups such as the Larsen B ice shelf breakup in 2002, said Scambos. A narrow beam of intact ice about 3.7 miles wide was protecting the remaining shelf from further breakup as of March 23.



Scientists track ice shelves and study collapses carefully because some of them hold back glaciers, which if unleashed, can accelerate and raise sea level, Scambos said. “The Wilkins disintegration won’t raise sea level because it already floats in the ocean, and few glaciers flow into it. However, the collapse underscores that the Wilkins region has experienced an intense melt season. Regional sea ice has all but vanished, leaving the ice shelf exposed to the action of waves.”


With Antarctica’s summer melt season drawing to a close, scientists do not expect the Wilkins to further disintegrate in the next several months. “This unusual show is over for this season,” Scambos said. “But come January, we’ll be watching to see if the Wilkins continues to fall apart.”



After images from NASA’s Moderate Resolution Imaging Spectroradiometer, or MODIS, and data from the ICESat satellite showed that a portion of the ice shelf was in a state of collapse in March, Scambos alerted colleagues around the world.



The British Antarctic Survey flew over the shelf, collecting video footage and other observations. BAS glaciologist David Vaughan, who said the ice shelf is supported by a single strip of ice strung between two islands, said the Wilkins is the largest ice shelf on West Antarctica yet to be threatened. “This shelf is hanging by a thread.”



Associate Professor Cheng-Chien Liu at Taiwan’s National Cheng-Kung University used high-resolution color satellite images of the area from Taiwan’s Formosat-2 satellite operated by the National Space Organization to analyze the activity. “It looks as if something is slicing the ice shelf piece by piece on an incredible scale, kilometers long but only a few hundred meters in width,” Cheng-Chien said.



In addition, Andrés Rivera and Gino Cassasa at the Laboratory for Glaciology and Climate Change at the Center of Scientific Study in Chile acquired images of the Wilkins from the ASTER instrument aboard NASA’s Terra satellite.



The combined efforts have begun to provide observational data that will improve scientific understanding of the mechanisms behind ice shelf collapse, Scambos said. “The Wilkins is an example of an event we don’t see very often, but it’s a key process in being able to predict how sea level will change in the future.”



The Wilkins is one of a string of ice shelves that have collapsed in the West Antarctic Peninsula in the past 30 years. The Larsen B became the most well-known of these, disappearing in just over 30 days in 2002. The Prince Gustav Channel, Larsen Inlet, Larsen A, Wordie, Muller and Jones ice shelf collapses also underscore the unprecedented warming in this region of Antarctica, said Scambos.