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Wilkins Ice
Shelf hanging by its last thread
European Space Agency 10 July
2008 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 kmē with a rough
estimate of 500 to 700 kmē in addition being lost if the bridge to Charcot
Island collapses.
Annotated image of 9 July 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.
Wilkins Ice Shelf in 1992 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 kmē 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 kmē
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.
Break-ups of Larsen-B and Wilkins
ice shelves 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.
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