|
Polar ice sheet shrinking at alarming rate:
Inland thinning of Pine Island Glacier, West
Antarctica
Antarctica
Photo
of the Pine Island Glacier, taken by Tom Kellogg onboard
the
U.S. Coast Guard icebreaker Glacier, 1985, in Pine Island Bay
British
scientists have detected ominous signs of the ice thinning in west
Antarctica. Researchers from University College London (UCL) and the British
Antarctic Survey have reported in the latest issue of Science magazine that
the Pine Island glacier, the largest in the western Antarctic, has lost 32
cubic kilometers of ice over a 5,000 square-kilometer area since 1992
There
have been fears for more than a decade that the west Antarctic ice sheet
could be unstable.
"For
the past 25 years there has been speculation about whether a retreat of a
west Antarctic glacier could accelerate ice flow from its interior,
producing rise in sea level," said Dr Andrew Shepherd of UCL, who led
the study. "We have shown for the first time that such a retreat is
indeed occurring. It is of paramount importance to determine whether the
thinning is accelerating. "Our present theoretical understanding is not
sufficient to predict firmly the future evolution of the Pine Island
glacier." "The Pine Island Glacier is key,'' said Shepherd.
"It is totally exposed to the sea, and people have identified it as the
weak underbelly of the West Antarctica Ice Sheet."
The
scientists said the discovery added weight to the argument that small
changes at the edge of the continent - such as the effects of global warming
- could be transmitted swiftly inland, leading to a faster rise in the sea
level.
Antarctica
contains about 7.2 million cubic miles of ice, about 84 per cent of all the
glacial ice on Earth, according to the USGS. Melting all the Antarctica ice
would cause a global sea level rise of about 240 feet. Such a rise would
flood virtually all the world's coastal areas and drown many islands.
The change in surface elevation 13 km
upstream of the grounding line of Pine Island Glacier between 1992 and 1999,
observed by the ERS-1 (stars) and ERS-2 (squares) satellite altimeters. The
6-month period of simultaneous operation permitted cross-calibration of the
altimeters. Data gaps are the result of instrument operations.
Giant rivers of ice thread their
way across the Antarctic Ice Sheet to the sea. The rivers, termed by scientists
"streams", are the largest flows of ice in the world. Some streams are
over 2 kilometres thick, 30 km wide and travel at speeds up to 1 km per year.
Radar observations by polar orbiting, European ERS satellites have been used by
CPOM scientists to map in detail the geography of the streams, many of which
were hitherto unknown. A major task of CPOM is to determine if the speed of the
streams is increasing; if so sea level will rise as a consequence. Image
courtesy of J.L. Bamber, copyright Science magazine
University
College London Press Release
Scientists
Detect Thinning in West Antarctic
A
major glacial formation in Antarctica is shrinking, a report in Science
magazine states. But questions still remain about the speed at which the ice
sheet thinning is taking place.
Scientists
at University College London (UCL) and The British Antarctic Survey have used
satellite data to show that the interior of the West Antarctic Ice Sheet
(WAIS) is thinning inland. Since 1992, 31 cubic kilometres of ice has been
lost from its interior. The loss can be pinpointed to the fast flowing Pine
Island Glacier-the largest glacier in West Antarctica-which transports ice
from the deep interior of the ice sheet to the ocean.
Occupying
what is considered to be one of the most remote regions of Antarctica-visits
by man can be numbered by the handful-the Pine Island glacier is up to 2500
meters thick with a bedrock over 1500 meters below sea level. The thinning has
caused the glacier to retreat by over 5 kilometres inland, and this adds
further weight to the argument that small changes at the coast of the
Antarctic continent-such as the effects of global warming-may be transmitted
rapidly inland leading to an acceleration of sea level rise.
Using
high precision radar measurements from the ESR satellite altimeter-accurate to
within 20 centimeters-the height of the WAIS has been mapped at regular
intervals since 19992. The data revealed a clear pattern of ice thinning
within a 5000 square kilometre section of Pine Island Glacier drainage basin
during the last 8 years. A map of glacial velocity, much of which was
previously uncharted, was constructed using ERS SAR interferometry in order to
clarify which regions within the vast section were actually thinning. The
combination of these two datasets- derived from separate instruments on board
the same satellite-showed that the ice has thinned by as much as 10 meters and
was restricted to the fastest flowing sections of the glacier.
Professor
Duncan Wingham at University College London, insists that the success of the
research lies in the performance of the ERS satellite radar.
"The
extreme precision with which we can now make satellite measurements of the
Earth's surface allows us to see the internal changes in the Antarctic Ice
Sheet for the first time."
The
scientific team believe that their results points unambiguously to thinning in
this part of the Antarctic Ice Sheet, and that it is associated with the flow
of ice from the interior. If the present rate of thinning continues the team
believe that the Pine Island Glacier will be lost to the ocean within a few
hundred years. Dr. Andrew Shepard of UCL said;
"For
the past 25 years there has been speculation about whether a retreat of a
west Antarctic glacier could accelerate ice flow from its interior,
producing rise in sea level. We have shown for the first time that such a retreat is
indeed occurring. It is of paramount importance to determine whether the
thinning is accelerating. What is of paramount importance is to determine
whether the thinning is accelerating. Our present theoretical understanding is
not sufficient to firmly predict the future evolution of the Pine Island
Glacier."
|
