Sound Alarm Over Melting Antarctic Ice Sheets
By Steve Connor
18 February, 2007
The long-term stability of the
massive ice sheets of Antarctica, which have the potential to raise
sea levels by hundreds of meters, has been called into question with
the discovery of fast-moving rivers of water sliding beneath their base.
Scientists analyzing satellite data were astonished to discover the
size of the vast lakes and river systems flowing beneath the Antarctic
ice sheets, which may lubricate the movement of these glaciers as they
flow into the surrounding sea.
The discovery raises fresh
questions about the speed at which sea levels might rise in a warmer
world due to the rate at which parts of the ice sheets slide from the
land into the ocean, scientists said at the American Association for
the Advancement of Science in San Francisco.
"We've found that there
are substantial subglacial lakes under ice that's moving a couple of
meters per day. It's really ripping along. It's the fast-moving ice
that determines how the ice sheet responds to climate change on a short
timescale," said Robert Bindschadler, a Nasa scientist at the Goddard
Space Flight Centre in Maryland, one of the study's co-authors.
"We aren't yet able
to predict what these ice streams are going to do. We're still learning
about the controlling processes. Water is critical, because it's essentially
the grease on the wheel. But we don't know the details yet," Dr
Bindschadler said. "Until now, we've had just a few glimpses into
what's going on down there. This is the most complete picture to date
about what's going on," he said.
The findings, to be published
in the journal Science, came from satellite surveillance of the surface
elevation of the ice sheets, which found that they rise or lower depending
on the amount of water flowing between the base of the ice sheet and
the rock beneath.
The scientists identified
many regions of the ice sheet either rose or deflated between 2003 and
2006 as a result of water movements below. Water would be capable of
this because it is highly pressurized under the weight of the overlying
ice, they said.
Glaciologists have known
for some time that water exists under the Antarctic ice sheets - which
can be hundreds of meters thick - but they were surprised to find how
much water is involved and the speed at which it moves from one subglacial
reservoir to another, said Helen Fricker at the Scripps Institution
of Oceanography in San Diego.
"We didn't realize that
the water under these ice streams was moving in such large quantities,
and on such short time scales. We thought these changes took place over
years and decades, but we are seeing large changes over months. The
detected motions are astonishing in magnitude, dynamic nature and spatial
extent," Dr Fricker said.
The West Antarctic ice sheet
is the second biggest on the continent, and the rate at which ice flows
from it to the Ross ice shelf, and then ultimately into the sea, is
critical in assessing the likely impact of climate change on global
The study provides evidence
that subglacial water is stored in a linked system of reservoirs underneath
the ice and can move quickly into and out of those reservoirs. This
activity may play a major role in controlling the rate at which ice
moves off the continent, Dr Fricker said.
"The links between ice
stream activity and the climate are not well understood. To predict
how the ice sheets might respond to global warming, this new information
is vital as it gives us a more complete picture of what is happening
under the ice," she said.
The study was conductedusing
the Icesat satellite. It carries a laser altimeter instrument to detect
changes as small as 1.5 centimeters in the elevation of the ice sheet's
surface, from an orbit of 400 miles above the earth. "From 600
kilometers up in space, we were able to see small portions of the ice
sheet rise and sink," Dr Bindschadler said.
©Copyright 2007 Independent/UK
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