http://news.bbc.co.uk/2/hi/science/nature/3132074.stm
Last Updated: Tuesday,
23 September, 2003, 11:23 GMT 12:23 UK
BBC
[ Map
showing location of Ward Hunt Ice Shelf ... ]
Arctic
ice shelf splits
The largest ice shelf in the Arctic has fractured, releasing
all the water from the freshwater lake it dammed.
The Ward Hunt Ice Shelf
is located on the north coast of
Ellesmere Island in Canada's Nunavut territory.
The huge mass of floating
ice, which has been in place for at
least 3,000 years, is now in two major pieces.
The scientists who
report the break-up in the journal Geophysical
Research Letters (GRL) say it is further evidence of ongoing and
accelerated climate change in the north polar region.
The researchers - Warwick
Vincent and Derek Mueller of Laval University
in Quebec City, Canada; and Martin Jeffries of the University
of Alaska
Fairbanks, US - have been studying the shelf onsite and through
satellite
radar imagery and helicopter overflights.
Lost water
The Ward Hunt Ice Shelf,
which is 443 square kilometres in size,
now has a major crack that runs right through it from north to
south.
The scientists say
the fracturing - which has been developing since
the spring of 2000 - is the end result of a three-decade-long
decline.
"We're now seeing
some very extensive fractures in it that extend
many kilometres horizontally across the ice-shelf; and they extend
all the way through from the top to the bottom, many tens of metres
through the ice shelf. And we've never seen fractures like this,"
Dr Jeffries told the BBC.
They warn that major
free-floating ice islands could pose a danger
to shipping and to drilling platforms in the Beaufort Sea.
The immediate consequence
of the rupture has been the loss of almost
all of the freshwater from the Northern Hemisphere's largest epishelf
lake (a body of mostly freshwater trapped behind an ice shelf).
The freshwater lay
in the 30-kilometre- [20-mile] long Disraeli Fiord.
At its deepest, the
freshwater measured 43 metres [140 feet], and
sat atop 360 metres [1,200 feet] of denser ocean water.
Other worlds
The loss of fresh and
brackish water has changed the environment
for the microscopic animals and algae living in the area.
"These are very
rare and unusual ecosystems and they have been
studied as possible analogues for life on a colder Earth and life
on the planets," Dr Jeffries said.
"And if we are
losing them, we are losing the opportunity to study
life earlier in Earth history and elsewhere in the Solar System."
Scientists monitor
continuously ice-shelf development in both
the Arctic and the Antarctic.
In the southern polar
region, recent times have witnessed some
dramatic changes.
Last year, the 3,250-square-km
Larsen B Ice Shelf on the Antarctic
Peninsula shattered over a period of a month into thousands of
icebergs.
The peninsula is one
of the three fastest-warming regions on Earth
- temperatures have gone up 2.5 degrees in 50 years.
Global change
Mueller, Vincent, and
Jeffries say their calculations suggest changes
of a similar nature have been taking place in the Ellesmere Island
area.
A century ago, the
entire northern coast of the island was reported
to be fringed with a continuous ice shelf. About 90% of that ice
area
had been lost by 1982, the scientists say.
The precise timing
of the break-up of the remnant Ward Hunt Ice Shelf
may have been influenced by freeze-thaw cycles, wind, and tides,
they tell GRL.
Other factors may include
changes in Arctic Ocean temperature,
salinity, and flow patterns, they add.
"Computer models
show quite convincingly that global climate
change would be manifested first and amplified in the polar
regions and in particular in the Arctic," Dr Jeffries said.
"Our observations
at Ward Hunt Ice Shelf fit in with a broader
picture of Arctic change which fits in with our understanding
of how the Arctic climate would respond to global change."
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