Download Arctic`s Biggest Ice Shelf, a Sentinel of Climate Change, Cracks Apart

Arctic's Biggest Ice
Shelf, a Sentinel of
Climate Change, Cracks
Apart
The breakup is apparent
evidence of global warming. It
also has drained a freshwater
lake containing a rare
ecosystem.
By Usha Lee McFarling
Times Staff Writer
September 23, 2003
The largest ice shelf in the Arctic — an 80-footthick slab of ice nearly the size of Lake Tahoe —
has broken up, providing more evidence that the
Earth's polar regions are responding to ongoing and
accelerating rates of climatic change, researchers
reported Monday.
The Ward Hunt ice shelf, located 500 miles from
the North Pole on the edge of Canada's Ellesmere
Island, has broken into two main parts and a series
of ice islands. A massive freshwater lake long held
back by the ice has drained away.
"Large blocks of ice are moving out. It's really a
breakup," said Warwick Vincent, a professor of
biology at Laval University in Quebec and coauthor of the report, which will be published in an
upcoming issue of the journal Geophysical Review
Letters. "We'd been measuring incremental changes
each year. Suddenly in one year, everything
changed."
While far larger shelves of ice have cracked off the
edges of Antarctica, this is the largest ice separation
in the Arctic, occurring in an area of the eastern
Arctic long thought to be more protected against the
gradual warming of the planet.
"This type of catastrophic [event] is quite
unprecedented," said Martin Jeffries, a professor of
geophysics at the University of Alaska Fairbanks
and co-author of the report.
Because of their longevity and sensitivity to
temperature, ice shelves are considered "sentinels of
climate change." In recent years, scientists have
seen ice shelves the size of Rhode Island break off
of western Antarctica as it warms and have
measured glaciers' retreat in response to warmer
temperatures throughout the western Arctic.
Weather data recorded at the nearby military station
Alert on Ellesmere Island show that temperatures
there have been warming since 1967 at the same
rate as in western Antarctica: about one degree
Fahrenheit per decade. The average July
temperature of recent years of 34 degrees was above
the temperature — 32 degrees — at which ice
shelves are known to break up.
The researchers said they considered the weakening
of the ice additional evidence of climate change in
the high Arctic and said the report fit with studies
that show global warming trends are connected to
the human production of greenhouse gases. Those
trends have been seen first and amplified in the
Arctic.
But they said other factors, including ocean
circulation and atmospheric patterns that can last for
decades, could be contributing to the changes in the
ice.
"The picture is a little murky," Jeffries said.
Jeffries, who has worked on the region's ice sheets
for two decades, said the ice appears to have
thinned dramatically in that time. The Ward Hunt
ice shelf was measured at 150 feet thick in 1980 and
now appears to be less than half that in some places.
The ice shelf has lost 90% of its area since 1907,
when explorer Robert E. Peary crossed it on his way
to the North Pole and complained bitterly about its
undulating terrain.
Researchers were lucky to catch the breakup in such
a remote and relatively unstudied area. Derek
Mueller, a graduate student of Vincent's, had
reached the ice shelf by helicopter last summer to
study the strange microbes living there when he saw
that the massive cracks extended all the way
through the ice.
Using a satellite phone, he called Vincent. Canada's
RADARSAT satellite then captured fresh images of
the ice shelf as it was breaking up.
Vincent is very concerned about the ecosystem he
and his students were studying. It has basically been
flushed out to sea. The weakening and cracking of
the ice shelf allowed a freshwater lake that had been
dammed behind the ice to drain suddenly.
The ice shelf kept about 140 feet of freshwater
pooled atop 1,200 feet of denser seawater. The
layers of fresh and salty water supported an
ecosystem of strange microbes, or extremophiles,
that are of particular interest to scientists trying to
understand the limits of life on Earth and in outer
space.
"The whole lake just drained. It just disappeared
entirely," Vincent said. "We're at a point where
we're starting to lose these unique cryo-ecosystems
of the north before we can understand them."
Other researchers are concerned about the
increasing amount of fresh water pouring into the
Arctic Ocean from breaking ice shelves, melting
glaciers and rain-swollen rivers.
Cold, salty water in the Arctic and North Atlantic
oceans plays a major role in driving ocean currents
that transport heat around the globe.
One of the most important of these is the Gulf
Stream, which carries warm water up the East Coast
of the United States and across the Atlantic to
northern Europe.
In previous geological eras, warmer climates and
the release of freshwater lakes that had been
dammed by ice have caused this current to slow and
shut down, drastically cooling parts of Europe.
A study in the journal Science in December
reported massive amounts of fresh water entering
the Arctic Ocean from Russia's largest rivers, due to
increases in precipitation linked to warmer
temperatures.
If temperatures rise globally by several degrees in
the next century, as many scientists predict,
increased river runoff, melting of glaciers on
Greenland and melting of ice shelves "would bring
us well within the range of what models say could
be a serious disruption to ocean circulation," said
Bruce Peterson, a senior scientist at the Marine
Biological Laboratory in Woods Hole, Mass.
While the amount of fresh water released from the
breaking of the Ward Hunt ice shelf is relatively
small, some scientists say it is part of a larger
pattern of freshening of ocean waters that could
prove dangerous in the future.
"The question is, at what point do those currents
become unhappy?" said Richard Alley, a professor
of geosciences at Penn State University and an
expert on ice sheets and abrupt climate change.
"We're just not good enough to tell right now."