Largest Arctic Ice Shelf No More

Elias Sinderson elias at cse.ucsc.edu
Wed Sep 24 09:34:55 PDT 2003


For almost as long s I am able to remember discussion about global 
warming, there have been naysayers arguing for more research before 
passing legislation to restrict emissions that scientists thought were 
responsible. Several years back, just afdter Bush took office, the US 
pulled out of the Kyoto accords, widely regarded as the most important 
environmental protection agreement ever - limiting the amount of 
greenhouse gasses that countries can release into the atmosphere. 
Thankfully, other concerned parties signed without the US, leaving 
America with the equivalent of international egg on its face. Sad, 
really, when you think about it.

I read the following article this morning with a sense of loss. Not that 
I planned to vacation to the Arctic, or visit this ice shelf with my 
kids or anything, but the changes we are making to the planet are, in 
many ways, irreversible. I have read with great fascination the results 
of studies on the fragile ecosystems in large arctic lakes, and this 
lake in particular, but it is no more. All we can do now is study how 
this damage will affect what was once a relatively pristine environment 
that has now been broken. The long term records of climate change, and 
the deliterious effects of global warming, are building  - how much more 
research is really needed before the US changes course?


Elias
_________________________________________

September 22, 2003
Largest Arctic Ice Shelf Breaks Up, Draining Freshwater Lake
<http://earthobservatory.nasa.gov/Newsroom/NasaNews/2003/2003092215961.html>

The largest ice shelf in the Arctic has broken, and scientists who have 
studied it closely say it is evidence of ongoing and accelerated climate 
change in the north polar region. The Ward Hunt Ice Shelf is located on 
the north coast of Ellesmere Island in Canada's Nunavut territory and 
its northernmost national park. This ancient feature of thick ice 
floating on the sea began forming some 4,500 years ago and has been in 
place for at least 3,000 years.

Warwick Vincent and Derek Mueller of Laval University in Quebec City, 
Quebec, and Martin Jeffries of the University of Alaska Fairbanks have 
studied the Ward Hunt Ice Shelf on site and through RADARSAT imagery and 
helicopter overflights. They report in the journal Geophysical Research 
Letters that a three decade long decline in the Ward Hunt Ice Shelf 
culminated in its sudden break-up between 2000 and 2002. It fragmented 
into two main parts with many additional fissures. It also calved a 
number of ice islands, some of which are large enough to pose a danger 
to shipping and to drilling platforms in the Beaufort Sea.

An immediate consequence of the ice shelf's rupture was the loss of 
almost all of the freshwater from the northern hemisphere's largest 
epishelf lake, which had been dammed behind it in 30 kilometer [20 mile] 
long Disraeli Fiord. An epishelf lake is a body of mostly freshwater 
trapped behind an ice shelf. The freshwater layer in the Disraeli Fiord 
measured 43 meters [140 feet] in depth and lay atop 360 meters [1,200 
feet] of denser ocean water. The loss of fresh and brackish water has 
affected a previously reported unique biological community, consisting 
of both freshwater and marine species of plankton. The breakup of the 
ice shelf has also reduced the habitat available for cold-tolerant 
communities of microscopic animals and algae that live on the upper ice 
surface.

A century ago, the entire northern coast of Ellesmere Island, the 
northernmost land mass of North America, was fringed with a continuous 
ice shelf, as explorer Robert E. Peary reported in 1907. About 90 
percent of the ice area had been lost, through calving from its northern 
edge, by 1982, the authors say. Since then, the remnant ice shelves, 
including Ward Hunt, had remained relatively stable until April 2000, 
when RADARSAT's synthetic aperture radar revealed the first sign of 
cracking. Subsequent imagery showed the crack extending in length, and 
in 2002, observations from a helicopter showed that the fracture now 
extended fully from the fiord to the open ocean, breaking the ice shelf 
into two major parts and many smaller ones.

In July and August 2002, Vincent's team landed on the Ward Hunt Ice 
Shelf to make direct measurements of its break-up. They found cracks 
that separated the central part of the shelf into free floating ice 
blocks. These were held in place by parts of the ice shelf that remained 
intact. Then, in August 2002, the northern edge of the ice shelf calved, 
resulting in the loss of six square kilometers [two square miles] of ice 
islands and 20 square kilometers [eight square miles] of thick 
multi-year sea ice attached to the ice shelf. The remaining ice shelf 
may only be about half the thickness previously reported, the 
researchers say.

The scientists note that in the West Antarctic, atmospheric warming has 
been cited as the cause for ice shelf collapses. There, temperatures 
have risen by about one-half of a degree Celsius [one degree Fahrenheit] 
per decade over the past 60 years. On northern Ellesmere Island, the 
longest temperature records have been maintained at Alert, 175 
kilometers [109 miles] to the east of Disraeli Fiord.

At Alert, a temperature increase of just one-tenth of a degree Celsius 
[one-fifth of a degree Fahrenheit] per decade has been observed since 
1951. But during the period 1967 to the present, the temperature 
increase has been about four times that rate, about equal to that of 
Antarctica. The actual temperature on the ice shelf was measured in 2001 
and 2002 and correlated with the Alert data, in order to project 
backwards the ice shelf temperature. This yielded an average July 
surface temperature of 1.3 degrees Celsius [34 degrees Fahrenheit] for 
the years 1967-2002, which is well above the zero degrees Celsius [32 
degrees Fahrenheit] that is considered the critical threshold for ice 
shelf breakup in Antarctica, according to the researchers.

Mueller, Vincent, and Jeffries attribute the disintegration of the 
Ellesmere Ice Shelf and the breakup of the Ward Hunt Ice Shelf to the 
cumulative effects of long-term warming since the 19th century. The 
precise timing and pattern of fracturing of the climate-weakened ice 
shelf may have been influenced by freeze- thaw cycles, wind, and tides, 
they say. Other factors may include changes in Arctic Ocean temperature, 
salinity, and flow patterns, they add.

The research was supported by Canada's Natural Sciences and Engineering 
Research Council; Polar Continental Shelf Project, Parks Canada; NASA; 
and the Geophysical Institute and Alaska Satellite Facility, University 
of Alaska Fairbanks.

###
Contacts:

Harvey Leifert
American Geophysical Union
+1 (202) 777-7507
hleifert at agu.org <mailto:hleifert at agu.org>
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