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----- Original Message -----
From: NASA Jet Propulsion Laboratory
To: Ronaldo Pedrao
Sent: Tuesday, July 07, 2009 4:42 PM
Subject: New NASA Satellite Survey Reveals Dramatic Arctic Sea Ice Thinning






Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@...

Steve Cole 202-358-0918
NASA Headquarters, Washington
Stephen.e.cole@...

NEWS RELEASE: 2009-107
July 7, 2009

New NASA Satellite Survey Reveals Dramatic Arctic Sea Ice Thinning

PASADENA, Calif. – Arctic sea ice thinned dramatically between the
winters of 2004 and 2008, with thin seasonal ice replacing thick older ice as
the dominant type for the first time on record. The new results, based on data
from a NASA Earth-orbiting spacecraft, provide further evidence for the rapid,
ongoing transformation of the Arctic's ice cover.

Scientists from NASA and the University of Washington in Seattle conducted
the most comprehensive survey to date using observations from NASA's Ice, Cloud
and land Elevation Satellite, known as ICESat, to make the first basin-wide
estimate of the thickness and volume of the Arctic Ocean's ice cover. Ron Kwok
of NASA's Jet Propulsion Laboratory in Pasadena, Calif., led the research team,
which published its findings July 7 in the Journal of Geophysical
Research-Oceans.

The Arctic ice cap grows each winter as the sun sets for several months
and intense cold ensues. In the summer, wind and ocean currents cause some of
the ice naturally to flow out of the Arctic, while much of it melts in place.
But not all of the Arctic ice melts each summer; the thicker, older ice is more
likely to survive. Seasonal sea ice usually reaches about 2 meters (6 feet) in
thickness, while multi-year ice averages 3 meters (9 feet).

Using ICESat measurements, scientists found that overall Arctic sea ice
thinned about 0.17 meters (7 inches) a year, for a total of 0.68 meters (2.2
feet) over four winters. The total area covered by the thicker, older
"multi-year" ice that has survived one or more summers shrank by 42 percent.

Previously, scientists relied only on measurements of area to determine
how much of the Arctic Ocean is covered in ice, but ICESat makes it possible to
monitor ice thickness and volume changes over the entire Arctic Ocean for the
first time. The results give scientists a better understanding of the regional
distribution of ice and provide better insight into what is happening in the
Arctic.

"Ice volume allows us to calculate annual ice production and gives us an
inventory of the freshwater and total ice mass stored in Arctic sea ice," said
Kwok. "Even in years when the overall extent of sea ice remains stable or grows
slightly, the thickness and volume of the ice cover is continuing to decline,
making the ice more vulnerable to continued shrinkage. Our data will help
scientists better understand how fast the volume of Arctic ice is decreasing and
how soon we might see a nearly ice-free Arctic in the summer."

In recent years, the amount of ice replaced in the winter has not been
sufficient to offset summer ice losses. The result is more open water in summer,
which then absorbs more heat, warming the ocean and further melting the ice.
Between 2004 and 2008, multi-year ice cover shrank 1.54 million square
kilometers (595,000 square miles) -- nearly the size of Alaska's land area.

During the study period, the relative contributions of the two ice types
to the total volume of the Arctic's ice cover were reversed. In 2003, 62 percent
of the Arctic's total ice volume was stored in multi-year ice, with 38 percent
stored in first-year seasonal ice. By 2008, 68 percent of the total ice volume
was first-year ice, with 32 percent multi-year ice.

"One of the main things that has been missing from information about what
is happening with sea ice is comprehensive data about ice thickness," said Jay
Zwally, study co-author and ICESat project scientist at NASA's Goddard Space
Flight Center in Greenbelt, Md. "U.S. Navy submarines provide a long-term,
high-resolution record of ice thickness over only parts of the Arctic. The
submarine data agree with the ICESat measurements, giving us great confidence in
satellites as a way of monitoring thickness across the whole Arctic Basin."

The research team attributes the changes in the overall thickness and
volume of Arctic Ocean sea ice to the recent warming and anomalies in patterns
of sea ice circulation.

"The near-zero replenishment of the multi-year ice cover, combined with
unusual exports of ice out of the Arctic after the summers of 2005 and 2007,
have both played significant roles in the loss of Arctic sea ice volume over the
ICESat record," said Kwok.

For images of the Arctic sea ice decline, visit:
http://www.nasa.gov/topics/earth/features/icesat-20090707.html .

For more information about ICESat, visit: http://icesat.gsfc.nasa.gov .

For more information about NASA and agency programs, visit:
http://www.nasa.gov .

JPL is managed for NASA by the California Institute of Technology in
Pasadena.




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