NASA sea ice study may stir up climate models
- Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.
NASA ARCTIC SEA ICE STUDY MAY STIR UP CLIMATE MODELS
Contrary to historical observations, sea ice in the high Arctic
undergoes very small, back and forth movements twice a day, even in
the dead of winter. It was once believed ice deformation at such a
scale was almost non-existent.
According to a recent NASA-funded study, the finding is significant.
Such movements may substantially increase the production of new ice
and should be factored into Arctic climate models. The phenomenon of
short-period Arctic sea ice motion was investigated in detail in 1967
and has been the subject of numerous research studies since.
A 1978 study found short-period ice motions disappeared almost
entirely during the winter once the Arctic Ocean froze. A subsequent
investigation in 2002, conducted using measurements from ocean buoys
spaced hundreds of kilometers apart, found sea ice movement occurs
during all seasons.
Since buoy observations are poor for understanding short length-scale
motion and deformation, researchers Ron Kwok and Glenn Cunningham of
NASA's Jet Propulsion Laboratory, Pasadena, Calif., and William Hibler
III of the University of Alaska, Fairbanks, set out to examine the
phenomenon in greater detail.
The researchers used high-resolution synthetic aperture radar imagery
from Canada's RADARSAT Earth observation satellite, which can image
the region up to five times a day. Their findings were published
recently in Geophysical Research Letters. The researchers studied an
approximate 200 by 200 kilometer (124 by 124 mile) area in the Canada
Basin region of the high Arctic for about three weeks in May 2002
and in February 2003.
This region is representative of the behavior of the central Arctic
Ocean ice cover due to its location and thickness. The time frame was
selected because Arctic sea ice motion is least expected during those
times of year.
The study provided a more detailed picture of the phenomenon reported
in the 2002 buoy research. It found sea ice moved back and forth and
deformed slightly in a persistent 12-hour oscillating pattern. Subtle
motions triggered by the Earth's rotation rather than by tidal
movement likely caused the pattern. In the absence of external forces,
any object will move in a circular motion due to the Earth's rotation.
The researchers attributed the winter behavior of the ice cover, not
observed in studies before 1970, to either a previous lack of detailed
data or perhaps an indication of recent thinning of the Arctic ice cover.
"If Arctic pack ice is continually opening and closing during the
Arctic winter on a widespread basis, it could significantly increase
the rate of Arctic ice production and therefore increase the total
amount of ice in the Arctic," Kwok said. "A simple simulation of this
ice production process shows that it can account for an equivalent of
10 centimeters (4 inches) of ice thickness over six months of winter.
That's approximately 20 percent of the base growth of thick ice during
the central Arctic winter."
Kwok said current models of the dynamics of Arctic sea ice typically
don't take into account processes occurring at short, 12-hour time
scales, and the impact of such processes must be assessed. "As climate
models continue to get better and better, it becomes increasingly
important to understand the physics of small-scale processes so that
we can understand their large-scale consequences," he said. "If these
Arctic sea ice processes are indeed important over the entire Arctic
basin, their contribution to the overall amount of ice in the Arctic
should be included in simulations of the interactions that take place
between the Arctic's ice, ocean and atmosphere to create the overall
"If such oscillations in Arctic sea ice increase as the sea ice cover
thins due to warmer atmospheric temperatures, then this mechanism of
ice production may actually serve to slow down the overall depletion
of ice in the Arctic Ocean," he added. Kwok said other parts of the
Arctic Ocean would be analyzed in future studies.
For information about the study on the Internet, visit: