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 6 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 Arctic climate.
"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.
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