NASA - National Aeronautics and Space Administration

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.

Below are images related to the release:

	Figure 1: ICESat measures the distances to the top of the snow cover and to the sea surface. The difference between the two quantities gives the total “freeboard” measurement; that is, the amount of ice above the water line relative to the local sea level. Credit: Courtesy of Norbert Untersteiner, University of Washington > Larger image
	Figure 2: This schematic shows the geometric relationship between freeboard (the amount of ice above the water line), snow depth, and ice thickness. Buoyancy causes a fraction (about 10 percent) of sea ice to stick out above the sea surface. By knowing the density of the ice and applying “Archimedes’ Principle” -- an object immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object -- the total thickness of the ice can be calculated. Credit: Ron Kwok, NASA/JPL > Larger image
	Figure 3: ICESat measurements of the distribution of winter sea ice thickness over the Arctic Ocean between 2004 and 2008, along with the corresponding trends in overall, multi-year and first-year winter ice thickness. Credit: Ron Kwok, NASA/JPL > Larger image
	Figure 4: ICESat measurements of winter multi-year ice cover in the Arctic Ocean between 2004 and 2008, along with the corresponding downward trend in overall winter sea ice volume, and switch in dominant ice type from multi-year ice to first-year ice. Credit: Ron Kwok, NASA/JPL > Larger image

Supplemental Imagery

	Data visualization of Arctic sea ice thickness, as measured by ICESat, shows the decline of the thickest ice (white, 4 to 5 meters thick) and increase in thinner ice (deep blue, 0 to 1 meter) from 2003 to 2008. Credit: NASA Goddard's Scientific Visualization Studio > View Quicktime video > View color bar
	Data visualization of ice thickness, as measured by ICESat, shows the yearly growth (winter) and retreat (fall) of ice in the Arctic Ocean. Credit: NASA Goddard's Scientific Visualization Studio > View Quicktime video > View color bar

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The above data visualizations show a time series of Arctic sea ice thickness made by ICESat from 2003 to 2008. White patches are 4 to 5 meters thick; deep blue patches are 0 to 1 meter. Credit: NASA Goddard's Scientific Visualization Studio 2003 | 2004 | 2005 | 2006 | 2007 | 2008 > View color bar

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Related Links

> Satellites Show Arctic Literally on Thin Ice (Feature Story)
> Arctic Sea Ice Reaches Lowest Coverage For 2008
> NSIDC Arctic Sea Ice News and Analysis
> NASA and the International Polar Year
> ICESat