The Arctic Ocean's perennial sea ice, which survives the summer melt season and remains year-round, shrank abruptly by 14 percent between 2004 and 2005, according to a newly published study. Researchers found that the loss of perennial ice in the East Arctic Ocean, above Europe and Asia, neared 50 percent during that time as some of the ice moved to the West Arctic Ocean, above North America.

The overall decrease in winter Arctic perennial sea ice totaled 280,000 square miles - an area the size of Texas. Perennial ice can be 10 feet thick, or more. It was replaced in the winter by new, seasonal ice, which was only about 1 foot to 7 feet thick and more vulnerable to summer melt. The research was published in early September in the journal Geophysical Research Letters.

The decrease in perennial ice raises the possibility that Arctic sea ice will retreat to another record low extent this year. This follows four summers of very low ice-cover, as observed by active and passive microwave instruments aboard NASA's Quick Scatterometer (QuikSCAT) satellite, the researchers report. A team of seven scientists, led by Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena, Calif., used satellite data to measure the extent and distribution of perennial and seasonal sea ice in the Arctic. While the total area of all Arctic sea ice was stable in winter, the distribution of seasonal and perennial sea ice changed significantly.

"Recent changes in Arctic sea ice are rapid and dramatic," reveals Nghiem. "If the seasonal ice in the East Arctic Ocean were to be removed by summer melt, a vast ice-free area would open up. Such an ice-free area would have profound impacts on the environment, as well as on marine transportation and commerce."

The researchers are examining what caused the rapid decrease in the perennial sea ice. Data from the National Centers for Environmental Prediction in Boulder, Colo., suggest that winds pushed perennial ice from the East to the West Arctic Ocean and moved ice through the Fram Strait, a deep passage between Greenland and Spitsbergen, Norway. This movement of ice out of the Arctic is a different mechanism for ice shrinkage than the melting of Arctic sea ice, but it produces the same result - a reduction in the amount of perennial Arctic sea ice.

The researchers say that if the sea ice cover continues to decline, the surrounding ocean will warm, further accelerating summer ice melts and impeding fall freeze-ups. This longer melt season will, in turn, further diminish the Arctic ice cover.

Nghiem cautions that the recent Arctic changes are not well understood and that many questions remain. "It's vital that we continue to closely monitor this region, using both satellite and surface-based data," he notes.