Sept. 14 (Bloomberg) -- The Arctic's perennial sea ice lost an area the size of Texas last year, in a change that may have an impact on the environment and marine transport, NASA said.

About 720,000 square kilometers (288,000 square miles) of perennial ice, which normally doesn't melt during the summer, was lost from 2004 to 2005, scientists found using data from the National Aeronautics and Space Administration's QuickScat satellite, the agency said. The loss is additional to seasonal ice that is more vulnerable to melting during the summer.

``Recent changes in Arctic sea ice are rapid and dramatic,'' said Son Nghiem, who led the team of scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, in a statement e- mailed late yesterday. ``If the seasonal ice in the east Arctic Ocean were to be removed by summer melt, a vast ice-free area would open up.''

Scientists last year already reported that the extent of floating Arctic sea ice -- including both perennial and seasonal ice -- shrank to the lowest in at least a century. Further losses of sea ice may see the Arctic Ocean completely ice-free by 2100, the Boulder, Colorado-based U.S. National Snow and Ice Data Center said last year.

``Such an ice-free area would have profound impacts on the environment, as well as on marine transportation,'' Nghiem said. He warned that the changes aren't ``well understood,'' and that further study is ``vital.''

2005 Record

Nghiem's team found that total ice extent was stable over the winter, though the change in distribution between perennial and seasonal ice was marked.

Perennial sea ice can be 3 or more meters (10 or more feet) thick, while seasonal ice tends to measure between 0.3 and 2 meters, according to NASA. Across the Arctic, about 14 percent of the perennial ice was lost last year, with the proportion in the east Arctic Ocean rising to almost a half, the agency said.

``The decrease in the perennial ice raises the possibility that Arctic sea ice will retreat to another record low extent this year,'' NASA said. ``This follows a series of very low ice- cover years observed over the past four summers.''

Sea ice extent, the area of ocean covered by at least 15 percent ice, was about 5.32 million square kilometers last year, according to a five-day average ending Sept. 21, the National Snow and Ice Data Center said last year. That was the lowest extent ever observed during a satellite record stretching back to 1978, and meant ice coverage in 2005 was probably the lowest in at least a century, the center said.

Hunting Ground

The center's current online sea ice tracker shows coverage at just above last year's levels at the same date, having been below 2005's extent throughout June and July. The annual minimum coverage typically occurs toward the end of September, when last year's record was established. The center is due on Oct. 3 to provide an update of this summer's total melting.

The NSIDC warned last year that a continuation of the melting trend poses a risk both to the lifestyles of indigenous peoples of the Arctic, and to animals such as polar bears, which rely on the surface as their main habitat and hunting ground. A U.S. Minerals Management Service study presented in December indicated that polar bears were drowning as a consequence of having to swim farther in search of food.

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.

Last Updated: September 14, 2006 08:49 EDT