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Scientists Find Increase in Melting of Older Sea Ice
A mosaic of satellite images show the movement of fragmented ice away from ice edge, which scientists use to track the loss of multiyear ice due to melt.
Credit: NASA Earth Observatory

The loss of older sea ice that has built up over several years in the Arctic basin has been fully measured for the first time.

The loss of this ice has been determined to be the result of melting as opposed to removal from cold, polar waters by wind, a new study finds.

Scientists track the annual cycle of Arctic sea ice coverage as it melts through the summer to reach a minimum extent each September, before refreezing through fall and winter. Much of the ice that melts then is called seasonal ice, meaning that it forms and melts within the year. So-called "multiyear" ice tends to be thicker and more resistant to the summer melt season.

But since the start of the satellite record in 1979, scientists have observed the disappearance of older multiyear sea ice along with a steady decline in overall Arctic sea ice coverage. Arctic sea ice extent after the 2010 summer melt season was the third-lowest on record.

Some scientists suspected that this loss was due entirely to wind pushing the ice out of the Arctic Basin a process known as "export."

A recent study from NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., used satellite data to explain the role of export versus melt within the Arctic Ocean. The research showed that between 1993 and 2009, 336 cubic miles (1,400 cubic kilometers) of ice was lost due to melt.

"The paper shows that there is indeed melt of old ice within the Arctic basin and the melt area has been increasing over the past several years," said JPL study member Ron Kwok. "The story is always more complicated there is melt as well as export but this is another step in calculating the mass and area balance of the Arctic ice cover."

The results will impact researchers' understanding of how Arctic sea ice is redistributed, where melt occurs in the Arctic Ocean and how the ocean, ice and atmosphere interact as a system to affect Earth's climate.

The findings were published October 2010 in the journal Geophysical Research Letters.