Global warming may not be the only reason Arctic ice is rapidly melting, a new study suggests.
A University of Washington team, analyzing data from a NASA satellite and NOAA deep-sea pressure gauges, concludes that the Arctic Ocean is undergoing a circulation reversal.
The reversal appears to be tied to a decade-long atmospheric cycle known as the Arctic Oscillation, which could explain part of the past two decades' dramatic fluctuations in sea ice.
"Our study confirms many changes seen in upper Arctic Ocean circulation in the 1990s were mostly decadal in nature, rather than trends caused by global warming," said study team leader James Morison, according to a NASA press release.
Morison's researchers say the data show that between 2002 and 2006, Arctic water circulation began a process of shifting from a counterclockwise to a clockwise pattern.
A clockwise pattern dominated before around 1990, when the recent counterclockwise pattern set in, the study concludes.
"While some 1990s climate trends, such as declines in Arctic sea ice extent, have continued, these results suggest at least for the 'wet' part of the Arctic — the Arctic Ocean — circulation reverted to conditions like those prevalent before the 1990s," Morison said.
Arctic sea ice minimums varied greatly during the first part of 1990s, then declined gradually before stabilizing somewhat around 2000.
But this past summer saw a sharp reduction, with only about half as much ice in August and September as was recorded during the 1980s.