According to a National Aeronautics and Space Administration report published April 3, a NASA study has found that in 2005 very little of the thick Arctic sea ice lost in summer was replenished during the winter.
“Replenishment of this thick, perennial sea ice each year is essential to the maintenance and stability of the Arctic summer ice cover,” the report says.
Using satellite radar data NASA had previously discovered a 14 percent decline in perennial ice cover between 2004 and 2005 — the lack of replenishment suggests that this declining trend will continue, the report says. Some perennial ice, 10 feet or more thick, typically disperses during summer melting, but new, thinner ice forms during the following winter. Survival of some new ice through the next summer then replenishes the perennial ice cover.
“Recent studies indicate Arctic perennial ice is declining 7 to 10 percent each decade,” said Ron Kwok of NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Our study gives the first reliable estimates of how perennial ice replenishment varies each year at the end of summer. The amount of first-year ice that survives the summer directly influences how thick the ice cover will be at the start of the next melt season.”
Air movement variationsKwok suggested that variations during the 1990s in a large-scale air movement pattern known as the North Atlantic Circulation may have provided the trigger for the decline that is now seen in perennial ice — changing air circulation patterns appear to have caused a large increase in Arctic ice export.
Kwok said that unusual wind conditions in the Fram Strait on the northeast side of Greenland had also pushed ice out of the Arctic at an exceptionally high rate in 2005. And a study of Arctic temperature records back to 1958 found a warming trend that accelerated after the mid-1980s, a trend that suggests the likely continuing decline of perennial ice. Abnormally warm conditions in both the winters and the summers prior to the fall of 2005 have contributed to the recent loss of ice, Kwok said.
“We’re seeing a decreasing trend in perennial ice coverage,” Kwok said. “Our study suggests that, on average, the area of seasonal ice that survives the summer may no longer be large enough to sustain a stable perennial ice cover, especially in the face of accelerating climate warming and Arctic sea ice thinning.”