A new NASA study has found that in 2005 the Arctic replaced very little of the thick sea ice it normally loses and replenishes each year. Replenishment of this thick, perennial sea ice each year is essential to the maintenance and stability of the Arctic summer ice cover.

The findings complement a NASA study released in fall 2006 that found a 14-percent drop in this perennial ice between 2004 and 2005. The lack of replenishment suggests that the decline may continue in the near future.

Perennial ice coverage fluctuates seasonally for two reasons: summer melting and the transport of ice out of the Arctic. When perennial ice, which is three or more meters (10 or more feet) thick, is lost in these ways, new, thinner, first-year seasonal ice typically replaces it. Some of this seasonal ice melts in the following summer, and some is thick enough to survive and replenish the perennial ice cover.

“Recent studies indicate Arctic perennial ice is declining seven to 10 percent each decade,” explained 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.”

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