July 27, 2011

Tundra Fire Releases 50 Years Of Carbon Into The Atmosphere

Scientists say a tundra fire in the circumpolar arctic released about as much carbon into the atmosphere as the tundra has stored in the previous 50 years.

The study, published in the July 28 issue of Nature, of the Anaktuvuk River fire on Alaska's North Slope revealed just how quick a single tundra fire can offset or reverse a half-century worth of soil-stored carbon.

"Fire has been largely absent from tundra for the past 11,000 or so years, but the frequency of tundra fires is increasing, probably as a response to climate warming," said co-author Syndonia "Donie" Bret-Harte, an ecosystem ecologist at the University of Alaska Fairbanks Institute of Arctic Biology, said in a press release.

The fire burned 401 square miles and released over 2.3 million tons of carbon into the atmosphere.  Radiocarbon dating of the soils revealed the maximum age of the soil emitted from the fire was 50 years.

"The amount of carbon released into the atmosphere from this fire is equivalent to the amount of carbon stored by the global tundra biome," lead author Michelle Mack, a biologist from the University of Florida said in a press release. "This was a boreal forest-sized fire."

Cool, wet soils underlain by permafrost are thought to restrict fires to aboveground plants and ground-level plant litter leaving the carbon stored in soils intact.  As arctic summers get warmer and dryer, so do the soils, which are highly flammable.

"If the frequency of these fires remains at long intervals, 80 to 150 years, then the tundra has time to recover," Bret-Hart said in a press release. "If these fires occur more frequently, say every 10 years or so, then the landscape cannot recover."

The Anaktuvuk River fire was started by a lightning strike in July 2007. 

"Normally we would expect the fire to go out in the moist soil, but this summer was so dry that the fire didn't go out and strong winds in September caused it to burn a very large area," Bret-Harte, who noted that 40 percent of the fire was classified as a severe burn "“ high for a tundra fire, said in a press release.

Fire removes organic material that insulates permafrost from warm summer temperatures.  Insufficient insulation can lead to thawing permafrost, destabilization of the ground surface and exposure of deep soil carbon to decomposition and release into the atmosphere.

The authors said their observations of carbon loss from the Anaktuvuk River fire shed more like that on the idea that tundra fires have the potential to release large amounts of carbon and decrease landscape carbon stocks.


Image Caption: Aerial image of the Anaktuvuk River fire, North Slope, Alaska on August 16, 2007. Credit: Michael D. Flemin/Stinger Ghaffarian Technologies


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