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In 2007, the largest recorded tundra fire in the Arctic released approximately as much carbon into the atmosphere as the tundra has stored in the previous 50 years.

A study of the Anaktuvuk River fire on Alaska’s North Slope revealed how rapidly a single tundra fire can offset or reverse a half-century worth of soil-stored carbon. The study’s results are published in the July 28 issue of the journal Nature.

Tundra soils store huge amounts of carbon hundreds to thousands of years old. Layers of organic soil insulate the permanently frozen ground, called permafrost, below and restrict fires to aboveground plants and plant litter leaving the carbon stored in soils relatively intact.

As arctic summers get warmer and dryer, so too do the soils, which are highly flammable and able to burn more deeply when dry. This allows fires to burn more deeply into the ground. When aboveground plant materials burn, that not only releases carbon into the atmosphere, it also speeds thawing of the permafrost below. The once-frozen organic material in the thawing permafrost then begins to decompose, releasing additional carbon and amplifying climate warming.

“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. “If the frequency of these fires remains at long intervals, 80 to 150 years, then the tundra has time to recover. If these fires occur more frequently, say every 10 years or so, then the landscape cannot recover.”

The Anaktuvuk River fire burned 401 square miles, an area roughly the size of Cape Cod and visible from space, and released more than 2.3 million tons of carbon into the atmosphere. Radiocarbon dating of the soils revealed the maximum age of the soil carbon 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,” said lead author Michelle Mack, a biologist from the University of Florida. “This was a boreal forest-sized fire.”

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,” said Bret-Harte. The wall of smoke from the fire was visible 15 miles south at the Toolik Field Station, where the scientists were working.

In addition to the direct release of carbon into the atmosphere, tundra fires are important because of the potential effects on global climate change. “These fires could be a radical and very rapid positive feedback to atmospheric carbon dioxide,” said Mack.

According to the authors, their observations of carbon loss from the Anaktuvuk River fire support the idea that tundra fires have the potential to release large amounts of carbon and decrease landscape carbon stocks, having an immediate impact on atmospheric carbon and climate.

 

University of Alaska Fairbanks Institute of Arctic Biology