After 10,000 year absence, wildfires have returned to Arctic tundra

The huge stock of carbon contained in tundra could increase atmospheric CO2 drastically, when released by a fire.

After a 10,000-year absence, wildfires have returned to the Arctic tundra, and a new study shows their impact could extend far beyond the areas blackened by flames. Researchers determined that a 400-square-mile tundra fire on the North Slope of Alaska’s Brooks Range released 2.1 million metric tons of soil-bound carbon into the atmosphere – roughly twice the amount of greenhouse gases the city of Miami puts out in a year.

University of Florida (UF) ecologist Michelle Mack said the fire under study – the 2007 Anaktuvuk River fire – released an amount of carbon significant enough to suggest that Arctic fires could impact the global climate. Findings of the study appear in the July 28, 2011, issue of the journal Nature.

A lightning strike caused this tundra fire in Noatak National Preserve. Image Credit: Western Arctic National Parklands

Alaskan tundra in August, near the tree line. Image Credit: travelinknu

Mack said:

The 2007 fire was the canary in the coal mine. In this wilderness, hundreds of miles away from the nearest city or source of pollution, we’re seeing the effects of a warming atmosphere. It’s a wakeup call that the Arctic carbon cycle could change rapidly, and we need to know what the consequences will be.

Smoke from the fire pumped greenhouse gases into the atmosphere, but that’s just one part of a tundra fire’s potential impact. The fire also consumed up to 30 percent of the insulating layer of organic matter that protects the permafrost beneath the tundra’s shrub- and moss-covered landscape.

Thick tundra beside a lake in Alaska. Image Credit: madpai

In a pine forest, fire would burn up leaf litter on the ground but not the soil beneath. Because the Arctic tundra has a carbon-rich peaty soil, however, the ground itself is combustible, and when the fire recedes, some of the soil is gone. In a double whammy, the vulnerable permafrost is not only more exposed but also covered by blackened ground, which absorbs more of the sun’s heat and could accelerate thawing.

Mack explained:

When the permafrost warms, microbes will begin to decompose that organic matter and could release even more carbon that’s been stored in the permafrost for hundreds or thousands of years into the atmosphere. If that huge stock of carbon is released, it could increase atmospheric carbon dioxide drastically.

The Alaska tundra in June. Image Credit: madpai

The study shows how isolated fires can have a widespread impact, said University of Alaska biology professor Terry Chapin:

When you think about the massive carbon stocks and massive area of tundra throughout the world, and its increasing vulnerability to fire as climate warms, it suggests that fire may become the dominant factor that governs the future carbon balance of this biome. The paper by Michelle and her colleagues raises this possibility for the first time. It presents a very different perspective on the way in which climate change may affect this biome in the future.

Using radiocarbon dating, co-author Schuur and researchers from the University of Alaska at Fairbanks, the Alaska Fire Service and Woods Hole Marine Biological Laboratory found that carbon up to 50 years old had been burned in the 2007 fire.

Mack hopes her findings will open a dialogue about how tundra fires are managed. Because the Anaktuvuk River fire was in a wilderness area, it was not suppressed or contained. With better data on the long-term impact of tundra fire on global climate warming, Mack says, putting out these fires might become more of a priority. Mack said:

This fire was a big wakeup call, and it can happen again, not just in Alaska but in other parts of the Arctic, like Canada and Russia. Suppressing a fire in the wilderness is costly, but what if the fire causes the permafrost to melt? We need to have that discussion.

Image Credit: alaskanent

Bottom line: University of Florida ecologist Michelle Mack and a team of scientists studied the Anaktuvuk River fire on the arctic tundra of Alaska, and determined that the amount of soil-bound carbon released in the fire could accelerate global warming. The study appears in the July 28, 2011 issue of Nature.

Via University of Florida News

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