By Yereth Rosen
ANCHORAGE, Alaska (Reuters) - A wildfire that burned over 400 square miles of Alaska tundra in the scorching summer of 2007 poured as much carbon into the atmosphere as the entire Arctic normally absorbs each year, according to a new study in the scientific journal Nature.
The tundra fire, near the Anaktuvuk River of Alaska's North Slope, was considered an unprecedented event at the time. It was, by far, the largest single wildfire on treeless Arctic tundra ever recorded, and was twice as big as all previously recorded Alaska tundra fires combined.
But it may be an ominous sign of climate problems in the future, according to the study and the researchers who conducted it.
The study, published on Thursday, measured the volume of carbon emitted by the months-long fire -- although massive it covered only a tiny portion of the vast North Slope -- at 2.1 million metric tons.
"It was the same order of magnitude as what the Arctic takes up and stores in plant biomass," said Syndonia Bret-Harte of the Institute of Arctic Biology at the University of Alaska, Fairbanks, one of the study's authors.
That creates the potential for a "positive feedback" loop that would reinforce the warming trend in the far north, according to the study.
Repeated large fires might even cancel out any potential carbon-absorption benefits from increased plant growth in the Arctic that has been made possible by the region's warming climate, the researchers said.
Fires on the Arctic tundra are not unusual, but most blazes are very small and short-lived because of the cool climate and the dampness of the environment, Bret-Harte said.
The 2007 fire, however, occurred under extreme conditions -- an especially hot, dry year, marked by the smallest Arctic sea ice cover ever recorded by satellite, plus strong winds. The lightning-sparked blaze began in July of that year and smoldered for weeks before it was whipped up by winds in September, when tundra plants were dried out, she said.
All indications are that climate changes in the Arctic will make future fires more likely, Bret-Harte said. Lightning strikes on the North Slope have increased dramatically over the last 20 years, raising the potential for fire starts, while temperatures are rising, he said.
"The expectation would be that conditions that allowed that to happen could probably recur in the future," Bret-Harte said. "We'll probably see it more frequently than we have in the past."
One bright note in the study was the discovery that none of the material burned in the fire was older than 50 years, contrary to fears the fire released carbon that had been stored in the soils from vegetation that grew hundreds or thousands of years ago.
"It actually turns out that it was mostly fairly young carbon," proof much of the available carbon-containing material in the soil remained intact, she said.
Meanwhile, the burned tundra is recovering, said Bret-Harte, who spoke from the remote Toolik Field Station, a University of Alaska research facility located relatively close to the Anaktuvuk River fire site.
Slow-growing lichens, an important food source for caribou, and mosses have yet to return, she said. But vascular plants such as cotton grass and shrubs are growing well again, and there is a good crop of cloudberries at the site, she said.
"At first glance, it looks pretty green," she said. "It's not just a black pit in the landscape."
(Editing by Steve Gorman and Jerry Norton)