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Methane seeps rise from Siberian sea shelves

March 4, 2010 |  1:55 pm

Shakhova1HR

Carbon dioxide (C02) is the most prevalent greenhouse gas that is trapping heat in the atmosphere, warming the planet to what most climate scientists consider dangerous levels. But methane, a greenhouse gas that is 25 times more powerful than CO2, has also been growing at an alarming rate, with concentrations more than doubling since pre-industrial times.

A paper published Thursday in the journal Science reveals that parts of the East Siberian continental shelf, which extends up to 1000 miles out into Arctic waters, show concentrations of methane in surface waters that are 100 times higher than expected. And in the air, more than 5,000 measurements taken by scientists on Russian icebreakers and on helicopters document methane levels more than four times higher than elsewhere in the Arctic basin.

The researchers, led by Natalia Shakhova of the University of Alaska, along with Swedish and Russian colleagues, found that the amount of methane seeping into the atmosphere from below the Arctic Ocean is comparable to previous emissions estimates for all the world's oceans. The Arctic is warming faster than any other part of the planet, and scientists fear that methane emissions could rise even more dramatically in a feedback loop: As the atmosphere warms, the permafrost that has locked in methane gas in wetlands and beneath continental shelves melts, releasing more methane, which then warms the planet more.

"Wetlands and permafrost soils, including the subsea permafrost under the Arctic Ocean, contain at least twice the amount of carbon that is currently in the atmosphere as carbon dioxide," Martin Heimann wrote in an article accompanying the paper. "Release of a sizeable fraction of this carbon as carbon dioxide and/or methane would lead to warmer atmospheric temperatures, causing yet more methane to be released." The researchers recommend that their data be immediately incorporated into current assessments of how fast the Arctic is likely to warm in the near future.

The Science paper comes as other researchers have documented rising methane emissions from Alaskan and Siberian lakes. In a report from the Seward Peninsula last year, the Los Angeles Times followed University of Alaska limnologist Katey Walter and her team as they measured methane seeps from thawing permafrost. In a video and audio slide show, the scientists can be seen lighting up the normally invisible gas.

More than half the world's methane results from human activities. It wafts from natural gas wells, from garbage dumps, from cattle manure and from rice farming. California and other jurisdictions are struggling to bring man-made methane sources under control, but only a dramatic reduction in overall greenhouse gases would be likely to reduce the feedback loop from natural methane sources in the Arctic.

-- Margot Roosevelt

Image: Positions of oceanographic stations in the eastern Laptev Sea and East Siberian Sea; bathymetry (depth contour) lines for 10-, 20-, and 50-meter depths are shown in blue. Credit: Science/AAAS


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