Massive methane leak in Arctic could trigger abrupt warming

Jeremy Hance
March 04, 2010

Methane, a greenhouse gas 30 times more potent than carbon, is spewing from what was believed to be an impermeable barrier in Siberia in amounts equal to methane releases from the world's oceans. The discovery has lead researchers to fear the possibility of abrupt climate warming. According to the study published in Science, subsea permafrost below the East Siberian Arctic Shelf has become compromised, leaking vast amounts of methane into the atmosphere.

The researchers have estimated that 6.5 to 10 teragrams of methane is emitted from the East Siberian Arctic Shelf every year: one teragram equals about 1.1 million tons. However, researchers are particularly worried about the amount of methane that could be released in the future.

The sea surface above the East Siberian Arctic Shelf is full of ice and bubbles. Sonar is the only way to detect the vast clouds of methane bubbles rising from the sea floor. Photo courtesy of Igor Semiletov, University of Alaska Fairbanks.
"Our concern is that the subsea permafrost has been showing signs of destabilization already," explains lead author Natalia Shakhova, a researcher at the University of Alaska Fairbank’s International Arctic Research Center. "If it further destabilizes, the methane emissions may not be teragrams, it would be significantly larger."

Since the methane is stored below the sea, the release of the potent greenhouse gas has the capacity of being far larger and quicker than methane released by thawing permafrost on land. In a podcast Shakhova compared the methane built up beneath the East Siberian Arctic Shelf permafrost to a bottle of champagne: in other words if an opening occurs in the permafrost vast stores of methane could be abruptly released into the atmosphere much like a cork being popped.

The East Siberian Arctic Shelf is 50 meters in depth or less: due to its shallowness in the shelf has been both submerged under the seawater and exposed depending on climate conditions during Earth's past. During cold periods, the shelf would remain frozen and not leak methane. However, as global temperatures warm and sea levels rise, the shallow shelf is flooded with seawater, which is 12-15 degrees warmer than the air temperature, leading to compromise of the permafrost and possible methane-release.

Fluxes of methane venting into the atmosphere over the East Siberian Arctic Shelf. Image courtesy of Science/AAAS.
"It was thought that seawater kept the East Siberian Arctic Shelf permafrost frozen," Shakhova said. "Nobody considered this huge area."

Shakhova points out that in Earth's geological record atmospheric methane concentrations have been between 0.3 to 0.4 parts per million in cold periods to 0.6 to 0.7 parts per million in warm periods. Yet, today, current average methane concentrations globally are 1.7 parts per million, more than double the average in warm periods. In the Arctic that average jumps to 1.85 parts per million: the highest concentration in 400,000 years. Yet, methane measurements above the East Siberian Arctic shelf are 10 percent higher. According to measurements 50 percent of the surface water in the area is supersaturated with methane and 80 percent of the deep water.

If the methane were being released in deep water, it would oxidize before reaching the surface and become carbon dioxide. However, since the East Siberian Arctic shelf is so shallow, this oxidization doesn't occur and the gas enters the atmosphere as the far more potent methane.

"The release to the atmosphere of only one percent of the methane assumed to be stored in shallow hydrate deposits might alter the current atmospheric burden of methane up to 3 to 4 times," Shakhova concludes, adding that "the climatic consequences of this are hard to predict."

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Jeremy Hance
mongabay.com (March 04, 2010).

Massive methane leak in Arctic could trigger abrupt warming.