Photograph courtesy Igor Semiletov, University of Alaska Fairbanks

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Ice and methane bubbles dance across the surface of the East Siberian Sea (file photo).

Photograph courtesy Igor Semiletov, University of Alaska Fairbanks

Arctic Sea Belching Tons of Methane

Ocean permafrost an overlooked greenhouse gas source, study says

Arctic seabeds are belching massive quantities of methane, according to a new study that says ocean permafrost is a huge and largely overlooked source of the powerful greenhouse gas, which has been linked to global warming.

But the permafrost lining the deep, cold seas was thought to be staying frozen solid, holding in untold amounts of trapped methane.

"It's not the case anymore," said study leader Natalia Shakhova, a biogeochemist at the University of Fairbanks, Alaska. "The permafrost is actually failing in its ability to preserve this leakage."

In fact, Shakhova and colleagues estimate that roughly eight million tons of methane are leaking into the atmosphere each year from the East Siberia Sea (map), fueling concerns of accelerated global warming.

Methane Feedback Fueling Global Warming?

Shakhova's team took detailed measurements of methane levels in the water column over the Siberian Arctic shelf during six research cruises from 2003 to 2008.

The 77,204-square-mile (2,000,000-square-kilometer) shelf is characterized by shallow seas less than 164 feet (50 meters) deep, and the permafrost layer extends throughout. (See a detailed map of the Arctic seafloor.)

The scientists found that much of the seawater above the shelf is laden with methane, which in turn is being released into the atmosphere.

Previous studies had found that current atmospheric methane levels in the Arctic are three times higher than those recorded across past climate cycles going back 400,000 years.

This phenomenon most likely isn't limited to the East Siberian Sea, the researchers note. If permafrost is melting in this part of the Arctic, all shallow areas along the Arctic shelf should be similarly affected.

To help find out, Shakhova and her colleagues plan to drill through the subsea permafrost next spring to establish a regional monitoring network

It's unclear whether human-induced climate change is causing the leakage. But global warming might be speeding up an otherwise natural part of the climate cycle, Shakhova noted, creating a feedback loop, in which released methane further warms the Earth, melting more permafrost and releasing more methane.

"This [human-made] contribution, or global climate change, might be the last straw, might be the accelerator or trigger," she said.

The research is published this week in the journal Science.