A large amount of methane is bubbling up from the ocean floor east of Siberia at a surprising rate and could accelerate climate change, researchers said yesterday.

The gas is bubbling up from the East Siberian Arctic Shelf because warming ocean water is thawing permafrost, allowing methane trapped underneath to escape. The amount of methane emitted by that one patch of seabed roughly equals the amount scientists believed was released by all of the world's oceans.

But just how the discovery will affect projections of future warming is hard to say, according to a team of scientists from the United States, Russia and Sweden who published their findings yesterday in the journal Science.

"Seabed deposits [of methane] were considered until recently to be reliably sealed by subsea permafrost," said the study's lead author, Natalia Shakhova of the University of Alaska, Fairbanks. "But what we are having now is up to 10 million tons annually escaping from this seabed. This means permafrost does not serve as an impermeable cap or seal to prevent this leakage any longer."

Shakhova said there is not enough information now to know whether the methane seeping up from the East Siberian Arctic Shelf -- which covers more than 810,000 square miles -- signals the emergence of a significant new source of the potent greenhouse gas. Methane is regarded as 20 to 30 times more potent as a greenhouse gas than carbon dioxide.

Uncertainty over whether the release will grow

Information she and her colleagues gathered during multiple research expeditions between 2003 and 2008 suggest that the area, home to 100 methane "hot spots," emits 8 million metric tons of the gas into the atmosphere.

That's a relatively small slice of the 440 million metric tons of methane emitted worldwide each year from a combination of human activities and natural sources like rotting plants in wetlands, termites and wildfires.

But Shakhova pointed out that scientists had not thought subsea permafrost would begin to thaw and release the gas. She said more research is needed to figure out whether the methane leaking from the East Siberian Arctic Shelf is an ongoing, steady phenomenon, or whether it suggests a new source of the gas is emerging as seafloor permafrost thaws.

Water over the Siberian site averages minus 1.8 to 1 degree Celsius, 12 to 17 degrees warmer than the air that helps permafrost on land stay frozen.

Martin Heimann, a scientist at the Max Planck Institute in Germany, said the amount of methane now escaping there is "negligible," though that could change.

"Will this persist into the future under sustained warming trends?" he said in a commentary published in Science. "We do not know."

Warming rivers melt the permafrost

News of methane escaping at the Siberian site follows a similar report last year, when British researchers said they found 250 plumes of methane rising from the seafloor in the Barents Sea north of Norway.

Speaking with reporters yesterday, Shakhova said it appears that river runoff flowing into the area she studied is getting warmer and raising the temperature of water near the ocean floor, where the permafrost lies.

She also noted that water over the East Siberian Arctic Shelf is unusually shallow, with an average depth of just 148 feet. That means the methane that escapes from the ocean floor has little chance of dissolving or oxidizing as it rises to the sea surface.

"It just escapes," she said.
