Climate-warming methane escaping Arctic Ocean

MARGARET MUNRO
Canwest News Service

Large amounts of methane, a potent climate warming gas, are escaping from a remote swath of the Arctic Ocean that holds vast stores of the gas, say scientists, who suspect the seabed is “destabilizing.”

An international team reports about seven-million tonnes of methane is venting out of the frigid waters north of Siberia each year, dwarfing marine emissions seen anywhere else on Earth.

“The amount of methane currently coming out of the East Siberian Arctic Shelf is comparable to the amount coming out of the entire world’s oceans,” says Natalia Shakhova, at the International Arctic Research Center at the University of Alaska.

She co-led the team of American, Russian and Swedish scientists who detail the findings March 5, in the journal Science.

There has long been concern the release of methane locked in the permafrost could trigger catastrophic and “abrupt” climate change.

Methane is more than 20 times more potent at warming the atmosphere than carbon dioxide.

Shakhova and her colleagues say it is not known if the Siberian venting is a “steadily ongoing” process or “signals the start of a more massive” methane release.

But they say there is an “urgent need” to find out.

Shakhova says her concern is that the sub-sea permafrost, which formed during the last ice age, is destabilizing and allowing trapped methane to leak out. “If it further destabilizes, the methane emissions may not be tetragrams [millions of tonnes], it would be significantly larger,” she says.

A leading Canadian permafrost specialist says the Siberian findings are important, but he sees no need for alarm.

“In my view, it’s much more likely to be a persistent ongoing phenomenon than the beginning of some catastrophe,” says Chris Burn, at Carleton University in Ottawa, who has been monitoring permafrost in Canada’s Western Arctic since 1982.

Burn says the Siberian shelf has probably been emitting large amounts of methane for thousands of years, as organic matter under the sea floor decomposes, but the emissions went unnoticed because the region is so remote.

Burns says the Siberian finding is most significant because it shows methane emissions from the ocean vary markedly — a realization that should help refine global climate models and forecasts for the future.

While seven-million tonnes of methane a year is a lot for a marine region, it is a tiny fraction of the estimated 440 million tonnes of methane that wafts into the global atmosphere from natural and human sources each year.

Given the huge store of methane in the permafrost, scientists say it is important to get a better read on how much is escaping in not only Siberia, but also the Canadian and Alaskan Arctic where the gas is also seeping and bubbling out of frozen ground and seabeds.

“There is more and more evidence that methane is being released in certain marine and terrestrial environments in the Arctic,” says geologist Scott Dallimore, at Natural Resources Canada.

His team is studying methane venting from hot spots in the Mackenzie River Delta and Beaufort Sea.

More work is needed to understand “where the gas is coming from and what processes are driving the gas release,” Dallimore said by e-mail from Norway, where he is attending international meetings to discuss Arctic methane.

The Siberian shelf, which covers two-million square kilometres, is the largest and shallowest continental shelf in the world’s oceans.

Little was known about emissions on the shelf, so Shakhova’s team headed out on icebreakers, snowmobiles and in helicopters and took more than 5,000 water and air samples between 2003 and 2008.

They report that more than 80 per cent of the shelf’s deep water and 50 per cent of surface water had methane levels more than eight times that of normal sea water.

In some spots, the methane levels in the sea water reached more than 250 times normal in the summer and 1,400 times higher in the winter, when methane gets trapped beneath sea ice.