The Heat Is Online

Methane Spike from Arctic Seabed Startles Scientists

Methane Releases from Arctic Shelf May Be Much Larger and Faster Than Anticipated

Science Daily, March 5, 2010

A section of the Arctic Ocean seafloor that holds vast stores of frozen methane is showing signs of instability and widespread venting of the powerful greenhouse gas, according to the findings of an international research team led by University of Alaska Fairbanks scientists Natalia Shakhova and Igor Semiletov.

The research results, published in the March 5 edition of the journal Science, show that the permafrost under the East Siberian Arctic Shelf, long thought to be an impermeable barrier sealing in methane, is perforated and is leaking large amounts of methane into the atmosphere. Release of even a fraction of the methane stored in the shelf could trigger abrupt climate warming.

"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," said Shakhova, a researcher at UAF's International Arctic Research Center. "Subsea permafrost is losing its ability to be an impermeable cap."

Methane is a greenhouse gas more than 30 times more potent than carbon dioxide. It is released from previously frozen soils in two ways. When the organic material -- which contains carbon -- stored in permafrost thaws, it begins to decompose and, under oxygen-free conditions, gradually release methane. Methane can also be stored in the seabed as methane gas or methane hydrates and then released as subsea permafrost thaws. These releases can be larger and more abrupt than those that result from decomposition.

The East Siberian Arctic Shelf is a methane-rich area that encompasses more than 2 million square kilometers of seafloor in the Arctic Ocean. It is more than three times as large as the nearby Siberian wetlands, which have been considered the primary Northern Hemisphere source of atmospheric methane. Shakhova's research results show that the East Siberian Arctic Shelf is already a significant methane source: 7 teragrams yearly, which is equal to the amount of methane emitted from the rest of the ocean. A teragram is equal to about 1.1 million tons.

"Our concern is that the subsea permafrost has been showing signs of destabilization already," she said. "If it further destabilizes, the methane emissions may not be teragrams, it would be significantly larger."

Shakhova notes that Earth's geological record indicates that atmospheric methane concentrations have varied between about .3 to .4 parts per million during cold periods to .6 to .7 parts per million during warm periods. Current average methane concentrations in the Arctic average about 1.85 parts per million, the highest in 400,000 years, she said. Concentrations above the East Siberian Arctic Shelf are even higher.

The East Siberian Arctic Shelf is a relative frontier in methane studies. The shelf is shallow, 50 meters or less in depth, which means it has been alternately submerged or terrestrial, depending on sea levels throughout Earth's history. During Earth's coldest periods, it is a frozen arctic coastal plain, and does not release methane. As the planet warms and sea levels rise, it is inundated with seawater, which is 12-15 degrees warmer than the average air temperature.

"It was thought that seawater kept the East Siberian Arctic Shelf permafrost frozen," Shakhova said. "Nobody considered this huge area."

Earlier studies in Siberia focused on methane escaping from thawing terrestrial permafrost. Semiletov's work during the 1990s showed, among other things, that the amount of methane being emitted from terrestrial sources decreased at higher latitudes. But those studies stopped at the coast. Starting in the fall of 2003, Shakhova, Semiletov and the rest of their team took the studies offshore. From 2003 through 2008, they took annual research cruises throughout the shelf and sampled seawater at various depths and the air 10 meters above the ocean. In September 2006, they flew a helicopter over the same area, taking air samples at up to 2,000 meters in the atmosphere. In April 2007, they conducted a winter expedition on the sea ice.

They found that more than 80 percent of the deep water and greater than half of surface water had methane levels more than eight times that of normal seawater. In some areas, the saturation levels reached at least 250 times that of background levels in the summer and 1,400 times higher in the winter.

They found corresponding results in the air directly above the ocean surface. Methane levels were elevated overall and the seascape was dotted with more than 100 hotspots. This, combined with winter expedition results that found methane gas trapped under and in the sea ice, showed the team that the methane was not only being dissolved in the water, it was bubbling out into the atmosphere.

These findings were further confirmed when Shakhova and her colleagues sampled methane levels at higher elevations. Methane levels throughout the Arctic are usually 8 to 10 percent higher than the global baseline. When they flew over the shelf, they found methane at levels another 5 to 10 percent higher than the already elevated arctic levels.

The East Siberian Arctic Shelf, in addition to holding large stores of frozen methane, is more of a concern because it is so shallow. In deep water, methane gas oxidizes into carbon dioxide before it reaches the surface. In the shallows of the East Siberian Arctic Shelf, methane simply doesn't have enough time to oxidize, which means more of it escapes into the atmosphere. That, combined with the sheer amount of methane in the region, could add a previously uncalculated variable to climate models.

"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 said. "The climatic consequences of this are hard to predict."

Shakhova, Semiletov and collaborators from 12 institutions in five countries plan to continue their studies in the region, tracking the source of the methane emissions and drilling into the seafloor in an effort to estimate how much methane is stored there.

Shakhova and Semiletov hold joint appointments with the Pacific Oceanological Institute, part of the Far Eastern Branch of the Russian Academy of Sciences. Their collaborators on this paper include Anatoly Salyuk, Vladimir Joussupov and Denis Kosmach, all of the Pacific Oceanological Institute, and Orjan Gustafsson of Stockholm University.

http://www.sciencedaily.com/releases/2010/03/100304142240.htm

Arctic permafrost leaking methane at record levels, figures show

The Guardian (U.K.), Jan. 14, 2010

Experts say methane emissions from the Arctic have risen by almost one-third in just five years, and that sharply rising temperatures are to blame

Scientists have recorded a massive spike in the amount of a powerful greenhouse gas seeping from Arctic permafrost, in a discovery that highlights the risks of a dangerous climate tipping point.

The discovery follows a string of reports from the region in recent years that previously frozen boggy soils are melting and releasing methane in greater quantities. Such Arctic soils currently lock away billions of tonnes of methane, a far more potent greenhouse gas than carbon dioxide, leading some scientists to describe melting permafrost as a ticking time bomb that could overwhelm efforts to tackle climate change.
 
They fear the warming caused by increased methane emissions will itself release yet more methane and lock the region into a destructive cycle that forces temperatures to rise faster than predicted.

Paul Palmer, a scientist at Edinburgh University who worked on the new study, said: "High latitude wetlands are currently only a small source of methane but for these emissions to increase by a third in just five years is very significant. It shows that even a relatively small amount of warming can cause a large increase in the amount of methane emissions."

Global warming is occuring twice as fast in the Arctic than anywhere else on Earth. Some regions have already warmed by 2.5C, and temperatures there are projected to increase by more than 10C by 2100 if carbon emissions continue to rise at current rates.

Palmer said: "This study does not show the Arctic has passed a tipping point, but it should open people's eyes. It shows there is a positive feedback and that higher temperatures bring higher emissions and faster warming."

The change in the Arctic is enough to explain a recent increase in global methane levels in the atmosphere, he said. Global levels have risen steadily since 2007, after a decade or so holding steady.

The new study, published in the journal Science, shows that methane emissions from the Arctic increased by 31% from 2003-07. The increase represents about 1m extra tonnes of methane each year. Palmer cautioned that the five-year increase was too short to call a definitive trend.

The findings are part of a wider study of methane emissions from global wetlands, such as paddy fields, marshes and bogs. To identify where methane was released, the researchers combined methane levels in the atmosphere with surface temperature changes. They did not measure methane emissions directly, but used satellite measurements of variations in groundwater depth, which alter the way bacteria break down organic matter to release or consume methane.

They found that just over half of all methane emissions came from the tropics, with some 20m tonnes released from the Amazon river basin each year, and 26m tonnes from the Congo basin. Rice paddy fields across China and south and south-east Asia produced just under one-third of global methane, some 33m tonnes. Just 2% of global methane comes from Arctic latitudes, the study found, though the region showed the largest increases. The 31% rise in methane emissions there from 2003-07 was enough to help lift the global average increase to 7%.

Palmer said: "Our study reinforces the idea that satellites can pinpoint changes in the amount of greenhouse gases emitted from a particular place on earth. This opens the door to quantifying greenhouse gas emissions made from a variety of natural and man-made sources."
 
Palmer said it was a "disgrace" that so few satellites were launched to monitor levels of greenhouse gases such as carbon dioxide and methane. He said it was unclear whether the team would be able to continue the methane monitoring in future. The pair of satellites used to analyse water, known as Grace, are already over their expected mission life time, while a European version launched last year, called Goce, is scheduled to fly for less than two years.

The new study follows repeated warnings that even modest levels of global warming could trigger huge increases in methane release from permafrost. Phillipe Ciais, a researcher with the Laboratory for Climate Sciences and the Environment in Gif-sur-Yvette, France, told a scientific meeting in Copenhagen last March that billions of tonnes could be released by just a 2C average global rise.

guardian.co.uk © Guardian News and Media Limited 2010

http://www.guardian.co.uk/environment/2010/jan/14/arctic-permafrost-methane