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, 2010 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
starting to leak large amounts of methane into the atmosphere. Release of even a fraction of the methane stored
in the shelf could trigger abrupt climate warming.
Equal to the Rest of the Oceans Combined!
"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."
The Power of Methane
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 anaerobic conditions, gradually releases 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, releasing 7 teragrams of methane yearly, which
is as much as is emitted from the rest of the ocean. A teragram is equal to about 1.1 million tons.
Methane Releases Could Accelerate
"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 the 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.
Repeated Submergence and Emergence
The East Siberian Arctic Shelf is a relative frontier in methane studies. The shelf is shallow, 50 meters (164 feet) or
less in depth, which means it has been alternately submerged or terrestrial, depending on sea levels throughout Earth's
history. During the Earth's coldest periods, it is a frozen arctic coastal plain, and does not release methane. As the
Earth warms and sea level rises, 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."
International Cooperation in Research
"This study is a testament to sustained, careful observations and to international cooperation in research," said Henrietta
Edmonds of the National Science Foundation, which partially funded the study. "The Arctic is a difficult place to get to
and to work in, but it is important that we do so in order to understand its role in global climate and its response and
contribution to ongoing environmental change. It is important to understand the size of the reservoir--the amount of
trapped methane that potentially could be released--as well as the processes that have kept it "trapped" and those
that control the release. Work like this helps us to understand and document these processes."
Historic Methane Studies Stopped at the Coast
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 (6,562 feet) in the atmosphere. In April 2007, they conducted
a winter expedition on the sea ice.
Discovering the Subsea Methane Source
They found that more than 80 percent of the deep water and more than 50 percent of surface water had methane levels more than
eight times that of normal seawater. In some areas, the saturation levels reached more than 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.
Shallow Water Vulnerability
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 Enormous Impact of Minor Thawing
"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.
Natalia Shakhova of the University of Alaska Fairbanks discusses methane in the East Siberian Arctic Shelf and how the thawing of a layer of permafrost that caps it could have a major impact upon Earth's climate.
In this video, Katey Walter Anthony, also of the University of Alaska Fairbanks, demonstrates how methane is released in abundance from frozen lakes near Fairbanks, Alaska.
Permafrost of the East Siberian Arctic Shelf (an area of about 2 million kilometers squared) is more porous than previously
thought. The ocean on top of it and the heat from the mantle below warm it and make it perforated like Swiss cheese. This allows
methane gas stored under it under pressure to burst into the atmosphere. The amount leaking from this locale is comparable to all
the methane from the rest of the world's oceans combined. Methane is a greenhouse gas more than 30 times more potent than carbon
dioxide. Image by Zina Deretsky, National Science Foundation. Enlarge
