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Archive for the ‘arctic ocean’ Category

Arctic Ocean Seafloor Methane Venting

Posted by feww on March 5, 2010

Who’s afraid of seafloor methane emissions?

National Science Foundation: Public Release

Methane releases from Arctic shelf may be much larger and faster than anticipated

Thawing by climate change of subsea layer of permafrost may release stores of underlying, seabed methane

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.


Structure of a gas hydrate block embedded in the sediment of hydrate ridge, off Oregon. GNU Free Documentation license. Details

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 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.

“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.”


Worldwide distribution of confirmed or inferred offshore gas hydrate-bearing sediments. USGS

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.


Laptev and East Siberian Seas. Credit: UAF.

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.

“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.”


Glacier clathrate hydrate (fire-ice). The indications are that nature has no intention of releasing the “methane burp” gradually—Fire-Earth

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.

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.”

“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.”

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.

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.

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.

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Contact: Dana Cruikshank
dcruiksh@nsf.gov
National Science Foundation

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Posted in arctic ocean, East Siberian Arctic Shelf, greenhouse gas, seabed methane | Tagged: , , , , , , , , | Leave a Comment »

US Gov Releases Intelligence Images of Arctic Ice

Posted by feww on July 17, 2009

The United States gov releases spy images of Arctic ice

The United States gov has released about  1,000 intelligence images of Arctic ice soon after the National Academy of Sciences said they could help researchers make up a clearer picture of the impact of climate change.

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East Siberian Sea (Preview Gallery 2008). Source: GFL – Image ID: esiber_20080609_1

A total of about 1,200 images taken from six  sites around the Arctic Ocean, and22 sites in the United States, are posted online at gfl.usgs.gov/.

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Chuckchi Sea (Preview Gallery 2008). Source: GFL – Image ID:chuckchi_20080612_1

“The Arctic images have a resolution of about 1 yard (1 meter), a vast improvement on previously available pictures of sea ice, said Thorsten Markus of NASA’s Goddard Space Flight Center.”

“These are one-meter-resolution images, which give you a big picture of the summertime Arctic,” Reuters reported Markus as saying on Thursday. “This is the main reason why we are so thrilled about it. One meter resolution is the dimension that’s missing.”

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Posted in arctic melt pools, arctic ocean, Climate Change, greenhouse gases, Medea program | Tagged: , , , , | Leave a Comment »

Arctic sea ice has thinned dramatically

Posted by feww on July 8, 2009

Arctic sea ice thinned dramatically between the winters of 2004 and 2008—NASA

Analysis of data from a NASA Earth-orbiting spacecraft shows that “Arctic sea ice thinned dramatically between the winters of 2004 and 2008, with thin seasonal ice replacing thick older ice as the dominant type for the first time on record.”  The latest discovery “provide further evidence for the rapid, ongoing transformation of the Arctic’s ice cover.”

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ICESat measures the distances to the top of the snow cover and to the sea surface. The difference between the two quantities gives the total “freeboard” measurement; that is, the amount of ice above the water line relative to the local sea level. Credit: Courtesy of Norbert Untersteiner, University of Washington

NASA says their and the University of Washington in Seattle researchers carried out “the most comprehensive survey to date using observations from NASA’s Ice, Cloud and land Elevation Satellite, known as ICESat,” to determine “the first basin-wide estimate of the thickness and volume of the Arctic Ocean’s ice cover.”  Their research team, led by Ron Kwok of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., published its findings on July 7 in the Journal of Geophysical Research-Oceans.

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This schematic shows the geometric relationship between freeboard (the amount of ice above the water line), snow depth, and ice thickness. Buoyancy causes a fraction (about 10 percent) of sea ice to stick out above the sea surface. By knowing the density of the ice and applying “Archimedes’ Principle” — an object immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object — the total thickness of the ice can be calculated. Credit: Ron Kwok, NASA/JPL

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ICESat measurements of winter multi-year ice cover in the Arctic Ocean between 2004 and 2008, along with the corresponding downward trend in overall winter sea ice volume, and switch in dominant ice type from multi-year ice to first-year ice. Credit: Ron Kwok, NASA/JPL

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ICESat measurements of winter multi-year ice cover in the Arctic Ocean between 2004 and 2008, along with the corresponding downward trend in overall winter sea ice volume, and switch in dominant ice type from multi-year ice to first-year ice. Credit: Ron Kwok, NASA/JPL


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Data visualization of Arctic sea ice thickness, as measured by ICESat, shows the decline of the thickest ice (white, 4 to 5 meters thick) and increase in thinner ice (deep blue, 0 to 1 meter) from 2003 to 2008. Credit: NASA Goddard’s Scientific Visualization Studio.

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326208main_seaicediscretecolorbarData visualization of ice thickness, as measured by ICESat, shows the yearly growth (winter) and retreat (fall) of ice in the Arctic Ocean. Credit: NASA Goddard’s Scientific Visualization Studio


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Posted in Archimedes’ Principle, arctic ocean, freeboard ice, winter sea ice | Tagged: , , , , | 2 Comments »