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Significant methane emissions in the Arctic from thawing seabed north of Siberia (05.03.2010)

The powerful greenhouse gas methane is being released into the atmosphere from an area of the East Siberian Sea equivalent to more than four times the area of Sweden. Permafrost in the seabed has been previously assumed to act as an effective cap for the enormous amount of methane in the area, which, if released, could lead to an abrupt global climate warming.

Source: Pixelio/schauhi In a comprehensive study in this week's issue of the journal Science, conducted by researchers at the Russian Academy of Sciences, the University of Alaska, USA, and Örjan Gustafsson of Stockholm University, it is shown that the area is currently leaking annually 8 million tonnes of methane into the atmosphere. The current flow is equivalent to what was previously understood to apply for the entire world ocean, although it is not at present contributing to an acute change in the atmospheric methane balance.

The Russo-Swedish research expedition, the International Siberian Shelf Study (ISSS), which was completed just over a year ago, is the most comprehensive so far in the inaccessible and poorly explored waters off north-eastern Siberia, despite the fact that they constitute the world's largest coastal sea. Climate models suggest that an increase in atmospheric methane equivalent to just one percent of what is estimated to be contained in the frozen seabed would be sufficient to cause a significant climate warming. Earlier periods of rapid climate warming in the Earth's geological history have been associated with sudden releases of methane from the seabed.

During the ISSS expedition measurements of methane were made in the seabed, at different depths in the water and in the overlying air at over one hundred locations. Combined with measurements from previous expeditions led by the Russian leaders of the study, Shakhova Natalya and Igor Semiletov, it can be seen that methane concentrations in seawater are elevated in 80% of sea bottom samples and in more than half of the surface water samples and air samples. In areas with concentrations up to 100 times above the natural background levels, the ISSS expedition documented, with the help of seismic instruments and echo sounding, the presence of methane chimneys on the ocean floor and fields of methane bubbles that rose to the surface of the sea so fast that the methane did not have time to dissolve in the seawater.

"The East Siberian coastal seas are an extension of the Siberian tundra, which was flooded when glaciers melted and sea levels rose at the end of the Ice Age. The thawing of the permafrost in the soil may largely be a result of natural causes, such as geothermal heat from below (through cracks in the earth's crust) and from the seawater above, during the 5000-8000 years since the permafrost was flooded," says Örjan Gustafsson, professor of biogeochemistry at the Stockholm University, leader for the Swedish ISSS delegation onboard and one of the authors of the article.

"The possibility cannot be excluded that the human contribution to warming of the Arctic, with an extended summer period with no ice and warmer water, as well as increased runoff of warmer river water, could be the straw that broke the camel's back, or rather that which pushes the temperature of the seabed permafrost above melting point," says Professor Gustafsson.

Professor Gustafsson stresses that the calculations show that there is no reason for excessive concern about the current situation where the atmospheric methane content is not significantly affected by the emissions that occur at this time. He emphasizes the importance of more extensive studies of methane emission from the Siberian coastal seas in order to better understand the risk of increased methane fluxes in the future.

"It is important to learn more about how permafrost is warmed and how this translates to methane emissions. Expeditions need to be repeated over several years to evaluate whether there is a trend of increased methane fluxes and this will require greater international cooperation."

The expedition is funded by Swedish, Russian, Nordic and American financiers; in particular the Swedish Knut and Alice Wallenberg Foundation.

For further information contact: wmedia.it.su.se/lhs/08086.wmv and www.vr.se

Source: Informationsdienst Wissenschaft

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