The seabed sediments of the shallow East Siberian Sea contain 200 times more methane than what is present in the atmosphere. The quantities of methane being released into the atmosphere from the sea north of East Siberia are larger than the total emissions from the rest of the world’s oceans. The high levels of methane in the seawater indicate that the submarine permafrost is thawing and releasing the methane. However, we have not yet reached a point where the flow of gas seriously affects the methane balance in the atmosphere.

Photo: Malin Stenberg

The research findings are based on a combination of thousands of measurements of seawater methane levels over a twelve-year period and samples collected from drilling up to 50 metres into the Laptev Shelf. In addition, the researchers have made geophysical observations using sonar technology in order to survey the amount of methane that is bubbling up from the seabed.

“We have shown that the thermal state of the seabed is very close to, or even at, the point where the permafrost begins to thaw, and that global warming contributes to the thawing of the permafrost in the seabed. Furthermore, an increase in storms in the Arctic would further speed up the release of methane in the atmosphere”, says Natalia Shakhova, lead author of the study and biogeochemist at the University of Alaska in Fairbanks.

The new calculations show that 17 million tons of methane are released into the atmosphere every year from the sediments of the East Siberian Shelf. This is twice as much as the previous calculations made by the research team for an article published in Science in 2010.
“Even though we had seen methane gas bubbles before, in our study in 2010 we were only able to calculate the atmospheric release from methane dissolved in the surface water. In the new study, the sonar technology enabled us to calculate how much methane is transported to the surface in the form of methane bubbles from the seabed”, says Örjan Gustafsson, co-author of both articles and professor of biogeochemistry at Stockholm University.

Methane exists in various forms in the seabed sediments. First, there is methane in the permafrost which used to be on land but was submerged when the sea level rose at the end of the last ice age 7,000 years ago. Second, there is frozen methane (methane hydrates) inside and underneath the seabed permafrost. Finally, there are huge bubbles of natural gas rising from deep oil wells, which are held back as long as the permafrost does not melt.

In order to predict the future development of these methane fluxes and estimate the risk of dramatically increasing emissions, there is great need to better understand the temperature of the submarine permafrost and the various sources’ relative contributions to the methane emissions.

Next summer, more measurements will be collected in order to gain further knowledge of methane in the large but still relatively unexplored seabed in the outer East Siberian Sea, and the flux of this methane into the atmosphere, when Swedish and Russian researchers go on a 90-day research expedition with the icebreaker Oden. The expedition will go under the name Swedish-Russian-US Arctic Ocean Investigation of Carbon-Climate-Cryosphere Interactions (SWERUS-C3) and is primarily funded by the Knut and Alice Wallenberg Foundation. Read more at: http://swerus-c3.geo.su.se