New Observations Find Underwater Arctic Shelf is Perforated and Venting Methane 3/6/2010
| Marilyn Sigman, Alaska SeaGrant/MAP
Tags: Climate Change, Underwater Methane, Arctic Ocean
By John Cook, Skeptical Science Blog
One of the positive feedbacks from global warming is the thawing of Arctic permafrost. This releases methane, a greenhouse gas over 20 times more potent than carbon dioxide, into the atmosphere. Investigations into Arctic methane have tended to focus on land permafrost. However, there are also vast amounts of methane held underwater in the East Siberian Arctic Shelf (ESAS). This encompasses over 2 million square kilometers, three times as large as the nearby Siberian wetlands, which have been considered the primary Northern Hemisphere source of atmospheric methane. Underwater permafrost acts as a lid to restrain methane stored in the seabed.
Until now, it was thought the permafrost was cold enough to remain frozen. However, recent observations have found that over 80% of the deep water over the ESAS is supersaturated, with methane levels more than eight times that of normal seawater (Shakhova 2010). More than half of the surface water is supersaturated also. The methane venting into the atmosphere from this one region is comparable to the amount of methane coming out of the entire world’s oceans.
To find out what was happening in the East Siberian Arctic Shelf, field measurements, ice expeditions and a helicopter survey were conducted to measure methane levels in ESAS waters. They took 5100 samples from 1080 stations, the largest database for any ocean methane study. They found widespread supersaturation over the region. Most of the bottom waters are supersaturated and over half of surface waters are supersaturated. 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.
The impact of positive feedback from ESAS methane is not currently included in climate model projections.
The scientific article was published in Science: Vol. 327. no. 5970, pp. 1246-1250, on March 5.
Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf.
Natalia Shakhova, Igor Semiletov, Anatoly Salyuk, Vladimir Yusupov, Denis Kosmach, Orjan Gustafsson
Links to article abstract and a podcast interview of Natalia Shakhova