Researchers from the University of Alaska, Fairbanks have found large measures of geologic methane seeping up the edges of the thawing permafrost and receding glaciers in Alaska and Greenland.
The retreat of Arctic permafrost and glaciers often reveal previously frozen organic matter like dead plants or animals, which subsequently decays and releases methane, often in huge proportions. “Now we are saying that as permafrost thaws and glaciers retreat it is going to let something out that has had a lid on it,” said University of Alaska Fairbanks researcher Katey Walter Anthony.
That “lid” is known as the cryosphere cap, and it is made up of glaciers, permafrost and ice sheets which are believed to keep geologic sources of methane — such as coal beds and natural gas deposits, different from the organic sources — from venting into the atmosphere.
Naturally, if you slowly melt that lid away, the methane will get out.
Katey Walter Anthony and her team flew across the state of Alaska — from the Kenai Peninsula to the North Slope — during the winters of 2008 through 2010, and hiked across lakes in Greenland during the winter of 2010. They ended up surveying nearly 7,000 lakes from the air and identified 77 of them that were likely to have sites where methane was seeping. The researchers then visited 50 of the lakes to confirm the presence of seeps and take samples of the gas boiling up from the floor.
They later tested the samples and determined the gas’s source was geologic, rather than the result of decaying organic material. The majority of the seeps were in the continuous permafrost zone in northern Alaska and in Southcentral Alaska, where glaciers were receding. In Greenland, the seeps were found only in the areas where the ice sheet had retreated during the past 150 years.
Walter Anthony said that according to the data from this study, geologic methane seeps in Alaska’s terrestrial environment may contribute about 250,000 metric tons of methane to the atmosphere each year. In comparison, Walter Anthony estimates that organic decay in Alaska’s lake bottoms contributes about three times that amount. However, she noted that those numbers don’t include microseeps of geologic methane, which could mean geologic sources roughly equal the organic sources.
“When the glaciers retreat or the permafrost thaws,” she said, “it creates conduits for deeper gas to make its way up through the Earth.”
And those conduits could become more widespread if worldwide temperatures continue to increase, Walter Anthony notes. “In a warmer world, thawing permafrost and wastage of glaciers and ice sheets could lead to a significant transitional degassing of subcap methane.”
Source: University of Alaska, Fairbanks
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