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Siberian lakes burp "time-bomb" greenhouse gas

September 08, 2006

FAIRBANKS, Alaska - Frozen bubbles in Siberian lakes are releasing methane, a greenhouse gas, at rates that appear to be "... five times higher than previously estimated" and acting as a positive feedback to climate warming, said Katey Walter, in a paper published today in the journal Nature.

Walter's project is the first time this type of bubbling has been accurately quantified. "We realized that our previous estimates were missing a very large and important component of lake emissions-in these bubbles were the dominant source of methane from lakes," said Walter, an International Polar Year post-doctoral fellow at the Institute of Arctic Biology at the University of Alaska Fairbanks.

According to Walter, her team's calculations increase the present estimate of methane emissions from northern wetlands by between 10 and 63 percent.

Water studied a unique type of permafrost in Siberia, called yedoma, which contains an estimated 500 gigatons of carbon, largely in the form of ancient dead plant material. "This material has been locked up in permafrost since the end of the last ice age," Walter said. "Now it is being released into the bottom of lakes, providing microbes a banquet from which they burp out methane as a byproduct of decomposition."

"Permafrost models predict significant thaw of permafrost during this century, which means that yedoma permafrost is like a time bomb waiting to go off-as it continues to thaw, tens of thousands of teragrams of methane can be released to the atmosphere enhancing climate warming," Walters said. "This newly recognized source of methane is so far not included in climate models."

Using remote sensing, aerial surveys and year-round, continuous measurements Walter and colleagues developed a new method of measuring ebullition (bubbling) point sources and used it to quantify methane emissions from two thaw lakes in North Siberia.

As they walked across the frozen lakes they mapped locations and types of discrete methane bubbling trapped in the ice. By placing bubble traps over these spots and under the water the researchers could get daily measurements of the volume of methane released by the bubbles.

Walter will continue her work on methane for her UAF International Polar Year post-doctoral project which will provide the first circumpolar estimate of methane emissions for arctic lakes, linking process-based field surveys with remote sensing analysis.

Institute of Arctic Biology

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