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Wetter permafrost clings to carbon better

In 12-year lab study, moist soil samples released less greenhouse gas as they warmed

CARBON ON ICE  In a 12-year lab study, thawing permafrost saturated with water lost less  carbon than dry permafrost did (soil sample from Greenland shown).

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Frozen soil saturated with water hung on to more carbon while thawing than drier permafrost did in a long-term lab study. Scientists may need to consider more than just temperature to predict how quickly greenhouse gases will escape from the vast supplies of carbon stored in the world’s permafrost.

In 1996, Bo Elberling of the University of Copenhagen and colleagues collected chunks of permafrost from northeastern Greenland to investigate thawing’s effects. Over 12 years, the team kept the samples at 5° Celsius. This constant incubation at a relatively high temperature is a good approximation of the cumulative warming Greenland could experience over the next 100 years, the researchers say.

The team periodically measured carbon dioxide released from the permafrost as it thawed. Dry shrubland lost about 55 percent of its carbon while soil from wet grassland lost just 9 percent, the researchers report July 28 in Nature Climate Change. The dry soil naturally contains more oxygen, Elberling explains. The reason it released more carbon is probably that microbes in well-oxygenated conditions decompose matter more efficiently than anaerobic microbes do. Therefore, Elberling says, scientists should pay more attention to drainage patterns around permafrost.

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