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"Abrupt thawing" of permafrost under lakes could significantly affect the climate models

Methane released by the thawing of permafrost from some Arctic lakes could significantly accelerate climate change, according to a study by the University of Alaska Fairbanks

Methane bubbles are trapped in the ice of a pond near Fairbanks, Alaska. Credit: Katey Walter Anthony

The study, published on August 15, in the journal Nature Communications focuses on the carbon released by the thawing of permafrost under thermal ice lakes. Such lakes develop when soil warming melts ground ice, causing the surface to collapse and form streams of water. These pools accelerate the thawing of permafrost among the expanding lakes and provide food for microbes that produce the greenhouse gases carbon dioxide and methane.

Lead author Katey Walter Anthony and her colleagues studied hundreds of thermal water lakes in Alaska and Siberia for 12 years. They measure their growth and how much methane bubbles on their surface. By combining fieldwork results with remote sensing data from marine changes over the past two years, they have found that the "abrupt thaw" among these lakes is likely to release large amounts of permafrost carbon into the atmosphere this century. The activity of the lake could potentially double the release from terrestrial landscapes by 2050.

The efforts, undertaken by a team of American and German researchers, are part of a 10-year NASA-funded project to better understand the impact of climate change on the US Arctic. Additional support from the National Science Foundation has enabled scientists from UAF and the Alaska Division of Geological and Geophysical Surveys to gather data on permafrost location, thaw, and associated release of greenhouse gases from lakes in the Goldstream Valley in Interior Alaska.

The researchers found the release of greenhouse gases under thermocarst lakes are relatively fast, with deep thawing occurring over the decades. Permafrost in terrestrial environments generally experiences prolonged seasonal thawing over extended periods of time. The release of this surface permafrost carbon is often compensated by an increased growth of the vegetation.

"Thermal lake lakes offer a completely different scenario: as the lakes form, they thaw out these permafrost areas," said Walter Anthony, an adjunct professor at the UAF Center for Water and Environmental Research. "Instead of dew point centimeters, which are common in terrestrial environments, we've seen 15 meters of condensation in newly formed lakes in the Goldstream Valley over the last 60 years."

Emissions from Thermokarst lakes are currently not recorded globally Climate models because their small size makes it difficult to include individual lakes. However, the authors of the study show that these lakes are permafrost carbon release hotspots. They argue that if they are not included in global climate models, their feedback effect, which occurs when the release of greenhouse gases from permafrost increases warming, is overlooked. This feedback is significant because methane is about 30 times more potent than carbon dioxide as a heat storage gas.

Existing models currently attribute about 20 percent of permafrost carbon feedback to methane in this century, while the remainder is due to carbon dioxide terrestrial soils. With the inclusion of Thermokarst lakes, methane becomes the dominant driver responsible for 70 to 80 percent of permafrost carbon warming this century. Adding Thermokarst methane to the models makes the feedback similar to that of land use changes, which are the second largest source of human-induced warming.

In contrast to the shallow, gradual thawing of terrestrial permafrost, abrupt thawing below thermo-karst lakes is irreversible this century. Even climate models that project only moderate warming in this century must, according to the study, take their emissions into account.

"They can not stop the release of carbon from these lakes once they are formed," said Walter Anthony. "We can not handle this source of warming."

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