Arctic Thermokarst Lakes Soak Up Greenhouse Gases

Climate-cooling Arctic thermokarst lakes stabilize climate change by soaking up more greenhouse gases than they emit into the atmosphere, according to new research.

This discovery contradicts the widely held view that thawing permafrost actually accelerates atmospheric warming. But the study, published in the journal Nature, contends that arctic thermokarst lakes are in fact "net climate coolers" when observed over longer periods of time.

"Until now, we've only thought of thermokarst lakes as positive contributors to climate warming," lead author Katey Walter Anthony, associate research professor at the University of Alaska Fairbanks (UAF) Institute of Northern Engineering, said in a statement.

"It is true that they do warm climate by strong methane emissions when they first form, but on a longer-term scale, they switch to become climate coolers because they ultimately soak up more carbon from the atmosphere than they ever release."

Found in the Arctic and cold mountain regions, thermokarst lakes form as permafrost thaws and creates surface depressions that fill with melted fresh water, converting what was previously frozen land into lakes.

About 30 percent of global permafrost carbon is concentrated within seven percent of the permafrost region in Alaska, Canada and Siberia. Scientists did not observe the cooling effects of these carbon-containing hubs until 5,000 years ago.

"While methane and carbon dioxide emissions following thaw lead to immediate radiative warming," the authors write, "carbon uptake in peat-rich sediments occurs over millennial time scales."

Using field observations of Siberian permafrost and thermokarsts, radiocarbon dating, atmospheric modeling and spatial analyses, researchers were able to figure out just what role thawing permafrost is playing in the battle against climate change.

It turns out that thawing permafrost acts like fertilizers in lakes, allowing mosses and other plants to flourish, which thereby store the greenhouse gas carbon dioxide - their uptake rates are among the highest in the world.

And even when these lakes drain and are gone they are helping the environment. Researchers found that when the lakes drain, previously thawed organic-rich lake sediments refreeze. The new permafrost formation then stores a large amount of carbon processed in and under thermokarst lakes.

However, the UAF team notes that this carbon storage is not forever, since future warming will likely start rethawing the permafrost and release the carbon it contains.