Arctic Lakes May Soak Up Greenhouse Gases as Permafrost Melts

Scientists have found a new natural system that may help combat climate change. It turns out that Arctic thermokarst lakes may help thwart global warming by storing more greenhouse gases than they emit into the atmosphere.

Thermokarst lakes occur in the cold reaches of the world, forming when permafrost thaws and creates a small surface depression that then fills with melted freshwater. This converts what was once frozen land into a land of lakes. Researchers have long thought that melting permafrost would accelerate climate change due to the gases being released. Yet scientists have found that roughly 5,000 years ago, thermokarst lakes in ice-rich regions of North Siberia and Alaska actually began cooling the atmosphere.

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

In order to see how permafrost and thermokarsts might impact climate, the researchers used data from the circumpolar arctic and their own field observations, radiocarbon dating, atmospheric modeling and spatial analysis.

So what did they find? It turns out that thermokarst basins switched from a net radiative warming to a net cooling climate effect 5,000 years ago. High rates of carbon accumulation in lake sediments were stimulated by thermokarst erosion and deposition of terrestrial organic matter, nutrient release from thawing permafrost that stimulated lake productivity, and slow decomposition in cold, anoxic lake bottoms.

"These lakes are being fertilized by thawing yedoma permafrost," said Miriam Jones, one of the researchers. "So mosses and other plants flourish in these lakes, leading to carbon uptake rates that are among the highest in the world, even compared to carbon-rich peatlands."

The findings reveal that thawing permafrost may not result in the runaway climate warming that researchers once expected. Because thermokarst lakes can offset greenhouse gas emissions, it's likely that melting ice may not be as devastating as scientists once expected.

The findings are published in the journal Nature.