Upland Yedoma permafrost: a huge, previously overlooked source of methane
Methane escapes from upland Arctic Yedoma permafrost soils in quantities that exceed those in regions further north by far – emissions that have only recently been discovered by researchers and are not yet taken into account in current climate models.
Climate researchers have long been concerned about the huge amounts of carbon stored in permafrost soils, which are increasingly being released into the atmosphere as global warming increases. A research team led by the University of Alaska Fairbanks has now discovered that upland dry Yedoma permafrost landscapes, which were previously considered carbon sinks, release huge amounts of methane – much more than wetlands further north, for example.
In their study, which was published in Nature Communications in July, the researchers, led by Katey Walter Anthony, Professor of Limnology at the University of Fairbanks, report unexpectedly high methane emissions from upland Yedoma. At one of the study sites, just a few kilometers northwest of Fairbanks, the values for annual emissions were 240 times higher than the emissions in the northern upland areas, with 70 percent of the emissions being released in winter.
“I went through the forest, the birch trees and the spruce trees, and there was methane gas coming out of the ground in large, strong streams.”
Katey Walther Anthony
Yedoma is a special type of permafrost that occurs in the Arctic regions of Alaska, Canada and Siberia and can be up to 50 meters thick. It is characterized by a high content of organic material deposited during the Pleistocene and contains an unusually large amount of ice, 50 to 90 percent of its volume. Yedoma covers only three percent of the permafrost region, but contain more than 25 percent of the total carbon stored in the northern permafrost soils. Due to their high carbon content, these soils are considered a significant source of the greenhouse gases methane and carbon dioxide, which could be increasingly released as global warming progresses.
The radiocarbon analysis revealed that the carbon from the sampled methane bubbles, with an age of around 6650 years, was thousands of years older than the carbon that the researchers had previously observed in upland areas.
“It’s a totally different paradigm from the way anyone thinks about methane,” said Professor Walther Anthony in a university press release.
The discovery by Professor Walther Anthony and her team is certainly a cause for concern, as methane is a greenhouse gas 25 to 34 times more potent than carbon dioxide and because current climate models, which do not bode well anyway, do not take this source of emissions into account yet. Instead, they are based on the assumption that upland tundra landscapes and boreal forests only release very small amounts of methane into the atmosphere or even act as methane sinks.
Until now, it was assumed that methane mainly escapes in wetlands. The water-saturated soils contain little oxygen, which favors methane-producing microorganisms. The researchers were therefore surprised to measure higher emissions at some of the well-drained, drier study sites.
Taliks as a source of methane
Professor Walther Anthony and her team identified a total of 26 sites in dry upland forests, grasslands and tundra in Alaska that release methane. For three years, all year round, the research team measured methane emissions at 1,200 sites, only three of which did not release any methane.
These areas are characterized by thermokarst mounds – a sign of thawing permafrost: where ground ice thaws, parts of the ground sink and leave behind cone-shaped mounds that can reach a height of four to six metres.
The research team discovered that methane mainly escapes from so-called taliks – pockets of permanently unfrozen ground in permafrost regions.
Taliks often form under lakes or rivers, insulating the ground and preventing complete freezing. They play an important role in the hydrological cycle of permafrost regions and can also have an influence on the stability of the permafrost, as they can store heat and promote the thawing of the surrounding frozen ground.
The comparatively warm taliks enable the microorganisms in the soil to decompose carbon and produce methane even in winter. The authors expect that taliks will shape the Arctic upland landscape in the 21st and 22nd century.
“Everywhere you have upland Yedoma that forms a talik, we can expect a strong source of methane, especially in the winter,” says Professor Walther Anthony. “It means the permafrost carbon feedback is going to be a lot bigger this century than anybody thought.”
Higher risk of forest fires – methane reinforces the vicious circle
The methane escaping from permafrost regions not only has an impact on global warming, but also increases the likelihood and spread of fires. In a study published in Nature Scientific Reports in 2020, a Chinese research team reported a potentially higher risk of forest and tundra fires due to spontaneous combustion of the highly flammable gas. The fires in turn release large amounts of carbon and heat, which further increases the greenhouse effect. In addition, the affected permafrost soils thaw faster, which triples the metabolic rate of methane-producing microorganisms. This leads to a significant increase in the release of greenhouse gases such as carbon dioxide, methane and nitrous oxide into the atmosphere. In addition, fires affect the water and heat conditions in permafrost areas, lower the surface albedo and deepen the active soil layer, which accelerates the loss of organic carbon and nutrients. Overall, the ecosystem needs more than a century to fully recover after a fire.
Given the discovery that previously overlooked methane sources in upland Yedoma areas with thermokarst hills exhibit some of the highest methane emissions among Arctic land ecosystems, we can expect that previous projections of global temperature rise will likely need to be revised upwards. In any case, these findings will contribute to the improvement of climate models.
Julia Hager, Polar Journal AG
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