Thawing permafrost could make way for greenhouse gases buried deeper

A study led by researchers at the University of Bonn (Germany) found that methane concentrations in northern Siberia differ from nearby geological maps and these results indicate that increased gas emissions came from limestone formations.

The study is published in the journal Proceedings of the National Academy of Sciences (PNAS).

Permafrost is the layer of soil that remains below freezing for two or more consecutive years. In other words, permafrost is permanently frozen soil that covers large areas in North America and Asia. Permafrost is found mostly in northern parts of these areas. If deep permafrost thaws in a warming world, this will release more carbon into the atmosphere – an aggravating factor of human greenhouse gas emissions.

In the past, most projections showed that greenhouse gases from melting permafrost would only contribute about 0.2 degrees Celsius to global warming by 2100.

However, pessimists spoke of an “imminent” methane bomb – meaning the sudden release of large quantities of methane gas into the atmosphere as a result of thawing permafrost streams. This assumption has now been challenged by a new study by Nikolaus Froitzheim and his colleagues Jaroslaw Majka (Krakow/Uppsala) and Dmitry Zastrozhnov (St. Petersburg).

Previously, most studies only dealt with how emissions form from the decay of plant and animal remains in the permafrost soil. Researchers studied methane concentrations in Siberian air using satellite-based spectroscopy and geological maps. The researchers found significantly elevated concentrations of methane at two areas: the Taymir Fold Belt and the rim of Siberian Platform.

What is striking about these two elongated areas, according to scientists, is that the bedrock there are formed of limestone formations from Paleozoic era.

In both areas, the elevated concentrations appeared during the extreme heatwave in summer 2020 and persisted for months after. But how did the additional methane occur in the first place? “The soil formations in the observed areas are very thin to nonexistent, making methane emission from the decay of organic soil matter unlikely,” says Niko Froitzheim. He and his colleagues therefore suggest that fracture and cave systems in the limestone, which had been clogged by a mixture of ice and gas hydrate, became permeable upon warming. “As a result, natural gas being mainly methane from reservoirs within and below the permafrost can reach the Earth’s surface,” he says.

The scientists now plan to investigate this hypothesis by measurements and model calculations to find out how much and how fast natural gas may be released.

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