Heat wave reveals methane surge: study
Source found in thawing rock formations
Scientists have long been worried about what many call “the methane bomb” — the potentially catastrophic release of methane from thawing wetlands in Siberia's permafrost.
But now a study by three geologists says that a heat wave in 2020 has revealed a surge in methane emissions “potentially in much higher amounts” from a different source: thawing rock formations in the Arctic permafrost.
The difference is that thawing wetlands release “microbial” methane from the decay of soil and organic matter, while thawing limestone releases hydrocarbons and gas hydrates from reservoirs both below and within the permafrost, making it “much more dangerous” than past studies have suggested.
Nikolaus Froitzheim, who teaches at the Institute of Geosciences at the University of Bonn, said that he and two colleagues used satellite maps that measured intense methane concentrations over two “conspicuous elongated areas” of limestone — stripes that were several kilometres wide and up to 604 kilometres long — in the Taymyr Peninsula and the area around northern Siberia.
The study was published by the Proceedings of the National Academy of Sciences.
Surface temperatures during the heat wave in 2020 soared to -11.78 C above the 1979-2000 norms. In the long stripes, there is hardly any soil, and vegetation is scarce, the study says. So the limestone crops out of the surface. As the rock formations warm up, cracks and pockets opened up, releasing methane that had been trapped inside.
Further tests showed the continued concentration of methane through the spring of 2021 despite the return of low temperatures and snow in the region.
“We would have expected elevated methane in areas with wetlands,” Froitzheim said. “But these were not over wetlands but on limestone outcrops.
“It's intriguing. It's not good news if it's right,” said Robert Max Holmes, a senior scientist at the Woods Hole Research Center. “What we do know with quite a lot of confidence is how much carbon is locked up in the permafrost. It's a big number, and as the Earth warms and permafrost thaws, that ancient organic matter is available to microbes for microbial processes and that releases CO2 and methane. If something in the Arctic is going to keep me up at night, that's still what it is.”
But he said the paper warranted further study.
Normally, the frozen permafrost acts as a cap, sealing methane below. It can also lock up gas hydrates, which are crystalline solids of frozen water that contain huge amounts of methane. Unstable at normal sea-level pressure and temperatures, gas hydrates can be explosive as temperatures rise.
The study said that gas hydrates in the Earth's permafrost are estimated to contain 20 gigatons of carbon, four times the amount present in atmospheric methane.
The Arctic delivered other sobering news. Polar Portal, a website where Danish Arctic research institutions present updated information about ice, said a “massive melting event” had been big enough to cover Florida with nine centimetres of water.