“The big finding was that we really have something that’s coming out from a deep pool,” said Steinbach. As the permafrost thaws, it opens up new pathways that allow methane to pass through.

For the first time since records began, the Laptev Sea has not yet formed sea ice by the end of October. Scientists attribute the lack of ice to early summer warming and an extreme heatwave in Siberia, as well as warm Atlantic currents flowing into the Arctic.

The finding is prompting concerns that a new feedback loop that accelerates climate change may have already been triggered.

Unusual amounts of multiyear ice in the Laptev and Siberian Sea could lead to difficult summer navigation along parts of Russia’s Northern Sea Route this summer, says the country’s Arctic and Antarctic Research Institute.