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Retreating glaciers in the Arctic are exposing groundwater springs containing very high concentrations of methane, which may add significant quantities of the greenhouse gas to the atmosphere.

“This is a novel methane emissions pathway that we hadn’t identified before,” says at the University of Cambridge.

Hundreds of springs have emerged at the base of retreating glaciers across the Norwegian Arctic archipelago of Svalbard. Kleber was intrigued by the springs, partly because of their “sulphuric, eggy smell”. Although methane is odourless, microbes in high-methane conditions sometimes produce gases like hydrogen sulphide that have this distinctive smell. “We knew there was something weird going on in the waters,” she says.

At first Kleber and her colleagues assumed a lack of oxygen was allowing higher-than-normal methane concentrations to develop in the water. But subsequent laboratory testing revealed the groundwater from these springs contained methane in concentrations up to 600,000 times greater than that in the atmosphere, suggesting the springs are acting as an escape route for gas trapped in the rocks below.

Over the course of three years, Kleber and her colleagues took samples from 123 springs at 78 different glaciers, across 6000 square kilometres in Svalbard, where glaciers are melting faster than in other areas of the Arctic.

All but one spring they sampled was supersaturated with methane, says Kleber, meaning the water contained more methane than it can normally dissolve at that temperature. Satellite observations revealed a further 23 glaciers with springs forming in the region.

The methane can rapidly escape into the air once exposed and Kleber warns that this is likely to trigger further warming in a feedback loop. Methane is 28 to 34 times more powerful than carbon dioxide in terms of its global warming effect.

The study estimates that 2000 tonnes of methane a year may be emitted from springs across Svalbard. While that is only a small fraction of global methane emissions, similar springs could be emerging across the Arctic.

“We don’t know what’s happening on Greenland, in Canada, in Russia,” says Kleber. “These are all places that have very large reservoirs of organic carbon in their rocks. We can assume that this is happening in other regions and we just don’t know how much is being released.”

This pollution source could grow in importance as more glaciers retreat, says Kleber, potentially providing an escape route for huge stores of methane trapped beneath the ground in the Arctic.

“I’m not saying there’s potential for some catastrophic release,” she says. “But there’s definitely the potential that more and more [methane] will be released to the point where it is potentially globally relevant.”

at the University of Manchester, UK, says further research is now needed to confirm whether the methane being released is from ancient underground stores, and the potential scale of this new emissions source.

“It is hard to say what magnitude of emissions from this source there may be right now as we don’t have measurements of this source across the whole Arctic, much less are able to predict it into the future as the climate continues to change,” he says. “This fact alone makes it very concerning and a priority for further measurement and modelling science.”

at Stockholm University in Sweden says the research demonstrates that there are multiple processes under way in the Arctic that may strengthen global warming by triggering feedback loops.

But he warns that the importance of this source of methane emissions is “far overstated” in the study, with thawing permafrost playing a much more significant role in the release of methane gas. “The estimated methane flux from subsea permafrost and land permafrost in the Arctic is much more than 1000 times bigger,” he says.