Melting Arctic Glaciers Are Flushing Ancient Methane From Rocks Into the Air

The rivers pouring off Svalbard’s glaciers carry more than meltwater. According to new research published in Nature Communications, they are also transporting ancient methane, a potent greenhouse gas, from rock formations buried deep beneath the ice and releasing it into the open air. The study, led by Gabrielle Kleber of the iC3 Polar Research Hub in Tromsø, Norway, offers the most extensive assessment yet of methane in glacier meltwater in the Arctic archipelago, and it points to a natural feedback loop that could intensify as the climate continues to warm. Put simply, the more glaciers melt, the more methane they are likely to release.

The research team collected 148 water samples from 19 glacier-fed rivers across central Svalbard, spanning a wide variety of rock types and ice conditions. Every single river they tested contained more methane than would be expected from ordinary contact with the atmosphere. The most methane-rich waters reached concentrations up to 425 times atmospheric equilibrium levels, a striking signal that something beneath the ice is supplying the gas in abundance. Co-author Silje Waaler explained that the survey was deliberately designed to capture the diversity of glaciers across the region, giving the team a clearer picture of why some glacier rivers carry far more methane than others.

One of the study’s most important conclusions concerns the origin of the methane. In Greenland, scientists have previously documented microbes producing methane beneath the ice. On Svalbard, however, the methane appears to be geological rather than biological. Much of the archipelago is underlain by old shale layers rich in organic carbon. Over millions of years, heat and pressure have transformed that buried organic material into methane and other gases, creating a vast reservoir of ancient carbon locked in the bedrock. When meltwater reaches these rocks, it can pick up the gas and carry it away.

To confirm the methane’s source, the researchers analysed the carbon isotopic composition of the gas and measured related hydrocarbons, including ethane and propane, in some samples. The presence of these heavier gas companions is a classic fingerprint of thermogenic gas produced deep within sedimentary basins, distinguishing it from the isotopically lighter methane that microbes generate. The combined geochemical evidence indicated that much of the methane in the rivers came from geological sources rather than subglacial microbial activity, reinforcing the idea that Svalbard’s bedrock is the primary supplier.

The mechanism linking ice to gas is hydrological. Kleber noted that these glaciers mostly melt on their surfaces, but the meltwater finds its way to the bottom of the glaciers through crevasses and holes, a process known as moulin drainage. Once at the bed, the water interacts with the rocks underneath, and where those rocks contain ancient gas, the water can flush methane out into rivers. In effect, each summer’s melt acts as a pump, drawing surface water down through the ice and pushing methane-laden water out the other side, where it degasses into the atmosphere.

Geology alone, however, did not explain the full pattern. The team found that the physical and thermal state of the glacier bed matters enormously. Glaciers with thawed, wet and actively sliding beds were far more efficient at picking up methane, because liquid water moving along the base can access fractures in the rock and dissolve the gas. Glaciers frozen to their beds were much less connected to the rocks below, and even where methane-rich geology was present, the gas stayed put. This means the subglacial thermal regime acts as a gatekeeper controlling how much ancient carbon can escape.

To map these conditions, the researchers combined river chemistry with ice-penetrating radar surveys conducted on selected glaciers, including winter fieldwork on the ice itself. The radar data allowed them to estimate how much of each glacier bed was thawed and capable of transmitting water. Co-author Leonard Magerl emphasized that the temperature at the base of glaciers is a crucial piece of the puzzle. The biggest methane releases occurred where the right rocks and the right glacier conditions came together, an insight he said can help estimate emissions from other ice-covered regions where direct measurements are lacking.

Scaling their findings across the archipelago, the researchers estimate that land-terminating glaciers on Svalbard may transport roughly 182 to 368 tonnes of methane per year in meltwater, depending on how the estimate is extrapolated. That figure comes in addition to earlier, much larger estimates for methane released by groundwater springs emerging in front of retreating glaciers, which previous iC3 work had uncovered. Even at the lower end, the new pathway represents a widespread and previously undercounted route for ancient carbon to reach the atmosphere, one that standard emissions inventories have not captured.

The broader significance lies in the feedback structure. Methane is a powerful greenhouse gas, and while the amounts documented here are small compared with human-caused emissions from fossil fuels, farming and waste, the pathway is not confined to Svalbard. Similar methane-release mechanisms likely operate in other glaciated regions where ice overlies organic-rich rocks or sediments, including large parts of the Arctic, the Himalayas and Antarctica. As glaciers thin and retreat, more meltwater may reach their beds, increasing contact with fractured rock, sediment and groundwater, and in some places flushing out still more methane in a self-reinforcing loop driven by warming.

The picture is not entirely one-directional, however. Some Svalbard glaciers are actually becoming colder at their beds as they shrink and lose insulating ice thickness. If a glacier becomes frozen to its bed, its ability to flush methane through subglacial rivers may decline, potentially cutting off the pathway even as melting accelerates at the surface. Kleber stressed that future methane release will depend on both geology and glacier change, which makes it essential to know what lies beneath the ice, not only how fast the ice is melting. The study builds directly on earlier iC3 findings that meltwater from a single Svalbard glacier could carry geologic methane from beneath the ice, releasing more methane per unit area than Greenland glaciers. The new work, published open access in Nature Communications, shows that this phenomenon is not an isolated curiosity but a region-wide feature of central Svalbard, strongest where shale-rich geology and thawed glacier beds overlap, and a warning sign for ice-covered landscapes across the warming Arctic.

Subject of Research: Geological methane emissions from meltwater draining Svalbard glaciers

Article Title: New study raises concerns about climate feedback loop as melting Arctic glaciers flush ancient methane from rocks beneath the ice

Article References: New study raises concerns about climate feedback loop as melting Arctic glaciers flush ancient methane from rocks beneath the ice. (n.d.). Original publication

Image Credits: AI Generated

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Keywords: Svalbard, glaciers, methane, Arctic, climate feedback loop, subglacial hydrology, shale, greenhouse gas, Nature Communications, glacier meltwater, geological methane, polar research