Study finds methane in meltwater of 19 Svalbard glaciers

Every one of the 19 valley glaciers sampled in central Svalbard fed rivers carrying more methane than the atmosphere would leave in water, according to a study published in Nature Communications on Tuesday 8 September. Peaks reached up to 425 times equilibrium. The gas is largely thermogenic, meaning it formed from buried organic matter under heat and pressure, and the study links it to rocks beneath the ice.

The researchers analysed 148 river samples from the 19 glaciers. Carbon isotope readings, together with ethane and propane in the samples, pointed to mostly thermogenic methane. Three of the 19 rivers, at the glacier terminus, showed a microbial signature.

Ground-penetrating radar surveys showed that temperate ice, which is above the pressure melting point, spread across the glacier bed plays a critical part in how methane is picked up, the authors said. The effect is strongest where the bed lies on organic-rich, shale-dominated rock. Samples taken nearest the glacier termini held 9 to 1,700 nanomoles of methane per litre, with a median of 46.

The authors said the mechanism matters for glaciated regions with organic-rich geology around the world, and suggests that faster glacier melt may increase the release of methane from beneath glaciers. An earlier study at Vallåkrabreen showed that meltwater flushes ancient thermogenic methane out of the subglacial geology.

Geology explained more than half of the variation in methane concentrations in the samples nearest the glaciers, the study said. Geology and the share of temperate ice at the bed together explained three quarters of it. The highest concentration, 1,700 nanomoles per litre, was measured at Ragna Mariebreen.

Valley glaciers on Svalbard change as they retreat and thin in a warming climate, the authors wrote. Less of the bed stays thawed, until the glacier is frozen to its bed. The methane carried by meltwater is likely to increase for some time and may then decline, they wrote. The findings contrast with glacial rivers in Greenland, where the methane in meltwater comes from microbes, the study said.

In 68% of the rivers, the peak concentration lay far downstream of the glacier front. The authors wrote that this indicated that methane from groundwater might matter more than the methane delivered by the drainage beneath the glacier. They estimated that meltwater from Svalbard's land-terminating glaciers carries 182 to 368 tonnes of methane a year, depending on the method, and called the estimates likely conservative.

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