This document represents first study of methane emissions from glacial rivers in Spitsbergen and suggests that summer methane flushing from beneath the approximately 1,400 continental glaciers in Spitsbergen may represent a significant seasonal source of emissions.

Main findings of the study:

• Researchers monitored methane concentrations in proglacial underground springs and the river network of a valley glacier in the central part of Spitsbergen during the summer of 2021.
• They found that methane concentrations in the glacial river reach up to 3170 nM, which is almost 800 times higher than the atmospheric equilibrium concentration.
• Isotopic analysis showed that the methane is of thermogenic origin.
• It is estimated that a total of 1.0 t of methane was released from the basin during the 2021 melt, almost two-thirds of which was washed out from under the glacier by the melting river.
• The potential methane flux from the Vallåkrabreen basin during the melt season was found to be equivalent to 1.7 mg CH4 m-2 d-1 when normalized to the area of the glacier foreland, or 0.18 mg CH4 m-2 d-1 when normalized to the area of the entire hydrological basin.
• Glacier river emissions are estimated to account for 63 % of total emissions, while groundwater and ebullition contributed 35 % and 2 %, respectively.
• Meltwater from small valley glaciers can mobilize significant amounts of methane, which challenges previous theories that subglacial methane is produced mainly microbially in the anoxic environment beneath large glaciers.
• The study demonstrated an alternative source of methane in glacial environments, where ancient thermogenic methane stored in rocks beneath glaciers is leached out by melting water.
• Methane mobilization in a glacial basin appears to depend on its different hydrological systems.
• Groundwater plays a large role in transporting underground methane to the surface, especially at the edge of the glacier, where melting glaciers expose unfrozen "taliks" in Spitsbergen.
• Increased melt flows due to accelerating glacier ablation are likely to dominate future changes in methane emissions by leaching more methane through subglacial and subsurface flows until maximum water production is reached.

Important points:

• Glacial rivers in Spitsbergen may be a significant source of methane, which has been overlooked until now.
• Small valley glaciers can mobilize more methane per unit area than larger ice sheets.
• The methane in the Vallåkrabreen glacial river is predominantly of geological origin, not microbial.
• Accelerating melting of glaciers may lead to increased methane release.

Implications: The findings suggest that methane emissions from glacial rivers are likely more widespread than previously thought, and contributions from valley and mountain glaciers in the Arctic should not be neglected. Spring

Glossary of key terms

• Proglacial: An area or environment located directly in front of or near a glacier.
• Thermogenic methane: Methane formed from organic material deep underground due to heat and pressure, associated with oil and natural gas.
• δ13C-CH4 (Delta C-13 CH4): A measure of the ratio of stable carbon isotopes in a methane molecule. Helps identify the source of the methane, whether microbial or thermogenic.
• Ebullition: The release of gas bubbles from a liquid.
• Methanotrophy: A biological process by which microorganisms consume methane.
• Anoxic environment: An oxygen-free environment.
• Hydrological basin: An area of land where all the water that falls drains into a common drain.
• Litorostratigraphic unit: A unit of geological rocks characterized by its stratigraphy and rock properties.
• Cryospheric cover: A boundary system in which frozen water exists on the Earth's surface.