| Summary: | Acknowledgements: This work was supported by the CLIMAGAS and HYDRO-SURGE projects, both funded by the Research Council of Norway (project no. 294764 (A.J.H.) and 329174 (G.E.K.), respectively). Funding for fieldwork was also provided by the Robert Scott Fund granted by The Geological Society of London (G.E.K.). We thank the governor of Svalbard for granting us access to restricted zones to conduct fieldwork, as well as S. M. Cohen and the rest of the UNIS Logistics team for their field support. We are grateful to M. Gevers, E. Jones, K. Redeker, M. T. Hornum and P. Betlem for their help in the field and valuable discussions on methane fluxes, glacial hydrology and gas hydrate stability zones. <jats:title>Abstract</jats:title><jats:p>Permafrost and glaciers in the high Arctic form an impermeable ‘cryospheric cap’ that traps a large reservoir of subsurface methane, preventing it from reaching the atmosphere. Cryospheric vulnerability to climate warming is making releases of this methane possible. On Svalbard, where air temperatures are rising more than two times faster than the average for the Arctic, glaciers are retreating and leaving behind exposed forefields that enable rapid methane escape. Here we document how methane-rich groundwater springs have formed in recently revealed forefields of 78 land-terminating glaciers across central Svalbard, bringing deep-seated methane gas to the surface. Waters collected from these springs during February–May of 2021 and 2022 are supersaturated with methane up to 600,000 times greater than atmospheric equilibration. Spatial sampling reveals a geological dependency on the extent of methane supersaturation, with isotopic evidence of a thermogenic source. We estimate annual methane emissions from proglacial groundwaters to be up to 2.31 kt across the Svalbard archipelago. Further investigations into marine-terminating glaciers indicate future methane emission sources as these glaciers transition into fully land-based systems. Our findings reveal that ...
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