Groundwater springs formed during glacial retreat are a large source of methane in the high Arctic. Current research with the researcher Gabby Kelder (Columbia) et Andy Hodson (UNIS). Svalbard 2023
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 climate-driven glacial retreat facilitates widespread release of methane, a positive feedback loop that is probably prevalent across other regions of the rapidly warming Arctic.
Main
Globally relevant amounts of methane in subsurface natural gas deposits and coal beds of the Arctic1 are assumed to be sealed beneath a perennially frozen ‘cryospheric cap’ of permafrost and glaciers2,3,4,5. At sufficiently high pressures and low temperatures, the methane beneath permafrost and glaciers can be trapped as a solid gas hydrate6. These pressure and temperature conditions may shift with climate warming and glacial retreat, potentially causing the disintegration of gas hydrates and release of deep, subsurface methane to the Arctic atmosphere4,7,8,9,10,11. In cases where pressures are too low for gas hydrate stability, increased summer mass losses of glaciers are able to recharge groundwater aquifers beneath the permafrost and encourage the migration of gas to the surface12.
Permafrost degradation due to increasing Arctic air temperatures is slow relative to glacial retreat. In the case of land-terminating glaciers, glacial retreat can expose forefields (land that was previously covered by the glacier) with areas where permafrost is out of equilibrium with the climate and therefore either absent or discontinuous. These forefields provide an outlet for subpermafrost groundwaters that were previously sealed beneath the overburden glacier and permafrost and facilitate the formation of terrestrial methane seepage (Fig. 1). Mean annual air temperatures on Svalbard, a Norwegian archipelago in the high Arctic, are rising at a rate five to seven times faster than the global average and twice as fast as elsewhere in the Arctic13. Rising temperatures have led to a 30% volume loss of glaciers on Svalbard since 1936, which has been accompanied by a decrease in glacial coverage by about 10.4% (ref. 14). Increased summer ablation and rapidly expanding glacial forefields due to glacial retreat are causing new methane seepage pathways to form in association with proglacial groundwater springs. This study presents evidence that these seepage pathways induce widespread groundwater-driven methane escape from glacial forefields in the Eurasian High Arctic, a region known for its vast subpermafrost gas reserves1.
More info about the paper on Nature from my colleague Gabby Kelder : lien
