2023-07-06 ケンブリッジ大学
◆これまで注目されていなかったメタン排出源である湧水は、世界のメタン予算の見積もりに欠けていました。今後、湧水が増えることでこのメタン源はより重要になると予想されています。この研究は、北極の解凍によるメタン排出が人為的な地球温暖化を加速する可能性を示しており、早急な対策が必要とされています。
＜関連情報＞
氷河後退時に形成される地下水泉は高緯度北極圏におけるメタンの大きな供給源である Groundwater springs formed during glacial retreat are a large source of methane in the high Arctic
Gabrielle E. Kleber,Andrew J. Hodson,Leonard Magerl,Erik Schytt Mannerfelt,Harold J. Bradbury,Yizhu Zhu,Mark Trimmer & Alexandra V. Turchyn
Nature Geoscience Published:06 July 2023
DOI:https://doi.org/10.1038/s41561-023-01210-6
Abstract
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.
