Intermittently Bubbling Well With He-Rich N2-Bubbles Constrain the Possibility of Atmospheric and Biogenic N2 Exsolution and the History of He-Rich Groundwater From Basement to Surface
Résumé
Using Henry's law for di-nitrogen and simple budget equations, we show theoretically that generating ${\mathrm{N}}_{2}$ bubbles in spring water, by exsolution of atmospheric ${\mathrm{N}}_{2}$ formerly dissolved in recharge water, is possible if the water becomes warm and salty at depth in the basement before rising upward when pressure drop triggers bubble generation. Based on ${\delta }^{15}N$ results (Dantas Cardoso et al., 2023, https://doi.org/10.1016/j.chemgeo.2023.121588), we suggest that biogenic ${\mathrm{N}}_{2}$ may complement atmospheric ${\mathrm{N}}_{2}$, thus easing exsolution. This model is an alternative to the generation of ${\mathrm{N}}_{2}$ by mostly unknown metamorphic reactions in the basement. It can be coupled to Torgersen's equation (Torgersen, 1980, https://doi.org/10.1016/0375-6742(80)90021-7), describing long residence in the basement porosity, thus accounting for ${\mathrm{N}}_{2}$ bubbles with high He, as observed at the "Fontaines Salées" site, in the Morvan region of the northern Massif Central of France (Léger et al., 2025, https://doi.org/10.1029/2024gc012021).
Domaines
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Cite 10.5281/zenodo.14234232 Jeu de données LEGER, E. (2025). Dataset for ‘Deciphering degassing mechanisms of He and H$_2$ at the sedimentary basin-basement interface by surface geophysics and gas geochemistry’ [Data set]. Zenodo. https://doi.org/10.5281/ZENODO.14234232




