Dissolved helium distribution in deep groundwaters from the Tono area, central Japan: a tool for tracing groundwater flow in fractured granite

Morikawa, Noritoshi

doi:10.1007/s10201-004-0118-5

Cited by 4 publications

(1 citation statement)

References 30 publications

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“…1 ), the fractures associated with the fault might serve as a fast conduit for deeply produced H 2 . As previously reported from the surrounding area [34] , isotopic analyses of noble gases revealed high ratios of mantle-derived 3 He relative to radiogenic 4 He in groundwater from the monitoring boreholes (S4 Table and S2 Figure in S1 File ). Thus, H 2 generated in the mantle by high temperature reactions among dissolved gases in the C–H–O–S system [35] might be supplied along with 3 He to the granitic aquifer.…”

Section: Resultssupporting

confidence: 79%

Biogeochemical Signals from Deep Microbial Life in Terrestrial Crust

et al. 2014

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In contrast to the deep subseafloor biosphere, a volumetrically vast and stable habitat for microbial life in the terrestrial crust remains poorly explored. For the long-term sustainability of a crustal biome, high-energy fluxes derived from hydrothermal circulation and water radiolysis in uranium-enriched rocks are seemingly essential. However, the crustal habitability depending on a low supply of energy is unknown. We present multi-isotopic evidence of microbially mediated sulfate reduction in a granitic aquifer, a representative of the terrestrial crust habitat. Deep meteoric groundwater was collected from underground boreholes drilled into Cretaceous Toki granite (central Japan). A large sulfur isotopic fractionation of 20–60‰ diagnostic to microbial sulfate reduction is associated with the investigated groundwater containing sulfate below 0.2 mM. In contrast, a small carbon isotopic fractionation (<30‰) is not indicative of methanogenesis. Except for 2011, the concentrations of H2 ranged mostly from 1 to 5 nM, which is also consistent with an aquifer where a terminal electron accepting process is dominantly controlled by ongoing sulfate reduction. High isotopic ratios of mantle-derived 3He relative to radiogenic 4He in groundwater and the flux of H2 along adjacent faults suggest that, in addition to low concentrations of organic matter (<70 µM), H2 from deeper sources might partly fuel metabolic activities. Our results demonstrate that the deep biosphere in the terrestrial crust is metabolically active and playing a crucial role in the formation of reducing groundwater even under low-energy fluxes.

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Section: Resultssupporting

confidence: 79%