Combining 14CDOC and 81Kr with hydrochemical data to identify recharge processes in the South German Molasse Basin

Theis Winter, Florian Einsiedl

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To face the challenges of ongoing climate change, renewable energy sources are needed to reduce CO2 emissions to the atmosphere. The South German Molasse Basin (SGMB) contains an important geothermal aquifer in Germany; however, an enhanced understanding of the flow regime at the basin scale remains a fundamental limiting factor in assessing a long-term and sustainable strategy for using this green energy source. Here we report 14CDOC and 81Kr groundwater dating results together with hydrochemical data, stable water isotopes, noble gases and out-diffusion experiments that indicate that the thermal groundwater consists of at least two groundwater sources: a formerly unknown young groundwater component with apparent water ages between 9,800 and 18,700 a and an old groundwater component, which shows an apparent water age of up to approximately 300 ka. The results of the out-diffusion experiments with core material from the Upper Jurassic aquifer (UJA) suggest that diffusion processes between rock-matrix water and more mobile fracture water represent a controlling mechanism for groundwater flow and the observed extended apparent groundwater ages within the UJA. The observed elevated 14CDOC activities and the high spatial heterogeneity in groundwater ages close to the southern margin of the SGMB were interpreted as a recharge zone of the system. The combination of the 14CDOC and 81Kr methods shows the potential as a powerful groundwater dating tool for deep aquifers.

Original languageEnglish
Article number128020
JournalJournal of Hydrology
StatePublished - Sep 2022


  • C
  • Geothermal groundwater
  • Groundwater dating
  • Kr
  • South German Molasse Basin
  • Upper Jurassic Aquifer


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