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<p>Radiogenic helium (⁴He) has long been recognised as a potential indicator of groundwater residence time, but its quantitative application has remained largely site-dependent because helium concentrations integrate production, crustal fluxes, transport and mixing processes. In contrast, krypton-81 (⁸¹Kr) provides a conservative chronometer for old groundwater, yet paired ⁴He–⁸¹Kr datasets have remained extremely scarce. Here we compile a uniquely expanded global dataset of groundwater samples with paired dissolved radiogenic ⁴He concentrations and independently determined ⁸¹Kr residence times across diverse aquifer systems. Dissolved ⁴He increases monotonically with groundwater age over nearly three orders of magnitude and follows a simple empirical scaling for waters older than ~ 50 kyr that is robust to the exclusion of individual basins. More than 80% of helium-derived ages agree with corresponding ⁸¹Kr residence times within a factor of three under conservative cross-basin validation. These results demonstrate that radiogenic helium, when anchored to an absolute chronometer, can serve as a transferable first-order proxy for groundwater residence time, providing a practical basis for global groundwater age screening and targeted application of high-precision dating methods.</p>

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A global helium clock for groundwater residence time

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年6月1日

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  • Takuya Matsumoto,
  • Daniele Luigi Pinti,
  • Wei Jiang,
  • Zheng-Tian Lu,
  • Guo-Min Yang,
  • Peter Mueller,
  • Rachid Abdelouahab,
  • Adnane Souffi Moulla,
  • Darren Hillegonds,
  • Jennifer Mabry,
  • Nicolo Romeo

摘要

Radiogenic helium (⁴He) has long been recognised as a potential indicator of groundwater residence time, but its quantitative application has remained largely site-dependent because helium concentrations integrate production, crustal fluxes, transport and mixing processes. In contrast, krypton-81 (⁸¹Kr) provides a conservative chronometer for old groundwater, yet paired ⁴He–⁸¹Kr datasets have remained extremely scarce. Here we compile a uniquely expanded global dataset of groundwater samples with paired dissolved radiogenic ⁴He concentrations and independently determined ⁸¹Kr residence times across diverse aquifer systems. Dissolved ⁴He increases monotonically with groundwater age over nearly three orders of magnitude and follows a simple empirical scaling for waters older than ~ 50 kyr that is robust to the exclusion of individual basins. More than 80% of helium-derived ages agree with corresponding ⁸¹Kr residence times within a factor of three under conservative cross-basin validation. These results demonstrate that radiogenic helium, when anchored to an absolute chronometer, can serve as a transferable first-order proxy for groundwater residence time, providing a practical basis for global groundwater age screening and targeted application of high-precision dating methods.