Controls on the 36Cl/Cl input ratio of paleo-groundwater in arid environments: New evidence from 81Kr/Kr data

Roi Ram, Roland Purtschert, Eilon M. Adar, Michael Bishof, Wei Jiang, Zheng Tian Lu, Peter Mueller, Adrien Sy, Christof Vockenhuber, Yoseph Yechieli, Reika Yokochi, Jake C. Zappala, Avihu Burg

Research output: Contribution to journalArticlepeer-review

Abstract

Measurements of the long-lived 81Kr and 36Cl radioisotopes in groundwater from the Negev Desert (Israel) were used to assess the 36Cl/Cl input ratios and Cl contents for paleorecharge into the Nubian Sandstone Aquifer (NSA). The reconstructed Cl content of the recharge flux was on the order of 300–400 mg/L. An initial 36Cl/Cl ratio of 50 × 10−15 was assessed for the groundwater replenishment in the Negev Desert since the late Pleistocene, in agreement with the 36Cl/Cl ratios in recent local rainwater. This is despite possible changes in the climatic conditions and the 36Cl production rates in the atmosphere over this timeframe. This similarity in values is explained by the major role played by the erosion and weathering of near-surface materials in the desert environment that dominate the hydrochemistry of rains, floods, and the consequent groundwater recharge. Spatial variation in the reconstructed initial 36Cl/Cl ratio is accounted for by the differences in the mineral aerosol sources for specific recharge areas of the NSA. Accordingly, regional variations in the 36Cl/Cl input in groundwater reservoirs surrounding the Mediterranean Sea indicate various processes that govern the 36Cl/Cl system. Finally, the results of this study highlight the great advantage of integrating 81Kr age information in evaluating the initial 36Cl/Cl and Cl input, which is essential for the calibration of 36Cl radioisotope as an available long-term dating tool for a given basin.

Original languageEnglish
Article number144106
JournalScience of the Total Environment
Volume762
DOIs
StatePublished - 25 Mar 2021

Keywords

  • Cosmogenic nuclides
  • Epigenic Cl
  • Nubian Sandstone Aquifer
  • Old groundwater dating
  • Radiokrypton isotopes
  • Sinai-Negev Basin

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