Radiokrypton unveils dual moisture sources of a deep desert aquifer

Reika Yokochi, Roi Ram, Jake C. Zappala, Wei Jiang, Eilon Adar, Ryan Bernier, Avihu Burg, Uri Dayan, Zheng Tian Lu, Peter Mueller, Roland Purtschert, Yoseph Yechieli

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

In arid regions, groundwater is a vital resource that can also provide a long-term record of the regional water cycle. However, the use of groundwater as a paleoclimate proxy has been limited by the complex hydrology and the lack of appropriate chronometers to determine the recharge time without complication. Applying 81Kr, a long-lived radioisotope tracer, we investigate the paleohydroclimate and subsurface water storage properties of the Nubian Sandstone Aquifer in the Negev Desert, Israel. Based on the spatial distributions of stable isotopes and the abundance of 81Kr, we resolve subsurface mixing and identify two distinct moisture sources of the recharge: one recent (<38 ky ago) from the Mediterranean and the other 361 ± 30 ky ago from the tropical Atlantic, both of which occurred under conditions of low orbital eccentricity comparable to that of the present. The recent recharge provided by the moisture from Mediterranean cyclones can be attributed to the southward shift of the storm track during the Last Glacial Maximum, and the earlier recharge can be attributed to moisture from the Atlantic delivered as tropical plumes under a climate colder than the present. Furthermore, the residence time of the latter reveals that tectonically active terrain can store groundwater for an unexpectedly long period, likely due to strongly attenuated groundwater flow across the fault zones. With this tracer, groundwater can now serve as a direct record of paleoprecipitation over land and of subsurface water storage from the mid-Pleistocene and onward.

Original languageEnglish
Pages (from-to)16222-16227
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume116
Issue number33
DOIs
StatePublished - 13 Aug 2019

Keywords

  • Groundwater dating
  • Moisture sources
  • Paleohydroclimate
  • Radiokrypton isotopes
  • Subsurface water storage

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