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 language | English |
|---|---|
| Pages (from-to) | 16222-16227 |
| Number of pages | 6 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Volume | 116 |
| Issue number | 33 |
| DOIs | |
| State | Published - Aug 13 2019 |
| Externally published | Yes |
Funding
ACKNOWLEDGMENTS. This work was funded by the Ben Gurion University– Argonne National Laboratory–University of Chicago Collaborative Water Research Initiative, the United States-Israel Binational Science Foundation (Grant 2014351), and Israel Water Authority (Grant 4501284811). R.R. was supported by the Israel Ministry of Science and Technology and by the Pratt Foundation. J.C.Z., W.J., Z.-T.L., and P.M. acknowledge support by the Department of Energy, Office of Nuclear Physics, under contract DEAC02-06CH11357. We thank the Israel Water Authority, Dead Sea Works Ltd., and Mekorot Water Company Ltd. for providing access to their observation boreholes and production wells and Israeli Hydrological Service for providing the water head data. We thank Arik Kaplan for his support throughout the sampling campaign in Israel. We thank the field workers of the Geological Survey of Israel (GSI) for their help in sampling the water wells, the staff of the Geochemical Division of the GSI for the precise analytical work, and Christoph Raible for providing scientific inputs on climatic controls of atmospheric circulation over Europe. R.Y. thanks N. Sturchio, D. Rowley, E. Kite, N. Nakamura, T. Shaw, A. Marzocchi, D. Abbot, A. Pourmand, A. Vaks, G. Olack, A. Davis, and N. Dauphas for scientific discussions and advice. R.Y. thanks B. Lynch, J. Eason, and PSD Desktop Support for their support.
Keywords
- Groundwater dating
- Moisture sources
- Paleohydroclimate
- Radiokrypton isotopes
- Subsurface water storage