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Radiokrypton unveils dual moisture sources of a deep desert aquifer

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Yokochi Reika, Ram Roi, Zappala Jake C., Jiang Wei, Adar Eilon, Bernier Ryan, Burg Avihu, Dayan Uri, Lu Zheng-Tian, Mueller Peter, Purtschert Roland, Yechieli Yoseph,
Project Klima- und Umweltphysik: Isotope im Erdklimasystem (icoCEP)
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Original article (peer-reviewed)

Journal Proceedings of the National Academy of Sciences
Volume (Issue) 116
Page(s) 16222 - 16222
Title of proceedings Proceedings of the National Academy of Sciences

Abstract

Paleoprecipitation records and subsurface water storage properties are essential data ingredients for accurate hydroclimate and water balance projections. Although both types of data could be extracted from groundwater, their application over long timescales had been limited by the lack of appropriate chronometers. We used a long-lived radiokrypton isotope and identified two distinct moisture source contributions to a deep desert aquifer from low eccentricity periods, one recent and the other 360 ky ago. The groundwater recharge periods show the sensitivity of the moisture transport processes to orbital forcing, whereas the long storage reflects subsurface flow attenuation exerted by faults. Krypton-81 enables groundwater to serve as a direct record of paleoprecipitation over land and of subsurface water storage for the past 1,300 ky.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.
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