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

https://doi.org/10.1016/j.scitotenv.2020.144106Get rights and content

Highlights

  • 36Cl/Cl and Cl inputs for paleorecharge were determined using 81Kr data.

  • The identified initial 36Cl/Cl ratio coincides with observations from recent rains.

  • The 36Cl/Cl ratio of recharge is dominated by the dissolution of near-surface salts.

  • Groundwater basins surrounding the Mediterranean reveal very different 36Cl/Cl ratios.

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.

Introduction

Old groundwater (>104 years) dominates large aquifers around the globe (Jasechko et al., 2017). However, only a few environmental tracers can be used for groundwater age evaluation on the timescales of 104–106 years. Among these are two cosmogenic radioisotopes: 36Cl and 81Kr, with half-lives of 301 (±4) and 229 (±11) kyr, respectively (Baglin, 2008; Nica et al., 2012). While the latter, which is considered to be an ideal dating tool due to the inert properties of the noble gas, has become a practical tool only recently (Aeschbach-Hertig, 2014), 36Cl has been widely applied since the 1980s in various hydrological studies (e.g., Bentley et al., 1986b; Love et al., 2000; Paul et al., 1986; Phillips et al., 1986). However, these studies also shed light on the complex mechanisms and processes that can hamper the use of this radioactive tracer as an effective dating tool (Andrews and Fontes, 1992; Davis et al., 1998; Phillips, 2013).

For translating groundwater 36Cl raw data into tracer age, the initial input, including the Cl content (Ci) and 36Cl/Cl ratio (Ri) of the recharge water, must be evaluated. This input includes meteoric and epigene sources, which may vary both spatially and temporally (Bentley et al., 1986a; Phillips, 2000, Phillips, 2013). Spatial variations include differences in the atmospheric 36Cl fallout rates at different latitudes (Bentley et al., 1986a; Lal and Peters, 1967), and a decrease in the contribution of seaborne Cl with a low 36Cl/Cl ratio as a function of the distance from coastal areas (Davis et al., 2003; Johnston and McDermott, 2008; Moysey et al., 2003). Temporal variations in the atmospheric 36Cl production of up to double the rates were observed in Late Pleistocene to Holocene records (Baumgartner et al., 1998; Plummer et al., 1997; Wagner et al., 2000). Such temporal changes have not yet been identified in old (>105 years) groundwater systems (Phillips, 2013). Variations in the climatic conditions may cause further modifications in the initial Cl and 36Cl concentrations, including a positive correlation between precipitation amount and 36Cl input (Knies, 1994; Phillips, 2000), and by varying evapotranspiration rates that concentrate 36Cl and Cl equally, thus preserving the 36Cl/Cl ratio (Bentley et al., 1986a).

Epigene sources may derive from the production of 36Cl by various mechanisms related to the interaction of cosmic ray particles and secondary neutrons with Cl, Ca, and K elements (e.g. Evans et al., 1997; Gosse and Phillips, 2001; Marrero et al., 2016; Stone et al., 1996, Stone et al., 1998). Accordingly, contributions from eroded surface materials have previously been proposed to explain higher-than-predicted input ratios (Andrews et al., 1991; Andrews and Fontes, 1992; Phillips, 2000). In situ production could also occur in the deep subsurface, below the reach of cosmic ray particles (Lehmann et al., 1993; Phillips, 2000). Further modifications in the 36Cl/Cl ratio may occur in the saturated zone as a result of Cl introduction from external sources (e.g., brines or aquitards) or by the dissolution of Cl-bearing minerals (Phillips, 2013). Finally, in recent groundwater, the natural input can also be affected by the contribution of anthropogenic 36Cl (Fabryka-Martin et al., 1987), which may undergo recycling processes in the terrestrial environment (Corcho Alvarado et al., 2005; Tanaka and Thiry, 2020).

Unlike the 36Cl/Cl system, 81Kr/Kr input ratios are less affected by temporal and spatial variations (Buizert et al., 2014; Zappala et al., 2020), and in situ 81Kr production is estimated to be negligible in most groundwater systems (Lehmann et al., 1993; Purtschert et al., 2013). 81Kr was long ago identified as an ideal dating tool (Lehmann et al., 1985; Loosli and Oeschger, 1969; Mazor, 1972), but effective tools for the extraction, separation, and measurement of the rare noble gas were developed only during the last two decades (Chen et al., 1999; Lu et al., 2014; Yokochi, 2016). This recent availability of independent 81Kr age information offers the opportunity to assess the basic parameters required for accurate 36Cl dating in groundwater and to examine the more complex hydrological cycle of 36Cl. Indeed, the possible use of 81Kr to calibrate the 36Cl dating method has been demonstrated in two pioneering studies from the Great Artesian Basin (Australia) and Egypt's Western Desert (Lehmann et al., 2003; Sturchio et al., 2004).

In the present study, the simultaneous measurement of 81Kr/Kr and 36Cl/Cl ratios in groundwater from Israel's Negev Desert allows, for the first time, a reliable reconstruction of the initial Cl content and the 36Cl/Cl input ratio of the recharge flux into the regional ancient Nubian Sandstone Aquifer (NSA). Combined with published initial 36Cl/Cl ratios for other basins around the Mediterranean, the obtained results illuminate the dynamic processes in the hydrosphere that dominate the input, and specifically, the effect of eroded surface material on the initial 36Cl/Cl ratio of the recharge flux. Expanding the knowledge regarding the systematic processes that take place in the atmosphere and the epigene zone and that dictate the Cl and 36Cl inputs can potentially improve the availability of 36Cl as an age tracer.

Section snippets

Hydrogeological settings

This study focuses on the deep regional NSA, also known locally as the Kurnub Group (Lower Cretaceous) Aquifer. This aquifer stretches underneath vast parts of the Sinai Peninsula (Egypt) and the Negev Desert (Israel), and thus is also denoted the NSA of the Sinai-Negev Basin. Hyper-arid conditions with low precipitation, amounting to <100 mm/yr on average, currently prevail over most of the basin including the replenishment areas (Fig. 1a,b). The basin is bounded by the uplifted basement rocks

Field and lab methods

Groundwater samples were collected from several different aquifers in the Negev Desert (Fig. 1) between 2014 and 2019. For Kr isotope analysis, gas samples were extracted from typically 300–400 L of flowing groundwater using a field degassing device (Purtschert et al., 2013; Yokochi, 2016). Additional air samples were collected for measurements of atmospheric 85Kr activity (half-life of 10.74 yr). Water samples were collected for 36Cl/Cl analysis in 1-L (or smaller) plastic bottles, without any

Chemical and isotopic compositions of the NSA

The chemical and isotopic analyses of groundwater from the different aquifers in the Negev Desert, as well as computed deuterium excess values (dex = δ2H-8 × δ18O), are summarized in Table 1. In the confined parts of the NSA, 36Cl/Cl ratios and Cl contents range mostly from 20 to 30 × 10−15 and 600–800 mg/L, respectively. A clear correlation between δ18O, δ2H, and 81Kr ages in the aquifer (Fig. 2a, b) shows that the origin and age of most of the groundwater samples can be explained by the

Conclusions

The Nubian Sandstone Aquifer underneath Israel's arid Negev Desert contains groundwater with residence times of 104–105 years. This time-domain, determined by 81Kr dating, was used to examine the processes affecting 36Cl/Cl input ratios other than radioactive decay. The combined 81Kr and 14C age information enabled us to reconstruct a 36Cl/Cl ratio of about 50 × 10−15 for groundwater recharge in the Negev Desert. A similarity between the reconstructed 36Cl/Cl input for paleorecharge during the

CRediT authorship contribution statement

Roi Ram: Conceptualization, Investigation, Methodology, Writing – original draft, Visualization. Roland Purtschert: Conceptualization, Methodology, Investigation, Resources, Writing – original draft, Visualization. Eilon M. Adar: Conceptualization, Investigation, Writing – review & editing, Funding acquisition. Michael Bishof: Methodology, Validation. Wei Jiang: Methodology, Validation, Investigation, Resources, Writing – review & editing. Zheng-Tian Lu: Methodology, Validation, Investigation,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We thank the Israel Water Authority, the Mekorot LTD National Water Company, and the Dead Sea Works LTD for providing access to wells for sampling. We wish to thank Arik Kaplan and Gal Littman from the Zuckerberg Institute for Water Research (ZIWR) for their help in the fieldwork. The geochemical labs of the Geological Survey of Israel and the ZIWR are thanked for the precise analytical work. Special thanks go to Neil Sturchio and Avner Vengosh for data sharing, and Moshe Armon for the help

Funding

This work was funded by the Ben-Gurion University-Argonne National Laboratory-University of Chicago Collaboration Program; the United States-Israel Binational Science Foundation (Grant No. 2014351); the Israel Water Authority, Ministry of Energy (Grant No. 4501284811); and the RADIATE project under the Grant Agreement 824096 from the EU Research and Innovation programme HORIZON 2020. This project was also supported by the Swiss National Science Foundation Project (SNF-200020_172550). Work at

References (122)

  • O. Crouvi et al.

    Sand dunes as a major proximal dust source for late Pleistocene loess in the Negev Desert

    Israel. Quat. Res.

    (2008)
  • J. Dan et al.

    Evolution of reg soils in Southern Israel and Sinai

    Geoderma

    (1982)
  • Y. Enzel et al.

    The climatic and physiographic controls of the eastern Mediterranean over the late Pleistocene climates in the southern Levant and its neighboring deserts

    Glob. Planet. Change

    (2008)
  • J.M. Evans et al.

    Cosmogenic chlorine-36 production in K-feldspar

    Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms

    (1997)
  • J. Fabryka-Martin et al.

    Applications of 129I and 36Cl in hydrology

    Nucl. Inst. Methods Phys. Res. B

    (1987)
  • J.R. Gat et al.

    Desert isotope hydrology: water sources of the Sinai Desert

    Geochim. Cosmochim. Acta

    (1974)
  • J.C. Gosse et al.

    Terrestrial in situ cosmogenic nuclides: theory and application

    Quat. Sci. Rev.

    (2001)
  • A. Guendouz et al.

    Chlorine-36 dating of deep groundwater from northern Sahara

    J. Hydrol.

    (2006)
  • B. Herut et al.

    36Cl in chloride-rich rainwater

    Israel. Earth Planet. Sci. Lett.

    (1992)
  • B. Herut et al.

    Relationship between the acidity and chemical composition of rainwater and climatological conditions along a transition zone between large deserts and Mediterranean climate

    Israel. Atmos. Environ.

    (2000)
  • A. Issar

    The paleohydrology of southern Israel and its influence on the flushing of the Kurnub and 'Arad groups (Lower Cretaceous and Jurassic)

    J. Hydrol.

    (1979)
  • A. Issar

    The rate of flushing as a major factor in determining the chemistry of water in fossil aquifers in southern Israel

    J. Hydrol.

    (1981)
  • A. Issar et al.

    On the ancient water of the Upper Nubian Sandstone aquifer in central Sinai and southern Israel

    J. Hydrol.

    (1972)
  • W. Jiang et al.

    An atom counter for measuring 81Kr and 85Kr in environmental samples

    Geochim. Cosmochim. Acta

    (2012)
  • V.E. Johnston et al.

    The distribution of meteoric Cl-36 in precipitation across Europe in spring 2007

    Earth Planet. Sci. Lett.

    (2008)
  • V. Lavastre et al.

    Establishing constraints on groundwater ages with 36Cl, 14C, 3H, and noble gases: a case study in the eastern Paris basin

    France. Appl. Geochem.

    (2010)
  • B.E. Lehmann et al.

    A comparison of groundwater dating with 81Kr, 36Cl and 4He in four wells of the Great Artesian Basin

    Australia. Earth Planet. Sci. Lett.

    (2003)
  • H.H. Loosli et al.

    37Ar and 81Kr in the atmosphere

    Earth Planet. Sci. Lett.

    (1969)
  • Z.-T. Lu et al.

    Tracer applications of noble gas radionuclides in the geosciences

    Earth-Science Rev.

    (2014)
  • S.M. Marrero et al.

    CRONUS-Earth cosmogenic 36Cl calibration

    Quat. Geochronol.

    (2016)
  • A. Matmon et al.

    Controls on aggradation and incision in the NE Negev, Israel, since the middle Pleistocene

    Geomorphology

    (2016)
  • T. Matsumoto et al.

    Krypton-81 dating of the deep Continental Intercalaire aquifer with implications for chlorine-36 dating

    Earth Planet. Sci. Lett.

    (2020)
  • E. Mazor

    Paleotemperatures and other hydrological parameters deduced from noble gases dissolved in groundwaters; Jordan Rift Valley

    Israel. Geochim. Cosmochim. Acta

    (1972)
  • T. Müller et al.

    Use of multiple age tracers to estimate groundwater residence times and long-term recharge rates in arid southern Oman

    Appl. Geochem.

    (2016)
  • R. Nativ et al.

    Chemical composition of rainwater and floodwaters in the Negev Desert, Israel

    J. Hydrol.

    (1983)
  • R. Nativ et al.

    Water salinization in arid regions - observations from the Negev desert, Israel

    J. Hydrol.

    (1997)
  • N. Nica et al.

    Nuclear data sheets for A = 36. Nucl

    Data Sheets

    (2012)
  • Z.Y. Offer et al.

    Chemistry and granulometry of settled dust in the northern Negev Desert, Israel (1987–1988)

    Sci. Total Environ.

    (1992)
  • Z.Y. Offer et al.

    Chemistry and mineralogy of four dust storms in the northern Negev Desert, Israel (1988–1992)

    Sci. Total Environ.

    (1994)
  • J.O. Petersen et al.

    Quantifying paleorecharge in the Continental Intercalaire (CI) aquifer by a Monte-Carlo inversion approach of 36Cl/Cl data

    Appl. Geochem.

    (2014)
  • J.O. Petersen et al.

    Groundwater flowpaths and residence times inferred by 14C, 36Cl and 4He isotopes in the Continental Intercalaire aquifer (North-Western Africa)

    J. Hydrol.

    (2018)
  • F.M. Phillips et al.

    An improvement approach to calculating low-energy cosmic-ray neutron fluxes near the land/atmosphere interface

    Chem. Geol.

    (2001)
  • K. Pye

    The nature, origin and accumulation of loess

    Quat. Sci. Rev.

    (1995)
  • R. Ram et al.

    Identifying recharge processes into a vast “fossil” aquifer based on dynamic groundwater 81Kr age evolution

    J. Hydrol.

    (2020)
  • E. Rosenthal et al.

    The chemical evolution of Kurnub Group paleowater in the Sinai-Negev province - a mass balance approach

    Appl. Geochem.

    (1998)
  • L. Scheiber et al.

    Recent and old groundwater in the Niebla-Posadas regional aquifer (southern Spain): implications for its management

    J. Hydrol.

    (2015)
  • A. Shalaby et al.

    Structural constraints on the groundwater regime of the Cretaceous aquifers in Central Sinai

    Egypt. J. African Earth Sci.

    (2012)
  • S.G. Abd El Samie et al.

    Groundwater recharge and flow in the Lower Cretaceous Nubian Sandstone aquifer in the Sinai Peninsula, using isotopic techniques and hydrochemistry

    Hydrogeol. J.

    (2001)
  • A. Abouelmagd

    Paleoclimatic Regimes of the African Sahara Desert During Pleistocene and the Origin of Groundwater in the Nubian Sandstone Aquifer System

    (2012)
  • W. Aeschbach-Hertig

    Radiokrypton dating finally takes off

    Proc. Natl. Acad. Sci. U. S. A.

    (2014)
  • Cited by (9)

    • Residence times of groundwater along a flow path in the Great Artesian Basin determined by <sup>81</sup>Kr, <sup>36</sup>Cl and <sup>4</sup>He: Implications for palaeo hydrogeology

      2023, Science of the Total Environment
      Citation Excerpt :

      However, up until the present, it has not been possible for the 4He clock to be calibrated against a reliable residence time indicator, not only for the GAB, but also for other large aquifers systems around the globe (Torgersen, 2010). It is only recently that the detection of 81Kr at natural levels has been developed with a precision sufficient to date groundwater (Gerber et al., 2017; Jiang et al., 2020; Matsumoto et al., 2018; Ram et al., 2021; Sturchio et al., 2014; Yechieli et al., 2019; Yokochi et al., 2019; Yokochi et al., 2021), but it has for a long time been potentially considered to be the most reliable isotope to quantify long groundwater residence times (Lehmann et al., 1993; Lehmann et al., 2003). This is because krypton (Kr), being a noble gas is inert and as a result does not undergo chemical reactions.

    • Large-scale paleo water-table rise in a deep desert aquifer recorded by dissolved noble gases

      2022, Journal of Hydrology
      Citation Excerpt :

      The measured dissolved noble gas bulk concentrations in the NSA, including Ne, Ar, Kr, and Xe, are given in Table 1. Before any attempts at quantitatively modeling the noble gas data, we first show dissolved Ne concentrations alongside published 81Kr ages (Ram et al., 2020, 2021; Yokochi et al., 2019) and δ18O values for examination of the obtained noble gas data (Fig. 2). We observe an extreme Ne enrichment relative to ASW in the older, 18O-depleted groundwater from the southern Negev and the southern Arava Valley (hereafter defined as group 1), for which the recharge through the southern outcrops in Sinai is dominant (Yokochi et al., 2019).

    View all citing articles on Scopus
    View full text