Cosmogenic, radiogenic, and stable isotopic constraints on groundwater residence time in the Nubian Aquifer, Western Desert of Egypt

Leslie J. Patterson, Neil C. Sturchio, B. Mac K. Kennedy, Matthijs Van Soest, Mohamed Sultan, Zheng Tian Lu, Bernhard Lehmann, Roland Purtschert, Zeinhom El Alfy, Baher El Kaliouby, Yehia Dawood, Ali Abdallah

Research output: Contribution to journalArticle

42 Citations (Scopus)

Abstract

[1] Measurements of radiochlorine (36Cl), radiogenic noble gases (4He and 40Ar), and stable chlorine isotope ratios were obtained to assess the residence time of groundwater in the Nubian Aquifer of the Western Desert of Egypt. Measured 36Cl/Cl ratios yield apparent residence times from ∼0.2 to 1.2 × 106 years in the deep (600-1200 m) groundwater (assuming constant Cl) and ≤0.16 × 10 6 years in the shallow (<600 m) groundwater. Values of δ37Cl in the groundwater strengthen the application of the 36Cl dating method by constraining Cl sources and identifying groundwater mixing. Dissolved gases were measured in some of the deep groundwater samples. Measured 4He concentrations indicate accumulation of radiogenic 4He that is qualitatively consistent with the age progression indicated by the 36Cl/Cl ratios, but the flux of external 4He from the underlying crust has not been quantified and is not constant throughout the aquifer. Concentrations of 40Ar range from 3.3 to 6.7 × 10-4 ccSTP/g and indica e excess air incorpora ion a recharge. Measured 40Ar/36Ar ra ios do no exceed he a mospheric ratio. A two-dimensional numerical hydrodynamic transect of the aquifer was modeled from the area of the Uweinat Uplift to the northern Bahariya Oasis. Predicted groundwater velocities in the deep portion of the aquifer are 0.5-3.5 m/yr with groundwater residence times up to 9 × 105 years; residence times up to 1.3 × 106 years are predicted in the confining shale. Aquifer properties are estimated by using the model to fit the measured 36Cl/Cl ratios. Under these conditions, hydrodynamic residence times are within about 30% of those calculated from 36Cl when mixing of Cl- is accounted for in the highest-Cl- deep groundwaters. By mutually calibrating multiple methods (hydrodynamic, 36Cl, and 4He), a consistent picture of the Nubian Aquifer has emerged in which lateral flow from a southern recharge area dominates the deep horizons, while shallow horizons contain younger, autochthonous recharge.

Original languageEnglish (US)
Article numberQ01005
JournalGeochemistry, Geophysics, Geosystems
Volume6
Issue number1
DOIs
StatePublished - Jan 1 2005
Externally publishedYes

Fingerprint

Egypt
aquifers
deserts
ground water
Aquifers
Groundwater
residence time
desert
aquifer
groundwater
recharge
Hydrodynamics
hydrodynamics
Radiogenic gases
horizon
oases
chlorine isotope
Noble Gases
dissolved gases
dissolved gas

Keywords

  • Chlorine-36
  • Egypt
  • Groundwater

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Patterson, L. J., Sturchio, N. C., Kennedy, B. M. K., Van Soest, M., Sultan, M., Lu, Z. T., ... Abdallah, A. (2005). Cosmogenic, radiogenic, and stable isotopic constraints on groundwater residence time in the Nubian Aquifer, Western Desert of Egypt. Geochemistry, Geophysics, Geosystems, 6(1), [Q01005]. https://doi.org/10.1029/2004GC000779

Cosmogenic, radiogenic, and stable isotopic constraints on groundwater residence time in the Nubian Aquifer, Western Desert of Egypt. / Patterson, Leslie J.; Sturchio, Neil C.; Kennedy, B. Mac K.; Van Soest, Matthijs; Sultan, Mohamed; Lu, Zheng Tian; Lehmann, Bernhard; Purtschert, Roland; Alfy, Zeinhom El; Kaliouby, Baher El; Dawood, Yehia; Abdallah, Ali.

In: Geochemistry, Geophysics, Geosystems, Vol. 6, No. 1, Q01005, 01.01.2005.

Research output: Contribution to journalArticle

Patterson, LJ, Sturchio, NC, Kennedy, BMK, Van Soest, M, Sultan, M, Lu, ZT, Lehmann, B, Purtschert, R, Alfy, ZE, Kaliouby, BE, Dawood, Y & Abdallah, A 2005, 'Cosmogenic, radiogenic, and stable isotopic constraints on groundwater residence time in the Nubian Aquifer, Western Desert of Egypt', Geochemistry, Geophysics, Geosystems, vol. 6, no. 1, Q01005. https://doi.org/10.1029/2004GC000779
Patterson, Leslie J. ; Sturchio, Neil C. ; Kennedy, B. Mac K. ; Van Soest, Matthijs ; Sultan, Mohamed ; Lu, Zheng Tian ; Lehmann, Bernhard ; Purtschert, Roland ; Alfy, Zeinhom El ; Kaliouby, Baher El ; Dawood, Yehia ; Abdallah, Ali. / Cosmogenic, radiogenic, and stable isotopic constraints on groundwater residence time in the Nubian Aquifer, Western Desert of Egypt. In: Geochemistry, Geophysics, Geosystems. 2005 ; Vol. 6, No. 1.
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abstract = "[1] Measurements of radiochlorine (36Cl), radiogenic noble gases (4He and 40Ar), and stable chlorine isotope ratios were obtained to assess the residence time of groundwater in the Nubian Aquifer of the Western Desert of Egypt. Measured 36Cl/Cl ratios yield apparent residence times from ∼0.2 to 1.2 × 106 years in the deep (600-1200 m) groundwater (assuming constant Cl) and ≤0.16 × 10 6 years in the shallow (<600 m) groundwater. Values of δ37Cl in the groundwater strengthen the application of the 36Cl dating method by constraining Cl sources and identifying groundwater mixing. Dissolved gases were measured in some of the deep groundwater samples. Measured 4He concentrations indicate accumulation of radiogenic 4He that is qualitatively consistent with the age progression indicated by the 36Cl/Cl ratios, but the flux of external 4He from the underlying crust has not been quantified and is not constant throughout the aquifer. Concentrations of 40Ar range from 3.3 to 6.7 × 10-4 ccSTP/g and indica e excess air incorpora ion a recharge. Measured 40Ar/36Ar ra ios do no exceed he a mospheric ratio. A two-dimensional numerical hydrodynamic transect of the aquifer was modeled from the area of the Uweinat Uplift to the northern Bahariya Oasis. Predicted groundwater velocities in the deep portion of the aquifer are 0.5-3.5 m/yr with groundwater residence times up to 9 × 105 years; residence times up to 1.3 × 106 years are predicted in the confining shale. Aquifer properties are estimated by using the model to fit the measured 36Cl/Cl ratios. Under these conditions, hydrodynamic residence times are within about 30{\%} of those calculated from 36Cl when mixing of Cl- is accounted for in the highest-Cl- deep groundwaters. By mutually calibrating multiple methods (hydrodynamic, 36Cl, and 4He), a consistent picture of the Nubian Aquifer has emerged in which lateral flow from a southern recharge area dominates the deep horizons, while shallow horizons contain younger, autochthonous recharge.",
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AU - Sultan, Mohamed

AU - Lu, Zheng Tian

AU - Lehmann, Bernhard

AU - Purtschert, Roland

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N2 - [1] Measurements of radiochlorine (36Cl), radiogenic noble gases (4He and 40Ar), and stable chlorine isotope ratios were obtained to assess the residence time of groundwater in the Nubian Aquifer of the Western Desert of Egypt. Measured 36Cl/Cl ratios yield apparent residence times from ∼0.2 to 1.2 × 106 years in the deep (600-1200 m) groundwater (assuming constant Cl) and ≤0.16 × 10 6 years in the shallow (<600 m) groundwater. Values of δ37Cl in the groundwater strengthen the application of the 36Cl dating method by constraining Cl sources and identifying groundwater mixing. Dissolved gases were measured in some of the deep groundwater samples. Measured 4He concentrations indicate accumulation of radiogenic 4He that is qualitatively consistent with the age progression indicated by the 36Cl/Cl ratios, but the flux of external 4He from the underlying crust has not been quantified and is not constant throughout the aquifer. Concentrations of 40Ar range from 3.3 to 6.7 × 10-4 ccSTP/g and indica e excess air incorpora ion a recharge. Measured 40Ar/36Ar ra ios do no exceed he a mospheric ratio. A two-dimensional numerical hydrodynamic transect of the aquifer was modeled from the area of the Uweinat Uplift to the northern Bahariya Oasis. Predicted groundwater velocities in the deep portion of the aquifer are 0.5-3.5 m/yr with groundwater residence times up to 9 × 105 years; residence times up to 1.3 × 106 years are predicted in the confining shale. Aquifer properties are estimated by using the model to fit the measured 36Cl/Cl ratios. Under these conditions, hydrodynamic residence times are within about 30% of those calculated from 36Cl when mixing of Cl- is accounted for in the highest-Cl- deep groundwaters. By mutually calibrating multiple methods (hydrodynamic, 36Cl, and 4He), a consistent picture of the Nubian Aquifer has emerged in which lateral flow from a southern recharge area dominates the deep horizons, while shallow horizons contain younger, autochthonous recharge.

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