Characterization and dating of saline groundwater in the Dead Sea area Naama Avrahamov 1,2 Orit Sivan 1 , Yoseph Yechieli 2 , Boaz Lazar 3 1 Department of Geological & Environmental Sciences, Ben Gurion University of the Negev 2 Geological Survey of Israel, Jerusalem 3 The Institute of Earth Sciences, The Hebrew University, Jerusalem
Yechieli et al., 2004
Research motivation -370 -370 Groundwater level-1960 Dead Sea level-1960 -390 -390 2000 -410 -410 2000 -430 -430 -450 -450 Calculating flow rate of the different water bodies in this dynamic system
Research goals Using isotopes and chemical water composition for understanding the biochemical processes and carbon system at the fresh and saline groundwater at the Dead Sea area. Characterization of these processes for correcting 14 C dating and estimating flow rates
Research area
Hydrological section W E LEGEND salt gravel Quaternary . . .. ... sand sediments clay limestone Upper Cretaceous dolomite J udea Group marl fresh - saline water interface . . . . . . . . . . . . D E A D S E A ? ? . . . . . . . . . . . . . . . . . . . . . . . . fresh - saline water interface Rift border faults
Methods Water sampling Analytical methods • Ein Arugot- dripping • In the field: pH, DO, water to a bottle electrical conductivity, density • Arugot Wadi boreholes- bailer and submersible • Lab: tritium, general pump chemistry, alkalinity, δ 13 C DIC , 14 C DIC , CH 4 , δ 13 C CH4
Results
Groundwater 1980 DS Ein Gedi spring 2007 DS 600 500 Ca (mmol/KgH 2 O) 400 300 200 100 0 0 2000 4000 6000 8000 Cl (mmol/KgH 2 O)
9 8 7 TA (meql/KgH 2 O) 6 a=1 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 DIC (mmol/KgH 2 O) TA=CA+BA
5 0 δ 13 C DIC ‰ (PDB) -5 -10 -15 -20 0 2000 4000 6000 8000 Cl (mmol/KgH 2 O)
SOURCE SINK Carbonate Mixing with other dissolution water bodies δ 13 C ≈ (-1) ‰ Diffusion (This work) Advection Carbonate precipitation Organic matter DIC Small ε (Mook 1968) δ 13 C ≈ -23 ‰ (stiller et al 1988) DIC ~ Isotopic exchange Methane δ 13 C↑ δ 13 C=(-45) ‰ (This work)
Groundwater 8 Fresh springs 7 1999 DSW 2003 DS 6 DIC (mmol/KgH 2 O) 5 4 3 2 1 0 0 2000 4000 6000 8000 Cl (mmol/KgH 2 O)
5 0 20 ‰ δ 13 C DIC ‰ (PDB) -5 -10 -15 -20 0 2000 4000 6000 8000 Cl (mmol/KgH 2 O)
DIC Mass balance DSW Saline GW 0.9mm * 2.75 ‰ + 0.5 mm * X‰ = 1.4mm * (-10.5 )‰ 0.9DIC * 2.75 ‰ + 0.5DIC * -45 ‰ = 1.4DIC *( -10 )‰ Low DIC value with especially light δ 13 C value Just methane oxidation enables this low δ 13 C value Indeed, methane was found in most of the groundwater samples with δ 13 C of -50 ‰!!
14 C Mass balance DSW Saline GW 0.9DIC X 82pMC + 0.5DIC * XpMC = 1.4DIC * pMC 0.9DIC X 82pMC + 0.5DIC * 0pMC = 1.4DIC * 52.7pMC 0.9DIC X 82pMC + 0.5DIC * 100pMC = 1.4DIC * 88.4pMC For groundwater samples with low DIC values, methane 14 C values have a significant effect on 14 C DIC values
100 90 1 80 2 70 14 C DIC (pMC) 14 C DIC (pMC) 60 50 3 40 30 20 10 0 0 2000 4000 6000 8000 Cl (mmol·KgH 2 O -1 ) Cl (mmol/KgH 2 O) 1. The groundwater flow toward the land 2. Processes when the DSW enter the aquifer 3. Mixing and aging
14 C values of groundwater at the shore line area can As much as the groundwater become less salty, their 14 C The lower sub-aquifer groundwater are indicate hydrological connection between the values decrease due to mixing processes with fresh characterized with low 14 C values, indicate ancient groundwater to the 80 ’s DS groundwater with relativity low 14 C values water presence
• Methane was found in most of the groundwater samples. The methane source and age will be detected • The low δ 13 C DIC values can be explained by methane oxidation own low δ 13 C CH4 values
2 open questions 14 C dating Hyper saline groundwater Methane Isotopic age and exchange source
Dissolved Methane extraction for radiocarbon dating
14 C of methane- PreCon scheme ← SAMELE ENTER AMPOULA CO 2 +H 2 O TRAP COMBATION 1000 o C GC → δ 13 C ANALASIS He purge → MS CO 2 TRAP
Isotopic exchange in different salinity solutions
Merci!
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