A Temperature and Monsoon Record
derived from Environmental Tracers in
Groundwater of Northwest India
Universität Heidelberg Institut für Umweltphysik IAEA, Monaco, 2011
M. Wieser, W. Aeschbach-Hertig, T. Schneider Institute of Environmental Physics, University of Heidelberg, Germany
R.D. Deshpande, S.K. Gupta Physical Research Laboratory, Ahmedabad, India
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Outline
• Study Area
• Age scale: 14C-dating supported by other tracers
– Comparison with study in Belgium
• Paleoclimate record: Isotopes and noble gases
– Comparison with study in China
• Holocene monsoon history: Isotopes and excess air
– Comparison with study in Niger
• Conclusions
Study Area: Cambay Basin
Cambay Basin
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India
Study Area: Cross-Section
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14C Age Scale: Dead Carbon Correction
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A14C ≈ 100 % d13C ≈ -25 ‰
A14C ≈ 0 % d13C ≈ 0 ‰
A14C ≈ 50 % d13C ≈ -12.5 ‰
Inorganic carbon in groundwater comes from soil CO2 and carbonates. Correction models for dead carbon use chemistry and/or d13C. Often no good agreement between models, overcorrection for young samples.
14C Age Scale: Dead Carbon Correction
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A14C ≈ 100 % d13C ≈ -17 ‰
Approach used in this study:
• Estimate recharge water composition (pH, HCO3
-, d13C, …) under mostly open conditions, assuming soil pCO2 and T
• New: Use NGT information to define groups with different recharge conditions
A14C ≈ 0 % d13C ≈ 0 ‰
A14C ≈ 80 % d13C ≈ -11 ‰
"Recharge water"
Inorganic carbon in groundwater comes from soil CO2 and carbonates. Correction models for dead carbon use chemistry and/or d13C. Often no good agreement between models, overcorrection for young samples.
Compare: Blaser et al., 2010. Appl. Geochem. 25: 437–455.
Comparison: 14C-Dating of Groundwater in Belgium
Study Area: Ledo-Paniselian Aquifer
7 Blaser et al., 2010. Appl. Geochem. 25: 437–455.
d13C of plausible recharge waters:
soil gas
rech. water
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14C Correction: Indications from Tritium
Approach used in this study:
1. Estimate correction factor q for A0 due to dead carbon
2. Calculate "corrected conventional" 14C age
3. New (for groundwater): Use "OxCal" to obtain calibrated ages
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14C Ages: Calibration
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14C Age Scale: Age Groups
Modern
Late Holocene
Holocene Optimum Transition
Last Glacial Period
Late Pleistocene
Crystalline
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14C Ages and non-Atmospheric Helium
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Origin of non-Atmospheric Helium
Paleoclimate Record: Stable Isotopes
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Ice volume effect Amount
effect ?
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Comparison: Stable Isotopes Record from China
Temperature effect
Amounteffect
Kreuzer et al., 2009. Chem. Geol. 259: 168-180.
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d18O in Stalagmite of the Dongge Cave
Dongge Cave: Increase of d18O by ~2 ‰ during the Holocene due to decreasing monsoon
Wang et al. (2005). Science 308: 854-857
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The Noble Gas Thermometer
0
0.05
0.1
0.15
0.2
0 5 10 15 20 25 30
Xe
Kr
Ne
Ar
He
Temperature [°C]
Bunsen S
olu
bili
ty b
[cm
3S
TP
cm
-3 a
tm-1
]
T, S, Ci
P, xi Air
Water
i,eq i iC pT,Sb
Dissolved noble gas concentrations in equilibrium with air:
Excess air:
DNe =Neex/Neeq·100%
Noble Gas Paleotemperature Record
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DT = 3.5 °C
28.7 °C
25.2 °C
Groundwater Noble Gas Studies Worldwide
DT Holocene – LGM < 5 °C
DT Holocene – LGM ~ 5 °C
DT Holocene – LGM > 5 °C 18
Paleoclimate Record: Excess Air
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humid
mo
nso
on
dry
stro
ng
wea
k
Holocene: Excess Air and Isotopes
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amount effect
dry
humid
wat
er t
able
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Comparison: Excess Air and d2H in Niger
Beyerle et al., 2003. GRL 30, 1173, doi:10.1029/2002GL016310.
amount effect dry
wet
wat
er t
able
Holocene: Excess Air and NGT
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dry warm
humid cool
DT in noble gas / soil temperatures, not air temperature
Conclusions
Environmental tracers in groundwater can provide information on paleotemperature and -humidity
Results from Northwest India (Cambay Basin)
• 14C dating improved by using NGT information
• Stable isotopes show ice volume and amount effect
• NGTs indicate 3.5 °C glacial – interglacial warming
• Excess air and stable isotope are humidity proxies:
→ Humid Holocence optimum, dry late Holocene
• Soil and noble gas temperatures elevated in dry periods
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Acknowledgments
Thanks to my co-authors …
… T. Schneider, Martin Wieser (working), R.D. Deshpande, S.K. Gupta
Thank You!