A Temperature and Monsoon Record derived from Environmental Tracers … AESCHBACH... · 2011-05-11 · A Temperature and Monsoon Record derived from Environmental Tracers in Groundwater

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!