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| Titel |
Carbon isotopes in drip water and stalagmites - tracers of soil processes |
| VerfasserIn |
J. Fohlmeister, D. Scholz, B. Kromer, A. Mangini |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024290
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| Zusammenfassung |
| The carbon isotope composition of soil air and soil water is influenced by climate. Here we
apply the carbon isotope composition of speleothems in the Ernesto cave in Trentino,
Italy, for the reconstruction of the conditions of the soil above the cave during the
Holocene.
In a first step a numerical model that describes the isotope composition of drip water upon
reaction with the calcite of the karst was developed. The model allows for open and
closed limestone dissolution systems as well as intermediate dissolution conditions
computed by successive contributions of the open and closed system. A second model
accounts for the isotope fractionation processes occurring during degassing of CO2
and precipitation of CaCO3 in caves. This model simulates a Rayleigh distillation
process under equilibrium fractionation and additional gas exchange with cave
air.
The reconstruction of recent and past soil pCO2 is then performed by inverse modelling
of the 14C and δ13C composition of monthly collected cave drip water and of a well dated
stalagmite. The model is assessed by the comparison of the calculated and of the monthly
measured soil pCO2. The reconstruction delivers a probable range and seasonality of recent
soil pCO2, although the solution is not unique, due to the uncertainties originating in the
unknown degree of open and closed system conditions during the limestone dissolution.
The convincing model performance for the present day situation allows to apply
the model to a Holocene stalagmite. This reconstruction of past soil conditions
reveals an increasing soil pCO2 within the last 5000 years in the soil above the
cave. |
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