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| Titel |
Kinetic isotopic fractionation versus thermodynamic equilibrium in modern speleothems: new insights from clumped isotopes |
| VerfasserIn |
M. Daëron, W. Guo, J. Eiler, D. Genty, D. Blamart, K. Wainer, R. Boch, R. Maire, P. Niles |
| 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 |
250026741
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| Zusammenfassung |
| Speleothems offer excellent conditions to record climate change over various time scales,
because they can be precisely and absolutely dated, and because several environmental
parameters directly or indirectly affect their isotopic composition. In particular, if, as
commonly assumed, speleothem carbonate precipitates at thermodynamic equilibrium, its
oxygen composition (δ18Oc) is a function of two variables only: the composition of local drip
water and the crystallization temperature. It has long been recognized, however, that a
speleothem’s carbon and oxygen compositions can also be affected by isotopic fractionation
caused by rapid CO2 degassing and/or crystallization, resulting in δ18Oc values heavier than
predicted by equilibrium thermodynamics. Although many of the caves described in the
literature have been reported as producing speleothems in quasi-equilibrium with their parent
waters, δ18Oc values are still typically 0.5-1.5 permil heavier than expected using
published inorganic carbonate-water 18O fractionation factors [McDermott et al.,
2006].
Based on ‘clumped isotope’ measurements of 13 well-constrained modern speleothems, we
determined that none of them appear to precipitate in thermodynamic equilibrium, neither
with respect to 18O nor to Î47. Based on a new theoretical model of kinetic isotopic
fractionation affecting speleothem growth, we propose a quantitative interpretation of the
physical processes affecting the isotopic composition of speleothems [Guo, 2008], and
discuss the implications on past climate reconstructions using fossil speleothem
records.
Guo (2008): Carbonate clumped isotope thermometry: application to carbonaceous
chondrites and effects of kinetic isotope fractionation. PhD thesis, Caltech. |
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