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| Titel |
Ice-vapor equilibrium fractionation factor of hydrogen and oxygen isotopes: Experimental investigations and implications for stable water isotope studies |
| VerfasserIn |
M. D. Ellehøj, S. J. Johnsen, H. C. Steen-Larsen, J. Sjolte, M. Werner |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061339
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| Zusammenfassung |
| Stable water isotopes have been used in climate research for several decades. The differences
in vapour pressure of the different isotopic species give rise to fractionation during phase
changes. The water isotopic composition in the precipitation therefore depends on the
condensation history of the air mass and source region evaporation. Through ice cores in
Greenland and Antarctica containing archived precipitation, knowledge about past
variations in the hydrological cycle and climate can therefore be obtained. The
ice-vapor equilibrium fractionation factor α controls the magnitude of the isotope
fractionation during phase changes, which makes it a core component in isotope
models e.g. used to interpret ice core data for palaeoclimate studies. In this work we
successfully designed and built an experimental setup with the purpose of investigating the
temperature dependency of α and extend the temperature range of earlier work. In our
experimental setup we used both a Picarro cavity ringdown spectrometer and a
conventional TC/EA-IRMS system. Comparing the results from the two systems
revealed good reproducibility. The results of the experiments show fractionation
factors for δD and δ18O, with a temperature dependency well in accordance with
theory for equilibrium fractionation, for temperatures between 0°C and -40°C. The
expressions for the results are: lnαδD= 0.2133-203.10/T+48888/T2 and lnαδ18O=
0.0831-49.192/T+8312.5/T2. Compared to previous experimental work, a significantly larger
α for δD is obtained while for δ18O α is larger for temperatures below -20°C and slightly
lower for temperatures above this. Sensitivity tests with the latest generation isotope
enabled general circulation model are preformed to show the differences in model
performance using the α of earlier work and this work. The model output is compared
to observations of the deuterium excess signal in both Greenland and Antarctica,
in order to assess the effect of the α in this work on the annual cycle and spatial
distribution of the deuterium excess. These preliminary tests provide guide lines for
the future use of the α in this work to investigate the present and past climates. |
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