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| Titel |
Isotopic re-equilibration of fluid inclusions in natural speleothem by artificial heating |
| VerfasserIn |
Ryu Uemura, Yudai Kina |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250142342
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| Publikation (Nr.) |
 EGU/EGU2017-5951.pdf |
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| Zusammenfassung |
| Isotopic compositions of inclusion water in speleothems are promising new climatic proxies.
Oxygen isotope ratio of water (δ18O) may provide direct estimate for past temperature
changes. Several studies, however, used hydrogen isotope ratio of water (δD) because the
δ18O may be affected by re-equilibration between water and host calcite. Thus, precise
knowledge about magnitude and reaction rate of the re-equilibration has a fundamental
importance for paleoclimate studies using speleothems.
To evaluate the re-equilibration effect, we measured isotope composition of fluid
inclusions in natural stalagmites, which had been heated in laboratory before isotope
measurement. Several (3-5) subsamples were cut from the same depth of stalagmites. Then,
each sub-sample was heated at different interval (0 – 80 hours) under continuous
evacuation using a turbomolecular pump. The experiments were conducted under
three different temperatures (25, 70, and 105˚ C). The δ18O and δD values of fluid
inclusions in a sub-sample was measured using a semi-automated system, which
was modified based on cavity ring-down spectroscopy technique (Uemura et al.,
2016).
Under the 105˚ C hating, the inclusion δ18O value of a layer shows a small
increase from the initial to ca.30 hours heating, and then after that it appears to stay
flat. This preliminary result suggests that a limited amount of calcite reacts with
inclusion water, and ca. 5% of fluid inclusion water may be re-equilibrated with
surrounding host calcite at the 105˚ C. The magnitude of re-equilibration effect is not
significant for estimating glacial-interglacial temperature changes but measurable.
On the other hand, the δ18O value shows no trend under the room temperature
experiment. The δD value shows no trend at any experimental conditions, suggesting
that loss of inclusion water during long-time evacuation does not cause the δ18O
enrichment.
Uemura, R. et al. (2016) Precise oxygen and hydrogen isotopic determination of
speleothem inclusion water in nanoliter quantities using cavity ring-down spectroscopic
techniques, Geochimica et Cosmochimica Acta, 172, 159-176, doi:10.1016/j.gca.2015.09.017 |
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