JpGU-AGU Joint Meeting 2017

Presentation information

[JJ] Poster

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS23] [JJ] Paleoclimatology and paleoceanography

Tue. May 23, 2017 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL7)

[MIS23-P03] Isotopic re-equilibration of fluid inclusions in natural speleothem by artificial heating

*Ryu Uemura1, Yudai Kina1, Kanako Omine2 (1.Department of Chemistry, Bioogy, and Marine Science, University of the Ryukyus, 2.University of the Ryukyus)

Keywords:speleothem, fluid inclusion, stable isotope, glacial interglacial cycle

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 is needed to evaluate paleoclimate records in speleothems.
To estimate 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 different temperatures of 25 and 105°C. The δ18O and δD values of fluid inclusions in a sub-sample were 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 values of a layer show a small increase from the initial value to ca.30 hours heating, and then after that it appears to stay flat. In contrast, the δ18O value shows no trend under the room temperature. 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. Preliminary data suggest ca. 5% of fluid inclusion water may re-equilibrated with surrounding host calcite at the 105°C heating experiment. The results prove the existence of re-equilibration effect, but its magnitude is not significant for estimating glacial-interglacial temperature changes.