[MIS23-P03] Isotopic re-equilibration of fluid inclusions in natural speleothem by artificial heating
Keywords:speleothem, fluid inclusion, stable isotope, glacial interglacial cycle
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.