Oxygen and hydrogen isotope measurements of water from fluid inclusions in stalagmites using cavity ring-down spectroscopy
Abstract
The oxygen isotope composition of stalagmite calcite is useful to reconstruct past climate change. However, the interpretation of the isotope record is not straightforward because it is controlled by both precipitation amount and temperature. If the isotope composition of the parent dripwaters could be measured, differences between inclusion and calcite isotope composition will give temperature changes where stalagmite formed. Several methods for extracting and measuring the isotope composition of fluid inclusion of stalagmites have been proposed. A traditional isotope ratio mass spectrometer requires pre-treatment processes (e.g., high-temperature furnace or equilibration device) because H2O has to be converted to other measurable gases (H2, CO, or CO2). To simplify such processes, we have developed a method to measure isotope ratios of water from fluid inclusions using cavity ring-down spectroscopy (Picarro L-2120i WS-CRDS), which can measure H2O molecules directly. The water from stalagmite sample was extracted by heating (up to 500 degC). The extracted water was purified, and then sent to the WS-CRDS with dry N2 gas. Stalagmites samples, which appear to be still growing, were collected in a cave (Gyokusendo, Okinawa, Japan). The isotope composition of water from inclusion are δ18O = -6.0 ± 0.4 permil, and δ2H = -34.8 ± 3.9 permil (n=4). The values are close to modern isotope compositions of precipitation in Okinawa (precipitation-amount weighted values (2008 to 2011); δ18O = -5.7 permil and δ2H = -32.3 permil) and modern cave dripwaters in the cave (average δ18O = -5.6 permil, and average δ2H = -32.2 permil, in 2010). The results suggest that isotope compositions of the past dripwaters can be recovered.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMPP31C2038U
- Keywords:
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- 1041 GEOCHEMISTRY / Stable isotope geochemistry;
- 1043 GEOCHEMISTRY / Fluid and melt inclusion geochemistry;
- 4924 PALEOCEANOGRAPHY / Geochemical tracers;
- 4994 PALEOCEANOGRAPHY / Instruments and techniques