Large kinetic isotope effects in modern speleothems
- Permanent Link:
- Large kinetic isotope effects in modern speleothems
- Series Title:
- GSA Bulletin
- Mickler, Patrick J.
Banner, Jay L.
- Publication Date:
- Subjects / Keywords:
- Kinetic Isotope Effects ( local )
Speleothems ( local )
Oxygen Isotopes ( local )
Carbon Isotopes ( local )
Non-Equilibrium ( local )
Barbados ( local )
- serial ( sobekcm )
- The application of stable isotopes in speleothem records requires an understanding of the extent to which speleothem calcite isotopic compositions reflect the compositions of the cave waters from which they precipitate. To test for equilibrium precipitation, modern speleothem calcite was grown on glass plates, so that the carbon and oxygen isotope composition of the calcite and the water from which it precipitated could be directly compared. The plates were placed on the tops of three actively growing stalagmites that occupy a 1 m2 area in Harrison's Cave, Barbados, West Indies. some of the plate Î´13C values and none of the plate Î´18O values correspond to equilibrium values, indicating significant kinetic isotope effects during speleothem calcite growth. We investigate herein mechanisms that may account for the kinetic isotope effects. On each plate, speleothem calcite was deposited with distinct Î´18O and Î´13C compositions that increase progressively away from the growth axis, with up to 6.6â€° 13C and 1.7â€° 18O enrichments. The positive Î´13C versus Î´18O trends are likely a result of 18O and 13C Rayleigh-distillation enrichment in the HCO3âˆ’ reservoir owing to progressive CO2 degassing and CaCO3 precipitation. The magnitude of the Î´13C versus Î´18O slope is likely controlled by the extent to which CO2 hydration-hydroxylation reactions buffer the oxygen isotope composition of the HCO3âˆ’ reservoir during calcite precipitation. Complete oxygen isotopic buffering of the HCO3âˆ’ reservoir by CO2 hydration-hydroxylation reactions will produce a vertical Î´13C versus Î´18O slope in calcite sampled along a growth layer. As oxygen isotope buffering of the HCO3âˆ’ reservoir decreases to no buffering, the Î´13C versus Î´18O slope in calcite sampled along a growth layer will decrease from vertical to 0.52 at the cave temperature. In this study, modern speleothem calcite sampled along the growth layer produced a Î´13C versus Î´18O slope of 3.9, indicating incomplete oxygen isotope buffering of the HCO3âˆ’ reservoir during calcite precipitatio
- Original Version:
- GSA Bulletin, Vol. 118, no. 2 (2006-01-01).
- Source Institution:
- University of South Florida Library
- Holding Location:
- University of South Florida
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- This object is protected by copyright, and is made available here for research and educational purposes. Permission to reuse, publish, or reproduce the object beyond the bounds of Fair Use or other exemptions to copyright law must be obtained from the copyright holder.
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