Stable isotope variations in modern tropical speleothems: Evaluating equilibrium vs. kinetic isotope effects
- Permanent Link:
- Stable isotope variations in modern tropical speleothems: Evaluating equilibrium vs. kinetic isotope effects
- Series Title:
- Geochimica et Cosmochimica Acta
- Mickler, Patrick J.
Banner, Jay L.
- Publication Date:
- Subjects / Keywords:
- Harrisonâ€™S Cave ( local )
Climatology ( local )
Speleothems ( local )
O Isotopic ( local )
- serial ( sobekcm )
- Applications of speleothem calcite geochemistry in climate change studies require the evaluation of the accuracy and sensitivity of speleothem proxies to correctly infer paleoclimatic information. The present study of Harrisonâ€™s Cave, Barbados, uses the analysis of the modern climatology and groundwater system to evaluate controls on the C and O isotopic composition of modern speleothems. This new approach directly compares the Î´18O and Î´13C values of modern speleothems with the values for their corresponding drip waters in order to assess the degree to which isotopic equilibrium is achieved during calcite precipitation. If modern speleothems can be demonstrated to precipitate in isotopic equilibrium, then ancient speleothems, suitable for paleoclimatic studies, from the same cave environment may also have been precipitated in isotopic equilibrium. If modern speleothems are precipitated out of isotopic equilibrium, then the magnitude and direction of the C and O isotopic offsets may allow specific kinetic and/or equilibrium isotopic fractionation mechanisms to be identified. Carbon isotope values for the majority of modern speleothem samples from Harrisonâ€™s Cave fall within the range of equilibrium values predicted from the combined use of (1) calcite-water fractionation factors from the literature, (2) measured temperatures, and (3) measured Î´13C values of the dissolved inorganic carbon of drip waters. Calcite samples range from âˆ¼0.8â€° higher to âˆ¼1.1â€° lower than predicted values. The 13C depletions are likely caused by kinetically driven departures in the fractionation between HCO3âˆ’ (aq) and CaCO3 from equilibrium conditions, caused by rapid calcite growth. 13C enrichments can be accounted for by Rayleigh distillation of the HCO3âˆ’ (aq) reservoir during degassing of 13C-depleted CO2. Modern speleothems from Harrisonâ€™s Cave are not in O isotopic equilibrium with their corresponding drip waters and are 0.2â€° to 2.3â€° enriched in 18O relative to equilibrium values. Î´18O variations in modern calcite are likely controlle
- Original Version:
- Geochimica et Cosmochimica Acta, Vol. 68, no. 21 (2004-11-01).
- Source Institution:
- University of South Florida Library
- Holding Location:
- University of South Florida
- Rights Management:
- 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.
No images or PDF downloads are available for this resource.
Cras ut cursus ante, a fringilla nunc. Mauris lorem nunc, cursus sit amet enim ac, vehicula vestibulum mi. Mauris viverra nisl vel enim faucibus porta. Praesent sit amet ornare diam, non finibus nulla.
Cras efficitur magna et sapien varius, luctus ullamcorper dolor convallis. Orci varius natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Fusce sit amet justo ut erat laoreet congue sed a ante.
Phasellus ornare in augue eu imperdiet. Donec malesuada sapien ante, at vehicula orci tempor molestie. Proin vitae urna elit. Pellentesque vitae nisi et diam euismod malesuada aliquet non erat.
Nunc fringilla dolor ut dictum placerat. Proin ac neque rutrum, consectetur ligula id, laoreet ligula. Nulla lorem massa, consectetur vitae consequat in, lobortis at dolor. Nunc sed leo odio.