Speleothem calcite farmed in situ: Modern calibration of Î´18O and Î´13C paleoclimate proxies in a continuously-monitored natural cave system
- Permanent Link:
- Speleothem calcite farmed in situ: Modern calibration of Î´18O and Î´13C paleoclimate proxies in a continuously-monitored natural cave system
- Series Title:
- Geochimica et Cosmochimica Acta
- Tremaine, Darrel M.
Froelich, Philip N.
- Publication Date:
- Subjects / Keywords:
- Co2 ( local )
Pco2 ( local )
Radon-222 ( local )
Speleothem ( local )
In Situ ( local )
Paleoclimate ( local )
- serial ( sobekcm )
- Understanding the relationships between speleothem stable isotopes (Î´13C Î´18O) and in situ cave forcing mechanisms is important to interpreting ancient stalagmite paleoclimate records. Cave studies have demonstrated that the Î´18O of inorganically precipitated (low temperature) speleothem calcite is systematically heavier than the Î´18O of laboratory-grown calcite for a given temperature. To understand this apparent offset, rainwater, cave drip water, groundwater, and modern naturally precipitated calcite (farmed in situ) were grown at multiple locations inside Hollow Ridge Cave in Marianna, Florida. High resolution micrometeorological, air chemistry time series and ventilation regimes were also monitored continuously at two locations inside the cave, supplemented with periodic bi-monthly air gas grab sample transects throughout the cave. Cave air chemistry and isotope monitoring reveal density-driven airflow pathways through Hollow Ridge Cave at velocities of up to 1.2 m sâˆ’1 in winter and 0.4 m sâˆ’1 in summer. Hollow Ridge Cave displays a strong ventilation gradient in the front of the cave near the entrances, resulting in cave air that is a mixture of soil gas and atmospheric CO2. A clear relationship is found between calcite Î´13C and cave air ventilation rates estimated by proxies pCO2 and 222Rn. Calcite Î´13C decreased linearly with distance from the front entrance to the interior of the cave during all seasons, with a maximum entrance-to-interior gradient of Î”Î´13CCaCO3 = âˆ’7â€°. A whole-cave â€œHendy testâ€ at multiple contemporaneous farming sites reveals that ventilation induces a +1.9 ± 0.96â€° Î´13C offset between calcite precipitated in a ventilation flow path and calcite precipitated on the edge or out of flow paths. This interpretation of the â€œHendy testâ€ has implications for interpreting Î´13C records in ancient speleothems. Calcite Î´13CCaCO3 may be a proxy not for atmospheric CO2 or overlying vegetation shifts but also for changes in cave ventilation due to dissolution fissures and ceiling collapse creating and
- Original Version:
- Geochimica et Cosmochimica Acta, Vol. 75, no. 17 (2011-09-01).
- 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.
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