2nd international workshop on clumped isotopes, London, August 10-12 2011
Carbonate Clumped Isotopes Thermometry: Equilibrium and
Kinetic Effects
Hagit P. Affek 1*, Shikma Zaarur 1, Tobias Kluge 1
1) Department of Geology and Geophysics, Yale University.
* Corresponding author: hagit.affek@yale.edu
The independence of carbonate clumped isotopes thermometry of the isotopic
composition of the solution in which the carbonate grows makes it a powerful proxy,
in particular for paleotemperature reconstruction on land, where other new
temperature proxies (such as Mg/Ca, alkenone unsaturation and TEX86) are not
useful and the complexity of the hydrological cycle prevents a simple use of 18O.
Clumped isotopes application is especially attractive in speleothems, one of the only
continuous, well dated, carbonate archives on land. However, measurements in
modern stalagmites have revealed clear deviations from the nominal equilibrium
47-T relationship.
This calibration 47-T relationship has been determined trough precipitation of calcite
via N2 bubbling through saturated Ca(HCO3)2 solutions at controlled temperatures. As
such, it does not a priori reflect equilibrium conditions. Biogenic carbonates,
however, more or less conform to the same relationship, in support of an isotope
equilibrium assumption. The talk will present additional data of synthetic calcite,
formed under similar conditions, and will discuss the accuracy of this calibration.
Deviation from this nominal equilibrium relationship, as observed in stalagmites,
therefore reflects kinetic isotope effects. These effects are associated with degassing
of CO2 out of the solution and probably result from calcite precipitation from a thin
film of solution that is faster than the time required for regaining equilibrium through
DIC-H2O isotope exchange. The talk will present synthetic calcite that was formed
under conditions mimicking precipitation from thin films, and the implication of this
47-T relationship to speleothem clumped isotopes thermometry.
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