Comparing and refining two novel methods for paleothermometry in speleothems - carbonate clumped isotopes vs. fluid inclusion noble gas concentrations

• Applicant: Dr. Tobias Kluge
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2010 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 165452359

Speleothem calcite is increasingly used as paleoclimate archive. However, their carbon and oxygen isotopes are affected by many parameters and therefore cannot be used for direct paleotemperature reconstruction. Innovative methods have been developed to determine absolute paleotemperatures independently of calcite δ18O. Fluid inclusion noble gases concentrations and carbonate clumped isotope thermometry are two of the most promising approaches. The clumped isotope thermometer is based on the temperature dependent abundance of 13C-18O bonds in the carbonate lattice and has been successfully applied in carbonate shells from a variety of marine organisms, reflecting the temperature during calcite formation. The noble gas method is based on the temperature dependent solubility of gases in water and is a variant of the traditional noble gas approach in groundwater, applied to speleothem fluid inclusions. The precision of both methods is up to ± 1°C. Preliminary tests of these methods in speleothems from Israel and Germany, respectively, resulted in reasonable temperature differences between distinct time periods though in both methods a temperature offset in the modern system was observed. Both methods are limited by different constraints; the not-well understood non-equilibrium fractionation in the case of clumped isotopes and a surplus component detected in some stalagmites in the case of the noble gas thermometry. The proposed research will compare the two thermometry methods by measuring clumped isotopes in modern speleothem samples and in samples where noble gas temperatures have been already determined. This will enable us to better understand the source of temperature offsets observed in both methods and to characterize the speleothem formation conditions in which these methods can be applied.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Dr. Hagit P. Affek