Ruprecht-Karls-Universität Heidelberg

Physics of Isotopologues


Research Profile

The research of Dr. Kluge's group has its major focus on the investigation of multiply-substituted isotopologues, the understanding of physical processes that lead to isotope fractionation, and the application of new proxie techniques for paleoclimate reconstruction. Amongst others, carbonate clumped isotopes and noble gases in fluid inclusions are promising new techniques for the assessment of past climate variations that are applied in this research group.

The research group is part of the Heidelberg Graduate School of Fundamental Physics (HGSFP).

Clumped isotopes in paleoclimate research
Clumped Isotopes yield the unique oppurtunity for absolute temperature determination and are thus an ideal tool for paleoclimate reconstructions on carbonates. The research group focusses on speleothems consisting an abundant, well dateable and partially high-resolution archive. Clumped isotope signals in stalagmites are systematically influenced by disequilibrium effects during CO2 degassing from the precipitating solution. However, in combination with one additional parameter speleothems provide either absolute temperatures (given the fluid δ18O value can be indenpendently constrained, e.g. by fluid inclusions) or fluid δ18O values (if independent temperature estimates are used).

Quantification of disequilbrium fractionation with clumped isotopes:
Many geological archives are influenced by disequilibrium effects. Carbonate clumped isotopes have proven to be very sensitive to disequilibrium in the CaCO3-H2O-CO2 system. As the disequilibrium in Δ47 and δ18O is linked, Δ47 measurements can under certain conditions help to quantify the disequilibrium (e.g., if the formation temperature is known). An exciting application is related to question what the true equilibrium fractionation factor between carbonate and water is. Using clumped isotope measurements we are able to determine if the respective carbonate sample precipitated at equilibrium (e.g., Kluge et al., 2014).

Clumped isotope application to carbonates formed under reservoir conditions:
Clumped Isotopes are a thermodynamic proxy that provides mineral formation temperatures independent from the knowledge of the fluid composition from which the carbonate precipitated. This technique was predominantly applied to carbonates that formed at Earth surface temperatures (0-40°C). Dr. Tobias Kluge investigated in the context of the Quatar Carbonates and Carbonate Storage Center (QCCSRC at Imperial College, London) constraints related to its application to reservoir conditions. Laboratory-based precipitation of carbonates at varying temperatures and different solution compositions provide the basis for broad-scale application to specific geoscience questions concerned with high temperature and high salinity environments. 

Noble gases in fluid inclusions:
Noble gas concentrations in groundwater directly provide recharge temperatures via the noble gas solubility (and an excess-air component). This concept has been applied successfully to groundwater for many paleoclimate studies and was recently transferred to fluid inclusions in speleothems. Although the technique is challenging (required absolute accuracy, tiny gas and water amounts) it has a promising outlook. In early pilot studies Kluge and co-workers showed that gases and water from fluid inclusions can be measured quantitatively with the necessary precision. A first application to stalagmites from Bunker cave resulted in reasonable temperature variations during Holocene and early Holocene (Kluge et al., 2008). Current studies aim to improve the method such that a larger group of stalagmites can successfully be investigated. The ratio of air-filled to water-filled inclusions is the parameter determining if a meaningful application is possible.

Former Research Projects

Radon as tracer for investigating groundwater-lake interaction:
Radon is a naturally occuring radioactive noble gas with a short half-life of ~3.8 d. Typically it is about 1000 times more abundant in groundwater compared to surface waters like lakes. Therefore, it is an ideal natural tracer to detect and quantify groundwater inflow in surface water systems. Dr. Kluge developed a simple and low-cost system at the Institute of Environmental Physics to precisely measure radon in lake water with extremely low radon concentrations of few Bq to few tens of Bq (Kluge et al., 2007). Using this new system they were able to quantify the groundwater inflow into a small km-scaled dreging lake and in addition could determine the preferential inflow area based on seasonal measurements (Kluge et al., 2012).

Radon-based techniques can be of great advantage in water ressources management concerning artificial aquifer recharge, river-bank exfiltration and the interaction of groundwater and lake water.

Tritium and 3H/3He dating:
Both tracers are applied for dating of water bodies, typically groundwater, on medium time scales of few years to several tens of years. Although the 'traditional' use of the tritium bomb peak is increasingly getting difficult and ambiguous, both age tracers may yield helpful data in future based on natural tritium levels in the input.

Both techniques were applied at the Institute of Environmental Physics to determine the percolation time of water through the epikarst at several drip sites in a German cave (Bunker Cave, Kluge et al., 2010). In general, 3H/3He data result in a lower age due to possible degassing of the water that passes through the epikarst, whereas the 3H  signal is negligibly influenced by air contact and, thus, more likely to give the correct estimate for the full water precolation time. 

The water percolation time in certain caves can take up to tens of years until the infiltrated water reaches the drip site where speleothems precipitate. Thus, it is of high importance to determine this parameter if correlations between speleothem isotope signals and surface climatic conditions are planned to be investigated. A precondition for percolation time studies is the precise knowledge of the local or at least regional tritium input function.