Towards a better understanding of climate proxies in stalagmites - Modelling processes from surface to cave

In recent years stalagmites revealed their high potential as archives for palaeo climate variability. However, the quantitative interpretation of the climate-related features - proxies - is still a challenging task. In this work two numerical models assessing the infuence of climate parameters on two stalagmite proxies - the Mg/Ca ratio and the d18O value - were developed. The models describe quantitatively how the proxies evolve from the atmospheric signals to the incorporation into stalagmite calcite. Both models were successfully applied to stalagmites from caves in western Germany. The models were used to establish two novel approaches of inverse modelling yielding simultaneously palaeo-temperatures and palaeo-precipitation from d18O and Mg/Ca values. Although both models are based on substantially di erent setups, their climate reconstructions show remarkable similarities applied on a Holocene stalagmite from western Germany. In addition, for the rst time a stalagmite model (the d18O model developed in this thesis)was forced with the output data of a General Circulation Model, as a new concept to understand the climate impact on d18O values of speleothems. The advantage is that this method can be applied to caves worldwide and for any given point in time without requiring observational climate data. An experiment including twelve European caves at 6ka before present shows the potential of this method to analyse synoptic-scale patterns of the climate of the past.