The European Holocene Climate from the Speleothem’s View : Investigating spatio-temporal coherent changes in European speleothem proxy time series

Abstract

Speleothems are recognised as valuable palaeo climate archives. This has lead to an increasing number of analysed speleothem proxy time series from caves that are distributed on a global scale. In particular speleothem δ18O and δ13C time series are investigated. A hotspot of analysed speleothem proxy time series is Europe, which makes it possible to perform spatio-temporal coherency analysis of speleothem proxy time series. For this aim a method is developed that is based on Principal Component Analysis (PCA). The method is based on a Monte Carlo approach and accounts for the speleothem age uncertainty and the different temporal resolution of speleothem proxy time series. This method is applied to compilations of European speleothem δ18O and δ13C time series. It is demonstrated that the results of the PCA for the compiled δ18O time series can be interpreted as a temperature proxy and as a precipitation/hydrology proxy for the compilation of δ13C time series. Furthermore, it is showed that the spatio-temporal coherence between the analysed speleothem δ18O and δ13C time series varied with time. Moreover, a change of the predominant pattern is observed at 4.0 ka. The second aim of this study is to analyse the change the observed speleothem δ18O gradient for European speleothems. A multi-box Rayleigh approach model is developed (Stable Isotope in Precipitation (SIP) model) that computes the stable isotope composition of precipitation, infiltrated water and calcite. The model is validated with measured precipitation δ18O and δD values from the GNIP dataset. It is demonstrated that the SIP model agrees with the observed δ18O and δD values for the analysed Central European and Northern European transect. Moreover, it is showed that the precipitation δ18O (δD) gradient depends on the North Atlantic Oscillation. This is interpreted as a change of the amount of moisture in the atmosphere for Central Europe. The application of the SIP model of palaeo climate speloethem δ18O gradients suggests that the climate was drier in the early- and mid-Holocene compared to present-day. In addition, the past δ18O gradients suggest a transition of the atmospheric circulation from a very negative NAO like pattern in the early-Holocene (11 ka) to a very positive NAO like pattern in mid-Holocene (4 ka) and that a reorganisation of the atmospheric circulation occurred at approximately 4 ka when present-day atmospheric circulation established.