Absolute paleotemperature evolution for MIS6 – MIS5 transition and moisture source changes based on Central European stalagmites

Speleothems represent high-resolution continental archives that provide important information about past climate and paleo environmental changes. Their suitability for uranium-thorium dating enables the development of precisely constrained chronologies. Speleothems often contain small amounts of paleo drip water, which was trapped in the stalagmite fabric during the time of formation. The fluid inclusion oxygen (δ¹⁸O_fi) and hydrogen (δ²H_fi) coupled to the calcite δ¹⁸O_calcite stable isotopes can be used for the reconstruction of absolute mean annual paleo temperatures. For our study site realm in Switzerland, δ¹⁸O_calcite was often suggested to be interpreted as a temperature signal, at least during warm intervals such as the Holocene. However, δ¹⁸O_calcite patterns are not able to provide absolute temperature estimates and can be controlled by several factors such as precipitation amount, temperature, and moisture source. Decoupling between δ¹⁸O_calcite evolution and temperature signal can be clarified by comparing with an unambiguous temperature record based on a strong chronology and from the same realm. Such temperature records are scarce for the Central European lowland realm. The existing records are essentially based on biogenic proxies, which are summer biased and where dating can be sometimes difficult.

In this study, we present a new absolute mean annual paleotemperature record for the Central European realm based on fluid inclusion stable isotopes from two Milandre caves (Switzerland) stalagmites. As demonstrated in previous studies conducted within this cave, δ²H_fi has been shown to function as a key proxy for the reconstruction of mean annual paleotemperatures for the central European low elevation realm (Affolter et al. 2019). Here we provide temperature snapshots for the glacial – interglacial transition starting at the penultimate glacial maximum (MIS6) with an average temperature of ca. 4°C until the thermal maximum (MIS5). During MIS6 and the following transition, δ¹⁸O_calcite pattern is decoupled from the temperature evolution. In order to shed light on the δ¹⁸O_calcite interpretation, we discuss the evolution of two high resolution δ¹⁸O_calcite pattern measured on the same stalagmites as the temperature snapshots. With the δ¹⁸O_calcite/temperature comparison we suggest that δ¹⁸O_calcite of the Milandre cave does not represent atmospheric temperature fluctuations during the examined time span. Instead, δ¹⁸O_calcite likely provides information about the moisture source and its changes during the glacial period and the following transition.