Late Quaternary and Holocene paleoclimate and paleoenvironmental reconstruction - a multi-proxy approach on Swiss speleothems

Detailed knowledge of the past climate and environmental variability is vital in order to predict future scenarios with more confidence. High resolution and highly-resolved natural archives are therefore in growing demand (PAGES report, 2009). This thesis is part of a coordinated effort, STALCLIM project, where a series of state-of-theart methods in speleothems proxies were used in order to develop the full potential of speleothemsas paleoclimate and paleoenvironmental archive. The thesis investigates climate variations as recorded by speleothems from Schafsloch and Milandre caves, spanning time intervals of high scientific interest: 0 to 14 550 years BP and 130 000 to 230 000 years BP. The locations of the caves, Jura Mountains and the Alpstein Mountains (Swiss Alps) are regions highly sensitive to climate-induced changes in temperature, atmospheric pathways and/or environment evolution. In order to establish new climate records and resolve the paleoclimate questions, continuous geochemical analyses were applied, with high resolution stable isotopic and trace elements analysis and 230Th age measurements, and these were combined with thin section analysis of the calcite petrology. Where possible, we conducted continuous and temporal measurements in the caves where the samples were collected, to provide a better understanding of the cave environment. Chapters 2 and 3 highlight the sensitivity of high altitude speleothem proxies to small changes in temperature and water availability, both induced by internal and external climate drivers. The MF3 stalagmite, from Schafsloch Cave, provides a unique opportunity to investigate a regional expression of millennial-scale climate variability in Central Europe during MIS 6 and Late MIS 7. The sample records in high detail the structure of the penultimate deglaciation in the Alps, and brings new evidence regarding the nature of this important climatic transition. Chapters 4 and 5 show the high resolution composite δ18O record and elemental composition of speleothems from Milandre Cave, covering the Lateglacial- Holocene interval. A detailed comparison with Greenland ice cores and Gerzensee lake sediments (Central Switzerland) indicates similarities in the long timescale changes of atmospheric circulation patterns in the whole North Atlantic region after the last deglaciation. In contrast, during the Holocene, the signature pattern in the isotopic calcite δ18O data differs to that seen in Central Europe. This provides important insights into the regional teleconnections and local environmental reaction to changes in the temperature, seasonality of precipitation and atmospheric processes. The use of a robust δ18O/temperature transfer function has enabled a high resolution temperature reconstruction of the autumn to spring temperatures at the Milandre site for the last 14 550 y BP. In summary, this thesis provides new results on environmental and climatic variability in Switzerland during specific intervals over the last 230 000 years. It suports large teleconnections over the northern hemisphere and emphasizes the role of insolation and obliquity as important climate triggers in the region. These new high-resolution and precisely dated records of δ18O and cold season temperature reconstruction for the Jura Mountains over the last 14 550 y BP, are proposed as being representative for Central Europe.