Lay summary
Seasonal to annual quantitative reconstructions of spatially-explicit climate state variables for the last 2000 years across the world are recognized as one of the primary targets for current climate research. Varved (annually laminated) lake sediments play a key role in this context because they provide seasonally resolved paleoclimate archives with a very good chronology. The minerogenic varves in Lake Oeschinen, a proglacial lake in the northern Swiss Alps will be used to establish the first quantitative summer precipitation record back to ca. 1000 AD for Switzerland. In a pilot study for the varves AD 1920-1986, we have established that varve thickness and mineralogical composition is a good predictor for MJJA precipitation (r=0.64, p<0.05). Phyllosilicate influx is related to rain stroms whereas calcite influx is related to glacial meltwater. Novel scanning techniques (reflectance spectroscopy 380-730 nm) will be explored to analyze sediment compositions at very high (mm-scale) resolution.