Recording changes in ENADW composition over the last 340 ka using high-precision lead isotopes in a Fe¯Mn crust

The effect of climate variations on the magnetic properties of sediments from two small Alpine lakes in the Bernese Alps, Switzerland was investigated. Although relatively similar in water volume and general environment, S?gistalsee and Hinterburgsee have different catchment vegetation and lithology due to their different elevation and geographic locations. The climatic signal in the mineral magnetic parameters of the sediments was validated and interpreted with the aid of palynological and geochemical data. The sediment age was determined with several accelerated mass spectrometry 14C dates. The results from the different lakes compare well on a common time scale and show that the influence of local conditions on the magnetic record is rather small. A climatic influence on the mineral magnetism has been recognized at both studied sites. This is interpreted as a consequence of the production of an authigenic mineral with particularly uniform magnetic properties during the warmer stages and the influx of heterogeneous detrital magnetic minerals during the colder stages. The clearest climate record is found in sediments with no organic matter whereas the anoxic conditions found in highly organic sediment can completely obliterate the climate signal recorded in the sediment magnetic properties.