Mineral-magnetic record of Late Quaternary climatic changes in a high Alpine lake

The magnetic properties of a sediment core from a high altitude lake in the Swiss Alps were compared with palynological and geochemical data to link c limatic and mineral magnetic variations. According to pollen data, the sedi ments extend from the present to the Younger Dryas, i.e., they cover more t han 10,000 years of environmental change in the Alps. The major change in m agnetic properties corresponds to the climatic warming of the early Holocen e. High-coercivity magnetic minerals that characterize the late-glacial per iod almost disappeared during the Holocene and the concentration of ferrima gnetic minerals increased sharply. The contribution of superparamagnetic gr ains also decreased in the Holocene sediments. Similar variations in SP con tent and coercivity, of smaller magnitude, are found in the Holocene and ar e interpreted to represent minor climatic variations. Comparison with the h istorical record of the last 1000 years confirms this interpretation. The m agnetic mineralogy, the superparamagnetic contents, and the IRM intensity i n the coarse-grained, late-glacial sediments are similar to those measured in the catchment bedrock. This indicates a detrital origin. The different p roperties and the higher concentration of magnetic minerals in the Holocene sediments are due to authigenic phases. Magnetic properties provide a high resolution record of climatic change. They are sensitive even to small var iations that are not recorded in the pollen or LOI data. Magnetic parameter s show fine-scale variation and constitute a valuable supplement to convent ional climatic indicators. (C) 1999 Elsevier Science B.V. All rights reserv ed.