The sediment record of the past 200 years in a Swiss high-alpine lake: Hagelseewli (2339 ma.s.l.)

During much of the time, the lake is in the shadow of a high cliff to the south, so that the lake is ice-covered during much of the year and thus decoupled from climatic forcing. Lake biology is therefore influenced more by the duration of ice-cover than by direct temperature effects during the short open-water season. Long periods of ice-cover result in anoxic water conditions and dissolution of authigenic calcites, leading to carbonate-free sediments.

Sediment cores spanning the last two centuries were taken in Hagelseewli, a high-elevation lake in the Swiss Alps. Contiguous 0.5 cm samples were analysed for biological remains, including diatoms, chironomids, cladocera, chrysophyte cysts, and fossil pigments. In addition, sedimentological and geochemical variables such as loss-on-ignition, total carbon, nitrogen, sulphur, grain-size and magnetic mineralogy were determined. The results of these analyses were compared to a long instrumental air temperature record that was adapted to the elevation of Hagelseewli by applying mean monthly lapse rates.