Diatomeen als Indikatoren für Umwelt- und Klimaänderungen

Abstract

The objective of this study was to reconstruct the palaeolimnological history of Lake Holzmaar, Germany in order to infer palaeoclimatological changes and to track anthropogenic activity during the time-span investigated (ca. 6340 - 1470 cal yr BP). Fossil diatom assemblages, geochemical parameters and varve substructure were used as basic tools for further reconstructions. The combined consideration of all proxy gathered information allowed to infer causally determined changes in diatom assemblage composition, annual algae succession and productivity. For example, it was deduced that changes in lake circulation patterns, precipitation rates and/or erosion rates which are ultimately controlled by climate, caused shifts in nutrient ratios and/or concentrations (e.g., silica and phosphorus) and subsequently in fossil algae composition. Major lacustrine changes which occurred ca. 5800, 5100, 4500, 3660 and 2660 cal yr BP correspond to glacier movements or to lake level changes observed at different locations in western Europe which may reflect large-scale Holocene variability over western Europe. In how far decreasing solar activity as it is proposed for the time around 2660 cal yr BP led to major changes within the lake and in the lake's catchment is difficult to disentangle from anthropogenic activity which increased sharply with the beginning of the Iron Age as evidenced by palynology and archaeology. A satisfying discrimination of anthropogenic and climate influence upon the lake is one of the future goals. A further aim is to look for possible periodicities inherent in the varve formation investigated. Answering those questions will help to better understand natural climatic processes and will allow to make suggestions upon future climate variability.