Dan Hammarlund

Late Weichselian lake sediments from a site in southern Sweden, were analysed for stable carbon and oxygen isotopes, as well as plant macrofossils and insect remains. By comparison of independent data sets, general climatic changes were demonstrated. Lithological, chemical and stable isotope data reveal two significant climatic oscillations at ca. 12 200-12 000 and ca. 11 000-10 200 yr BP respectively. Continental climatic conditions, indicated by evaporative enrichment of O-18 in lake marl, characterise parts of the early lake history, including the Older Dryas Stadial. Distinct variations of deltaC-13 in organic material is discussed in terms of climatically induced changes in lake-water chemistry. Different types of photosynthetic assimilation of dissolved inorganic carbon is proposed as a contributing factor influencing lake marl deltaC-13. The universal application of a positive correlation between lake marl deltaO-18 and mean annual air temperature is questioned. Quantifications of mean summer and winter temperatures based on beetle analysis show a climatic optimum around 12 000 yr BP, a marked cooling around 11 000 yr BP and a strong amelioration at ca. 10 200 yr BP. These climatic events were accompanied by distinct changes in aquatic vegetation. Plant macrofossil and insect analyses indicate an open vegetation during the entire period studied. Biostratigraphical data reflecting local limnic and terrestrial vegetation and regional climate facilitate the interpretation of stable isotope data.