Dan Hammarlund

Climatic and environmental changes during the Younger Dryas stadial (GS-1) and preceding and following transitions are inferred from stable carbon and oxygen isotope records obtained from the sediments of ancient Lake Torreberga, southern Sweden. Event GS-1 is represented in the sediment sequence by 3.5 m of clay containing lacustrine carbonates of various origins. Comparison of isotopic records obtained on mollusc shells, ostracod valves, and Chara encrustations precipitated during specific seasons of the year supports estimates of relative changes in both lake water and mean annual air temperatures. Variations in soil erosion rates can also be estimated from a simple isotope-mass-balance model to separate allochthonous and autochthonous carbonate contributions to the bulk carbonate content of the sediments. The well-known, rapid climatic shifts characterising the Last Termination in the North Atlantic region are clearly reflected in the isotopic data, as well as longer-term changes within GS-1. Following maximum cooling shortly after the Allerod-Younger Dryas (GI-1-GS-1) transition, a progressive warming and a slight increase in aquatic productivity is indicated. At the Younger Dryas-Preboreal (GS-1-PB) transition mean annual air temperature rapidly increased by more than 5 degrees C and summer lake-water temperature increased by ca. 12 degrees C. The subsequent Preboreal oscillation is characterised by an increase in soil erosion and a slight decrease in mean annual air temperature. These results are in harmony with recent findings about large-scale climate dynamics during the Last Termination. Copyright (C) 1999 John Wiley & Sons, Ltd.