Reconstructing Younger Dryas temperature variability in Central Europe based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) in Lake Trzechowskie, Poland

Abstract

The cause of the onset of the Younger Dryas is still a topic of discussion. High-resolution temperature reconstructions are necessary to examine this cold and dry phase of the last glacial period. These temperature records are scarce for the Younger Dryas, especially in Central Europe. Lake Trzechowskie, Central Poland, is an excellent location for high resolution climate studies, due to the accurate age model based on varve counting and tephrostratigraphy. This study is one of the first studies to apply the improved chromatography method that separates the 5- and 6-methyl isomer brGDGTs on a sediment core of a lake. The results show a gradual decrease in MAT of about 1.5 °C during the Younger Dryas. An increase in wind strength and an increase in aridity, based on n-alkane δD data of Collins et al. (unpublished), are recognized about 150 years after the onset of the temperature decline. The results support the theory that the temperature decline at the onset of the Younger Dryas is likely caused by a large influx of fresh water into the North Atlantic Ocean. This could have resulted in a decreased strength of the AMOC, an increase in sea ice in the North Atlantic Ocean and southward shift of the polar front. All these climatic changes have had a large impact on the European environments. A decreased impact of the westerlies on climate has been recognized on a west-east transect through Europe. The possibility of in situ production is an important drawback of the use of brGDGTs in lakes. This report also examines several approaches to verify the origin of brGDGTs in the lake and concludes that the results for the Trzechowskie Lake are valid.