Reconstruction of palaeoecological changes in Lake Łebsko on the basis diatom analysis (the southern Baltic coast, Poland)

This study focuses on diatom assemblages occurring in core Łeb1 of Late-glacial and Holocene deposits from Lake Łebsko, off the southern coast of the Baltic Sea. Diatom-inferred environmental characteristics, e.g., water level, water salinity (conductivity), trophic status and pH, from the Holocene are presented. In the sediments from the early Boreal/early Atlantic period, an increase in the participation of brackish-freshwater species is observed, as well as increased numbers of Chaetoceros spores in the samples. The Atlantic sediments of Lake Łebsko mirror conditions typical of the Littorina Sea phase during the development of the Baltic Sea (from c. 7,500 BP to c. 5,000 BP). However, communities of that period dominated by fresh-brackish water species suggest the relatively low salinity of the waters. The presence of isolated frustules of Terpsinoe americana and other typically marine species, e.g., Mastogloia smithii, and the occurrence of silts with Cardium shell detritus point to the Littorina transgression and the functioning of a lagoon within the area of present-day Lake Łebsko. During Subboreal occurrence, a higher number of brackish-freshwater diatoms corresponds to an increase in the water level of the Baltic Sea (approximately 3,000 14C BP). Changes in diatom community structure imply a close relationship with the climate controlled eustatic rise of ocean level and the consequent Littorina transgression, as with other southern Baltic Sea localities.