Habitat transformations during abrupt climate changes at the Late Glacial\Holocene transition, as revealed by cladocerans

Abstract

We describe a high-resolution analysis of subfossil Cladocera conducted at the Lugi site in Poland, a peatland ecosystem that developed within a former lake in the Warta River Valley. Study focused on core sections corresponding to periods of rapid climatic change during the Late Glacial/Holocene transition, enabling detailed observation of environmental transformations. Palynological analysis facilitated the determination of boundaries between cold and warm periods. The Cladocera analysis revealed that, during the end of Oldest Dryas, the lake was shallow with conditions unfavourable for Cladocera development. At the onset of the Bølling period, warming led to increased species diversity and a rise in water levels within the lake. Following this warming and associated ecological changes, the Bølling-Allerød period was characterized by continued progressive warming, that was interrupted by the Older Dryas cooling event, marked by a sharp decline in Cladocera species. At the end of the Allerød, there was a decline in lake water levels, followed by the onset of the Younger Dryas, which brought a notable cooling trend. The Younger Dryas/Holocene transition was not captured due to a hiatus in sediment deposition. Data from the sediment section corresponding to the Holocene (Boreal period) revealed improved habitat conditions and a warming of the waters. These analyses and interpretations are aimed at comparing records of rapid climatic changes as recorded by Cladocera remains, and demonstrating differences in their course in basins that differ from each other as regards habitat features.