Isotope and Cladocera data and interpretation from the Eemian optimum and postoptimum deposits, Kaliska palaeolake (Central Poland)

During the Eemian optimum, calcareous gyttja and lake marl accumulated. The characteristic feature of calcareous gyttja is an occurrence of fragments of diatoms and plants, while in lake marl they are absent. In the carbonate-rich deposits no Cladocera remains are preserved. Based on the results of stable isotope analyses of carbonates, the eight isotopic horizons (Is) were defined and characterised. In the studied deposits, 15 species of subfossil Cladocera were identified and 6 zones of fauna development were distinguished. The defined Cladocera species are similar to ones known from the other Eemian site in Poland. The faunal taxa indicate the low trophy status of the lake initially, followed by an increase to eutrophic status. The Cladocera and isotopic compositions suggest that the hornbeam zone (E5) was a period of higher density of macrophytes as well as of an increase of biological activity associated with the low water level. The fluctuations of the isotopic curves caused by a shallowing of the basin and a change of sediment lithology are characteristic for the spruce zone (E6). The palaeolake transformed into a peatbog during the pine zone (E7). During the Early Vistulian renewed carbonate accumulation and Cladocera development took place indicating the repeated reservoir existence.