Reconstruction of environmental conditions of Eemian palaeolake at Studzieniec (Central Poland) on the basis of stable isotope and Cladocera analyses

The results of isotopic and Cladocera investigations of the Eemian lacustrine sediments of Studzieniec palaeolake (Central Poland) are presented. The 12-m thick section contains silty sands and clayey silts on the bottom, then gyttja, and organic silts and peat in the upper part. Based on the results of stable isotope analysis of carbonates the 11 isotopic horizons (Is) were defined and characterised. Results of isotopic analysis correlated with Cladocera and pollen data enabled reconstruction of varying environment conditions. The environmental changes were caused by: a transition from the glaciation to the interglacial period expressed by a significant decrease in δ18O (Is 3); a warming of climate characterised by a positive trend in δ18O (Is 3–6); an increase of biological activity noted as very high positive values of δ13C above+7‰ (Is 7). The fluctuations of the isotopic values at the upper part of the section probably point to a shallowing of the lake due to sedimentary infill (Is 9–10). In the studied deposits 23 species of the subfossil Cladocera were identified and seven zones of faunal development were distinguished. The Studzieniec palaeolake was sufficiently a shallow reservoir. The Cladocera composition indicates the initial oligotrophic status of the lake and then its subsequent increase and the periods of higher density of macrophytes during the interglacial optimum. The low frequency of Cladocera remains in carbonate-rich deposits may be caused by a state of preservation of faunal assemblages or the fast rate of sediment accumulation.