Isotopic and Cladocera records of climate changes of Early Eemian at Besiekierz (Central Poland)

Abstract

Results of stable isotope, Cladocera and pollen analyses of lacustrine sediments from Besiekierz (Central Poland) are presented. The Besiekierz palaeolake is located about 25 km north of Łódź (Central Poland) at 130 m a.s.l. The 4 m thick deposits comprise silty sands and clayey silts, overlain by calcareous gyttja and organic silts and peat. Pollen analysis documents that these deposits accumulated during the Eemian Interglacial and the Early Vistulian. Based on the results of stable isotope analyses, nine isotopic horizons (Is) were defined and characterized, and these enabled reconstruction of both climatic and hydrological changes. A positive trend in d18 O values and constant values of d13 C suggest gradual climatic warming, while constant values of d18 O and d13 C indicate stable conditions and/or a fast rate of sedimentation. The fluctuation of isotopic values in the upper part of the succession probably points to a shallowing of the lake due to sedimentary infill. The subfossil cladoceran fauna in the Besiekierz succession is represented by 11 solely littoral species belonging to 3 families. Four zones of Cladocera development were distinguished. The Besiekierz palaeolake was a shallow reservoir. The initial period of its existence probably saw its greatest depth. The Cladocera species present indicate the initial oligotrophic status of the lake and its subsequent increase in trophic status. We compare the results of the isotopic, cladoceran and published palynological analyses, to distinguish and explain the phases of evolution of the lake.