Climate reconstruction fromstable-isotope composition of the Mazovian Interglacial (Holsteinian) lake sediments in eastern Poland

Sediments of palaeolakes located in eastern Poland representing the Mazovian Interglacial (Holsteinian) and the initialpart of the succeeding Middle-Polish glaciation (Saalian) are unique in Europe. These sediments are very thick (up to 55 m) and homogeneous, composed of lake marl and calcareous gyttja. They are thoroughly interpreted in terms of geological and palaeobiological studies (palynology, macrofossils, diatoms and malacofauna) and represent continuous deposition. Analysis of stable oxygen and carbon isotopes in these deposits and of the shells of the malacofauna enables interpretation of the changes in the palaeoclimate and sedimentary environment that occurred in lake basins during this part of the Pleistocene. Maximum [delta]^18O (-3,6 promille) and minimum values of [delta]^13C (-6,4 promile) correspond to the first part of the interglacial optimum, while minimum delta^18O values (-10,1 promile) and maximum delta^13C values (10,0 promile) correspond to the coldest period, directly preceding the following glaciation. Climatic changes are well ducumented by isotopic curves correlated with the result of pollen analysis. The isotopic curves indicate relatively cool climatic conditions at the climaticoptimum of the Mazovian Interglacial. This may have been caused by increased atmospheric precipitation that led to deepening of the lakes and/or by influx of ground waters enriched in light isotopes. In the upper part of the successions,coresponding to the initial stage of the following glaciation, the concentration of 18^O and 13^C increases, which was probably associated with the lake shallowing and with enrichment in heavy isotopes through evaporation under conditions of a cool steppe climate and/or with the redeposition of "warm" interglacial deposits from shore areas exposed as the result of lake shallowing. The isotopic curves clearly illustrate changes in the relative influence of maritime and continental air circulation during the Mazovian Interglacial. The studied lakes were oligo- or mesotropic with dominant influence of continental air circulation before the interglacial climatic optimum. Maritime air circulation prevailed during the interglacial climatic optimum and the lakes became eutrophic. Cyclic climatic cooling during the post-interglacial period is recorded in oxygen isotopic curves trending towards their lower values. The carbon isotopic curves reach higher values, which is related to climatic cooling and shallowing of the lakes, caused by their infilling with deposits.