Lacustrine sediments of the Holsteinian interglacial and the early part of the Saalian glaciation from Eastern Poland are exceptional in Europe: they have a maximum thickness of at least 55 m, they are very homogeneous (lake marl and gyttja), they have been geologically and palaeobiologically investigated in great detail (pollen analysis, macrofossils, mollusc fauna). Oxygen and carbon isotope composition of these sediments allow a precise reconstruction of climatic variations to be made: Minimum values of δ13C (-6.4 ‰) were found in the earliest part of the interglacial period, maximum (+10.0 ‰) values could be detected at the onset of the Saalian glaciation. The distribution of the δ18O values follows an inverse trend. The maximum values (-3.6 ‰) occur at the initial period of the interglacial and the minimal (-10.1 ‰) are associated with a progressive temperature decrease at the end of the interglacial. Generally the isotope data satisfactorily reflect the palynologically well-documented climatic changes. However there are two sections in the profile, where this correlation is poor: 1. At the palynologically defined interglacial climatic optimum the 18O curves indicate relatively cool climatic conditions. 2. In the upper part of the sediment profile, which probably reflects the onset of the Saalian glaciation, the 18O and 13C - isotope curves have relatively high values, indicating too high temperatures.
For the first case an inflow of 18O depleted groundwater or/and an increase of precipitation with a rise of the lake level is postulated. In the second case the poor correlation is quite likely caused by a redeposition of sediments of the warm interglacial period, and/or by an enrichment of 18O and 13C due to intense evaporation.