The Eemian Lakeland of the central Polish Plain: Environmental changes and palaeogeography

Abstract The current state of recognition of Eemian/Eemian–Vistulian subfossil flora sites in Central Poland is presented, as well as the results of cladoceran and isotopic investigations of the lake-bog successions of five key sites (Ruszkowek, Kaliska, Kublowo, Besiekierz and Parchliny “2014”) and inferred environmental variability. The distribution of 58 sites is also commented on in relation to the origin of palaeolakes, the nature of their infillings and their palaeolandscape. Most (90%) of these palaeolakes were created by the melting of buried ice remaining after the Wartanian (late Saalian, MIS 6) ice-sheet. It has been determined, from palynostratigraphy, that the decline of postglacial lakes may have taken more than 75,000 years. In the key palaeolakes, the beginning of Cladocera succession started at the end of the Wartanian and finished in the Middle Plenivistulian (MIS 3). The Middle and late Eemian was a period of intense Cladocera development in terms of biodiversity and specimen frequency. The significant differences in Cladocera succession and development of lakes reflect in detail the significant climate changes taking place between cold and warm periods, and the most pronounced differences result from variations in the morphometry and thus hydrological stability of the investigated palaeolakes. In the largest lakes (Kublowo) the survival chances of organisms increased in difficult times. The studied sediments are characterised by similar geochemical and isotopic features. The early Eemian warming is expressed by a positive trend in δ18Ocarb and δ13Ccarb and an increasing amount of organic matter. The late Eemian isotopic fluctuations are probably affected by the sedimentary infilling of the palaeolakes. The Vistulian cooling is reflected by distinctly lower values of δ18Ocarb than in the Eemian. The lowest amounts of total organic carbon are recorded in the coldest periods during the Herning, Rederstall and Schalkholz Stadials, but increased systematically during the warmer periods.