ИСТИНА

Arctic generally lacks sound and continuous records of the last interglacial paleoenvironmental evolution. The high-resolution investigation of the 4.5 m thick sequence of Eemian marine beds directly overlying Saalian till in Bychye section (Pyoza River, NE White Sea Region) now allows for detailed reconstruction of past events on the basis of obvious changes in microfossils (foraminifers, ostracods, pollen, aquatic palynomorphs). The early stage of inundation is featured by accumulation of marine clays overlying the till and stands out as a period of harsh fluvially-affected environment with cold turbid waters and heavy seasonal sea-ice cover as suggested by the predominance of opportunistic species Elphidium clavatum and river-proximal foraminifers, and heterotrophic cryophile species Islandinium minutum among extremely poor in diversity dinocyst assemblage. The main trend in the evolution of vegetation is gradual supplanting of the late Saalian - earliest Eemian arctic-type periglacial treeless vegetation by birch and light-coniferous forests during early Eemian. Further climate amelioration and increasing influence of open-sea waters correlative with accumulation of silts and sands of the middle part of the section are evidenced by increasing total abundance and diversity of microfossils, high percentage of foraminifers characteristic for the Arctic shelves with high seasonal productivity (Islandiella spp., Nonion labradoricum), occurrence of relatively deep-water Arctic species among foraminifers (Melonis barleeanus) and ostracods (Krithe glacialis), and growing percentages of thermophylic broad-leaved species (Quercus, Ulmus, Corylus, Carpinus) in pollen spectra. Highest content of spruce, alder and other mixed forest hylophytes supplemented by hazel maximum and single Tilia cordata L. pollen grain occurrence in the 200–120 cm interval of the section characterize the most humid and warm period. Accumulation of sands in the upper part of the section corresponds to the regressive stage and is characterized by gradually decreasing taxonomic diversity and abundance of microfossils, and growing proportion of relatively warm-water and shallow-water species especially among ostracods (Finmarchinella finmarchica, Patagonicythere dubia, Cythere lutea, Hemicytherura clathrata). Gradual climatic deterioration towards the end of the record is manifested by birch prevalence over pine and hornbeam and disappearance of spruce, alder and mesophilous representatives among forbs. There are no direct indicators of Atlantic water penetration in the composition of microfossils, and the presence of subarctic ostracods and bivalves as well as single dynocysts of autotrophic species Penthapharsodinium dalei, Spiniferites cf. pachydermus and Nematosphaeropsis labyrintus in the upper part of the section should be due to shallowing and surface water warming.