Environmental changes during the Late glacial period inferred from sedimentological archives of NE Poland, Lithuania and Belarus

The area of NE Poland, Lithuania and NW Belarus is often studied in terms of palaeoenvironmental changes that occurred at the end of the last glaciation In this area there are numerous lakes, peat bogs, river valleys, kettle holes where limnic and paludic sediments accumulated. Based on the literature, 55 sites from this region were analysed. On the basis of palynological studies, and radiocarbon dating their deposition time was determined as Late glacial period (LG). There are also sites whose age is determined only on the basis of palynology or plant macrofossils. Often in the analysed sediment profiles there is no record of the full LG succession, but there is usually a BØ-AL-YD sequence. The thickness of the described LG sediments ranges from 8 cm to 325 cm. Large thickness LG sediments were found at the sites Stare Biele (thickness 325 cm, Poland, Podlasie; Kupryjanowicz, 2000), Ginkūnai (290 cm, Middle Lithuania; Stančikaitė et al., 2015), Lopaičiai (180 cm, NW Lithuania; Kabailienė et al., 2015). The range of radiocarbon averaged ages for the analysed sediment profiles is from 9,176 to 25,250 ka cal BP. Some of them are subject to error (aged by pollen redeposition or rejuvenated by reservoir effect). Typically, macrofossils isolated from gyttjas, peats or silts were dated.

A few km north-east of Suwałki (NE Poland) there is an extensive, irregularly shaped depression, consisting of several larger reservoirs connected by constrictions. Most of its area is covered with peat bogs. Using the GEOPROPBE intact biogenic sediment profile was drilled (profile OS – 10,40 m). So far, palaeobotanical, geochemical, and stable oxygen and carbon isotopes have been performed in the collected sediments. In the near future, ¹⁴C AMS dating of selected plant remains is planned.

The conducted palynological analysis of OS profile shows that the functioning of the water reservoir near Suwałki began in the OstD, when the area was overgrown by vegetation of open communities. Slight warming of BØ resulted in high Pinus pollen values, which may indicate the development of rare interstadial pine forests. Re-cooling of OD resulted in the withdrawal of these communities and the spreading of herbaceous and shrubs vegetation. Another warming - AL, led to the development of rare pine and birch forests with numerous sea buckthorn. The cooling of the YD brought the domination of open shruby and steppe-tundra communities. The thickness of the sediments from the LG period containing the full record is 81cm. Considering the location of the Osinki site and the significant continental character of this region climate, it can be concluded that it is a stratotype site of LG for this part of Europe.

The above research results are presented thanks to the grant of the National Science Center (2018/31/B/ST10/00976) "Geomorphological evidence and palaeogeographic implications of catastrophic floods and glacial charges of the southern sector of the Scandinavian late Vistulian ice sheet (MEASSIS)" and the funds of Nicolaus Copernicus University in Toruń as part of the Emerging Filds "Global changes in the environment".