Stadial-interstadial cycles during the Weichselian glaciation in the central part of Fennoscandia Ice Sheet Pertti Sarala1,2 1 Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland; 2 Oulu Mining School, P.O. Box 3000, FI-90014 University of Oulu, Finland; e-mail [email protected] Debate for the duration of the stadials and interstadials during the Weichselian glaciation, i.e. 115,000-10,000 years ago, has been active in glaciated terrains for several decades. Based on the different oxygen isotope curves from the ice cores and marine sediments the knowledge of variable climate conditions during the ice age has been increased. Recently, terrestrial chronological results have turned the old theory of one single glacial phase into the multiphase, cold-warm cycling system. It seems that glaciers disappeared several times also from the central areas of glaciated terrains during the Weichselian ice age. The centre of the Fennoscandian Ice Sheet was located several times in Finland during Quaternary. Till stratigraphy is composed of several till beds being the most complete in northern Finland with six till beds (Hirvas 1991). Furthermore, the observations of inter-till stratified sand and gravel deposits were done in numerous places in northern and western Finland. Many of them were included organic peat and gyttja having infinite radiocarbon ages 45 ka or more i.e. indicating the limit of the dating method to be reached (e.g. Nenonen 1995). During last decade, many of the earlier sratigraphical key sections were re- examined and dated by Optical Stimulated Luminescence (OSL). In addition, several new inter-till stratified sections were observed and studied. The determined ages of Weichselian age form three groups: old 115-70 ka (MIS 5), middle 53-67 ka and young 21-46 ka (MIS 3). New dating results prove that the extent of glaciers and the length of glaciations were mostly short through Weichselian in Finland. During Early Weichselian, there were three short stadials, which occurred only in the northernmost Finland. Middle (MIS 4) and Late Weichselian (MIS 2) stadials lasted longer, and according to Sarala (2005) and Salonen et al. (2008) they were probably the only stages when glaciers covered central and southern Finland. Instead, during the MIS 3 northern Finland seems to be ice-free for a long time (cf. Mäkinen, 2005; Auri et al. 2008; Sarala & Eskola 2011; Sarala et al. 2010, 2016; Salonen et al. 2014). References Auri, J. et al. 2008. Tiedonanto eräiden myöhäispleistoseenikerrostumien avainkohteiden ajoittamisesta Suomessa. Geologi 60, 68-74. Hirvas, H. 1991. Pleistocene stratigraphy of Finnish Lapland. Geological Survey of Finland, Bulletin 354, 123 p. Mäkinen, K. 2005. Dating the Quaternary in SW-Lapland. Geological Survey of Finland, Special Paper 40, 67–78. Nenonen, K. 1995. Pleistocene stratigraphy and reference sections in southern and western Finland. Geological Survey of Finland. Kuopio. 205 p. Salonen, V.-P. et al. 2008. Middle Weichselian glacial event in the central part of the Scandinavian Ice Sheet recorded in the Hitura pit, Ostrobothnia, Finland. Boreas 37, 38-54. Salonen, V.-P. et al. 2014. Mid-Weichselian interstadial in Kolari, western Finnish Lapland. Boreas 43(3), 627–638. Sarala, P. 2005. Glacial morphology and dynamics with till geochemical exploration in the ribbed moraine area of Peräpohjola, Finnish Lapland. PhD thesis. Espoo, Geological Survey of Finland. 17 p. + 6 original papers. Sarala, P., Eskola, T. 2011. Middle Weichselian interstadial deposit in Petäjäselkä, Northern Finland. E&G – Quaternary Science Journal 60(4), 488-492. Sarala, P. et al. 2010. Composition and origin of the Middle Weichselian interstadial deposit in Veskoniemi, Finnish Lapland. Estonian Journal of Earth Sciences 59(2), 117-124. Sarala, P. et al. 2016. First physical evidence for forested environment in the Arctic during MIS 3. Scientific Reports 6, 29054. .