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).

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