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The Eemian Interglacial in Sweden, and Comparison with Finland

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The Eemian Interglacial in Sweden, and Comparison with Finland Geologie en Mijnbouw / Netherlands Journal of Geosciences 79 (2/3): 325-333 (2000) The Eemian interglacial in Sweden, and comparison with Finland Ann-Marie Robertsson1 1 Department of Quaternary Research, Stockholm University, S-10691 STOCKHOLM, "Ik ""¥"" Sweden L^^ I Manuscript accepted in revised form: 5 April 2000 I Abstract The current status of knowledge concerning the Eemian interglacial in Sweden is surveyed, and comparisons are made with northern and western Finland. The course of shore displacement is fragmentarily known for Sweden, since brackish-marine sediments have been identified, on the basis of diatom analysis, at only few sites. In Finland, on the other hand, a shore- displacement curve has been constructed for the Eemian Baltic Sea in Ostrobothnia, central western Finland. The vegetation history is summarised for the southernmost part of Sweden, and can be correlated with that documented in Denmark. For the central part of Sweden, information is sparse, but the composition of the forests has been outlined for most of the interglacial, although information on regional pollen assemblage zones E3 and E4 (early-temperate substage) are main­ ly missing. A more complete picture of the interglacial vegetational history is known from Ostrobothnia in Finland. The ther- mophilous indicators Viscum, Ilex, Hedera and Osmunda grew far North during the Eemian. Corylus and Carpinus expanded much further to the North than during the Holocene. In Swedish and Finnish Lapland, the vegetation history is similar ex­ cept that Larix was common in Finland during the Eemian, but its presence has so far not been confirmed in Sweden. Eemian deposits relocated during the Weichselian glaciation contain pollen and diatoms that can be used for reconstruction of the Eemian environment. No clear indication of a rapid climatic deterioration during the Eemian has been found so far in either Swedish or Finnish sequences. Key words: Eemian, Finland, rebedded pollen, relocated deposits, shore displacement, Sweden, vegetation history Introduction tain organic-bearing sediments accumulated during at least two (Early) Weichselian interstadials (Nord- Deposits thought to represent the entire Eemian in­ kalott Project, Hirvas et at, 1988; Lagerback & Ro­ terglacial have so far been found at only a few sites in bertsson, 1988). These sequences do, however, not Sweden (Fig. 1). Our knowledge of climate change, include Eemian deposits. There is, sofar, only one site vegetation history and shore displacement in Sweden - Leveaniemi - known to represent a more or less during the Eemian is thus fragmentary. The main rea­ complete interglacial succession correlated with the son is that the ice sheet tectonised, dislocated and Eemian (Lundqvist, 1971; Robertsson, 1997). The eroded interglacial deposits during the first Weich­ sites Katkijarvet and Seitevare in Norrbotten have selian stadial. The erosional effect was, however, gen­ also been suggested to contain Eemian sediments erally strong in several parts of the country. In some (Robertsson & Rodhe, 1988; Robertsson, 1991).The areas, such as Norrbotten in northernmost Sweden, correlation of these interglacial sequences with the ice was partly cold-based and it affected the mor­ Eemian sites in NW Europe is problematic because of phology of the landscape to a very limited extent the great distance. The flora was much less diverse in (Lagerback, 1988; Kleman, 1994; Hattestrand, 1997). northern Scandinavia, which means that thermophi- In Norrbotten, many sites have been found that con­ lous elements, for example mixed oak forest (QM), Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 325 Downloaded from https://www.cambridge.org/core. IP address: 170.106.33.42, on 29 Sep 2021 at 18:24:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600021806 Fig. 1. Survey map of Sweden and Fin­ land showing sites and areas discussed in the text. Katkijarvet Slenberget. Carpinus, Viscum, Hedera and Ilex, are missing from and spores. In the many samples analysed, a certain the pollen flora. Some of these plants are, however, pattern can be seen in the presence and composition present in the pollen flora identified at Eemian sites of the pollen flora. An interglacial 'signature' has been in southern Sweden (Berglund & Lagerlund, 1981; found in samples taken from sediments and tills cov­ Passe, 1992). ered by at least two different till beds. In contrast, more superficial sediment and till layers are usually Redeposited interglacial (Eemian) pollen flora void of pollen, or the pollen flora has an 'interstadiaP composition dominated by herbs and shrubs, and The presence of interglacial (possibly Eemian) de­ with birch as the only tree species represented (Ro­ posits has been shown by analysis of pollen and bertsson & Lagerback, 1988; Lundqvist & Miller, spores occurring as redeposited microfossils in tills 1992). and sediment clasts in tills deposited during the Weichselian (Miller, 1977; Lagerback & Robertsson, Eemian shoreline displacement 1988; Lundqvist & Miller, 1992; Robertsson & Gar­ cia Ambrosiani, 1992). During mapping of Quater­ Along the Swedish east coast, the sites Bollnas, N. nary deposits in northern Sweden, the lithostratigra­ Sannas, Skulla and Nykoping have been shown to phy has been documented in several hundred ma­ contain brackish-marine diatoms in sediments of sup­ chine-excavated pits (Hirvas et al., 1988; Eklund et posedly Eemian age (Erikson, 1912; Halden, 1915; al., 1991). Fine-grained mineral sediments, including Miller & Persson, 1973; Robertsson & Garcia Am­ tills, have been analysed for their content of pollen brosiani, 1992; Robertsson et al., 1997). 326 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 Downloaded from https://www.cambridge.org/core. IP address: 170.106.33.42, on 29 Sep 2021 at 18:24:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600021806 Bollnas occurs at the highest altitude (approx. 88 This sparse information on the Eemian Sea and m) of the sites studied. The bulk sample, which con­ shoreline displacement in Sweden can be compared tained brackish and marine diatoms, has not been with Finland, where the stratigraphy at many sites has analysed for its pollen content, so it is unknown been found to represent various stages of the Eemian which Eemian regional pollen zone the sediments sea (Fig. lb). During an early phase of the inter­ represent. The highest Holocene marine limit in the glacial, the Baltic was a fresh-water basin, comparable area was formed by the Litorina Sea, which reached to the Holocene Ancylus Lake, as indicated by diatom approx. 120 m above present sea level. analyses from the Norinkyla, Viitala and Mertuanoja A clay containing brackish marine diatoms at N. sites in Ostrobothnia (Gronlund, 1991a,b; Eriksson Sannas is situated approx. 25 m above present sea et al., 1999). The existence of a connection between level and the composition of the pollen flora indicates the Baltic basin and the White Sea in the North has the later half of the interglacial, since Picea occurs at been confirmed by finds of Arctic marine silicoflagel- 17% of total land pollen. At this low altitude, brack­ lates in the marine Eemian sediments at Ostrobothnia ish-marine conditions may have prevailed for a long (Gronlund, 1991a,b). Based on the results from a part of the Eemian interglacial. number of sites, it appeared even possible to recon­ Skulla is situated approx. 55 m above sea level. The struct a shore-displacement curve for the Eemian Sea slightly brackish diatom flora is suggested to repre­ in Ostrobothnia (Forsstrom et al., 1988).The highest sent the beginning of a transgressive phase or isola­ Eemian marine shoreline reached over 20 m above tion from the sea (Robertsson & Garcia Ambrosiani, the Holocene Litorina Sea level in the same area 1992). According to pollen analyses, the till-covered (Saarnisto & Salonen, 1995). clay was originally deposited before the spread of The type site for the Eemian stage in Ostrobothnia spruce and hornbeam (Fig. 2), i.e., during regional is Evijarvi (Eriksson et al., 1980; Donner, 1995) and pollen assemblage zone (PAZ) E4.The Holocene ma­ in Finnish Lapland it is Tepsankumpu (Saarnisto et rine (Litorina) shoreline limit in the area is at 70-75 al., 1999). m above sea level. The clay found redeposited in glacial sand in Eemian vegetation history Nykoping was deposited under marine conditions (Miller & Persson, 1973). The composition of the di­ The northernmost part of Sweden and Finland atom flora suggests higher salinity than during the Holocene, whilst the pollen flora indicates deposition Analysis of pollen, macrofossils and insect remains before the immigration of Picea. Very few pollen from the organic sequence at Leveaniemi has given grains, mainly including Tilia, were noted, however. the following (most complete) picture of the vegeta- 1 U II I I I I I I I I I I I I I IH J J I I I I I I I I I I I I I ItJ 14 i I.I III I,I i,11,i| i,i i,iq 20 40 60 80 100 20 20 40 20 Fig. 2. Pollen spectra from a redeposited supposedly Eemian clay at Skulla, southern Sweden. A brackish-water diatom flora was identified in sample no. 2 (cf. Robertsson & Garcia Ambrosiani, 1992). Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 327 Downloaded from https://www.cambridge.org/core. IP address: 170.106.33.42, on 29 Sep 2021 at 18:24:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600021806 Fig. 3. Simplified pollen diagram for Local Leveaniemi, northernmost Sweden (af­ _3 Betula Pinus > Picea ter Robertsson, 1997). o PAZ Substage O Pinus - Betula Betula- Post- Juniperus- temperate Populus Picea- Late- Pinus temperate Pinus- Early- Betula- temperate Alnus Pre- Betula - Junip.
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