The last interglacial in northernmost Sweden

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<ul><li><p>Quaternary International, Vol. 10-12, pp. 173-181, 1991. 1040-6182/91 $0.00 + .50 Printed in Great Britain. All rights reserved. (~) 1992 INQUA/Pergamon Press Ltd </p><p>THE LAST INTERGLACIAL INNORTHERNMOST SWEDEN </p><p>Ann-Mar ie Rober tsson Geological Survey of Sweden, Box 670, 751 28 Uppsala, Sweden </p><p>An outline is given of the present knowledge about the last interglacial in northernmost Sweden. Until now only one site, Leve~iniemi, has been found with deposits covering the whole interglacial cycle. The Leve~iniemi sediments have been thoroughly investigated by means of different biostratigraphical methods including micro- and macrofossils. Two other localities with Eemian deposits, K~itkij~irvet and Seitevare, are also described and discussed. At K~itkij~irvet the main part of the interglacial is represented, while at Seitevare only the later part is present. The climate during the last interglacial was more favourable than during the Holocene in the same area. Plant and insect remains suggest a more continental (higher summer temperatures) character to the climate. At K~itkij~irvet, open vegetation prevailed during the interglacial, but the forest limit was possibly located at a higher altitude than today. Coniferous forests including pine and spruce were growing closer to the site during part of the interglacial. Correlations with northern Norway and Finland are discussed. </p><p>30* INTRODUCTION </p><p>The present knowledge about the palaeoenviron- ment in northern Sweden during the Eemian Inter- glacial is still limited. Up to now most information has. been obtained from one important site, namely Leve~iniemi in northern Lapland (Lundqvist, 1971). There, a till-covered basin was found, containing freshwater gyttja and peat covering a whole interglacial cycle. Since then Leve/iniemi, has been the only site in Sweden where a more or less complete interglacial sequence has been documented. </p><p>A large amount of new information about the Pleistocene stratigraphy in the northernmost latitudes of Scandinavia, called Nordkalotten, was gained in connection with the Nordkalott project (Nordkalott Project, 1986a,b; Hirvas et al., 1988). This was a joint venture between the Geological Surveys of Norway, Sweden and Finland, and comprised different aspects of the geology for the three countries north of 66 latitude (Hirvas et al., 1988). </p><p>The Pleistocene stratigraphy in northernmost Sweden has been examined and documented in about 700 machine-made pits and more than 100 boreholes. Some 150 of these sites were presented in the Nord- kalott maps (Nordkalott Project, 1986a). Two sites, K~itkij~rvet and Seitevare (Fig. 1), were found to include interglacial deposits. The Quaternary deposits often displayed two or more different till beds some- times intercalated by water-laid fine-grained sediments. The till beds represent different Weichselian stadials and ice-flows with till-covered, more or less organic bearing sediments, that proved to represent two (Early) Weichselian interstadials. The environmental conditions and their development during the inter- stadials of the latest glaciation have been reconstructed (Lagerb~ick, 1988a,b; Lagerback and Robertsson, 1988). </p><p>10 20* </p><p>70* </p><p>68*_ </p><p>66* </p><p>SWEDEN 64* </p><p>NORWAY </p><p>30* </p><p>\ 20* </p><p>0 300 km </p><p>FIG. 1. Location map with the interglacial sites described. K = K~itkij/irvet, L = Leve~iniemi and S = Seitevare. </p><p>PRE-WEICHSELIAN DEPOSITS </p><p>In the Swedish part of the Nordkalott area 18 localities with till beds interpreted as pre-Weichselian have been observed and documented (Nordkalott Project, 1986a). The older till is resting on chemically weathered bedrock at Vahtanvaara, ca. 20 km NNE of Levehniemi. Fabric analyses of the older till indicate </p><p>173 </p></li><li><p>174 A.-M. Robertsson </p><p>that westerly or northerly ice flows dominated during the deposition of the till beds, but the observations are too few to allow any conclusions about regional patterns (Fig. 2, Hirvas et al., 1988; Nordkalott Project, 1986b). </p><p>The site at Seitevare (Fig. 1) contains an organic layer suggested to have been deposited during the Eemian Interglacial. Below the thin peat layer a till bed was observed (Robertsson and Rodhe, 1988). It was a gravelly-sandy greyish till, resting on unweathered granitic bedrock, on which no striations were found. The till is suggested to have been transported from the northwest, but other directions cannot be excluded. The petrographical composition of this oldest till is not very different from the younger till beds occurring above the interglacial sequence (Robertsson and Rodhe, 1988, Fig. 3). Pre-Weichselian till beds have also been identified at sites in northernmost Finland and Norway (Nordkalott Project, 1986a; Olsen, 1988, 1989). </p><p>Few observations exist of pre-Weichselian till beds and ice flow directions in northernmost Sweden (Fig. 2), and the rest of the Nordkalott area. This supports the evidence for a very active early Weichselian glaciation (Hirvas et al., 1988; Lagerback, 1988a; Lagerback and Robertsson, 1988; Olsen, 1988). </p><p>SEQUENCES CORRELATED WITH THE EEMIAN </p><p>Leveiiniemi The site (Latitude 6738N, Longitude 2101E, Fig. </p><p>1) is presently located in the northern boreal coniferous forest region, with pine, spruce and birch as the dominant trees. The present day mean July tempera- ture is 13C. </p><p>The stratigraphy includes the following main units from the surface downwards (Lundqvist, 1971; Garcia Ambrosiani, 1990): 1.0-1.5 m peat, Holocene; 3.0-4.0 m till, upper bed, transported from southwest; 0.2-0.5 m sediments, minerogenic fine-grained, glaciofluvial or glaciolacustrine; 3.0-4.0 m till, lower bed, transported from northwest; 0.5-1.5 m organic sequence: peat and lacustrine gyttja sediments; and bedrock, weathered. </p><p>The Weichselian till beds and the intercalated interstadial sediments, above the interglacial sequence, were studied by Garcia Ambrosiani (1990), who corre- lates the intertill glaciofluviaYlacustrine sediments with an Early Weichselian interstadial, most probably the Perapohjola (Brorup). </p><p>The interglacial organic layers correlated to the Eemian were investigated by means of macrofossils, plant remains and insects, and microfossils, pollen and diatoms (Tralau, Lindroth and Coope, Robertsson and </p><p>9 SO </p><p>FIG. 2. Pre-Weichselian ice-flow directions in the Nordkalott area (Nordkalott Project, 1988b, map sheet 5:4). </p></li><li><p>The Last Interglacial in Northernmost Sweden 175 </p><p>Miller in Lundqvist (1971) as Appendices 2, 3, 4 and 5). Identified carpological remains (mainly seeds and fruits) provided the following results (Tralau in Lund- qvist, 1971, p. 68): </p><p>(1) Some of the species occurred far beyond their present northern range limits, e.g. Potamogeton friesii, Carex pseudocyperus and Calla palustris; </p><p>(2) plants with a modern southeastern and southern distribution, such as Lysimachia thyrsiflora were present; </p><p>(3) the general climatic conditions under which the fossil flora grew were more favourable than today at the same latitude; </p><p>(4) the fossil flora seems to have its modern equiva- lent in the Baltic coastal areas of northern Sweden and Finland (Fig. 3); and </p><p>(5) the aquatic species found indicate a eutrophic lake with alkaline water (Potarnogeton friesii, P. spp., Myriophyllum spicatum, M. alterniflorum). </p><p>Identified beetles gave the following information on the Eemian climatic conditions (Lindroth and Coope, in Lundqvist, 1971): </p><p>(1) The majority of the species observed are foreign to the area today; </p><p>(2) the climate during the interglacial optimum was more temperate than during the Holocene optimum and had a pronounced continental character with warmer summers; and </p><p>(3) the 14 species identified can only be found </p><p>10" 30* I 20* </p><p>_ __A~c_Lie cJr_eJ_e_ _ [_ </p><p>SWEDEN </p><p>NORWAy </p><p>20 Beetles: </p><p>Present occutence of the 14 species identified in the Leve~lnlerni semplas </p><p>0 300 km t I I I </p><p>Macrofossll plant remains: </p><p>/ .~ Phytogeographlcal modern f - - - - equivalent to the fossil </p><p>~-~ aquatic flora </p><p>FIG. 3. The modern equivalent areas in Fennoscandia to the beetle fauna and aquatic flora identified in the Leve~iniemi interglacial </p><p>deposits. </p><p>together today in inner central Finland (Fig. 3), where the mean July temperature of today is 15C or 2 higher than at present for Leve~iniemi. </p><p>The pollen-analytical results can be summarized as follows (Robertsson, in Lundqvist, 1971): </p><p>(1) Six pollen zones a-f, were identified, reflecting a whole interglacial cycle (Fig. 4): Zone a; the initial phase with herbs, shrubs, birch, pine; Zone b, c; the climatic optimum with birch, pine, alder and possibly some hazel; Zone c, d; soil degeneration (podsoliza- tion), start of climatic deterioration, immigration of spruce; Zone e, f; final phase with increasing erosion and solifluction, birch and pine predominate. </p><p>Leve~niemi C </p><p>70 </p><p>80 </p><p>90 </p><p>oo ! </p><p>----t I10 </p><p>2O </p><p>":'":' o r </p><p>30/, 303 309 30B 310 30S 303 303 306 255 152 </p><p>264 " </p><p>Am~.ysteglo- ~ Ctoy ~ Sancl cor;c[an p la t </p><p>Or,,, o.o, ~ . .d . l, oam ~ Coarsesand </p><p>FIG. 4. Arboreal pollen diagram from Leve~iniemi, section C Robertsson, in Lundqvist, 1971, Fig. 4:1). </p><p>QH </p><p>Qr F- t~ </p><p>i 5% 5% 5% </p><p>(from </p></li><li><p>176 A.-M. Robertsson </p><p>(2) The forests were dominated by birch, pine, alder and spruce. During the climatic optimum some stands of hazel could have existed in sheltered positions, indicating more favourable conditions than during the Holocene optimum in the same area. </p><p>(3) A rich aquatic flora is represented in the pollen flora with Potamogeton, Typha-Sparganium, Nuphar, Nymphaea and Myriophyllum. Leaf tips of Ceratophyl- lum were also identified. </p><p>The composition of the diatom flora (nine diatom zones were identified) gave information about the aquatic changes in the basin during the Eemian (Miller, in Lundqvist, 1971). The main conclusions drawn on the basis of the diatom analytical results were: (Fig. 5) </p><p>(1) The basin was a small, shallow freshwater lake; (2) eutrophic conditions with alkaline, slightly </p><p>brackish, transparent water rich in mineral salts, prevailed during the beginning of the interglacial; </p><p>(3) after the climatic optimum a poor diatom flora indicates drainage of the basin (lowering of the water table) and accumulation of drift sediments; </p><p>(4) acid water with oligotrophic-dystrophic condi- tions during peat formation; </p><p>(5) the terrestrial phase exposes acidic conditions and a diatom flora of low diversity; and </p><p>(6) the interglacial ends with a moister phase when an admixture of acid and alkaline diatoms occur (barren soils, erosion ?). </p><p>In total the following main conclusions were drawn (Lundqvist, 1971, pp. 22-24): Summer temperatures at Leve~iniemi were probably 1-2C higher than today, but the mean annual temperature was possibly as much as 4 higher than today in the same area. </p><p>LEVE~NIEHI : In te rgtac ia t C </p><p>8. FALKENSTR~H o.U. HILLER lg70 </p><p>FIG. 5. Diagram showing the ecological development of the diatom flora at section C, Leve~iniemi. Stratigraphical legend see Fig. 4 </p><p>(from Miller, in Lundqvist, 1971, Fig. 5:3b). </p><p>A continental climate (= warm summers) is indi- cated by the occurrence of southeastern plant and beetle taxa. </p><p>Kiitkiji~rvet The site (Latitude 6847'N, Longitude 2048'E, Fig. </p><p>1) is located in northwestern Lapland close to a cluster </p><p>KATKI JARVET &gt;- "I" o. ,&lt; n- co </p><p>v n" </p><p>U.I "I- </p><p>--I </p><p>6,5. A o OID </p><p>silty r . o </p><p> [2 o </p><p>7,0 Ndlment~ Ao o </p><p>TOTAL POLLEN SPECTRA ILl </p><p>[ ] TREES SHRUBS HERBS E (.9 </p><p>o Betu la Betu la Ar temls la ~J &lt; ' P lnus nana- type -~ z ~; </p><p>a A lnus [ ] Sa l lx [ ] DWARF SHRUBS ~. ~ ~ ~7 </p><p>, P,o.a . ~ o </p><p>5'o~ 124 </p><p>J : 426 </p><p> :" 1341 </p><p>m-. '= I ; : 308 </p><p>7,5, rh o I _ 323 </p><p>A ea o "" 310 </p><p>8,0 , 0 0 , ~, ~, . , 450 </p><p>8,3 silty a o l __. 307 </p><p>8,4 a a o ~ :::':: 340 sad l - </p><p>8,5 a o _" 490 </p><p>8,6 rnsnts </p><p> o o ~ : ' : - 436 "iI 8,9 qm o 440 9,1 eO o I _ 306 </p><p>, [] O -'.l : 412 </p><p>c lay - a o ll:. 400 9,9 ::lByey sill Au Io ~ ~ </p><p>- : : . 305 silt with m o m =:':':': 400 </p><p>o --:';';" 210 p~mt ae [] o ~. : 408 </p><p>10,1 remains (mosaes) A ~ o " - ' ' 400 </p><p>10,3 ,ItL </p><p>varved --- iN </p><p>10,5 &amp; 12 o </p><p>11,3 siRy </p><p>10,65 - 11,50 m : no pollen noted </p><p>NAP </p><p>11,5 </p><p>11,7 </p><p>sandy </p><p>sdlments </p><p>Aan o </p><p>Betu la </p><p>NAP-P lnu- </p><p>-P Icea </p><p>NAP </p><p>11,9 </p><p>Betu la </p><p>12,1 </p><p>150 A lnus </p><p>_ :.:-: 428 P lcea </p><p>o o ,l : : : : ' 351 </p><p>very few pollen noted 5 ' ' </p><p>till </p><p>12,3 till with . . . ~ (Reworked u~ |~ ~ [] O '1 = :""" i 435 ~,,~~, poll,,,.) </p><p>Ann-Made Robertsson 1988-89 </p><p>FIG. 6. Pollen diagram from K~itkij/irvet. Herbaceous pollen and spores identified are listed in Table 1. </p></li><li><p>The Last Interglacial in Northernmost Sweden 177 </p><p>of small pingos on a treeless mountain plateau, about 750 m above sea level (Lagerb/ick and Rodhe, 1985). Today the area is covered by mountain heath vegeta- tion including Empetrum hermaphroditum, Vaccinium myrtillus, Festuca ovina, Calamagrostis lapponica and Betula nana. Along the lake shores and rivers, Salix spp. and Carex spp. occur in plant communities characterized as dry or wet fens (von Sydow, 1983, Andersson et al., 1985). Fens with hummocky vegeta- tion of dwarf shrubs and Sphagnum spp. are also present. </p><p>The investigation area is situated 150-200 m above the present tree limit. Mountain birch (Betula tortuosa) is the only tree species growing in the closest forest 9- 10 km to the northeast of K~itkij/irvet. Pine and spruce forests are over 100 km away today. The sequence, sampled by drilling, includes the following stratigraphy (R. Lagerb/ick, pers. commun.): 0-1.50 m: peat, silt, sand (Holocene); 1.50-4.50 m: till, silty-sandy; sedi- ment series: 4.50-5.20 m: silty sediments, disturbed; 5.20-9.55 m: silty sediments, varved, low organic content; 9.55-9.95 m: clay-clayey silt; 9.95-10.20 m: silt with moss remains, increased organic content; 10.20-10.85 m: silt, varved, downwards decreasing organic content; 10.85-11.90 m: silty-sandy sediments, no visible organic remains; 11.90-12.35 m: till, silty, including some organic material; and 12.35-29.90 m: mainly till (not sampled). </p><p>A drilling in one of the pingos revealed a stratigraphy containing ice with thin minerogenic layers in the upper part below a cover of 5.5 m till, silt and sand. Downwards more or less pure ice occurs to a depth of at least 15 m below the surface (Lagerb/ick and Rodhe, 1985, Fig. 4). Based on the composition of the pollen flora the sediment sequence (6.5-11.9 m) can be divided into three main pollen assemblage zones (Fig. 6). </p><p>The pollen of herbs and spores identified are listed in Table 1. Pollen analysis at 12.35 m indicates that the till contains redeposited pollen. </p><p>NAP-Betula-Alnus-Picea (11.85-10.00 m) Pollen of trees, including Picea compose approxi- </p><p>mately 50% of the total pollen flora, while herb pollen are frequent along with shrubs. Betula spp., both tree birch and dwarf birch, dominate the tree pollen flora. Alnus (viridis-type) occurs at more than 10%. Herbs are represented by graminids, Cyperaceae and Artemi- sia. Ericales are also registered together with Salix. </p><p>NAP-Pinus-Picea (10.00--9.90 m) Pinus poll...</p></li></ul>