Quaternary Research 57, 191–199 (2002) doi:10.1006/qres.2001.2313, available online at http://www.idealibrary.com on Holocene Climate Reconstructions from the Fennoscandian Tree-Line Area Based on Pollen Data from Toskaljavri Heikki Sepp¨ a Department of Earth Sciences, Uppsala University, Villav¨ agen 16, SE-752 36 Uppsala, Sweden and H. J. B. Birks Botanical Institute, University of Bergen, All´ egaten 41, N-5007 Bergen, Norway and Environmental Change Research Centre, University College London, 26 Bedford Way, London WC1H OAP, United Kingdom Received May 16, 2001 Due to its location on the eastern North Atlantic seaboard, the Fennoscandian tree-line area is an ideal area to use biological prox- ies to assess the relative roles of the Scandinavian ice sheet and of oceanic, atmospheric, and astronomic forcings on regional climate history. Here we report pollen-based July mean temperature (T jul ) and annual precipitation (P ann ) reconstructions from a sediment core from a high-altitude tree-line lake in northwestern Finland. The reconstructions suggest that at 9600–8300 cal yr B.P. T jul val- ues were low but steadily rising while P ann was high. The period of warmest summers, with T jul values ca. 1.8 ◦ –1.6 ◦ C higher than at present, occurred at ca. 8000–6500 cal yr B.P. Since then cli- mate has become gradually cooler. T jul values during the “Medieval Warm Period” (ca. 1400–1000 cal yr B.P.) were ca. 0.8 ◦ C higher that at present but decreased rapidly to the low “Little Ice Age” levels at 800 cal yr B.P. We compare these results with an earlier pollen-based climate reconstruction from the same region. The re- constructions indicate a similar general Holocene T jul pattern with lower values in the reconstruction from the high-altitude lake. How- ever, most of the small-scale variations are not synchronous, sug- gesting that they may represent noise rather than signal in our data. C  2002 University of Washington. Key Words: Holocene; pollen; temperature; precipitation. INTRODUCTION The climate of northern Fennoscandia is anomalously mild in relation to its latidudinal location. At 70 ◦ N latitude the annual incoming solar radiation at the Earth’s surface is only ca. 70,000 cal./cm 2 , whereas the outgoing radiation is ca. 136,000 cal./cm 2 (Wall´ en, 1970). In northern Europe, the deficit is partly balanced by oceanic and atmospheric circulation pro- cesses that carry heat from lower latitudes. The heat transport is driven by the North Atlantic thermohaline circulation, an oceanic system carrying warm surface waters from the subtrop- ical Atlantic to the North Atlantic (Manabe and Stouffer, 1999). From there, the heat is transported to continental Europe by westerly air flow, especially as migratory cyclones (Lamb and Johnson, 1959; Johannessen, 1970; Kozuchowski, 1993). Thus, the climate and the associated location of the tree line in northern Fennoscandia at roughly 70 ◦ N are critically dependent on the intensity and dynamics of the North Atlantic ocean–atmosphere circulation. Recently, much paleoclimatic interest has been directed to the short- and long-term dynamics of North Atlantic atmospheric circulation patterns (Hurrell, 1995). The most conspicuous demonstration of this dynamism is the North Atlantic Oscil- lation (NAO), an oscillatory atmospheric air pressure pattern, in which a large-scale air displacement takes place between the Azores subtropical high and the low pressure system of Iceland in the North Atlantic (Stephenson et al., 2000). During a high- index mode the air pressure difference between the systems is enhanced while the systems exhibit a synchronous shift north- ward (Paeth et al., 1999). Over the Holocene time scale, an even larger scale dynamism in the North Atlantic has been suggested, namely cyclic weakenings in the North Atlantic thermohaline circulation and an associated occurrence of short-term cold pe- riods (Bond et al., 1997). Here we present a high-resolution Holocene climate recon- struction from Toskaljavri, a tree-line lake situated in the conti- nental sector of northern Fennoscandia, but only ca. 70 km from the Norwegian Sea coast (Fig. 1). We use a recently developed pollen-climate reconstruction model and a new pollen stratigra- phy to derive quantitative estimates of annual precipitation and July mean temperature. We used a similar approach to derive July mean temperature and annual precipitation reconstructions from Tsuolbmajavri, another small lake located 60 km south- east of Toskaljavri, in the same climatic and vegetational area, but at a slightly lower altitude (Sepp¨ a and Birks, 2001). The aim of this paper is to evaluate the climatic interpretation based on the Tsuolbmajavri data in the light of our new Toskaljavri 191 0033-5894/02 $35.00 Copyright C  2002 by the University of Washington. All rights of reproduction in any form reserved.