In April 1999 a 11.9-m long core from the 26-m water depth has beentaken in Lake Lyadhej-To (68°15'N, 65°45'E, 150 m a.s.l.) situated atthe NW rim of the Polar Urals. The lake has an area of 4 km2 and amaximum depth of 26 m. Lacustrine sediments are represented by thestratified to laminated clayey gyttja (6.9-1.5 m) and stratified siltygyttja (1.5-0 m). The 17 14C-AMS dates on picked plant remains and 3dates on dispersed organic carbon in bulk till samples provide the basisto develop the age-depth model for the core. The age-depth modelsuggests that lacustrine sedimentation started at about 10,950 cal yrBP. Here we present pollen-based reconstruction of the vegetation andclimate history of the area since that time.Pollen assemblages at ca 10,950-10,700 cal yr BP are dominated by Pre-Quaternary spores and redeposited Pinaceae pollen, pointing to a highterrestrial input. The rare Cyperaceae pollen and Equisetum sporessuggest sparse, treeless vegetation and severe climate conditions in thecatchment area. Between ca 10,700-8500 cal yr pollen spectra aredominated by Betula pollen. The pollen concentration is highest throughthe whole record. This may reflects a northward shift of the treeline andthe warmest conditions during the Holocene. Decrease in Betula pollencontent and increase in herbaceous pollen content registered in thepollen assemblages suggest cooling after ca 8500 cal yr BP. The coolingcontinues after ca 7500 cal yr BP, marked by the ongoing decrease oftree birch pollen and the simultaneous increase of dwarf birch pollen.A low pollen concentration in the upper part of the record together withthe low concentration of arboreal pollen and pollen of Alnus fruticosasuggests a southward migration of the tree line and tundra vegetationand comparatively cold climate around the lake during the last 6000years.Best modern analogue method (Guiot, 1990) has been applied to thepollen spectra from the upper 6.5 m of the core in order to getquantitative reconstruction of the Holocene climate. The lower part ofthe record with high content of re-deposited ancient pollen and sporeswas rejected. In the present study the reference modern pollen dataset is that compiled by Tarasov et al. (1999a; 1999b; 2002) fromnorthern Eurasia. It includes 1110 surface spectra for which taxapercentages were calculated based on the sum of 77 terrestrial pollentaxa. The same taxa were selected in the fossil records. For eachanalyzed fossil spectrum 10 modern spectra which have the smallestchord distance were considered as the best modern analogues followingGuiot (1990). Reconstructed mean July temperature (TVII) and annualsum of day temperatures above 5°C (GDD5) show similar changes,suggesting warmer than present summers 10,500-7500 cal yr BP. Firstsignificant cooling occurred ca 7000 cal yr BP, second ca 5500-3500 calyr BP, third after 1000 cal yr BP. During the early Holocene climaticoptimum TVII was likely 12-13°C, GDD5 - 400-600°C day, annualprecipitation - 400-500 mm. During the cold phases TVII most probablywas between 7 and 10°C, GDD5 between 100-300°C day and annualprecipitation - between 100 and 300 mm.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL6-Earth climate variability since the Pliocene