Spätpleistozäne und frühholozäne Vegetationsentwicklung im Verkhoyansker Gebirge (Zentral Yakutien) - Eine Rekonstruktion anhand von Pollendaten

Despite increased paleoenvironmental studies in Northern Yakutia (ANDREEV et al. 2002 and references therein), little is known of past climatic and environmental fluctuations during the Middle and Late Weichselian (Karginsky interstadial and Sartan stage). New pollen and radiocarbon data from the Verkhoyansk Mountains document the Late Pleistocene and early Holocene environmental history of the area.The climate of the region is extreme continental and arid. In Yakutsk the absolute minimum temperature reaches -64°C, absolute maximum +38°C, and annual precipitation is 180-250 mm. But more than 350-400 mm vapors from June to September (GAVRILOVA 1973). Today larch (Larix dahurica) forest (taiga) with herbs dominate the vegetation. Few other trees (Betula pendula, Pinus sylvestris, Picea obovata) and shrubs (Alnus fruticosa, Pinus pumila, Betula nana) also grow in the area. The samples came from a site at the Tumara River valley (63N, 130W).The pollen spectra show that open tundra-like Poaceae and Cyperaceae associations with some other herbs (Caryophyllaceae, Ranunculaceae, and Asteraceae) dominated the area about 50-40 14C ka ago. Steppe-like communities with Artemisia, Cichoriaceae, Thalictrum, and rare shrubby tundra communities with Salix and Betula sect. Nanae were also present in the vegetation cover. An increase of Chenopodiaceae pollen and Equisetum spore contents, which are mainly pioneer species on disturbed soils, and the presence of charcoal particles in the sediments dated ca 48-50 14C ka most likely reflect fire activity at that time.Higher content of Salix pollen, Polypodiaceae and Lycopodium spores during ca 48-30 14C ka may reflect climate conditions warmer and wetter than during the previous interval. A find of Linum perenne pollen grains indicate the existence of dry steppe habitats in the area as well. The presence of this species reflects that temperatures were at least 12.5°C during the growing season. This relatively warm interval corresponds well with the Karginsky Interstadial (Stage 3) recorded in Siberia.Spores of Selaginella rupestris, an indicator of very dry environment, are common in the spectra at around 23 14C ka. A decrease of pollen and spores concentration reflects further deterioration of environmental conditions. A decrease of Salix pollen content and the presence of Artemisia, Cichoriaceae, Thalictrum pollen and an increase of the charcoal particle content also point to rather dry climate conditions. This relatively cold and dry interval corresponds well with the Sartan stadial (Stage 2) recorded in Northern Eurasia. During the Last Glacial Maximum (14C dated at about 19 ka BP) pollen concentration significantly decreased. Many pollen taxa completely disappeared from the spectra pointing to an extremely severe environment.Higher tree pollen contents (mostly Salix and Betula sect. Albae) at the Late Glacial/early Holocene transition (10-9 14C ka) reflect rather favorable climate conditions for the development of taiga vegetation during that interval. This data are in good agreement with other early Holocene pollen records from Northern Yakutia (e.g. PISARIC 2001, ANDREEV 2002)