Climate and environment on the Karelian Isthmus, northwestern Russia, 13000-9000 cal. yrs BP

Sediment sequences retrieved from Lake Medvedevskoye (60degrees13'N 29degrees54'E) and Lake Pastorskoye (60degrees13'N, 30degrees02'E). Karelian Isthmus, northwestern Russia, were analysed for lithology, pollen and diatom stratigraphy, total organic carbon content and mineral magnetic parameters. Age control for both sequences was provided by AMS (14)C measurements and the Vedde Ash tephra. The reconstructed climatic and environmental development shows the deglaciation of the sites a-ad the establishment of sparse shrub and herb/grass vegetation before 12650 cal. yrs BP ('Allerod'; GI-1a). Steppe tundra and cold, dry conditions prevailed until about 11000 cal. yrs BP. i.e. throughout the 'Younger Dryas' (GS-1) and the earliest Holocene. The establishment of open Picea-Pinus-Betula forest around the lakes at about 11000 cal. yrs BP coincides with the first distinct change towards gradually warmer and more humid climatic conditions. Boreal forest with Picea, Pinus, Betula, Alnus incana and Corylus was present at the lower altitude site between c. 10700 and 10200 cal. yrs BP. while open Betula-Pinus forest continued to dominate the vegetation around the higher altitude site. After a short, possibly colder, phase around 10200-10000 cal. yrs BP, which is expressed by a marked reduction in vegetation Cover and decreased lake productivity. Climatic conditions became significantly warmer and possibly more humid. Boreal forest with Pinus, Betula, Picea, Alnus incana, Con-his and Ulmus became widespread in the region after 10000 cal. yrs BP, The delayed environmental response of the lakes and their catchment to hemispheric warming at the Pleistocene/Holocene boundary may be explained by a sustained blocking of westerly air masses due to the presence of the Scandinavian ice sheet and associated strengthened easterlies and anticyclonic circulation and/or extensive permafrost.