RECORDS OF ENVIRONMENTAL CHANGES IN LACUSTRINE-SWAMP SEQUENCES WITHIN MOUNTAIN AREA OF THE ITURUP ISLAND SINCE THE LATE GLACIAL

Abstract

We received a unique material on the natural environment development for the last 12 400 cal. yr. BP in the central part of Iturup Island. The high-resolution paleoreconstructions were based on multi-proxy study of the paleolake sediments found on the plateau (height 400–420 m) located northwest of the Baransky Volcano. For the first time, a record of paleogeographic events was obtained for the Late Glacial and the early Holocene. The age model is based on 9 radiocarbon dates. Diatom analysis allowed us to distinguish 11 stages of lake-swamp evolution. The paleolake reached its maximum depth at ~9 890–7 900 cal. yr. BP and became extinct at 1 400 cal. yr. BP. The stages of vegetation development and the factors determining the change of landscapes have been restored. The Younger Dryas cooling recorded in Iturup was characterized by humidity changes. The role of forest vegetation abruptly increased at the Pleistocene-Holocene boundary of ~11 470 cal. yr. BP) under warmer climatic conditions. Distribution of shrub pine as an indicator of stable snow cover was analyzed. Dark-coniferous forests existed in the mountainous part of the island since the Late Glacial and were most widely developed in the early Holocene. The onset of birch forest expansion at 6 200 cal. yr. BP was associated with the intensification of volcanic activity and frequent ash falls. A number of cold events were identified, whose manifestations were enhanced by the weakening of the Soya warm current. The intensive transfer of allochthonous pollen from the southern Kuril Islands and the Japanese Islands at 3 540 cal. yr. BP is a sign of cyclogenesis intensification in the Kuril Islands. Manifestations of the Holocene climatic rhythms in the landscape development of the Iturup mountainous part, as well as the influence of warm and cold currents and other regional factors, were analyzed.