Late Holocene environmental changes recorded in the deposits of paleolake of the Shkotovskoe Plateau, Sikhote-Alin Mountains, Russian Far East

Abstract

New data have been obtained on the landscape evolution within basalt plateau under conditions of climatic fluctuations in the Late Holocene. The reconstructions were based on the studies of the lacustrine-swamp sequence of the Larchenkovo swamp in the central part of the Shkotovskoe Plateau. The swamp appeared in place of a paleolake, the latter having passed through several stages in its evolution. Within the considered period the lake had the greatest area and depth about 4.48–3.9cal.ka BP, under conditions of warming and increased rainfall. At the final stage, there were alternating intervals of the lake deepening and shallowing, against the background of general waterlogging and paludification. In the upper part of the peat sequence there is a volcanic ash layer B-Tm attributed to the Baitoushan volcano eruption in AD 969. The studies permitted to identify stages in the environmental evolution and to determine the critical points in their development; to analyze the natural landscape-forming factors and the rate of the biotic component transformation; and to make certain inferences about the geosystem stability in the past. The contribution of global and regional paleoclimatic events has been estimated. The intervals of warming were typically marked by increasing proportion of broadleaf species in the forests, while coolings featured a higher share of Korean pine and dark coniferous, particularly spruce. The expansion of dark coniferous forests occurred under conditions close to recent ones at about 2.63cal.ka BP, while the coniferous-broadleaf forests retreated towards the plateau margins. Role broadleaf/Korean pine forests increased at the Medieval Climate Anomaly, while the Korean pine and spruce proportion grew at the Little Ice Age. The changes in the last 230–240years could be related both to the natural processes, such as windfalls, and to forest felling. Larch forest persisted around the lake over the entire considered period and most probably is a relict of the last ice age.