Records of climatic changes in the palaeolake sediments on Boisman Bay coast, South Primorye

Evolution of two coastal paleo-lakes and short-term climatic changes were reconstructed on the basis of multy-proxy study (diatom, botanical analyses, and ash content). The age-depth models were made using 10 radiocarbon dates and tephrostratigraphy. The sediments contain tephra from the Baitoushan volcano: the caldera-forming eruption of 946/947 and 1903 CE. Based on Bayesian modeling, sedimentation rates and changes in biotic components in time and their diversity are estimated. The formation of the “southern” paleolake on the place of freshened lagoon occurred ~4060 BP. At the initial stage, the diversity of the diatoms in the lake was maximal, although the conditions for diatom development cannot was favorable – the concentration of frustules sharply decreased. The swamping began to develop ~3370 yr BP, that was close to the beginning of the period of prolonged droughts in the region associated with a decrease in the intensity of the summer monsoon. High-resolution records show that the area manifested two “dry” cold events comparable to global (2800–2600, 1700–1300 yr BP) and the Little Ice Age with high humidity. The second half of Medieval Warm Period (945–830 yr BP) was the warmest, and the moisture content decreased. The processes in the Pacific Ocean played a major role in regional hydroclimatic changes, and the links between these climatic changes and the intensity of the summer monsoon, as well as the dynamics of sea surface temperature, El Niño, the activity of the Kuroshio Current, and other factors determining the movement of air masses are considered. The phases of vegetation development of heavily watered bogs formed on the place of coastal lakes. Correlation of the paleoclimatic changes with regional records (northeastern China, South Korea, and Japan) was carried out. The studied sections recorded the passage of extreme hydrological events, including the tsunami of 1026 CE.

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