Atmospheric Anomaly Bioindicators in Peat Sections on the Eastern Macroslope of the Sikhote-Alin Range in the Late Holocene

The studies of peat stratigraphy in the upper reaches of the Milogradovka River made it possible to reconstruct changes in humidity as a source of moisture in the Sikhote-Alin middle mountains over the last 3400 years. High-resolution reconstructions were based on the biostratigraphic analyses (botanic and diatom) data; the ash content of peat was also studied. Radiocarbon dating of the events was carried out using an age–depth model. B–Tm cryptotephra of the Baitoushan caldera-forming volcano was found in the upper part of the section; it was identified from the volcanic glass chemical composition. Long-term rains are assumed to have caused a massive landslide with the formation of a dam and a shallow reservoir turned the river valley into a bog. The bioindicators of humidity variations in the river valley and of flood events were determined. The events were correlated with the data on the main watershed of the Sikhote-Alin Range, mountainous plateaus, lakes on the slopes of the ancient Solontsovsky Volcano, and the eastern Primorye coast. The peat section in the valley recorded the hydrological changes related to the nature of cyclogenesis in more detail. Paleoevents and large-scale atmospheric circulation anomalies were revealed to be interrelated. Long-term dry phases under global cooling were accompanied by the East Asia aridization caused by a slacking of the East Asian summer monsoon. According to the study results, floods occurred in the summer–autumn period even during dry phases. The flooding phases were related to the summer monsoon activation, as well as to more intensive cyclogenesis. The most complicated climate rhythmicity was established for the last 1340 years.