Lacustrine Records of Hydroclimatic Changes on North-Western Japan Sea Coast in Context of ‘Ocean-Land’ Interaction in Middle Late Holocene

This study reconstructs a 6320-yr environmental history of the Amur Bay coast (Japan Sea) via a multi-proxy analysis of two lacustrine sequences from the Peschany Peninsula, Russia The aim of the study was to reconstruct hydroclimatic changes and examine their links to summer monsoon intensity and cyclone activity. A chronological framework is established on an age-depth model based on radiocarbon dating, combined with tephrochronology of the caldera-forming eruption of the Changbaishan (Baitoushan) volcano in 946/947 CE, which is situated on the border between China and the Democratic Republic of Korea. Diatom and pollen analyses reveal climate fluctuations during the Middle-Late Holocene and vegetation responses to changes in temperature and humidity. Shallow, oligotrophic-dystrophic lake formed on an accumulative landform with two-way feeding during minor regression 6320 yr BP. Overgrowing of the Middle Holocene paleolake began at the end of the Holocene thermal optimum ( ~ 5410 yr ago). Active development of marsh processes near the lake took place 4250–3750 yr BP. A desalinated shallow lagoon formed on the isthmus ~ 3860 yr BP when the tombolo connected the paleo-island with the mainland. The formation of the moderately swampy paleolake in place of a lagoon occurred 2860 yr BP. Several periods of watering due to increased precipitation are distinguished in the development of the Middle Holocene and Late Holocene paleolakes. Redeposited freshwater diatoms from subbasalt deposits are bioindicators of intensive planar washout during heavy rains associated with typhoons. Especially high planar washout and typhoon activation occur at 4020–3750 yr BP. Single marine and brackish diatoms among freshwater assemblages indicate the passage of extreme storms. Dry periods are usually associated with a cooling and a decrease in intensity of the summer monsoon. Humidity decreased noticeably at 3300–3100 yr BP, which coincided with a decrease in the intensity of the summer monsoon. A combination of diatoms from different ecologies shows long-term dry seasons during cooling since 2800 yr BP. At the Medieval Warm Period, the climate became wetter. During the Little Ice Age, flooding of the swamp with a relict lake on the isthmus increased sharply. Pollen zones indicate alternating dynamics of Korean pine/broadleaf forests with fir and birch. Since the Holocene Optimum, ecotopes with contrasting heat and moisture supply developed, and human impacts on vegetation were recorded. Several short-term Middle-Late Holocene climatic events are identified. The abundance of thermophiles increased at 5820–5510, 4610–4310, 4800–3600, and 4020–3750 yr BP, corresponding to warming. A significant increased role of coniferous trees in the forests occurred in the Little Ice Age. Cold and warm events with different humidity are compared with regional data and global events, demonstrating links with ocean anomalies and the intensity of the summer monsoon. The drier conditions may be associated with an increase in the intensity of El Niño.