[M-IS14] Paleoclimatology and paleoceanography

[MIS14-07] Reconstruction of spatio-temporal vegetation change in East Asian mid-latitudes since the last glacial

*Kohei Miyamoto¹, Koji Shichi², Hitoshi Hasegawa¹, N. Ichinnorov⁴, D. Davaasuren ⁵, Ryosuke Imaoka¹, Nagayoshi Katsuta³, Masafumi MURAYAMA¹, Masao IWAI¹, Masami Izuho⁶, Kazutaka Yasukawa⁷ (1.kochi university, 2.Forest Research and Management Organization, 3.Gifu University, 4.Mongolian Academy of Sciences, 5.National University of Mongolia, 6.Tokyo Metropolitan University, 7.University of Tokyo)

Keywords:Pollen, Vegetation, Permafrost, Westerlies, East Asian Summer Monsoon, Holocene

The mid-latitude region of East Asia is located between the Siberian permafrost in the north, the arid deserts of the Gobi and Taklamakan Deserts in the south, and the East Asian summer monsoon front in the east. In this study, we focused on the lake sediments of Sangiin Dalai Lake in northwestern Mongolia. This lake is located at the boundary between the southern limit of Siberian permafrost and the Gobi Desert. First, we reconstructed the vegetation changes in this region since the last glacial by analyzing pollen assemblages. We also compared the results with pollen records from the surrounding area (Walter et al., 2014),and westerly-wind-driven rainfall variability (Wirth et al., 2013) to reconstruct spatio-temporal changes in the vegetation since the last glacial period (past 20,000 years) in mid-latitude East Asia, to consider factors contributing to such change.
The sample used in this study was a 19SD composite core (about 12.2 m long) drilled in Sangiin Dalai Lake. The results of ¹⁴C dating of soil TOC indicates that the deepest part of the core is about 45 ka, and the core depth of 3.3 m part is about 10 ka. Pollen analysis was conducted on 144 samples divided by 1cm. As a result of pollen analysis, grass-dominated dry environment was prevailed during the last glacial period. On the other hand, in the early Holocene, pioneer tree species of Betula and dried herb Ephedra tended to increase. In the middle Holocene, conifers such as Picea and Pinus increased, suggesting the expansion of a warm and humid forest-steppe environment. In the late Holocene, semiarid herb plants increased again, suggesting a change to a semi-arid steppe environment similar to the present-day. The timing of the wetting of Sangiin Dalai Lake coincides with temperature fluctuations in inland Asia reconstructed from multiple lake sediment records (Lan et al., 2021).
Next, we compared the results with pollen records from the surrounding areas (northern China, southern Russia, and eastern Kazakhstan; Wang & Feng et al., 2013; Zhang & Feng et al., 2018; Shichi et al., 2013, 2023), and identified six areas that show similar vegetation change patterns. In areas where permafrost is distributed, vegetation change began at lower elevations, and the timing of permafrost thawing and freezing in response to solar insolation changes was interpreted as an important factor for this vegetation changes. On the other hands, in areas where permafrost is not distributed, changes in rainfall pattern induced by westerly winds and the East Asian summer monsoon may have affected the vegetation changes. Our findings suggest that permafrost dynamics and changes in rainfall pattern have caused different environmental changes and vegetation transitions in the East Asian mid-latitudes since the last glacial period.