[M-IS03] Evolution and variability of the Asian Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS03-05] The environmental dynamics of saline lakes in Mongolia based on characteristics of sediment obtained by sediment trapping and coring

*Shuukhaaz Ganbat¹, Noriko Hasebe², Davaadorj Davaasuren³, Keisuke Fukushi², Shinya Ochiai², Baasansuren Gankhurel^2,4, Uyangaa Udaanjargal⁴, Takuma Kitajima¹, Shibuya Yuma (1.Graduate School of Natural Science and Technology, Division of Natural System, Kanazawa University, 2.Institute of Nature and Environmental Technology, Kanazawa University, 3.School of Arts and Sciences, National University of Mongolia, 4.Graduate School, National University of Mongolia)

Keywords:Endorheic lake, lake sediment, Sediment characteristic, 210-lead dating, Authigenic mineral

Endorheic lake basins are a great record of changes in regional hydrology and environmental conditions. Especially their lake sediment plays an important role as a valuable archive, recording temporal environmental changes over time. In this study, we investigated sedimentation dynamics for the saline lakes in the arid region of Mongolia. We retrieved a sediment core sample (18TS1, 137 cm in length) from Tsagaan Lake in 2018 and sediment traps were deployed in Boontsagaan Lake and inflowing Baidrag River in the summer of 2022 and 2023. Sediment characteristics, including organic matter (OM), carbonate (CaCO₃), amorphous silica (A-Si), grain size, and mineral assemblages, were measured for both the sediment core and sediment trap samples. 210-lead dating method was applied for the sediment core sample and different age estimation models (CRS – Constant Rate of Supply, CIC – Constant Initial Concentration, and CFCS – Constant Flux and Constant Supply) were tested. In summary, various age models resulted relatively different age ranges for the 18TS1 core. The CRS model, however, provides a more reliable age estimation for Tsagaan Lake’s sedimentation dynamics considering the applied model assumption. The MAR (Mass Accumulation Rate) in Tsagaan lake estimated using age models was relatively lower than that calculated using sediment trapping in Boontsagaan Lake. The comparison between climate factors and sediment characteristics indicates an increasing trend of CaCO₃, OM, and A-Si in the sediment sequence, which might indicate a dry climate-inducing period. Various carbonate minerals were also detected in these carbonate-rich sequences within the sediment core. Analyses of sediment trap samples show the presence of monohydrocalcite in the lake, but no monohydrocalcite in the river’s sample. In those saline lakes, carbonate mineral forms, and those carbonate-rich layers may indicate accelerated authigenic mineral formation during favored conditions such as more alkaline water under drought-inducing periods.