Hydroclimatic changes in southeastern Mongolia from the earlier Late Pleistocene to the mid-Holocene: a multi-proxy record from a glacier-decoupled closed-basin sedimentary sequence in Bayan Tohom Gobi

This study reconstructs hydroclimatic changes from the earlier Late Pleistocene to the mid-Holocene using the 3.88 m BT-1 trench profile in Bayan Tohom Gobi, southeastern Mongolia (45°06′50.6″ N, 112°31′47.1″ E; ∼970 m a.s.l.). Accelerator mass spectrometry radiocarbon and optically stimulated luminescence dating provide discrete chronological constraints for grain-size and geochemical records interpreted using end-member modelling and principal component analysis. Organic-rich fine basin fill deposited during the earlier Late Pleistocene is separated by a sharp contact, potentially representing erosion or non-deposition, from coarse sedimentation within a broadly constrained later-glacial interval encompassing the Last Glacial Maximum. This coarse deposition involved aeolian input, basin-floor reworking, and episodic runoff, followed by finer sedimentation during the deglacial interval. Shallow-water to playa deposition, with its onset broadly bracketed around the Younger Dryas–Early Holocene transition, was accompanied by HCl-soluble enrichment consistent with carbonate accumulation, before renewed fine-grained shallow-water or wetland deposition during the Early to mid-Holocene. The glacier-decoupled BT-1 archive records changes in effective moisture and sediment mobility governed by precipitation, local runoff, potential groundwater input, and temperature-dependent evaporation. Comparison with Lake Ulaan and Orog Nuur highlights the influence of catchment water and sediment sources on the expression of regional hydroclimatic change in Mongolian closed basins.