Mongolian glaciers have been the subject of relatively little research, resulting in less geochronological constraint than other parts of Central Asia. The Khentey Mountains (latitude 47–51°N, longitude 105–112°E) are a typical landlocked mountain range exhibiting clear geomorphic evidence of late Quaternary glaciation. Yet, compared to western parts of Mongolia such as the Mongolian Altay, Gobi Altay, Khangay, and Khovsgol, glacial history of the Khentey Mountains is poorly understood. To address this, and permit comparison of the Khentey glacier–climate record with other alpine regions in Mongolia, we performed geomorphological mapping and cosmogenic 10Be surface‐exposure dating in two glaciated regions of the Khentey Mountains: Yestii and Khagiin Khar. Specifically, we measured 10Be in 34 samples collected from five moraine sequences, which, together with morphostratigraphy, correspond to four main glacial stages: (i) The My1 terminal moraine sequence for Yestii (21.0±4.9 ka) and the Mk1 moraine for Khagiin Khar (19.6±2.6 ka), both of which represent the Last Glacial Maximum; (ii) the Lateglacial Mk2 moraine, dated to 16.0±3.5 ka; (iii) the Mk3 moraine, dated to either 17.6±7.0 ka (Lateglacial) or 12.1±1.1 ka (Younger Dryas); and (iv) the currently undated Mk4 moraine (~2200 m a.s.l.), to which we assign a Holocene age. Our results suggest that the timing of maximum glacier extent in Mongolia was regionally variable. In the Khentey Mountains, maximum glaciation occurred during Marine Isotope Stage (MIS) 2, whereas the maximum occurred during MIS 3 in Khangay and Khovsgol and during MIS 4 in the Altay. The MIS 2 glacial maximum in the Khentey Mountains coincided with the global sea level minimum during the Last Glacial Maximum, and was followed by at least three glacial re‐advances during the Lateglacial to possibly the Holocene.
Abstract. Most mid-latitude mountain glaciers reached their maximum extent around the global Last Glacial Maximum (gLGM). However, some also strongly responded to the regional climate change or local non-climatic factors such as topography, leading to asynchronous maximum advances. This study documents the maximum extent and chronology of two paleoglaciers in the Ih Bogd massif of Mongolia: one facing north into the Jargalant Valley and the other facing south into the Ih Artsan valley. 10Be surface exposure age dating revealed that the Ih Artsan short valley glacier reached its maximum position (MIh1) around 20.1 ± 0.7 ka, coinciding with the gLGM. In contrast, the Jargalant paleoglacier (MJ1) reached its maximum extent around 17.2 ± 1.5 ka, around Heinrich 1 stadial and during the post-gLGM northern hemisphere warming. Our 2D ice surface model, which includes the temperature-index melt model, suggests that an aspect can result in a melt difference between north and south-facing slopes. Glaciers retreated from their maximum modeled extent asynchronously when we assign a 0.5 ℃ lower temperature for Jargalant valley (northern slope), based on the observation that present-day mean annual Jargalant temperatures are lower than in the south-facing Ih Arstan. Modelled timing of the maximum extents (20.23 ka in Ih Artsan, 17.13 ka in Jargalant) are consistent with 10Be exposure age results (20.1 ka in Ih Artsan, 17.2 ka in Jargalant). We also observed several sequences of post LGM or/and Holocene moraines in both cirques. Extremely old ages ranging from 636.2 ka to 35.9 ka were measured for the inner moraines in the Jargalant cirque (MJ2–MJ4), suggesting a problem with inheritance from boulders eroded from the summit plateau.
Abstract. Mountain glacier mass balance is affected by factors other than climate, such as topography, slope, and aspect. In midlatitude high-mountain regions, the north–south aspect contrast can cause significant changes in insolation and melt, resulting in local asynchrony in glacial dynamics. This study documents the asynchronous response of two paleoglaciers in southwestern Mongolia to the local topoclimatic factors using 10Be exposure age dating and 2D ice surface modeling. 10Be surface exposure age dating revealed that the Ikh Artsan south-facing valley glacier culminated (MIA1) at 20.1 ± 0.7 ka, coinciding with the global Last Glacial Maximum (gLGM). In contrast, the north-facing Jargalant paleoglacier (MJ1) culminated at 17.2 ± 1.5 ka, around Heinrich Stadial 1 and during the post-gLGM Northern Hemisphere warming. Our temperature-index melt model predicts that ablation will be substantially lower on the north-facing slope, as it is exposed to less solar radiation and cooler temperatures than the south-facing slope. The 2D ice surface modeling also revealed that the south-facing Ikh Artsan Glacier abruptly retreated from its maximum extent at 20 ka, but the Jargalant Glacier on the shaded slope consistently advanced and thickened due to reduced melt until 17 ka. The timing of the modeled glacier culmination is consistent within ± 1σ of the 10Be exposure age results. Extremely old ages ranging from 636.2 to 35.9 ka were measured for the inner moraines in the Jargalant cirque (MJ2–MJ4), suggesting a problem with inheritance from boulders eroded from the summit plateau.
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