Asynchronous glacial dynamics of LastGlacial Maximum mountain glaciers in the Ikh Bogd Massif,Gobi Altai mountain range, southwestern Mongolia: aspect control on glacier massbalance

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 Be-10 exposure age dating and 2D ice surface modeling. Be-10 surface exposure age dating revealed that the Ikh Artsan south-facing valley glacier culminated (M-IA1) at 20.1 +/- 0.7 ka, coinciding with the global Last Glacial Maximum (gLGM). In contrast, the north-facing Jargalant paleoglacier (M-J1) 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 +/- 1 sigma of the Be-10 exposure age results. Extremely old ages ranging from 636.2 to 35.9 ka were measured for the inner moraines in the Jargalant cirque (M-J2-M-J4), suggesting a problem with inheritance from boulders eroded from the summit plateau.