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Permafrost underlying forested north-facing slopes and seasonally frozen ground underlying mountain steppes on south-facing slopes co-exist within a small mountain basin that represents the most general landscape type in northern central Mongolia. A 5-year time series of hydro-meteorological parameters on these slopes is presented in order to identify the factors controlling ground temperature regimes. A thick organic layer (0.2-0.4 m) beneath the forest on a north-facing slope impedes the effects of summer air temperature on the ground, and the forest canopy strongly blocks downward shortwave radiation during summer. Active layer thickness was determined by summer warmth. The mountain steppe on a dry south-facing slope receives a large amount of downward shortwave radiation compared to an adjacent forested slope, and therefore the surface temperature exceeds air temperature during summer, leading to a warm soil profile. In winter, snow cover was the main factor controlling interannual variations in the thickness of seasonally frozen ground. The onset of soil thawing in the forested area was later than in the mountain steppe, even though soil freezing began simultaneously in both areas. Overall, the forest cover keeps the ground cool and allows permafrost to persist in this region.

Ground thermal conditions in marginal permafrost in Mongolia were assessed using ground temperatures measured year‐round at 69 borehole sites. Permafrost is continuous in northern Mongolia and exists as sporadic/isolated patches in the south. Ground temperatures are strongly controlled by local environmental factors, such as topographic depressions that concentrate cold air during winter, ice‐rich strata that prevent penetration of sensible heat, and tree cover that reduces incident solar radiation. Permafrost temperatures are typically between −1 and 0°C; colder permafrost (< −2°C) occurs in the northern extent of continuous permafrost and at high elevations in the sporadic/isolated permafrost zones. Relict permafrost, which is thermally disconnected from seasonal air temperature fluctuations, is present near the latitudinal and elevational limits of perennially frozen ground. Cold and thermally responsive permafrost is dominant in the continuous and discontinuous zones, while warm and thermally unresponsive permafrost is dominant in the sporadic and isolated zones. Overall, the climate‐driven permafrost in the colder regions is stable, while the ecosystem‐driven permafrost in the warmer regions is degrading.

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The Turgen Mountains lie in northwestern Mongolia, roughly 80 km south of the Russian border. The area was visited in 1910 by a Royal Geographical Society expedition led by Douglas Carruthers. The party undertook an extensive survey of the range and also documented the extent of the glaciers with photographs. One hundred years later, in summer 2010, a US-Mongolian expedition retraced portions of the 1910 expedition. Camera locations were matched to the historical photographs and repeated photographs taken. In addition, the termini of the two main glacial lobes were surveyed by GPS. Analyses of field data, repeated photographs from 1910 and 2010, topographic maps from 1970, and satellite imagery from 1992 and 2010 were used to describe the changes in the glacial system. The results suggest that while the snow and ice volume on the summits appears to be intact, lower elevation glaciers show significant recession and ablation. From 1910 to 2010, West Turgen Glacier receded by c. 600 m and down-wasted by c. 70 m. This study successively demonstrates the utility of using historic expedition documents to extend the modern record of glacial change.

Understanding paleo—and recent environmental changes and the dynamics of individual drivers of water availability is essential for water resources management in the Mongolian Altai. Here, we follow a holistic approach to uncover changes in glaciers, permafrost, lake levels and climate at the Tsengel Khairkhan massif. Our general approach to describe glacier and lake level changes is to combine traditional geomorphological field mapping with bathymetric measurements, satellite imagery interpretation, and GIS analyses. We also analysed climate data from two nearby stations, and measured permafrost temperature conditions at five boreholes located at different elevations. We identified four glacial moraine systems (M4-M1) and attribute them to the period from the penultimate glaciation (MIS 4/5) until the Little Ice Age (MIS 1). During the Local Last Glacial Maximum (LLGM; MIS 2), a glacier reached down into the western Kharganat Valley and blocked it, resulting in the formation of the endorheic Khar Lake basin. Subsequently, the lake was fed mainly by precipitation and permafrost meltwater. In recent years, glaciers have been in strong recession, yet Khar Lake levels have remained relatively stable, which is in contrast to mainly decreasing lake levels in other regions throughout Mongolia. While temperatures in the Altai are increasing (leading to increasing evaporation), precipitation in higher elevations has increased, which—in addition to increased glacier and permafrost melting—would counteract the increasing aridity effects. A systematic and holistic monitoring of glaciers, permafrost, lake levels and climate in the Mongolian Altai is necessary, and results from (sub-)disciplines need to be correlated

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