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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Permafrost in Mongolia shows highly heterogeneous features in space and the contents of ground ice are dependent on the local geographies such as topography, ground wetness, and vegetation cover. Recent permafrost degradation would cause thawing and disappearance of ground ice, destabilizing and subsiding the ground surface. This study aimed to detect topographic deformation related to irreversibly changing ground ice over the permafrost terrain of Mongolia. To end this we used interferometric synthetic aperture RADAR (InSAR) technique, which is capable to measure vertical ground deformation on a centimeter scale. Advanced land observing satellite-based phased array type L-band synthetic aperture radar (PALSAR) images (June to September 2007 to 2010) and PALSAR-2 images (June to September 2014 to 2017) quantified near-year-round displacement of the ground surface. The overall deformation was in a range of À3 to 3 cm (subsidence and uplift, respectively) between the image interval and relatively high subsidence occurred during warm years. The areas experiencing consecutive uplift and subsidence correspond to ground underlain by ice-rich soils, indicating the dominant roles of thawing and growing ground ice for local deformation over permafrost terrain. We discuss the relation of observed ground deformation trends with regional climate and local geohydrology that influence ground ice formation.

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