Organic Carbon Pools and Genesis of Alpine Soils with Permafrost: A Review

Abstract

Soils with mountain permafrost occupy 3.5 million km2 worldwide, with 70% in central Asia. High-mountain environments have “warm” permafrost, with surface permafrost temperatures of -0.5 to -2 °C and deep active layers (2 to 8 m). From a global database of 41 sites and 312 pedons, alpine soils with permafrost are strongly acid (pH = 5.0 to 5.5), have intermediate cation-exchange capacities (20 to 25 cmolc/kg) and base saturation (44% to 85%), and commonly have an isotic mineral class. Soil organic carbon is concentrated in the upper 30 to 40 cm, with profile density averaging 15.2 ± 1.3 kg m-2 (range = <1.0 to 88.3 kg m-2), which is comparable to temperate grasslands (13 kg m-2) but substantially less than moist arctic tundra (32 kg m-2). Mountain soils with permafrost contain 66.3 Pg of soil organic carbon (SOC), which constitutes 4.5% of the global pool. In contrast, the SOC pool in the Arctic is 496 Pg (33% of the global pool). Alpine soils with deep active layers contrast strongly with high-latitude soils in areas of continuous permafrost. Permafrost in the upper 2 m induces cryoturbation in the profile, acts as a barrier to water movement, and generates cooler temperatures resulting in greater SOC levels. High-elevation and high-latitude soils are experiencing warming of air temperature and permafrost and a thickening of the active layer.