Soil organic carbon distribution for 0–3 m soils at 1 km² scale of the frozen ground in the Third Pole Regions

Abstract. Soil organic carbon (SOC) is very important in the vulnerable ecological environment of the Third Pole; however, data regarding the spatial distribution of SOC are still scarce and uncertain. Based on multiple environmental variables and soil profile data from 458 pits (depth of 0–1 m) and 114 cores (depth of 0–3 m), this study uses a machine-learning approach to evaluate the SOC storage and spatial distribution at a depth interval of 0–3 m in the frozen ground area of the Third Pole region. Our results showed that SOC stocks (SOCS) exhibited a decreasing spatial pattern from the southeast towards the northwest. The estimated SOC storage in the upper 3 m of the soil profile was 46.18 Pg for an area of 3.27 × 10⁶ km², which included 21.69 Pg and 24.49 Pg for areas of permafrost and seasonally frozen ground, respectively. The mean SOCS under different vegetation types showed a decreasing pattern as follows: forest > shrub > cropland > grassland > desert. Among all soil orders, histosols and gleisoil had the largest SOCSs, while gypsisols and salt flats had the smallest SOCS. Our results provide information on the storage and patterns of SOCS at a 1 km² scale for areas of frozen ground in the Third Pole region, thus providing a scientific basis for future studies pertaining to Earth system models. The dataset is open-access and available at https://doi.org/10.5281/zenodo.4293454 (Wang et al., 2020).