This research examined soil organic carbon (SOC), total nitrogen (TN) and aboveground phytomass carbon(PhC) stocks in two areas of the Taymyr Peninsula, northern Siberia.We combined field sampling, chemical and14C radiocarbon dating analyses with land cover classifications for landscape-level assessments. The estimatedmean for the 0–100-cm depth SOC stocks was 14.8 and 20.8 kgCm−2 in Ary-Mas and Logata, respectively. Thecorresponding values for TN were 1.0 and 1.3 kgNm−2. On average, about 2% only (range 0–12%) of the totalecosystem C is stored in PhC. In both study areas about 34% of the SOC at 0–100 cm is stored in cryoturbatedpockets, which have formed since at least the early Holocene. The larger carbon/nitrogen (C/N) ratio of thiscryoturbated material indicates that it consists of relatively undecomposed soil organic matter (SOM). Thereare substantial differences in SOC stocks and SOM properties within and between the two study areas, whichemphasizes the need to consider both geomorphology and soil texture in the assessment of landscape-level andregional SOC stocks.

Highlights

• This research addresses landscape-scale and regional variation in SOC stocks.

• Landform and soil texture are taken into account in the analysis.

• The contribution of phytomass to total ecosystem C stored is limited.

• Large SOC stocks are susceptible to decomposition following permafrost thaw.

This study describes and compares soil organic matter (SOM) quantity and characteristics in two areas of continuous permafrost, a mountainous region in NE Greenland (Zackenberg study site) and a lowland region in NE Siberia (Cherskiy and Shalaurovo study sites). Our assessments are based on stratified-random landscape-level inventories of soil profiles down to 1 m depth, with physico-chemical, elemental, and radiocarbon-dating analyses. The estimated mean soil organic carbon (SOC) storage in the upper meter of soils in the NE Greenland site is 8.3 ± 1.8 kg C m^-2 compared to 20.3 ± 2.2 kg C m^-2 and 30.0 ± 2.0 kg C m^-2 in the NE Siberian sites (95% confidence intervals). The lower SOC storage in the High Arctic site in NE Greenland can be largely explained by the fact that 59% of the study area is located at higher elevation with mostly barren ground and thus very low SOC contents. In addition, SOC-rich fens and bogs occupy a much smaller proportion of the landscape in NE Greenland (∼3%) than in NE Siberia (∼20%). The contribution of deeper buried C-enriched material in the mineral soil horizons to the total SOC storage is lower in the NE Greenland site (∼13%) compared to the NE Siberian sites (∼24%–30%). Buried SOM seems generally more decomposed in NE Greenland than in NE Siberia, which we relate to different burial mechanisms prevailing in these regions.

This study aims to improve the previous soil organic carbon (SOC) storage estimates for the Zackenberg area (NE Greenland) that were based on a land cover classification (LCC) approach, by using geomorphological upscaling. In addition, novel SOC estimates for deeper deposits (to 300 cm depth) are presented. We hypothesize that landforms will better represent the long-term slope and depositional processes that result in deep SOC burial in this type of mountain permafrost environments. The updated mean SOC storage for the 0–100 cm soil depth is 4.8 kg C m⁻², which is 42% lower than the previous estimate of 8.3 kg C m⁻² based on land cover upscaling. We ascribe the difference to a previous areal overestimate of SOC-rich vegetated land cover classes. The landform-based approach more correctly constrains the depositional areas in alluvial fans and deltas with high SOC storage. These are also areas of deep carbon storage with an additional 2.4 kg C m⁻² in the 100–300 cm depth interval. This research emphasizes the need to consider geomorphology when assessing SOC pools in mountain permafrost landscapes.

This meta-analysis aims to describe the relationship between grain size distributions and soil organic carbon (SOC) storage in mineral subsoil and carbon (C)-enriched cryoturbated pockets in five areas of continuous permafrost that differ in glaciation history and soil parent materials. Our results show a positive relationship between fine-grained (colloid to medium silt) fractions and SOC storage. Finer textured soils had a significantly higher SOC storage in mineral subsoil samples (not C-enriched through cryoturbation) than coarser textured soils. However, the process of C-enrichment through cryoturbation was most pronounced in soils with coarser grain sizes in the range of coarse silt and very fine sand. Even though fine-grained textures provide a better physical and biochemical protection for soil organic matter, their strong cohesion reduces the mixing of soil horizons and the effectiveness of cryoturbation. A higher % coarse silt to % clay ratio in samples was a good predictor of C-enrichment through cryoturbation across soil samples, soil profiles and study areas.