Structure of Carbon Pools in Surface and Subsurface Horizons of the Main Soil Types in the Russian Arctic

Arctic and subarctic soils store approximately half of the global soil organic carbon (SOC) pool, yet the structural stability and vulnerability of these carbon reservoirs remain poorly constrained. Most regional assessments treat the cryopedosphere as a homogeneous entity, overlooking the profound taxonomic diversity and vertical stratification that govern carbon stabilization mechanisms. This study investigates the structure of carbon and nitrogen pools across the main soil types of the Russian Arctic (Podzols, Cryosols, Gleysols, and Leptosols) using the soils of the Yamalo-Nenets Autonomous Okrug (YNAO) as an example to elucidate the pedogenic controls on organic matter persistence in permafrost-affected landscapes. Soil profiles were sampled across three geomorphological sites (Lower Ob Basin, Rai-Iz mountain massif, southern Yamal Peninsula). Physical fractionation isolated granulometric fractions with particulate organic carbon (POC), mineral-associated organic carbon (MAOC) and, mineral-associated organic nitrogen (MAON). Topsoil carbon pools exhibited strong taxonomic divergence. Podzols were POC-dominated (86% of SOC) with wide C/N ratios (38), reflecting podzolization and acidic illuviation; Leptosols exhibited the highest MAOC proportion (65%) with narrow C/N ratios (7), indicating rapid mineral stabilization; Cryosols accumulated the highest absolute SOC and total nitrogen (TN) contents but maintained a structurally constrained allocation regardless of total carbon concentration. Subsoil horizons demonstrated shifts toward mineralogical limitation, with near-perfect linear scaling between SOC and MAOC. Vertical decoupling was pronounced, with topsoil SOC poorly predicting subsoil content, and MAOC proportions did not exhibit a statistically significant linear correlation across depths. Carbon stabilization in the Arctic soils is governed by distinct elementary pedogenic processes (podzolization, cryoturbation, gleying, and initial soil formation) operating under divergent climatic constraints. The vertical decoupling of carbon pools and the taxonomic divergence in stabilization mechanisms underscore the need for soil-type-specific parameterization in regional carbon models.