Abstract <p>The study is aimed at solving the fundamental problems of soil science and ecology related to the assessment of carbon budget in coastal soils and ecosystems of the Arctic and Subarctic, as well as their functioning in changing climate. The study estimated for the first time the stocks of “blue carbon” and the emission of carbon dioxide from soils of marsh ecosystems at the Pomor coast of the White Sea. Carbon stocks in the most seaward part of the coastal zone accumulate due to the input of allochthonous, thalassogenic organic matter: mean stocks at the lower marsh level are 25.5 ± 4.3 t/ha. At a distance from the boundary of daily flooding, the stocks of soil carbon are mostly formed by the biogenic accumulation of organic matter: the mean value at the upper marsh is 37.6 ± 23.6 t/ha. Soils of marsh ecosystems at the Pomor coast of the White Sea are characterized by low values of carbon dioxide emission (98 ± 16 mg CO₂/(m² h), July–August 2023), which attests to their low biological activity. Statistically significant differences in the average values of carbon dioxide emission are revealed at the ecosystem level: CO₂ emission from soils of marsh ecosystems is lower than that from soils of forest ecosystems of the bedrock coast. The average values of CO₂ emission from soils do not differ statistically significantly at middle and upper marsh levels. Minimum emission values are typical for soils at lower marsh levels and mudflats (Watten). Spatial variation and relationship of CO₂ emission from soils of marsh ecosystems with theenvironment factors are assessed. The results of the study, based on statistical analysis of a large database, contribute to a better understanding of the role of marsh ecosystems of the western sector of the Russian Arctic in the carbon budget.</p>