Abstract <p>The study is aimed at solving the fundamental problems of soil science and ecology related to assessing the carbon budget in coastal soils and ecosystems of the Russian Arctic, as well as their functioning in a changing climate. In the course of the study, the carbon dioxide emission was assessed for the first time from soils of marsh ecosystems on the southeastern coast of the Barents Sea. Soils of marsh ecosystems show high values of carbon dioxide emission (4.03 ± 0.17 g С/(m² day), June–July 2024), which points to their high biological activity. The analysis of data on CO₂ emission from soils of marsh ecosystems testifies mainly to their high spatial variability. Soils at different levels of marsh ecosystems differ statistically significantly in the magnitude of CO₂ emission and line up in the increasing order: mudflats, beaches &lt; littoral pools, eroded marsh benches &lt; ecotone zones, lower marshes, splash zones of backflow channels (creeks) &lt; middle and upper marshes. The lower values of CO₂ emission are revealed on marshes subject to intense wind waves, which is due to the armoring effect of coastal landforms upon thalassogenic matter migration. Despite an insignificant area of the coastal zone in the southeastern Barents Sea, the contribution of soils of marsh ecosystems to the global flux of greenhouse gases cannot be neglected. The research results obtained from the statistical analysis of a large array of data contribute to a better understanding of the role of marsh ecosystems in the carbon budget in the western sector of the Russian Arctic.</p>