This article considers carbon stocks in the tundra ecosystems of northern Fennoscandia with different meso- and macrorelief features in relation with the value and structure of the phytomass of these ecosystems and their volume weight of fine-grained soil. The basic stocks of ecosystem carbon (60–97%) are concentrated in shallow soils. The value of the soil pool of carbon is influenced not only by its concentration but also by the thickness and level of stoniness of soil horizons. Phytomass is the second most significant carbon pool. It was established that most of the tundra ecosystems have stocks of this element largely in belowground phytomass, which, on the whole, reflects the correlation between its aboveground and belowground parts. The carbon stocks in the mortmass of tundra ecosystems are comparable with or slightly exceed the carbon stocks in the live phytomass.