Carbon balance of the continuous permafrost zone of Russia

Abstract

An increase in the atmospheric concentration of CO, is prolected to cause climate warming. Warming of the permafrost environment could change the balance between carbon accumulation and decomposition processes and substantially disrupt the equilibrium of the carbon cycle. Warming may accelerate the rate of decomposition, which is limited by low temperatures, and thaw deeper layers of formerly frozen organic soils, making them available for decomposition. At the same time, productivity of vegetation may increase in response to warming. The continuous permafrost zone occupies approximately 40% of Russian territory, and 5 % of the land surface area of the world. Disruption of the carbon cycle within the permafrost zone in Russia could have a profound effect on the global terrestrial carbon cycle. To evaluate changes in the carbon cycle within the permafrost environment of Russia, it is necessary to quantify the present carbon pools and fluxes Once the carbon balance is established under the present clunate, potential disruptions under a warming climate can be identlfied. A framework to assess the carbon balance for the continuous permafrost zone of Russia was created. Under the present climate, the phytomass (live vegetation, aboveand below-ground) carbon pool was 17.0 Gt (10' t). The mortmass (coarse woody debris) carbon pool was 16.1 Gt. The litter carbon pool was 6.4 Gt C and the soil carbon pool including peatlands was 139.4 Gt. Live vegetation and plant detritus (mortmass and litter) taken together were approximately one-third of the soil carbon pool. The rate of carbon turnover was 1.58 Gt yr-l and the rate of humus formation was 0.083 Gt C yr-'. The phytomass carbon pool of the permafrost zone was 19 % of the former Soviet Union (FSU) phytomass pool and 3 % of the world biomass carbon pool. The permafrost zone accumulated a significant amount of aboveand below-ground plant detritus (mortmass and litter). Climate warming may cause forest migration to the north and increase net carbon accumulation in shrubby tundra ecosystems and ecosystems on soils of low permeabhty, compensating for possible carbon losses from tussock tundra. Shrubby tundra formations and gleylc soils occupy approximately one-half of the area of the Russian tundra biome. The degradation of permafrost would not directly affect the rate of carbon emissions from mineral soils and peatlands. The present depth of the active layer (i.e. layer of seasonal freezing and thawing) in mineral soils exceeds the depth of the organic horizons. In peatlands, thawing of the active layer could cause an additional mass of organic matter to become available for decomposition. However, thawing of the active layer in peatlands may not be this extensive because of the low thermal conductivity and high latent heat capacity of peat.