Figure 2.

Key biological processes in the carbon cycle of permafrost environments. Permafrost thawing at the transition zone introduces previously unavailable organic matter into the expanded active layer of soil. Enzymatic hydrolysis decomposes complex organic matter into soluble substrates for microbial fermentation, producing a mixture of organic acids, alcohols and microbial biomass. Methanogenic archaea convert acetate, methylated compounds or H₂ and CO₂ into CH₄ that can be released to the atmosphere through ebullition, diffusion or aerenchyma. Methanotrophs oxidize some of this CH₄, converting it to CO₂.