Soils in polar environments have acted for thousands of years as carbon sinks. Now, about 1330–1580 Pg C of carbon is stored in these soils. However, as a result of global warming, soils are thawing and releasing greenhouse gases (GHG) such as methane and carbon dioxide. In order to help understand this phenomenon, this study focused on the relationship between carbon emissions and soil parameters, as well as microbial evolution during a permafrost thaw equivalent to the time of an Arctic summer. Therefore, these samples from the Lena Delta and samples with different moisture conditions were incubated at two different temperatures and microbiological assessment was performed in parallel. Samples located in upland or on the slop remained in a lag phase during the whole incubation, while those located in the floodplain showed a high production of CH4 and CO2. A relationship was established between these high productions and landscape localisation. Annual or biannual flooding allowed to establish favourable methanogenesis conditions. The presence of a higher number of methanogenic Archaea in the active layer of the floodplain supported this hypothesis.