Arctic warming increases the degradation of permafrost soils. This makes large deposits of formerly frozen organic matter vulnerable to microbial decomposition, resulting in the release of methane (CH4) and carbon dioxide (CO2) to the atmosphere. The active floodplains in Arctic river deltas are highly dynamic permafrost environments due to active erosion and sedimentation but they are so far understudied. Therefore, this study aims to determine soil organic carbon (SOC) and soil nitrogen (SN) stocks, accumulation rates, and the potential CH4 and CO2 release from the active floodplains of Kurungnakh and Samoylov Island in the Lena River Delta. Key soil properties were analyzed and a 68-day incubation at 20 °C under aerobic and anaerobic conditions was performed. The mean SOC and SN stocks were 12.89 ± 6.02 kg C m-2 and 0.56 ± 0.38 kg N m-2, respectively, with ~40% stored in the upper 30 cm. The stocks showed a high heterogeneity in terms of depth-distribution. The estimated SOC pool for the active floodplains in the entire Lena River Delta was ~114 ± 53 Tg C. Total anaerobic CH4 emissions ranged from 0.03 ± 0.01 to 176.95 ± 13.35 μg CH4-C gsoil-1. The active layer samples did not reach a steady state during incubation period, and the permafrost layer samples showed a 30-day lag phase. CO2 emissions (9.14 ± 1.31 to 417.33 ± 31.39 μg CO2-C gsoil-1 anaerobically and 17.47 ± 1.57 to 856.12 ± 61.37 μg CO2-C gsoil-1 aerobically) were mostly two times higher under aerobic conditions than under anaerobic conditions, but both treatments showed a similar pattern during incubation. Correlations were found between emissions (per gram of dry soil) and total organic carbon, and soil texture. The comparison of emissions per gram of dry soil and per gram of soil carbon indicated that not only carbon quantity but also its quality had an important impact on decomposition. This comprehensive study provides valuable information on the carbon stocks and carbon release from active floodplains in the Lena River Delta and highlights the need to include these dynamic permafrost environments in future estimates of the permafrost carbon climate feedback.