Arctic permafrost contains large amounts of nitrogen (N), which may be bioavailable upon permafrost thaw. Here, we have compiled inorganic N data from published studies on the active layer and permafrost layers combined with new data to quantify the spatial variability of bioavailable inorganic N in permafrost-affected ecosystems across the Northern Hemisphere. Ammonium (NH₄⁺) and nitrate (NO₃⁻) are typically extracted from samples using different agents and strength. The results of an extraction experiment are here used to recalculate published concentrations on NH₄⁺ and NO₃⁻ to a “water extractable fraction.” The results show that upper permafrost across all sites and samples contains significantly more NH₄⁺ compared to the root zone and was significantly and positively correlated with an increasing water/ice content despite a surprisingly high variation within and between sites. Based on the average reported permafrost thaw rates (0.4–0.8 cm y⁻¹) for wet and dry landscape types, the average release of inorganic N (NH₄⁺ and NO₃⁻) from wet tundra ecosystems was calculated to be 2.0 [1.13–2.61] kg N ha⁻¹ decade⁻¹ and 1.3 [0.78–1.81] kg N ha⁻¹ decade⁻¹ for dry ecosystems. This brings permafrost-derived inorganic N on the same order of magnitude as biological nitrogen fixation in relatively dry tundra ecosystems but only marginally compared to nitrogen fixation in wet ecosystems. These landscape-specific variations highlight the need for improving the understanding of N mobilization linked to permafrost thawing, but also that N transfer from well-drained slopes to lower parts of the landscape can be important for the potential plant growth (greening) downslope from surrounding landscape types with faster permafrost thawing.