Permafrost Thaw Drives Iron and Organic Carbon Release Into Soil Pore Water During Palsa to Degraded Palsa Transition

ABSTRACT Permafrost degradation, driven by rising temperatures in high‐latitude regions, destabilizes previously sequestered soil organic carbon (OC), increasing greenhouse gas emissions and amplifying global warming. In these ecosystems, interactions with mineral surfaces and metal oxides, particularly iron (Fe), stabilize up to 80% of soil OC. This study investigates the mechanisms of Fe solubilization and OC release across a permafrost thaw gradient in Stordalen, Abisko, Sweden, including palsa, intermediate, and highly degraded permafrost stages. By integrating geophysical measurements—including relative elevation, thaw depth, soil water content, and soil temperature with redox potential and soil pore water chemistry, we identify the environmental conditions driving iron and organic carbon release into soil pore waters with permafrost degradation. Our results show that combining relative elevation, thaw depth, soil water content, soil pore water pH, and soil pore water conductivity with shifts in vegetation species enables very‐high‐resolution detection of permafrost degradation at submeter scales, distinguishing intact from degraded permafrost soils. We show that small‐scale changes in thaw depth and water content alter soil pH and redox conditions, driving the release of Fe and dissolved organic carbon (DOC) and promoting the formation of Fe‐DOC complexes in soil pore water. The amount of exported Fe‐DOC complexes from thawed soils varies with the stage of permafrost degradation, and the fate of Fe‐DOC complexes is likely to evolve along the soil–stream continuum. This study highlights how environmental conditions upon thaw control the type of Fe‐DOC association in soil pore waters, a parameter to consider when quantifying what DOC is available for microbial and photo‐degradation in aquatic systems which are significant sources of greenhouse gas emissions across Arctic landscapes.