Arctic coastal lowlands are highly dynamic landscapes, shaped by coastal erosion and thermokarst processes. We investigated organic matter alteration of different landscape units and permafrost degradation stages close to Utqiaġvik, Alaska. Our key question was how permafrost thaw and salinity gradients influence carbon cycling. Geochemical proxies, including C:N ratios, δ¹³C values, and nalkane biomarkers, were used to trace carbon mobilization and degradation pathways. To simulate microbial response upon thaw, we conducted a year-long aerobic incubation experiment assessing CO₂ and CH₄ production. Our results show that saline marine deposits underlying the terrestrial coastal zone accelerate permafrost thaw via freezing point depression. This process initiates cryopeg formation beneath thermokarst lakes, intensifying organic carbon degradation. Notably, CO₂ and CH₄ production began immediately after thaw, suggesting no lag in microbial activity. Moreover, terrestrial organic matter deposited in coastal lagoons remains unfrozen due to hypersaline conditions caused by bedfast ice concentrating salts in the sediment. This creates a persistent microbial habitat, even in the Artic harsh winter climate, and poses a heightened risk of greenhouse gas production from what was previously considered stable permafrost carbon. These findings highlight the urgent need for localized investigations and broader upscaling efforts to assess the vulnerability of saline permafrost systems to climate-driven thaw.