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The formation of reactive manganese (Mn) species is emerging as a key regulator of carbon oxidation rates, and thus CO₂ emissions, in soils and sediments. Many subsurface environments are characterized by steep oxygen gradients, forming oxic–anoxic interfaces that enable rapid redox cycling of Mn. Here, we examined the impact of Mn(II)_aq oxidation along oxic–anoxic interfaces on carbon oxidation in soils using laboratory-based diffusion reactors. A combination of cyclic voltammetry, X-ray absorption spectroscopy, and X-ray microprobe imaging revealed a tight coupling between Mn(II)_aq oxidation and carbon oxidation at the oxic–anoxic interface. Specifically, zones of Mn(II)_aq oxidation across the oxic–anoxic transition also exhibited the greatest lignin oxidation potential, carbon solubilization, and oxidation. Microprobe imaging further revealed that the generation of Mn(III)-dominated precipitates coincided …