We explored CO₂ from the soil to subsurface at Milandre cave, finding very high concentrations at all depths. While forest soils produced modern CO₂ year-round, cave and meadow soil CO₂ influences vary with temperature-controlled cave ventilation, with older CO₂ input in winter from old organic matter stored underground. These findings show that CO₂ fluxes in karst systems are highly dynamic, and a better understanding of them is important for accurate carbon cycle modelling.