Sweden is dotted with thousands of peatlands, acting as localized reservoirs of soil organic carbon and its decomposition end-products; carbon dioxide (CO2) and methane (CH4), two potent greenhouse gases (GHG). The stability of this vast GHG storage is critical to limit the current growth in atmospheric climate forcing. This project sets out to assess the stability of the GHG storage within two contrasting peatlands types, a northern poor fen (Degerö Stormyr - Sweden) and an ombrotrophic bog (Mer Bleue- Canada). This will be achieved through the use of new sensor technology, allowing to continuously measure CO2 concentrations at different depths across vertical peat profiles. The preliminary data reveals rapid sequential losses in CO2 concentrations, from the surface down to 1.5m depth at Degerö Stormyr. These losses reoccur every year at the same period, mostly in autumn, when the thermal stratification of the peat profile is removed by surface cooling. The estimated loss of CO2 from the catotelm during those events is sufficiently large to neutralize the peatland’s annual C sink. These results indicate that the hydrological and physical processes controlling the storage and transport of GHG in the catotelm have not been well understood. This raises concerns regarding the stability of the GHG storage in northern peatlands, which appear far more dynamic than currently assumed.