Permafrost soils are found at high latitudes and altitudes, and contain three times more carbon than in the atmosphere. As permafrost thaws, a portion of this carbon - still largely uncertain - is released in the form of greenhouse gases (GHG), resulting in a permafrost carbon-climate-feedback. This feedback still awaits to be integrated in global models of GHG emissions used by the IPCC, but is estimated as equivalent to the emissions from one additional large industrialized country. The uncertainties are partly attributable to the unknown contribution of the thawing of ice-rich permafrost, which manifests by physical degradation, named thermokarst terrains. Another source of uncertainty relates to the proportion of organic carbon (OC) that is linked to mineral surfaces or mineral elements, as mineral-interacting OC. These stabilization mechanisms are presumed to render the corresponding OC fraction less accessible to decomposition and emissions as GHGs. This thesis investigates the abundance, nature and control of mineral-OC interactions in permafrost soils and sediments affected by thermokarst disturbances. Chemical stabilization mechanisms have been shown to stabilize on average 31 ± 12% of total OC, and this pool of mineral-interacting OC is preserved in materials exported by the thermo-erosion process. We also show that historical permafrost thaw dynamics have a decisive influence on the concentration and proportion of mineral-interacting OC in permafrost environments. Finally, we have shown that the formation of lowland thermokarst landscapes has progressed locally five times faster in recent years than in the last few decades, with an expected release of mineral-bound OC. Such findings demonstrate the urgent need to integrate OC-mineral interactions into global ecosystem carbon balance models. This requires establishing links between concentrations and proportions of mineral-interacting OC and GHG emissions.
Maxime Thomas (Wed,) studied this question.