| Summary: | In the Arctic, recent studies show that air temperatures are rising up to 4 times faster than the global average. This polar amplification exposes permafrost – soil, sediment or rock frozen for at least two years – to thawing. This phenomenon could induce a permafrost-carbon-climate feedback, since it contains roughly half the soil carbon present in all other terrestrial biomes (0 - 3 m) and three times more than the carbon currently stored in the atmospheric pool. It is estimated that CO2 and CH4 emissions from the Arctic could add 55 - 230 Pg of carbon (in CO2 equivalent) to the atmosphere, and must therefore be considered in climate models. These estimates are based on simulated volumes of organic carbon (OC) that will be exposed by the increase in thickness of the seasonally thawing active layer, through a process commonly referred to as gradual thawing. In order to refine these estimates, rapid thawing processes such as thermokarst, thermo-denudation and thermo-erosion – which could represent an additional release of greenhouse gases – should benefit from further studies. Here, we study two different types of hillslope thermokarst landforms: an Active Layer Detachment (ALD) which is a one-time event, and a Retrogressive Thaw Slumps (RTS) which repeats annually during summer months. In the Cape Bounty Arctic Watershed Observatory (Canada), we analyzed the total element concentrations, mineralogy, total OC and mineral-OC interactions within the headwalls of two disturbances, as well as within corresponding undisturbed zones. Our results show that 64 ± 10% of total OC is mineral-bound either as organometallic complexes, associated with mineral surfaces or physically protected in aggregates. In addition, there was a lower proportion of mineral-bound OC in the deeper layers exposed by the retrogressive thaw slump. These results therefore suggest that the OC exposed by thermokarst disturbances at Cape Bounty is largely protected by interactions with minerals, but that deep thaw features could expose OC ...
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