Carbon degradation and mobilisation potentials of thawing permafrost peatlands in Northern Norway

Abstract

Abstract. Permafrost soils are undergoing rapid thawing due to climate change and global warming. Permafrost peatlands are especially vulnerable since they are located near the southern margin of the permafrost domain in the discontinuous and sporadic permafrost zones. They store large quantities of carbon (C) which, upon thawing, are decomposed and released as carbon dioxide (CO2), methane (CH4) or dissolved organic carbon (DOC). This study compares carbon degradation in three permafrost peatland ecosystems in Finnmark, Norway, which represent a well-documented chronosequence of permafrost formation. Peat cores from active layer, transition zone and permafrost zone were thawed under controlled conditions and incubated for up until 350 days under initially-oxic or anoxic conditions while measuring CO2, CH4 and DOC production. Carbon degradation varied among the three peat plateaus but showed a similar trend over depth with largest CO2 production rates in the top of the active layer and in the permafrost. Despite marked differences in peat chemistry, post-thaw CO2 losses from permafrost peat throughout the first 350 days in the presence of oxygen reached 67–125 % of those observed from the top of the active layer. CH4 production was only measured after a prolonged anoxic lag phase in samples from transition zone and permafrost, but not in active layer samples. CH4 production was largest in thermokarst peat sampled next to decaying peat plateaus. DOC production by active layer samples throughout 350 days incubation exceeded gaseous C loss (up to 23-fold anoxically), whereas little DOC production or uptake was observed for permafrost peat after thawing. Taken together, permafrost peat in decaying Norwegian peat plateaus degrades at rates similar to active layer peat, while highest CH4 production can be expected after inundation of thawed permafrost material in thermokarst ponds.