Cryogenic disturbance and its impact on carbon fluxes in a subarctic heathland

Differential frost heave, alongwith the associated cryogenic disturbance that accompanies it, is an almost universal feature of arctic landscapes that potentially influences the fate of the soil carbon (C) stored in arctic soils. In this study, we quantify how gross ecosystem photosynthesis (GEP), soil respiration (Re) and the resulting net ecosystem exchange (NEE) vary in a patterned ground system (non-sorted circles) at plot-scale andwhole-patterned ground scales in response to cryogenic disturbances (differential heave and soil surface disruption).We found that: (i) all studied non-sorted circles (n=15) acted as net CO2 sources (positiveNEE); (ii)GEP showed aweaker decrease thanRe in response to increased cryogenic disturbance/decreased humus cover, indicating that undisturbed humus-covered sites are currently themain source of atmospheric CO2 in the studied system. Interestingly,Re fluxes normalized toC pools indicated that C is currently respiredmore rapidly at sites exposed to cryogenic disturbances; hence, higherNEEfluxes at less disturbed sites are likely an effect of amore slowly degrading but larger total pool that was built up in the past. Our results highlight the complex effects of cryogenic processes on theC cycle at various time scales.