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In addition to their effects on growing-season gas production, slumps and gullies, which create surface depressions, may have a profound impact on annual surface carbon balance by altering winter soil conditions. Experimental wintertime warming of 2–3 °C in tundra soils can result in the net release of 20–30 g carbon m -2 year -1 due to increased winter respiration (Natali et al., 2014). Upland thermokarst can warm annual soil temperature by 4 °C and wintertime temperature by 6 °C due to conductive heat flux to soils during summer and added insulation in winter from deeper snow, with elevated temperatures persisting for decades (Burn, 2000). If increases in wintertime respiration are proportional to those observed from experimental warming, gullies and slumps could substantially accelerate carbon and nitrogen mineralization from SOM [soil organic matter], intensifying the permafrost climate feedback in ways not accounted for in current models (Koven et al., 2015).
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The effect of thermokarst formation [permafrost collapse due to ground ice melt] on carbon and nitrogen cycling differed fundamentally by feature morphology [on the North Slope of AK]. (Fig. 10). The large proportion of ecosystem carbon exported off-site or incorporated into deeper soil by thaw slumps and active-layer detachment slides resulted in decreased Reco [ecosystem respiration] postfailure. Conversely, thermo-erosion gullies displaced a smaller portion of ecosystem carbon but nearly doubled postfailure Reco and increased soil N2O concentration through much of the growing season. Similar declines in Reco following slump and slide formation have been documented in boreal forest and high Arctic ecosystems, suggesting these morphologies of thermokarst may decrease growing-season CO2 flux (Beamish et al., 2014; Jensen et al., 2014). However, gullies, which strongly increase Reco and N2O, are the most abundant form of upland thermokarst, accounting for over half of total upland thermokarst area (Krieger, 2012).
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v3.2
