Permafrost

Recent Permafrost Degradation

Near-surface permafrost is expected to exhibit significant degradation over the coming century due to current and future climate warming, although this process may somewhat lag behind trends in warming surface air temperatures. Warming air temperatures lead to permafrost thaw and degradation, which can include thickening of the active layer, talik formation, thermokarst development, expansion or creation of thaw lakes, lateral permafrost thawing, and a northward migration of the southern permafrost boundary. These changes can have significant impacts on hydrology, ecosystems, and biogeochemical cycling. Permafrost warming and degradation may in turn be accelerated by positive feedbacks to include carbon release from freshly thawed soils, projected expansion of shrub cover, and wildfire occurrence.

Three types of permafrost degradation may occur as a result of climate warming: (1) overall permafrost thaw, (2) deepening active layers, and (3) thermokarst processes. Overall or “wholesale” permafrost thaw and thermal degradation result in widespread reductions in permafrost extent, allowing for a connection between deep groundwaters and surface water pathways. As opposed to active-layer and thermokarst processes, time lags involved with wholesale permafrost thaw can be significantly longer, where temperature changes at the ground surface may take from a few years to millennia to reach the bottom of the permafrost layers. Not only can permafrost warm and degrade from the surface as well as from the bottom, but permafrost may also degrade internally if it contains unfrozen water, as seen in some areas of Alaska. Although direct measurements of long-term permafrost dynamics are relatively rare and no real widespread pan-arctic wholesale permafrost thaw has been observed, some studies have in fact shown some substantial local and regional permafrost degradation through field observations. Active-layer thaw depths are also highly responsive to warming air temperatures and can be important indicators of permafrost stability. Deepening active layers may increase the interaction between surface waters and soils within the newly thawed portions of the active layer as well as liberate soluble biogeo-chemical constituents previously sequestered within the near-surface permafrost. Last, it is also important to address thermokarst processes in the context of permafrost degradation, which is the surface thawing of ice-rich ground and subsequent thaw slumping. Thermokarst is associated with warming air temperatures in discontinuous and sporadic zones of permafrost extent, but it can also occur in regions of continuous permafrost and is not always tied directly to wholesale permafrost degradation.

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