The Influence of Shallow Taliks on Permafrost Thaw and Active Layer Dynamics in Subarctic Canada

Abstract

Measurements of active layer thickness (ALT) are typically taken at the end of summer, a time synonymous with maximum thaw depth. By definition, the active layer is the layer above permafrost that freezes and thaws annually. This study, conducted in peatlands of subarctic Canada, in the zone of thawing discontinuous permafrost, demonstrates that the entire thickness of ground atop permafrost does not always refreeze over winter. In these instances, a talik exists between the permafrost and active layer, and ALT must therefore be measured by the depth of refreeze at the end of winter. As talik thickness increases at the expense of the underlying permafrost, ALT is shown to simultaneously decrease. This suggests that the active layer has a maximum thickness that is controlled by the amount of energy lost from the ground to the atmosphere during winter. The taliks documented in this study are relatively thin (<2 m) and exist on forested peat plateaus. The presence of taliks greatly affects the stability of the underlying permafrost. Vertical permafrost thaw was found to be significantly greater in areas with taliks (0.07 m year−1) than without (0.01 m year−1). Furthermore, the spatial distribution of areas with taliks increased between 2011 and 2015 from 20% to 48%, a phenomenon likely caused by an anomalously large ground heat flux input in 2012. Rapid talik development and accelerated permafrost thaw indicates that permafrost loss may exhibit a nonlinear response to warming temperatures. Documentation of refreeze depths and talik development is needed across the circumpolar north.

Hydrometeorological measurements in peatland‐dominated, discontinuous permafrost at Scotty Creek, Northwest Territories, Canada

“…A sharp decrease in liquid volumetric soil moisture indicates soil freezing. Liquid water content of frozen soils at this site typically ranges from 0.15 to 0.2 (Connon et al , ). In both the bog and thawing plateau, ground heat flux (Q G , W/m 2 ) was measured using a ground heat flux plate (Campbell Scientific, HFT3) installed at 5 cm below the ground surface (Figure c,f), calibrated according to the method described by Hayashi et al () and calculated to include heat storage between the ground surface and ground heat flux plate.…”

A Synthesis of Three Decades of Eco-Hydrological Research at Scotty Creek, NWT, Canada

“…Chasmer et al 2016). The increasing prevalence of taliks at Scotty Creek (Connon et al, 2018) has led other authors to investigate the extent of taliks in other regions (e.g. Lamontagne-Hallé et al, In press), many of whom also report an increase in the number 5 of active flowpaths, especially during the winter months when most hydrological processes were previously assumed to be dormant (Sjöberg et al, 2016;Walvoord et al, 2012).…”

“…In the discontinuous permafrost zone, permafrost thaw involves simultaneous lateral recession of the near vertical sides (which can be significant) (McClymont et al, 2013) of a permafrost body, and lowering of its permafrost table. Connon et al (2018) demonstrated that the development of talik is a kind of "tipping point" that greatly accelerates the rate 30 of permafrost thaw. Specifically, they found that the permafrost below areas with a talik thawed five times faster than areas without a talik, as the unfrozen talik prevents energy loss from the permafrost body to the atmosphere during the winter.…”

“…Similarly, Gibson et al (In press) concluded that sites with high talik presence after wildfire exhibited high rates of lateral bog expansion. Connon et al (2018) also identified the critical thaw depths associated with talik development. For example, in early April 2016, the depth of re-freeze was measured at 135 points along nine transects that have been monitored for thaw depth and soil moisture since 2011.…”

“…Since that study was published, the widespread occurrence of taliks has been demonstrated below linear (i.e. seismic) disturbances (Braverman and Quinton, 2016), in peatland areas 10-20 years following the occurrence of wildfire (Gibson et al, In press) as well as below large areas of peat plateaus (Connon et al, 2018). 15…”