the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Mar 2024
The cryostratigraphy of thermo-erosion gullies in the Canadian High Arctic demonstrates the resilience of permafrost
Abstract. Thermo-erosion gullies (TEGs) are one of the most common forms of abrupt permafrost degradation. They generally form in ice-wedge polygonal networks where the interconnected troughs can channel runoff water. Although TEG can form within a single thawing season, it takes them several decades for their complete stabilization. While the inception of TEGs has been examined in several studies, the processes of their stabilization remain poorly documented, especially the ground ice patterns that form following permafrost aggradation in stabilizing TEGs. For this study, we investigated the impacts of two TEGs in the Canadian High Arctic (Bylot Island, NU, Canada) on ground ice content, cryostratigraphic patterns, and geomorphology to examine permafrost recovery following thermal erosion in ice-wedge polygonal tundra. We sampled 17 permafrost cores from two TEGs – one still active (since 1999) and one stabilized (>100 years old) – to describe the surface conditions, interpret the cryostratigraphic patterns, and characterize the state of permafrost after TEG stabilization. We observed that although the TEG caused discernable cryostratigraphic patterns, ground ice content and active layer thickness of the TEGs were comparable to measurements made in undisturbed conditions. We also noted that once stabilized, TEGs permanently (at the Anthropocene scale) alter landscape morphology and hydrological connectivity. We concluded that although the formation of a TEG has profound effects on the short/medium term and leaves near permanent geomorphological and hydrological scars in periglacial landscapes, on the long term, High Arctic permafrost can recover and return to geocryological conditions similar to those pre-dating the initial disturbance. This suggests that in stable environmental conditions undergoing natural variability, permafrost can persist longer than the geomorphological landforms in which it forms.
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RC1: 'Comment on egusphere-2024-208', Sebastian Wetterich, 11 Apr 2024
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MS No.: egusphere-2024-208
Review on Gagnon et al. The cryostratigraphy of thermo-erosion gullies in the Canadian High Arctic demonstrates the resilience of permafrost
by Sebastian Wetterich
General remarks
The study by Gagnon et al. investigates by example to two thermo-erosional gully systems on Bylot Island (Canadian Archipelago) morphological dynamics and permafrost properties of such degradation features. The study is based on intense coring along several cross-transects from undisturbed surroundings to the gully bottom, detailed cryolithological core descriptions and analytical work covering relevant ground properties such as ice content, organic content and granulometry. CT imagery of the cores is of special value as it illustrates the ground composition and the cryostructures. The authors provide and discuss a conceptual framework of gully development including changes in permafrost state and subsequent dynamics in surface morphology. Therefore, the study addresses a relevant scientific topic and contains novel data and understanding suitable for publication in The Cryosphere. The employed field and lab methods are appropriate and allow deducing a comprehensive dataset that supports the interpretations and conclusions from the study. The paper is clearly and well-structured written in all parts, and relevant studies are cited. Some minor suggestions and comments are outlined below and in the attached PDF.
It would be useful to add in the Introduction section definitions on terminology that are used in the paper. As the authors refer to polygon development stages as high-center, low-center, flat and drained (firstly mentioned in ln109-110), this terminology should be explained in the Introduction section 1. In detail, I struggle to understand what is meant by drained polygons. Here, either the ponds filling the center of low-center polygons or the ponds above melting wedge ice surrounding polygon high centers might have drained. Please, clarify and use unambiguous terms. From the imagery shown in Fig. 1 it remains unclear what types of polygons occur in the study area. It is further unclear how polygons named as undisturbed (e.g., in Fig. 2) relate to the also used high-center/low-center polygons, although low-center polygons are mentioned in ln171-172. Such information should be given earlier, e.g., in section 2. Furthermore, a short definition of transient and protective layers in the Introduction section 1 would be helpful. The thaw front depth (TFD) seems to be used as synonym of the more common term active layer thickness (ALT). I wonder why, as ALT data are displayed in Fig. 4 and it is named in the title of section 4.1, but rarely in the text. And finally on terminology: cryostratigraphy (cryostratigraphic pattern, permafrost cryostratigraphy), cryostructures (ground-ice pattern) and geocryological layers seem to be used in places synonymously. Please, consider a short definition in the Introduction section 1 (e.g., ln41), and consistent and correct use of the terms as “cryostratigraphy refers to the relationship between the lithological characteristics of rocks and their ground-ice amounts and distribution” on large scale, while small-scale ground structures “formed by the amount and distribution of ice within sediment and rock are termed cryostructures” (French & Shur, 2010).
In the Study site section 2, background information on ground temperatures is missing, although it is further discussed in e.g., section 5.1.2 as ‘low permafrost temperatures’. Please, add according information in section 2.
The Material and Methods section 3 requires some additional information of the number of samples used for the different analyses. Furthermore, grain size analyses have been undertaken by sieving and particle size analyzer (ln147). Both methods are not described in the Methods and material section 3. If laser diffraction (i.e., particle size analyzer) was applied (1) the approach to combine the results from both methods in weight-based percentages (wt%) and volume-based percentages (vol%) should be described, and (2) I wonder why clay has not been measured.
A statement on data availability is missing and should be added.
Minor remarks
Please, find minor remarks in the commented PDF (egusphere-2024-208_minor comments.pdf).
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