Permafrost and Ground Ice Conditions in the Ogilvie Mountains, Central Yukon
Creators: name: Frappier, Roxanne
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2023
Subjects: Permafrost
Climate change
Geomorphology
Ground ice
Remote sensing
Modeling

description: Permafrost is vulnerable to climate changes and the associated landscape changes that are enhanced by amplification processes and feedbacks unique to the Arctic. Permafrost degradation leads to important changes in terrestrial and aquatic ecosystems, and determining regions that are sensitive to permafrost degradation therefore represents an urgent issue. The Tombstone Territorial Park (TTP) and its surroundings (Ogilvie Mountains, central Yukon) represent one of those sensitive permafrost environment that should be monitored. The central Yukon is an enigmatic permafrost environment that reflects both Pleistocene and Holocene permafrost and climate conditions. The area is particularly intriguing because of the extensive presence of permafrost landforms that are more typical of areas much further north, especially ice-wedge (IW) polygons. It also represents a major transportation corridor linking multiple northern communities (Dempster Highway). Despite access along the road, and signs of permafrost degradation, there have been a limited number of studies addressing permafrost and ground ice conditions throughout the landscape. Consequently, this PhD thesis aims to characterize IW polygons, define the type and magnitude of landscape changes, and model permafrost distribution, conditions and sensitivity to climate changes in the study area. Characterization of IW polygons reveals that they occupy 2.6% of the TTP and preferentially develop in woody sedge peat, glaciofluvial and alluvial deposits along the lower reaches of the Blackstone and East Blackstone rivers on hillslopes of ≤1°. Vegetation type, surface wetness, and polygon spatial pattern are influenced by the development stage of ice-wedge polygons, while the size and angles of polygons seem independent of the development stage. A Landsat-based landscape change analysis of the TTP and surrounding region covering the 1986-2021 period shows that statistically significant spectral changes occurred in 24% of the study area, and most of these changes are associated with vegetation succession and hydrological processes (i.e., erosion and deposition). Other landscape changes included wildfires, slumps, changes to riverbanks and lake shores, earlier melting of icings in the summer, degradation on the peripheries of some ice wedge polygonal terrain, and potential insect damage to forests. The analysis reveals that the extent and magnitude of landscape changes in the study area are influenced by the geomorphic setting, ecological succession and glacial history of the region. Modeling current and future permafrost conditions in the study area using the Northern Ecosystem Soil Temperature (NEST) model indicate that permafrost has persisted through the 20th century and beginning of the 21st century and is currently present throughout the area. Modeled mean permafrost depth (113.8 ± 49.6 m), active layer thickness (2.45 ± 7 m), surface, near-surface, and deep ground temperatures (−1 ± 1.2°C, −1.6 ± 1.2°C, −2.4 ± 1.3°C, respectively) are in the range of other local and regional measurements. Predicted ALTs and permafrost depth show areas of permafrost loss by 2100 (22% of study area under RCP4.5, and 29% under RCP8.5). Permafrost degradation in the study area could greatly impact slope stability and conditions of aquatic systems, and shrubification could contribute to increased degradation.