The Role of Land Cover Classes and Rainfall Events on the Active Layer Thermal Regime in the High Arctic

• Main Author: Rahman, Tabatha
• Other Authors: Lamoureux, Scott, Geography and Planning
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Active layer; Canadian High Arctic; Permafrost; Subsurface thermal regime; Land cover class; Rainfall; Arctic; Cape Bounty; Nunavut; Ice; permafrost; Tundra
• Online Access: http://hdl.handle.net/1974/29024

The active layer’s thermal regime, which includes surface energy exchanges and soil thawing/freezing characteristics, is sensitive to environmental factors and processes, and has important implications on biogeochemical, hydrological and geomorphic processes. High Arctic land cover classes were hypothesized to affect the active layer’s thermal regime because they represent variations in environmental factors (e.g., vegetation cover, snow cover and soil moisture content). The objectives of this research were to fill knowledge gaps on the: 1) relationship between land cover classes and active layer thermal regimes, and on the 2) role of rainfall on active layer temperatures in the High Arctic. To address these objectives, air temperature, precipitation, soil temperature and soil moisture data were recorded within three land cover classes (polar semi-desert, mesic tundra and wet sedge) at the Cape Bounty Arctic Watershed Observatory (CBAWO), Nunavut, between 2012 and 2019. The data were used to calculate surface energy exchange (n-factors, surface offsets), mean annual ground temperature at 15 cm depth (MAGT15cm), mean annual ground temperature at the top of permafrost (TTOP), and empirical and modelled maximum thaw depth (MTD). The data were also used to determine characteristics of soil thawing and freezing, ground ice formation and melt, and the active layer’s thermal responses to rainfall. Results showed significant (p < 0.05) interclass differences in n-factors between all three land cover classes. However, MAGT15cm, TTOP and MTD were not significantly different (p > 0.05) between land cover classes (excluding wet sedge where MTD was not calculated), and the empirical MTD was consistently shallower than the modelled MTD. The soil temperature responses to rainfall were consistent between land cover classes and mostly consisted of a dampening of peak diel soil temperatures and a convergence of temperatures with depth. This study was unsuccessful at identifying ice formation and melt within the active layer by purely thermal measures. These results improve our understanding of the relationships between High Arctic land cover classes, rainfall events and the active layer thermal regime, which is critical for our ability to accurately model and predict hydrological and biogeochemical processes, permafrost degradation and landscape stability in continuous permafrost regions. M.Sc.