Field and Modelling Investigations of Permafrost Conditions in Labrador, Northeast Canada
Creators: name: Way, Robert
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2017
Subjects: Permafrost
Labrador
Climate
Northern

description: The Permafrost Map of Canada shows the region of Labrador in northeast Canada as spanning conditions from continuous permafrost in the north to isolated patches in the south. However, few studies have documented this and the most detailed field information comes from research in the 1960s and 1970s, with contemporary permafrost distribution largely unexamined. An extensive investigation of contemporary permafrost conditions throughout Labrador and portions of northeastern Québec was undertaken between 2013 and 2017 to fill this knowledge gap. A multi-scale approach to analyzing permafrost distribution was employed, including collection of detailed field information at selected sites, establishment of climate and ground monitoring apparatus at more than 35 different locations and spatial numerical permafrost modelling of permafrost conditions across the region. Spatio-temporal infilling was used with thin plate spline interpolation to generate temporally-consistent climate grids for 1948-2016 at a monthly resolution for all of Labrador-Ungava. Evaluation of derived air temperature grids against meteorological observations and remote field monitoring stations showed an overall accuracy of 0.8 ± 0.3 °C on a monthly timescale. The grids were used to generate freezing and thawing degree-days maps to facilitate permafrost modelling. Field investigations in the coastal barrens of southeastern Labrador (51.5°N to 54°N) used geophysics (DC electrical resistivity tomography), standard field methods and ground temperature monitoring to characterize very isolated patches of permafrost observed to be up to 8 m thick beneath palsas and peat plateaus. Permafrost was inferred to be absent in wetland, forested and forest-tundra areas inland, notwithstanding average air temperatures lower than at the coast. However, field investigations undertaken farther north in the coastal community of Nain, NL (56.3°N) showed permafrost to be present at numerous sites within the community in tundra, forested and disturbed settings. Boreholes and geophysics showed permafrost less than 20 m thick at several locations including beneath existing and proposed building locations. These investigations of permafrost along a latitudinal gradient highlight the contrasting permafrost environments found in coastal regions of Labrador. Field data from monitoring stations across Labrador (n=83) were used to analyze the interrelationships of key variables in permafrost modelling. Snow depth, not mean annual air temperature, was the strongest single determinant of mean temperatures at the ground surface and at ~1 m depth. Ground temperature variability was most related to land cover class with a critical late-winter snow depth of 70 cm or less inferred to be sufficient to prevent the formation of permafrost at the monitoring sites. Testing of several different land cover datasets for permafrost model parameterization gave errors in ground surface temperature ranging from ±0.9 to ±2.1°C. A new estimate of the distribution of permafrost at high resolution (250 m x 250 m) was generated for all of Labrador-Ungava using a modified version of the temperature at the top of permafrost model. Predicted ground temperatures for long-term climate normal ranged regionally from -9°C (for high elevations in northern Québec) to +5°C (for southeastern Labrador-Québec). Modelling of permafrost for specific temporal windows (1948-1962; 1982-1996; 2000-2014) suggested that permafrost area increased from the middle of the 20th Century to a potential peak extent (36% of the total land area) in the 1990s. Subsequent warming is predicted to have caused a decrease in permafrost extent of one-quarter (95 000 km2) even if air temperatures rise no further, providing air and ground temperatures equilibrate. The field observations in this thesis validated research conducted in the interior of Labrador during 1970s which directly linked permafrost presence or absence to snow thickness. Permafrost was more widespread than would be expected in coastal areas based on the region’s mean annual air temperatures which suggests that specific geomorphologic and meteorological settings may allow permafrost to persist in otherwise unsuitable regions. Land cover type, through its influence on snow distribution, was shown to be a key variable whose changes must be considered when examining future permafrost conditions in the region.