Spatial and temporal variability in permafrost conditions, northern Canada

Abstract

The data from nine permafrost thermal monitoring sites at widely separated locations across northern Canada were examined individually, spatially, and temporally. Three sites are in Nunavut (Alert, Iqaluit, and Baker Lake), two in the Northwest Territories (Table Mountain and Wrigley), and four in the Yukon Territory (Wolf Creek, Sixty Mile, Alpine Burwash, and Red Creek). The sites have between one and five boreholes that are instrumented to between 3 and 60 m with records of varying durations. Most of the boreholes are co-located with weather stations recording air temperatures and snow depths. A comprehensive analysis of each site is presented assessing the relations between climate and permafrost temperatures, both in the near surface and at depth. The local characteristics at each site, and among sites, were assessed using various methods including mean annual temperatures, surface and thermal offsets, n-factors, and the apparent thermal diffusivity. Time series analyses were conducted at sites with longer air and ground temperature data records. Regional mean annual air temperatures were defined as the primary determinant of permafrost temperatures at the study sites, but this relationship is modulated by snow (depth, duration, and timing) and vegetation characteristics, the substrate material, and the moisture content, both frozen and unfrozen, within the active layer and the permafrost. Of the study sites, permafrost temperatures at Iqaluit are the most sensitive to changes in climate due to little buffering between the air and the permafrost, and permafrost temperatures at Wrigley, Table Mountain, and Wolf Creek are the least sensitive to changes in climate due to the significant latent heat effects in this isothermal permafrost associated with high amounts of ice and unfrozen moisture. Climatic cooling was observed in the earlier part of the record at Iqaluit from the late 1940's until the early 1990's, and at Alert between the early 1950's and the mid 1970's. Climatic warming was observed in mean annual and winter average temperatures at Alert, Baker Lake, Iqaluit, Table Mountain, and Wrigley in recent decades. This was reflected in warming permafrost temperatures at all of the long-term thermal monitoring sites. The greatest magnitude of ground temperature warming occurred at Iqaluit (+1.6 to +1.9°C/decade), then Alert (+0.2 to +0.6°C/decade), and Baker Lake (+0.3°C/decade). Ground temperatures at Table Mountain warmed the least (+0.1 to +0.2°C/decade), but the warming at this site is important because it represents a progressive change in unfrozen moisture in the fine-grained, ice rich permafrost.