Over-Winter Channel Bed Temperature Regimes Generated by Contrasting Snow
Accumulation in a High Arctic River
We report experimental results of near-surface winter temperatures along and adjacent to the channel bed of a High Arctic river on Melville Island, Canada. Temperature loggers 5 cm below the ground surface in areas where the terrain suggests varying snow accumulation patterns revealed that the maximum winter difference between air and near-surface temperatures ranged from 0 to +30°C during the winter of 2012–13, and that shallow near-surface freezing conditions were delayed for up to 21 days in some locations. Cooling to -10°C was delayed for up to 117 days. Modelled temperature at the top of permafrost indicates that permafrost at locations with thick snow can be up to 8°C warmer than those with thin snow. This thermal evidence for an ameliorated surface environment indicates the potential for substantial extended microbial and biogeochemical cycling during early winter. Rapid thaw of the bed during initiation of snowmelt in spring also indicates a high degree of hydrological connectivity. Therefore, snow-ﬁlled channels may contribute to biogeochemical and aquatic cycling in High Arctic rivers.
In the High Arctic, ground surface temperatures in winter relate closely to the presence of snow, which insulates the ground and limits heat loss. Lower-latitude cold environments (Low Arctic, forest-tundra or boreal forest) typically have large variations in snow depth across different types of topography and vegetation, both of which act to differentially accumulate wind-redistributed snow. Different vegetation types substantially affect the thermal regime of the ground and the ratio of surface to air temperatures (n-factors). By contrast, in the High Arctic, topography is more important than vegetation for snow accumulation. Hence, the thermal regime of the ground surface in winter depends primarily on topography, which controls the amount of snow accumulation, as well as the timing of the snowfall.
While it is well understood that snow preferentially accumulates within topographic hollows and stream channels, little quantitative information exists about the resulting differences in surface temperature, particularly in stream channels where snow often accumulates thickly. We hypothesise that the insulating effect of snow in the High Arctic can contribute to the occurrence of local ‘hotspots’ during winter that provide biological refugia, along with large temperature contrasts between the stream bed and the surrounding terrain. These insulated areas potentially lengthen periods of biological activity during early winter when the rest of the landscape is largely dormant biologically. The growing recognition that biogeochemical activity can occur at temperatures as low as -10°C further suggests the potential biological importance of heterogeneous thermal regimes across the landscape.
Here, we report an experiment...