Seasonal evolution of the effective thermal conductivity of the snow and the soil in high Arctic herb tundra at Bylot Island, Canada

Abstract. The values of the snow and soil thermal conductivity, k_snow and k_soil, strongly impact the thermal regime of the ground in the Arctic, but very few data are available to test model predictions for these variables. We have monitored k_snow and k_soil using heated needle probes at Bylot Island in the Canadian High Arctic (73° N, 80° W) between July 2013 and July 2015. Few k_snow data were obtained during the 2013–2014 winter, because little snow was present. During the 2014–2015 winter k_snow monitoring at 2, 12 and 22 cm heights and field observations show that a depth hoar layer with k_snow around 0.02 W m⁻¹ K⁻¹ rapidly formed. At 12 and 22 cm, wind slabs with k_snow around 0.2 to 0.3 W m⁻¹ K⁻¹ formed. The monitoring of k_soil at 10 cm depth shows that in thawed soil k_soil was around 0.7 W m⁻¹ K⁻¹, while in frozen soil it was around 1.9 W m⁻¹ K⁻¹. The transition between both values took place within a few days, with faster thawing than freezing and a hysteresis effect evidenced in the thermal conductivity–liquid water content relationship. The fast transitions suggest that the use of a bimodal distribution of k_soil for modelling may be an interesting option that deserves further testing. Simulations of k_snow using the snow physics model Crocus were performed. Contrary to observations, Crocus predicts high k_snow values at the base of the snowpack (0.12–0.27 W m⁻¹ K⁻¹) and low ones in its upper parts (0.02–0.12 W m⁻¹ K⁻¹). We diagnose that this is because Crocus does not describe the large upward water vapour fluxes caused by the temperature gradient in the snow and soil. These fluxes produce mass transfer between the soil and lower snow layers to the upper snow layers and the atmosphere. Finally, we discuss the importance of the structure and properties of the Arctic snowpack on subnivean life, as species such as lemmings live under the snow most of the year and must travel in the lower snow layer in search of food.