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One of the most important problems of cryopedology is the interaction of pedogenic processes with the processes that form the structure of the uppermost layers of the near‐surface permafrost. The thickness, structure, spatial variability, and other features are responsible for the reaction of the soil‐permafrost system to the bioclimatic fluctuations as well as the contemporary anthropogenic pressure. Together the soil profile and the upper layers of permafrost form the natural body of the "soil–cryogenic complex," which is the result of simultaneous late Pleistocene–Holocene soil and permafrost coevolution. Pedogenic and cryogenic processes together form organic‐accumulative horizons above the permafrost table that have often been described in the profiles of Cryosols in different regions of Arctic. The multiannual dynamics of summer thawing depth determine the involvement of the material of these shielding horizons into the zone of active modern pedogenesis or its exclusion from it in case of their frozen state. Soil surface microrelief, complexity of the vegetation, and spatial differences of thermal properties of the suprapermafrost soil horizons and the transient layer of permafrost are responsible for the complicated pattern of permafrost table microrelief. Thus, the long‐term study of cryogenic soils that are developed on the close underlying permafrost provides improved understanding of the natural‐historical body—soil‐cryogenic complex. [ABSTRACT FROM AUTHOR]

The values of the snow and soil thermal conductivity, ksnow and ksoil, 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 ksnow and ksoil using heated needle probes at Bylot Island in the Canadian High Arctic (73° N, 80° W) between July 2013 and July 2015. Few ksnow data were obtained during the 2013-2014 winter, because little snow was present. During the 2014-2015 winter ksnow monitoring at 2, 12 and 22 cm heights and field observations show that a depth hoar layer with ksnow around 0.02Wm-1 K-1 rapidly formed. At 12 and 22 cm, wind slabs with ksnow around 0.2 to 0.3Wm-1 K-1 formed. The monitoring of ksoil at 10 cm depth shows that in thawed soil ksoil was around 0.7Wm-1 K-1, while in frozen soil it was around 1.9Wm-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 ksoil for modelling may be an interesting option that deserves further testing. Simulations of ksnow using the snow physics model Crocus were performed. Contrary to observations, Crocus predicts high ksnow values at the base of the snowpack (0.12-0.27Wm-1 K-1) and low ones in its upper parts (0.02-0.12Wm-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. [ABSTRACT FROM AUTHOR]

Permafrost soils in boreal and Arctic ecosystems store almost twice as much carbon as is currently present in the atmosphere. Permafrost thaw and the microbial decomposition of previously frozen organic carbon is considered one of the most likely positive climate feedbacks from terrestrial ecosystems to the atmosphere in a warmer world. The rate of carbon release from permafrost soils is highly uncertain, but it is crucial for predicting the strength and timing of this carbon-cycle feedback effect, and thus how important permafrost thaw will be for climate change this century and beyond. Sustained transfers of carbon to the atmosphere that could cause a significant positive feedback to climate change must come from old carbon, which forms the bulk of the permafrost carbon pool that accumulated over thousands of years. Here we measure net ecosystem carbon exchange and the radiocarbon age of ecosystem respiration in a tundra landscape undergoing permafrost thaw to determine the influence of old carbon loss on ecosystem carbon balance. We find that areas that thawed over the past 15 years had 40 per cent more annual losses of old carbon than minimally thawed areas, but had overall net ecosystem carbon uptake as increased plant growth offset these losses. In contrast, areas that thawed decades earlier lost even more old carbon, a 78 per cent increase over minimally thawed areas; this old carbon loss contributed to overall net ecosystem carbon release despite increased plant growth. Our data document significant losses of soil carbon with permafrost thaw that, over decadal timescales, overwhelms increased plant carbon uptake at rates that could make permafrost a large biospheric carbon source in a warmer world. [ABSTRACT FROM AUTHOR]