In northern high latitudes, rapid warming is set to amplify carbon-climate feedbacks by enhancing permafrost thaw and biogeochemical transformation of large amounts of soil organic carbon. However, between 30 % and 80 % of permafrost soil organic carbon is considered to be stabilized by geochemical interactions with the soil mineral pool and thus less susceptible to be emitted as greenhouse gases. Quantification of the nature of and controls on mineral-organic carbon interactions is needed to better constrain permafrost-carbon-climate feed-backs, particularly in ice-rich environments resulting in rapid thaw and development of thermokarst landforms. On sloping terrain, mass wasting features called retrogressive thaw slumps are amongst the most dynamic forms of thermokarst. These multi-decadal disturbances grow due to ablation of an ice-rich headwall, and their enlargement due to warming of the Arctic is mobilizing vast stores of previously frozen materials. Here, we investigate headwall profiles of seven retrogressive thaw slumps and sediments displaced from these mass wasting features from the Peel Plateau, western Canadian Arctic. The disturbances varied in their headwall height (2 to 25 m) and affected land surface area ( 30 ha). We present total and water extractable mineral element concentrations, mineralogy, and mineral-organic carbon interactions in the headwall layers (active layer, permafrost materials above an early Holocene thaw unconformity, and Pleistocene-aged permafrost tills) and in displaced material (suspended sediments in runoff and material accumulated on the debris tongue). Our data show that the main mechanism of organic carbon stabilization through mineral-organic carbon interactions within the headwall is the complexation with metals (mainly iron), which stabilizes 30 +/- 15 % of the total organic carbon pool with higher concentrations in near-surface layers compared to deep permafrost. In the displaced material, this proportion drops to 18 +/- 5 %. In addition, we estimate that up to 12 +/- 5 % of the total organic carbon is stabilized by associations to poorly crystalline iron oxides, with no significant difference be-tween near-surface layers, deep permafrost and displaced material. Our findings suggest that the organic carbon interacting with the sediment mineral pool in slump headwalls is preserved in the material mobilized by slumping and displaced as debris. Overall, up to 32 +/- 6 % of the total organic carbon displaced by retrogressive thaw slumps is stabilized by organo-mineral interactions in this region. This indicates that organo-mineral in-teractions play a significant role in the preservation of organic carbon in the material displaced from retro-gressive thaw slumps over years to decades after their development resulting in decadal to centennial scale sequestration of this retrogressive thaw slump-mobilized organic carbon interacting with the soil mineral pool.

Field data on the rates of solifluction and associated parameters are compiled from the literature, in an attempt to evaluate factors controlling the spatial variability in solifluction processes and landforms, with special attention on the climate-solifluction. relationship. The analyzed data originate from 46 sites over a wide range of periglacial environments, from Antarctic nunataks to tropical high mountains. Solifluction, broadly defined as slow mass wasting resulting from freeze-thaw action in fine-textured soils, involves several components: needle ice creep and diurnal frost creep originating from diurnal freeze-thaw action; annual frost creep, gelifluction and plug-like flow originating from annual freeze-thaw action; and retrograde movement caused by soil cohesion. The depth and thickness of ice lenses and freeze-thaw frequency are the major controls on the spatial variation in solifluction processes. Near the warm margin of the solifluction-affected environment, diurnal freeze-thaw action induces shallow but relatively rapid movement of a superficial layer 5 - 10 cm thick on average, often creating the thin stone-banked lobes typically seen on tropical high mountains. In addition to diurnal movement, annual frost creep and gelifluction may occur on slopes with soil climates of seasonal frost to warm permafrost, dislocating a soil layer shallower than 60 cm at a rate of centimeters per year and eventually producing medium-size solifluction lobes. In High-Arctic cold permafrost regions, two-sided freezing can induce plug-like flow of a soil mass 60 cm or thicker. The correlation between process and landform. suggests that the riser height of lobes is indicative of the maximum depth of movement and prevailing freeze-thaw type. Climate change may result in new different ground freezing conditions, thereby influencing the surface velocity and maximum depth of soil movement. Soil moisture and topography also control solifluction. High moisture availability in the seasonal freezing period enhances diurnal freeze-thaw action and subsequent seasonal frost heaving. The latter contributes to raising the moisture content of the thawed layer and promotes gelifluction during the thawing period. The slope angle defines the upper limit of the surface velocity of solifluction. A diagram correlating the potential frost creep with the actual surface velocity permits an inter-site comparison of the relative magnitude of solifluction components. Physically based modelling of periglacial slope evolution requires synthetic and more detailed field monitoring and laboratory simulations of solifluction processes. (C) 2001 Elsevier Science B.V. All rights reserved.