Cryoturbation is a fundamental soil forming process with large importance for ecosystem functioning in the Arctic. Recent investigations have emphasized the effect of climate change on cryoturbation, but contrast in their predictions on cryoturbation under future climate warming. This study analyzed to what extent conclusions on the response of cryoturbation to environmental conditions depend on: 1) the proxy of cryogenic activity used; 2) the spatial scale of environmental predictor variables; and 3) the mesoclimatic regime of the study site. As an example of cryoturbated soil, 48 non-sorted patterned-ground features were sampled at eight sites along an elevational and a precipitation gradient and vegetation gradients nested within each site in the Abisko area, northernmost Sweden. To quantify cryogenic activity, eight proxies of cryogenic activity were used. In addition, environmental data were obtained at two spatial scales from field surveys and existing geodata. The results suggest a significant correlation between most activity proxies. Cryogenic activity increased along the precipitation gradient and peaked at intermediate elevations, while within-site variation was similar to between-site variation. The response of cryogenic activity to environmental factors was largly independent of the proxy used but varied with the spatial scale of predictor variables and across mesoclimatic regimes, with precipitation and vegetation cover being the most important predictors. The study indicates that spatial scale and mesoclimate should be considered when assessing the sensitivity of cryoturbation to climate changes. The results therefore provide possible explanations for contrasting previous predictions on the fate of cryoturbated patterned-ground ecosystems under future climate warming.

<p>Relict non-glacial surfaces occur in many formerly glaciated landscapes, where they represent areas that have escaped significant glacial modification. Frequently distinguished by blockfield mantles, relict non-glacial surfaces are important archives of long-term weathering and landscape evolution processes. The aim of this thesis is to examine the distribution, weathering, ages, and formation of relict non-glacial surfaces in the northern Swedish mountains.</p><p>Mapping of surfaces from aerial photographs and analysis in a GIS revealed five types of relict non-glacial surfaces that reflect differences in surface process types or rates according to elevation, gradient, and bedrock lithology. Clast characteristics and fine matrix granulometry, chemistry, and mineralogy reveal minimal chemical weathering of the blockfields.</p><p>Terrestrial cosmogenic nuclides were measured in quartz samples from two blockfield-mantled summits and a numerical ice sheet model was applied to account for periods of surface burial beneath ice sheets and nuclide production rate changes attributable to glacial isostasy. Total surface histories for each summit are almost certainly, but not unequivocally, confined to the Quaternary. Maximum modelled erosion rates are as low as 4.0 mm/kyr, which is likely to be near the low extreme for relict non-glacial surfaces in this landscape.</p><p>The blockfields of the northern Swedish mountains are Quaternary features formed through subsurface physical weathering processes. While there is no need to appeal to Neogene chemical weathering to explain blockfield origins, these surfaces have remained continuously regolith-mantled and non-glacial since their inception. Polygenetic surface histories are therefore indicated, where the large-scale surface morphologies are potentially older than their regolith mantles.</p>

Relict non-glacial surfaces occur in many formerly glaciated landscapes, where they represent areas that have escaped significant glacial modification. Frequently distinguished by blockfield mantles, relict non-glacial surfaces are important archives of long-term weathering and landscape evolution processes. The aim of this thesis is to examine the distribution, weathering, ages, and formation of relict non-glacial surfaces in the northern Swedish mountains. Mapping of surfaces from aerial photographs and analysis in a GIS revealed five types of relict non-glacial surfaces that reflect differences in surface process types or rates according to elevation, gradient, and bedrock lithology. Clast characteristics and fine matrix granulometry, chemistry, and mineralogy reveal minimal chemical weathering of the blockfields. Terrestrial cosmogenic nuclides were measured in quartz samples from two blockfield-mantled summits and a numerical ice sheet model was applied to account for periods of surface burial beneath ice sheets and nuclide production rate changes attributable to glacial isostasy. Total surface histories for each summit are almost certainly, but not unequivocally, confined to the Quaternary. Maximum modelled erosion rates are as low as 4.0 mm/kyr, which is likely to be near the low extreme for relict non-glacial surfaces in this landscape. The blockfields of the northern Swedish mountains are Quaternary features formed through subsurface physical weathering processes. While there is no need to appeal to Neogene chemical weathering to explain blockfield origins, these surfaces have remained continuously regolith-mantled and non-glacial since their inception. Polygenetic surface histories are therefore indicated, where the large-scale surface morphologies are potentially older than their regolith mantles.

Au Nunavik, l’augmentation des températures atmosphériques en lien avec les changements climatiques influence la capacité portante du sol en modifiant le régime thermique de la couche active et du pergélisol. Selon la nature du sol et des cryostructures, les processus de fluage et tassement différentiel du sol peuvent être considérables. La forte croissance démographique au Nunavik nécessite la construction de plusieurs nouvelles unités d’habitation. La présente étude a produit des outils pour permettre un aménagement durable du territoire par l’interprétation géomorphologique du paysage et l’étude des propriétés géotechniques des cryofaciès qui compose la cryostratigraphie des unités géomorphologiques de Puvirnituq afin d’estimer le comportement du pergélisol au dégel. Trois unités géomorphologiques principales ont été distinguées sur le territoire. Le socle rocheux est stable au dégel ainsi que les dépôts minces qui le recouvrent puisqu’ils sont contenus dans la couche active (unité P1). Le till remanié est dominé par du sable pauvre en glace, lui conférant une stabilité, mais les moraines de De Geer pourraient incorporer des dépôts marins riches en glace à l’intérieur d’un till remanié (unité P2). Les dépressions comblées de dépôts marins et littoraux sont probablement situées sur du till remanié mais contiennent une zone de transition riche en glace entre ~0,9 et 1,7 m de profondeur, excluant les possibilités de construction (unité P3). La principale contribution à l’aménagement du territoire découlant de cette étude a été la production de deux cartes. La première présente la distribution des unités géomorphologiques sur l’ensemble du territoire, permettant d’identifier rapidement le potentiel d’aménagement de l’environnement de Puvirnituq; la seconde carte montre l’emplacement des moraines de De Geer au-delà du village. Ces données trouveront des applications dans l’évaluation de substrats pour l’expansion de l’environnement bâti de Purvinituq et de granulats non-gélifs pour la construction des infrastructures construites sur remblais. Cette carte souligne l’importance de l’histoire Quaternaire sur les conditions actuelles de pergélisol. / In Nunavik, a sustained increase of surface temperatures linked to climate change, affects the bearing capacity of the permafrost by modifying its thermal regime. Depending on the nature of the soil as well as its cryostructures, creep and differential thaw-settlement processes can be significant. The rapid demographic growth in Nunavik requires the construction of several new housing units. In order to estimate the behaviour of permafrost to thaw, this study has contributed to a sustainable land-use planning by the geomorphological interpretation of the landscape and the study of geotechnical properties of the different cryofacies that compose the geomorphological units of Puvirnituq. Three main geomorphological units were distinguished within the territory. The bedrock is thaw-stable as well as the veneer of surficial deposits since they are contained within the active layer (P1 unit). The reworked till is dominated by ice-poor sand, providing a certain stability, but the De Geer moraines could incorporate ice-rich till and ice-rich thaw sensitive marine deposits (P2 unit). The depressions, filled with marine and littoral deposits, probably contain stable reworked till at the bottom but the presence of an ice-rich transition zone between ~0,9 and 1,7 m depth, makes this geomorphological unit improper for construction (P3 unit). The principal contribution to landuse planning of this study is the production of two maps. The first presents the distribution of the geomorphological units over the entire territory, allowing for a quick identification of potential areas to support the development of Puvirnituq; the second map shows the location of De Geer moraines beyond the study area to extrapolate the result of this study to the landscape scale.

Le site routier expérimental de Beaver Creek (62º 20’ 20’’ N – 140º 50’ 10’’ O) est sis sur la moraine de Beaver Creek pré datant le Dernier Maximum Glaciaire. Dans un périmètre d’un kilomètre carré, son relief, sa végétation, son sol et sa cryostratigraphie ont été étudiés avec une perspective géosystémique, afin d’en détailler la catena et sa structure. Ensuite, la cryostratigraphie a été interprétée pour suggérer un modèle d’évolution du paysage. Enfin, les changements récents y ont été intégrés en vue d’actualiser la tendance évolutive du géosystème. Il ressort de cet ouvrage que la durabilité du pergélisol est fortement appuyée par la présence des milieux humides dans les replats. Quelques affleurements de la moraine sont toujours visibles, quoique faiblement exprimés. Ils contiennent peu de glace et leur teneur en matière organique est mince. Quant aux dépressions, elles sont peu profondes et étendues. Non seulement elles ont hérité des sédiments érodés des crêtes, mais elles ont aussi fixé une quantité importante de glace et de matière organique par le truchement d’un pergélisol syngénétique (>15 m) généré par le climat et protégé par l’écosystème. Au moins un évènement de thermo-érosion est survenu avant le dernier stade d’aggradation syngénétique (Holocène), mais il n’a été que partiel. L’actuel réchauffement climatique menace d’engager un autre épisode de dégradation à l’échelle du bassin versant. Contrairement au changement climatique, l’utilisation du territoire provoque déjà la dégradation du pergélisol, mais de manière localisée seulement. / The Beaver Creek Road Experimental Site (62º 20’ 20’’ N – 140º 50’ 10’’ O) sits on the Beaver Creek moraine. This landform was already evolving before the Last Glacial Maximum. In a single square kilometer perimeter, its topography, vegetation, soil and cryostratigraphy have been studied with a geosystemic perspective to detail its catena and related structure. Furthermore, the cryostratigraphy has been interpreted considering the literature to suggest a landscape evolution model. Recent changes at the site were integrated in the model to actualize the geosystem’s evolutive trend. This work has shown that the durability of the permafrost is strongly supported by the wetlands associated to flat lowlands. On the one hand, some moraine hillcrests are still slightly outcropping. There, the limited moisture inhibited the development of peat and intrasedimentary ice (<1 m). On the other hand, the depressions are quite flat and extended. They inherited not only of the crest’s eroded sediments, but they also fixed an important quantity of ice and organic matter (>15 m) by the mean of syngenetic permafrost aggradation driven by the climate and preserved by the ecosystem. At least one thermoerosion event occurred before the last syngenetic aggradation stage (Holocene), but was only a partial one. The ongoing global warming threatens to trigger another permafrost degradation stage on the drainage basin scale. On the field unit scale, the land use is already degrading the local ice-rich permafrost.