A short-duration production test was undertaken at the Mallik site in Canada’s Mackenzie Delta in April 2007 as part of the JOGMEC/NRCan/Aurora Mallik 2007 Gas Hydrate Production Research Well Program. Reservoir stimulation was achieved by depressurization of a concentrated gas hydrate interval between 1093 and 1105m (RKB). Geologic and porous media conditions of the production interval have been quantified by geophysical studies undertaken in 2007 and geophysical and core studies undertaken by previous international partnerships in 1998 and 2002. These investigations have documented that the production interval consists of a sand-dominated succession with occasional silty sand interbeds. Gas hydrate occurs mainly within the sediment pore spaces, with concentrations ranging between 50-90%. Laboratory experiments conducted on reconstituted core samples have quantified the effects of pore water salinity and porous media conditions on pressure-temperature stability, suggesting that the partition between gas hydrate stability and instability should be considered as a phase boundary envelope or zone, rather than a discrete threshold. Strength testing on natural core samples has documented the dramatic changes in physical properties following gas hydrate dissociation, with sediments containing no hydrate behaving as unconsolidated sands. While operational problems limited the duration of the production test, a vigorous reservoir response to pressure draw down was observed with increasing gas flow during the testing period. We interpret that pressure temperature (P-T) conditions within the test zone were close to the gas hydrate phase equilibrium threshold, with dissociation initiated at 10 MPa bottomhole pressure (BHP), approximately 1 MPa below in situ conditions. The observation of an increase in production rates at approximately 8.2 MPa BHP may be consistent with the notion of an indistinct gas hydrate stability threshold, with rates increasing as P-T conditions traverse the phase boundary envelope. Significant sand inflow to the well during the test is interpreted to result from the loss of sediment strength during gas hydrate dissociation, with the sediment behaving as a gasified slurry. The increase in gas production rates during the final hours of the test may result from non-uniform gas hydrate dissociation and be affected by accelerated dissociation along water filled natural fractures or fine-scale geologic heterogeneities. These may initiate worm hole or high permeability conduits in association with sand production.

Net ecosystem carbon dioxide exchange (NEE) was measured using the eddy covariance (EC) technique at a wetland tundra-sedge fen near Churchill, Manitoba, Canada during two consecutive growing seasons (2007 and 2008). Mean daily NEE at the fen (DOY 157-254) was -3.5 (± 0.26 S.E.) g CO2 m-2 d-1 in 2007 and -4.6 (± 0.36) g CO2 m-2 d-1 in 2008. The fen was a net carbon dioxide (CO2) sink during both the 2007 and 2008 growing seasons of -343 (± 79) and -450 (± 87) g CO2 m-2, respectively. Mean air temperature during the summer (June 1-August 31) was about 1°C greater than the historical average (1971-2000) in 2007 and about 2°C greater in 2008. Growing season precipitation was 107.5 mm below normal in 2007 and 359.5 mm above normal in 2008. These data suggest that if future climate change brings warmer temperatures and near-to-above average precipitation maintaining the water table near the surface, similar subarctic ecosystems will experience increased gross ecosystem productivity enhancing CO2 sequestration during the growing season.

Net ecosystem carbon dioxide exchange (NEE) was measured using the eddy covariance (EC) technique at a wetland tundra-sedge fen near Churchill, Manitoba, Canada during two consecutive growing seasons (2007 and 2008). Mean daily NEE at the fen (DOY 157-254) was -3.5 (± 0.26 S.E.) g CO2 m-2 d-1 in 2007 and -4.6 (± 0.36) g CO2 m-2 d-1 in 2008. The fen was a net carbon dioxide (CO2) sink during both the 2007 and 2008 growing seasons of -343 (± 79) and -450 (± 87) g CO2 m-2, respectively. Mean air temperature during the summer (June 1-August 31) was about 1°C greater than the historical average (1971-2000) in 2007 and about 2°C greater in 2008. Growing season precipitation was 107.5 mm below normal in 2007 and 359.5 mm above normal in 2008. These data suggest that if future climate change brings warmer temperatures and near-to-above average precipitation maintaining the water table near the surface, similar subarctic ecosystems will experience increased gross ecosystem productivity enhancing CO2 sequestration during the growing season.

In Canada’s western Arctic, perennial discharge from permafrost watersheds is the surface manifestation of active groundwater flow systems, yet understanding the mechanisms of groundwater recharge and flow in periglacial environments remains enigmatic. This thesis addresses questions on how and where groundwater recharge occurs. Watersheds were selected in Yukon (Fishing Branch River at Bear Cave Mountain) and the Northwest Territories at latitudes spanning from continuous to discontinuous permafrost (five tributary rivers to the Mackenzie River from Wrigley to Aklavik). All are characterized by perennial flow with open water in the winter, and discharge from sedimentary formations of karstic carbonates and evaporate rocks. Determinations of groundwater contributions to discharge, mixing, recharge conditions and circulation times were made on the basis of a suite of analytical approaches involving measurements of major dissolved ions, δ18O, δD, δ13CDIC, 3H, noble gases and flow gauging was conducted at some sites. The application of these tracers show that hydrogeological conditions and flow paths in permafrost terrains are surprisingly similar to those of temperate regions. Groundwater recharge was determined to be a mix of annual precipitation with contributions from snowmelt and precipitation. All systems investigated show that groundwaters have recharged through organic soils with elevated PCO2, which suggests that recharge occurs largely during summer when biological activity is high. Noble gas concentrations show that the recharge temperature was between 0 and 6 °C, which, when considered in the context of discharge temperatures, suggests that there is no significant imbalance of energy flux into the subsurface. Groundwater ages were found using the 3H-3He method and were dependent on flow path. By characterizing groundwater and surface water chemistry, the proportion of groundwater was found in numerous water courses. The possible impact of ground ice formation and melting on noble gas concentrations in groundwater was considered. To assess this link, a new method to measure the noble gas composition of ground ice bodies was developed. The method can be used to determine the origin of ice, based on changes in noble gas ratios between ice originating from compaction of snow (e.g. glacier ice) vs. ice originating from freezing of water. No significant fractionation of noble gases during groundwater freezing and ground ice formation was identified. Applied to determination of the origin of ground ice bodies, the method was shown to be both diagnostic of ice origin and un-encumbered by reactivity in the subsurface, which compromises the use of the dominant atmospheric gases (O2 and N2).   Résumé Dans l’Ouest de l'Arctique canadien, la décharge pérenne dans certaines rivières en région de pergélisol est la manifestation en surface d’une circulation d’eau souterraine; cependant la compréhension des mécanismes d’écoulement et de recharge des eaux souterraines en région de pergélisol demeure énigmatique. Cette thèse s’intéresse à la question de savoir comment et où la recharge des eaux souterraines se produit. Des bassins versants ont été choisis au Yukon (Rivière Fishing Branch à Bear Cave Mountain) et dans les Territoire du Nord-Ouest à des latitudes s’étendant du pergélisol discontinu au pergélisol continu (cinq tributaires du Mackenzie entre Wrigley et Aklavik). Toutes ces rivières ont un écoulement d’eau pérenne avec des zones non gelées et une décharge dans des formations sédimentaires de roches carbonatées et d‘évaporites. L’identification des contributions des eaux à la décharge, les mélanges, les conditions de recharge, et les temps de circulation ont été faits à partir d’analyses qui ont inclus les concentrations en éléments majeurs, leur valeur isotopique (δ18O, δD, δ13C, 3H), ainsi que leur teneur en gaz rares. A certain des sites analysés des mesures d’écoulement ont été prises. L’application de ces traceurs montre que les conditions hydrauliques et le chemin des écoulements en région de pergélisol sont similaires à ceux des régions tempérées. La recharge en eau souterraine a été identifiée comme étant un mélange de précipitations annuelles, avec des contributions de neige et de pluies. Tous les systèmes étudiés montrent que les eaux souterraines se sont rechargées en traversant des sols organiques avec une PCO2 élevée, ce qui suggère que la recharge se produire largement durant l’été quand l’activité biologique est élevée. Cependant, les concentrations en gaz nobles montre que la température de recharge des eaux souterraines était entre 0 et 6 °C ce qui indique qu’il n’y a pas de déséquilibre de flux d’énergie à l’intérieur de la zone proche de la surface. L’âge des eaux a été déterminé par la méthode 3H-3He et cet âge est dépendant du chemin d'écoulement. En caractérisant les paramètres chimiques des eaux de surface et des eaux souterraines, il a été possible de trouver la contribution des eaux souterraines aux eaux surface. Le possible impact de la formation et de la fonte de la glace souterraine sur les concentrations des gaz nobles a été considéré. Pour déterminer s’il y a un lien entre ceux-ci, une nouvelle méthode pour mesurer la concentration en gaz nobles dans les glaces souterraines a été développée. La méthode peut être utilisée pour déterminer l’origine de la glace; elle est basée sur les changements dans les rapports des gaz nobles entre la glace issue de la compaction de la neige (c’est-à-dire la glace de glacier) par opposition à la glace issue du gel de l’eau. Aucun fractionnement significatif des gaz nobles durant l’engel des eaux souterraines et la formation de glaces souterraines n’a été identifié. Appliquée à l’identification de l’origine des masses de glace enfouies, on a montré que la méthode pouvait permettre d’identifier l’origine des glaces souterraines sans qu’elle soit affectée par des réactions biologiques de sub-surface, lesquelles rendent inutilisables les gaz atmosphériques (O2, and N2).

The Mackenzie Delta region of the Northwest Territories, Canada, has experienced rapid climate warming in the past century resulting in rapidly thawing permafrost in this region. This thesis examines spatial and temporal changes to sediment organic carbon and mercury flux in lakes from thermokarst regions by comparing sediment cores from lakes with and without retrogressive thaw slumps on their shorelines. We show that sediments from lakes with permafrost thaw slump development on their shorelines (slump lakes) had higher sedimentation rates as well as lower total Hg, methyl mercury (MeHg), and labile OC fractions when compared to lakes where thaw slumps were absent. Total Hg and MeHg concentrations in sediments were correlated with total organic carbon (TOC), S2 (labile algal-derived OC), and inferred chlorophyll a content, indicating an association between autochthonous organic carbon and Hg in these sediments. Correlations between mercury and S2 in these study lakes generally support the hypothesis that algal-derived materials correlate with Hg concentration in sediments. We observed higher S2 concentrations in reference lakes than in slump lakes, likely due to uninterrupted algal production, lower dilution by flux of inorganic matter, and possibly better anoxic preservation in reference lakes compared to slump lakes. It is evident that thaw slump development in this thermokarst region increases inorganic sedimentation in lakes, while decreasing concentrations of organic carbon and associated Hg and MeHg in sediments.

An important portion of the large northern permafrost soil organic carbon (SOC) pool might be released into the atmosphere as greenhouse gases following permafrost thawing and subsequent SOC decomposition under future warming conditions, resulting in a warming amplification known as the permafrost carbon feedback. Improved knowledge about the amount, composition and distribution of the permafrost SOC pool is essential when assessing the potential magnitude and timing of the permafrost carbon feedback. This study investigates and compares the SOC storage, composition and distribution in two contrasting permafrost environments: a lowland tundra area in NE Siberia (Tiksi study site), and an alpine area in the Russian Altai Mountains (Aktru Valley study site). Soil pedons were sampled down to 1 m depth and analyzed for key soil properties, i.e., DBD, water content, coarse fraction content, %OC, %IC, C/N ratios and δ¹⁵N values. These soil properties are upscaled by vertical subdivisions based on land cover classes. The role of geomorphology in the accumulation and distribution of SOC in the alpine study site is tested by using a landform and a combined land cover-land form upscaling approach. The estimated mean SOC storage in the upper meter of soils in the alpine site is 3.5 ± 0.8 kg C m¯² compared to 21.4 ± 3.2 kg C m¯² in the lowland tundra site (95% confidence intervals). The inclusion of geomorphology in the upscaling in some cases allows identification of SOC hotspots and areas with very low SOC storage within former land cover classes, therefore improving the landscape SOC storage distribution in the area. The much lower SOC stocks in the alpine site of Aktru Valley can be largely explained by the presence of extensive unvegetated areas in high altitudes (60%), the occurrence active layers deeper than the active soil formation, the enhanced SOM decomposition due to coarse grained, well-drained non-frozen soils, and the negligible occurrence of peatlands and buried organics. Instead, the lowland tundra site in NE Siberia presents important amounts of relatively undecomposed SOM in the permafrost layer. Thus, under future climate warming, alpine permafrost environments such as Aktru Valley may become a net C sink due to an upward shift of vegetation zones and an increase in plant productivity and soil development. Contrarily, lowland tundra areas such as Tiksi may become important C sources since the small increase in C uptake by photosynthetic plants will be outweighed by the thawing and subsequent decomposition of the much larger permafrost SOC pool.

Les glaciers rocheux sont l'une des expressions visibles du pergélisol de montagne et sont à ce titre l'objet d'études nombreuses et variées depuis plus de 20 ans. Deux principaux thèmes sont actuellement étudiés par la communauté scientifique : i) mieux appréhender les mouvements qui affectent les glaciers rocheux ainsi que les mécanismes qui les régissent et évaluer l'impact des changements atmosphériques globaux sur ces formes périglaciaires. Dans ces travaux de thèse nous proposons de contribuer au premier de ces deux thèmes de recherche en utilisant un des outils offerts par la télédétection, déjà utilisé dans d'autres pays pour l'étude des glaciers rocheux : l'interférométrie radar différentielle (D-InSAR). L'interférométrie radar différentielle (D-InSAR) est une méthode basée sur la mesure de la différence de phase entre deux images radar qui couvrent la même zone à différents intervalles de temps et depuis des orbites quasi-similaires. Déjà été utilisée dans d'autres domaines, notamment en glaciologie, volcanologie et sismologie, cette technique crée des interférogrammes, cartes de la déformation du sol en deux dimensions dans la ligne de visée du satellite, qui permettent de détecter et de quantifier un déplacement de quelques centimètres survenu au sol entre deux acquisitions radar. Des recherches en Suisse ont également montré que cette technique pouvait être utilisée pour semi-quantifier les mouvements de glaciers rocheux sur de vastes secteurs et parfois les quantifier (sous réserve de respecter certains critères lors de la création et l'analyse des interférogrammes). Dans ce travail de thèse, nous avons acquis des images radar provenant des satellites ERS (datant de 1991 à 1995) et TerraSAR-X (datant de l'été 2012) grâce à l'ESA (agence spatiale européenne) et au DLR (Deutschen Zentrums für Luft und Raumfahrt, agence spatiale Allemande) dans le but de créer et d'analyser des interférogrammes dans le secteur des Alpes françaises. Nous nous intéressons principalement à la détection des glaciers rocheux. Les archives des satellites ERS-1 et 2 nous ont permis de travailler à l'échelle de l'ensemble des Alpes françaises avec une résolution moyenne (25m en géométrie sol). Les données provenant de TerraSAR-X (TSX) ont permis des analyses plus fines grâce à une meilleure résolution en géométrie sol (10m). Cependant le secteur d'études s'est restreint à la Haute Maurienne/Haute Tarentaise à cause du coût des données et du temps nécessaire à la création et à l'analyse des interférogrammes. Pour les données ERS, nous avons pris en compte l'ensemble des images disponibles au-dessus des Alpes françaises et choisi celles adaptées pour notre étude. Finalement 9 interférogrammes ont été créés. Pour analyser ces données deux méthodes ont été employées : i) une analyse visuelle par des géomorphologues dans un SIG (aidée par des ortho-images et des données topographiques) ; ii) une évaluation de la pertinence des résultats par l'intermédiaire d'une comparaison entre les résultats D-InSAR et des inventaires de glaciers rocheux existants. Finalement une carte de l'ensemble des glaciers rocheux détectés dans les Alpes françaises a été produite. Les données TSX ont été analysées sensiblement de la même manière. Enfin, une troisième étude s'est concentrée sur le cas peu commun du glacier rocheux « déstabilisé » de Pierre Brune (mouvements > 2m/an). Une reconstitution historique des déplacements a été réalisée à partir d'images optiques d'archive et des données GPS ont été acquises durant l'été 2012 et comparées aux données obtenues par D-InSAR. En nous basant sur ces études aux résolutions d'image et aux échelles spatiales variées, nous proposons une discussion sur la pertinence de l'utilisation de la méthode D-InSAR pour du « monitoring » à moyen et long termes des glaciers rocheux mais également sur les atouts et inconvénients de la méthode. / Rockglaciers are one the visual expressions of mountain permafrost and have been the focus of numerous and various studies in the last two decades. Two main topics are studied by the scientific community: i) better understanding the movements of active rockglaciers and the phenomena that generate those movements; ii) assessing impact of global atmospheric change on these periglacial shapes. Here we propose to contribute to the first topic by using remote sensing method of displacement measurements already used in other countries for rockglaciers studies: Differential Interferometric Synthetic Aperture Radar (D-InSAR). D-InSAR is a method of measurement based on the phase difference between two radar images, which represent the same area but at different time intervals. The technique generates interferograms, maps of surface deformation in two-dimensions allowing for the detection and quantification (in centimeters) of variations in distance between the target and the radar between two different data acquisitions. Recent research has shown that the InSAR technique can be used to semi-quantify rockglacier deformation (under the assumption that certain conditions are respected with regard to generating and interpreting the interferograms). In the present thesis, ERS radar images (dating from 1991 to 1995) and TerraSAR-X data (dating from summer 2012) were obtained in courtesy of ESA (European Space Agency) and DLR (Deutschen Zentrums für Luft- und Raumfahrt, German Space Agency) with the aim of generating interferograms. We are interested by the detection of rockglacier movements. The ERS archives allowed us to work at French Alps scale with moderate resolution (25m in ground geometry) whereas TerraSAR-X data have better ground resolution (10m) but our analysis are more local (Haute Maurienne/Haute Tarentaise) due to the cost of the data and the time-consuming nature of the analyzes. With ERS, we selected all archives data and chose the more relevant of them. Finally 9 interferograms were generated. To analyse this amount of data two methods were employed: i) a GIS analysis of interferograms by geomorphologists (helped by ortho-images and topographic data), ii) a comparison between interferograms and existing rockglaciers shape inventory to evaluate the quality of the radar detections. At the end of the analysis a map of the French Alps with all detected rockglacier movements was produced. With TerraSAR-X data, the method of analysis was almost the same. Analyzes focused on the Haute Maurienne/Haute Tarentaise massif. A third scale of analysis is focus on Pierre Brune rockglacier which has been detected on ERS interferograms as destabilized rockglaciers (movement > 2 m/year). Further investigations have been carried out on this site (historical movements reconstitution and GPS acquisitions). Based on these studies with different scales and resolutions, we proposed a discussion about suitability of D-InSAR measurements method for long term rockglaciers monitoring as well as drawbacks and benefits of the method.

In Canada’s western Arctic, perennial discharge from permafrost watersheds is the surface manifestation of active groundwater flow systems, yet understanding the mechanisms of groundwater recharge and flow in periglacial environments remains enigmatic. This thesis addresses questions on how and where groundwater recharge occurs. Watersheds were selected in Yukon (Fishing Branch River at Bear Cave Mountain) and the Northwest Territories at latitudes spanning from continuous to discontinuous permafrost (five tributary rivers to the Mackenzie River from Wrigley to Aklavik). All are characterized by perennial flow with open water in the winter, and discharge from sedimentary formations of karstic carbonates and evaporate rocks. Determinations of groundwater contributions to discharge, mixing, recharge conditions and circulation times were made on the basis of a suite of analytical approaches involving measurements of major dissolved ions, δ18O, δD, δ13CDIC, 3H, noble gases and flow gauging was conducted at some sites. The application of these tracers show that hydrogeological conditions and flow paths in permafrost terrains are surprisingly similar to those of temperate regions. Groundwater recharge was determined to be a mix of annual precipitation with contributions from snowmelt and precipitation. All systems investigated show that groundwaters have recharged through organic soils with elevated PCO2, which suggests that recharge occurs largely during summer when biological activity is high. Noble gas concentrations show that the recharge temperature was between 0 and 6 °C, which, when considered in the context of discharge temperatures, suggests that there is no significant imbalance of energy flux into the subsurface. Groundwater ages were found using the 3H-3He method and were dependent on flow path. By characterizing groundwater and surface water chemistry, the proportion of groundwater was found in numerous water courses. The possible impact of ground ice formation and melting on noble gas concentrations in groundwater was considered. To assess this link, a new method to measure the noble gas composition of ground ice bodies was developed. The method can be used to determine the origin of ice, based on changes in noble gas ratios between ice originating from compaction of snow (e.g. glacier ice) vs. ice originating from freezing of water. No significant fractionation of noble gases during groundwater freezing and ground ice formation was identified. Applied to determination of the origin of ground ice bodies, the method was shown to be both diagnostic of ice origin and un-encumbered by reactivity in the subsurface, which compromises the use of the dominant atmospheric gases (O2 and N2).   Résumé Dans l’Ouest de l'Arctique canadien, la décharge pérenne dans certaines rivières en région de pergélisol est la manifestation en surface d’une circulation d’eau souterraine; cependant la compréhension des mécanismes d’écoulement et de recharge des eaux souterraines en région de pergélisol demeure énigmatique. Cette thèse s’intéresse à la question de savoir comment et où la recharge des eaux souterraines se produit. Des bassins versants ont été choisis au Yukon (Rivière Fishing Branch à Bear Cave Mountain) et dans les Territoire du Nord-Ouest à des latitudes s’étendant du pergélisol discontinu au pergélisol continu (cinq tributaires du Mackenzie entre Wrigley et Aklavik). Toutes ces rivières ont un écoulement d’eau pérenne avec des zones non gelées et une décharge dans des formations sédimentaires de roches carbonatées et d‘évaporites. L’identification des contributions des eaux à la décharge, les mélanges, les conditions de recharge, et les temps de circulation ont été faits à partir d’analyses qui ont inclus les concentrations en éléments majeurs, leur valeur isotopique (δ18O, δD, δ13C, 3H), ainsi que leur teneur en gaz rares. A certain des sites analysés des mesures d’écoulement ont été prises. L’application de ces traceurs montre que les conditions hydrauliques et le chemin des écoulements en région de pergélisol sont similaires à ceux des régions tempérées. La recharge en eau souterraine a été identifiée comme étant un mélange de précipitations annuelles, avec des contributions de neige et de pluies. Tous les systèmes étudiés montrent que les eaux souterraines se sont rechargées en traversant des sols organiques avec une PCO2 élevée, ce qui suggère que la recharge se produire largement durant l’été quand l’activité biologique est élevée. Cependant, les concentrations en gaz nobles montre que la température de recharge des eaux souterraines était entre 0 et 6 °C ce qui indique qu’il n’y a pas de déséquilibre de flux d’énergie à l’intérieur de la zone proche de la surface. L’âge des eaux a été déterminé par la méthode 3H-3He et cet âge est dépendant du chemin d'écoulement. En caractérisant les paramètres chimiques des eaux de surface et des eaux souterraines, il a été possible de trouver la contribution des eaux souterraines aux eaux surface. Le possible impact de la formation et de la fonte de la glace souterraine sur les concentrations des gaz nobles a été considéré. Pour déterminer s’il y a un lien entre ceux-ci, une nouvelle méthode pour mesurer la concentration en gaz nobles dans les glaces souterraines a été développée. La méthode peut être utilisée pour déterminer l’origine de la glace; elle est basée sur les changements dans les rapports des gaz nobles entre la glace issue de la compaction de la neige (c’est-à-dire la glace de glacier) par opposition à la glace issue du gel de l’eau. Aucun fractionnement significatif des gaz nobles durant l’engel des eaux souterraines et la formation de glaces souterraines n’a été identifié. Appliquée à l’identification de l’origine des masses de glace enfouies, on a montré que la méthode pouvait permettre d’identifier l’origine des glaces souterraines sans qu’elle soit affectée par des réactions biologiques de sub-surface, lesquelles rendent inutilisables les gaz atmosphériques (O2, and N2).

The Mackenzie Delta region of the Northwest Territories, Canada, has experienced rapid climate warming in the past century resulting in rapidly thawing permafrost in this region. This thesis examines spatial and temporal changes to sediment organic carbon and mercury flux in lakes from thermokarst regions by comparing sediment cores from lakes with and without retrogressive thaw slumps on their shorelines. We show that sediments from lakes with permafrost thaw slump development on their shorelines (slump lakes) had higher sedimentation rates as well as lower total Hg, methyl mercury (MeHg), and labile OC fractions when compared to lakes where thaw slumps were absent. Total Hg and MeHg concentrations in sediments were correlated with total organic carbon (TOC), S2 (labile algal-derived OC), and inferred chlorophyll a content, indicating an association between autochthonous organic carbon and Hg in these sediments. Correlations between mercury and S2 in these study lakes generally support the hypothesis that algal-derived materials correlate with Hg concentration in sediments. We observed higher S2 concentrations in reference lakes than in slump lakes, likely due to uninterrupted algal production, lower dilution by flux of inorganic matter, and possibly better anoxic preservation in reference lakes compared to slump lakes. It is evident that thaw slump development in this thermokarst region increases inorganic sedimentation in lakes, while decreasing concentrations of organic carbon and associated Hg and MeHg in sediments.

Recent studies have shown that permafrost soils in the northern circumpolar region store almost twice as much carbon as the atmosphere. Since soil organic carbon (SOC) pools have large regional and landscape-level variability, detailed SOC inventories from across the northern permafrost region are needed to assess potential remobilization of SOC with permafrost degradation and to quantify the permafrost carbon-climate feedback on global warming. This thesis provides high-resolution data on SOC storage in five study areas located in undersampled regions of the continuous permafrost zone (Zackenberg in NE Greenland; Shalaurovo and Cherskiy in NE Siberia; Ary-Mas and Logata in Taymyr Peninsula). The emphasis throughout the five different study areas is put on SOC partitioning within the landscape and soil horizon levels as well as on soil forming processes under periglacial conditions. Our results indicate large differences in mean SOC 0–100 cm storage among study areas, ranging from 4.8 to 30.0 kg C m-2, highlighting the need to consider numerous factors as topography, geomorphology, land cover, soil texture, soil moisture, etc. in the assessment of landscape-level and regional SOC stock estimates. In the high arctic mountainous area of Zackenberg, the mean SOC storage is low due to the high proportion of bare grounds. The geomorphology based upscaling resulted in a c. 40% lower estimate compared to a land cover based upscaling (4.8 vs 8.3 kg C m-2, respectively). A landform approach provides a better tool for identifying hotspots of SOC burial in the landscape, which in this area corresponds to alluvial fan deposits in the foothills of the mountains. SOC burial by cryoturbation was much more limited and largely restricted to soils in the lower central valley. In the lowland permafrost study areas of Russia the mean SOC 0–100 cm storage ranged from 14.8 to 30.0 kg C m-2. Cryoturbation is the main burial process of SOC, storing on average c. 30% of the total landscape SOC 0–100 cm in deeper C-enriched pockets in all study areas. In Taymyr Peninsula, the mean SOC storage between the Ary-Mas and Logata study areas differed by c. 40% (14.8 vs 20.8 kg C m-2, respectively). We ascribe this mainly to the finer soil texture in the latter study area. Grain size analyses show that cryoturbation is most prominent in silt loam soils with high coarse silt to very fine sand fractions. However, in profiles and samples not affected by C-enrichment, C concentrations and densities were higher in silt loam soils with higher clay to medium silt fractions. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>