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The distribution of mountain permafrost is generally modeled using a combination of statistical techniques and empirical variables. Such models, based on topographic, climatic and geomorphological predictors of permafrost, have been widely used to estimate the spatial distribution of mountain permafrost in North America and Europe. However at present, little knowledge about the distribution and characteristics of mountain permafrost is available for the Andes. In addition, the effects of climate change on slope stability and the hydrological system, and the pressure of mining activities have increased concerns about the knowledge of mountain permafrost in the Andes. In order to model permafrost distribution in the semi-arid Chilean Andes between ~29°S and 32°S, an inventory of rock glaciers is carried out to obtain a variable indicative of the presence and absence of permafrost conditions. Then a Linear Mixed-Effects Model (LMEM) is used to determine the spatial distribution of Mean Annual Air Temperature (MAATs), which is then used as one of the predictors of permafrost occurrence. Later, a Generalized Additive Model (GAM) with a logistic link function is used to predict permafrost occurrence in debris surfaces within the study area. Within the study area, 3575 rock glaciers were inventoried. Of these, 1075 were classified as active, 493 as inactive, 343 as intact and 1664 as relict forms, based on visual interpretation of satellite imagery. Many of the rock glaciers (~60-80%) are situated at positive MAAT, and the number of rock glaciers at negative MAAT greatly decreases from north to south. The results of spatial temperature distribution modeling indicated that the temperature changes by -0.71°C per each 100 m increase in altitude, and that there is a 4°C temperature difference between the northern and southern part of the study area. The altitudinal position of the 0°C MAAT isotherm is situated at ~4250 m a.s.l. in the northern (29°S) section and drops latitudinally to ~4000 m a.s.l. in the southern section (32°S) of the study area. For permafrost modeling purposes, 1911 rock glaciers (active, inactive and intact forms) were categorized into the class indicative of permafrost presence and 1664 (relict forms) as non-permafrost. The predictors MAAT and Potential Incoming Solar Radiation (PISR) and their nonlinear interaction were modeled by the GAM using LOESS smoothing function. A temperature offset term was applied to reduce the overestimation of permafrost occurrence in debris surface areas due to the use of rock glaciers as permafrost proxies. The dependency between the predictor variables shows that a high amount of PISR has a greater effect at positive MAAT levels than in negative ones. The GAM for permafrost distribution achieved an acceptable discrimination capability between permafrost classes (area under the ROC curve ~0.76). Considering a permafrost probability score (PPS) ≥ 0.5 and excluding steep bedrock and glacier surfaces, mountain permafrost can be potentially present in up to about 6.8% (2636 km2) of the study area, whereas with a PPS ≥ 0.75, the potential permafrost area decreases to 2.7% (1051 km2). Areas with the highest PPS are spatially concentrated in the north section of the study area where altitude rises considerably (the Huasco and Elqui watersheds), while permafrost is almost absent in the southern section where the topography is considerably lower (Limarí and Choapa watersheds). This research shows that the potential mountain permafrost distribution can be spatially modeled using topoclimatic information and rock glacier inventories. Furthermore, the results have provided the first local estimation of permafrost distribution in the semi-arid Chilean Andes. The results obtained can be used for local environmental planning and to aid future research in periglacial topics.

Permafrost is a variable in Antarctic terrestrial ecosystems, and the role it plays in the cryosphere is not well understood. There is much still to be learnt about the thermal state, physical properties, thickness and age of permafrost in Western Dronning Maud Land (WDML). Active layer dynamics and observed change over time have the potential to improve our knowledge of climate change. Understanding the effects of a warming climate on permafrost can also be of benefit to infrastructure, especially in areas with a large amount of frozen ground such as Scandinavia, Canada and Russia. Active layer and permafrost dynamics of WDML, Antarctica, are presented and discussed using data from six study sites, namely the Robertskollen, Vesleskarvet, Flarjuven, Grunehogna, Slettjfell nunataks and the Troll research station in the Jutulsessen area. Ground and ambient air temperature, as well as ground moisture data were collected for each site. An inventory of active layer and permafrost landforms was compiled, as were the frequency of cycles over the zero-degree isotherm, and the depth of the active layer. Furthermore, 3D models, geo-referenced maps and Digital Elevation Models were created of study areas with the use of an Unmanned Aerial Vehicle (UAV). Polygonal features are the most common landscape feature and are common to most of the study sites. Robertskollen has the deepest active layer at over 66cm and Slettfjell the shallowest at 9cm. A maximum recorded air temperature of 8.76°C (10/11/2014) occurred at Troll with the second highest maximum of 6.77°C (22/12/2010) recorded at Vesleskarvet. Robertskollen has the highest observable biological growth and a maximum recorded ground temperature of 22.84°C (10/01/2014). Troll and Valterkulten, registered the second and third highest ground temperatures respectively. The high ground Temperature observed for Robertskollen may be ascribed to it being the lowest altitude site. The highest number of cycles over the zero-degree isotherm was observed at Troll (11.01%), followed by Robertskollen (10.99%). For relatively warm areas, such as Robertskollen it is recommended that two metre borehole loggers are installed in order to capture a detailed understanding of the active layer. The UAV proved to be a beneficial tool for capturing aerial photographs for post fieldwork analysis and 3D modelling.

Permafrost ist ein Bestandteil der Kryosphäre der Erde, der für Ökosysteme und Infrastruktur in der Arktis von Bedeutung ist und auch eine Schlüsselrolle im globalen Kohlenstoffkreislauf einnimmt. Das Auftauen von Permafrost infolge einer Klimaerwärmung zu projizieren ist mit sehr großen Unsicherheiten behaftet, da großskalige Klimamodelle entscheidende Komplexitäten von Permafrostlandschaften nicht berücksichtigen. Insbesondere bleiben in diesen Modellen Auftauprozesse in eisreichem Permafrost unberücksichtigt, welche weitreichende Landschaftsveränderungen – sogenannter Thermokarst – hervorrufen. Im Rahmen dieser Dissertation habe ich ein numerisches Modell entwickelt, um Auftauprozesse in eisreichen Permafrostlandschaften zu untersuchen, und habe es angewendet, um verbesserte Projektionen darüber zu erhalten, wie viel Permafrost infolge einer Klimaerwärmung auftauen würde. Der Schwerpunkt meiner Forschung lag auf besonders kalten, eis- und kohlenstoffreichen Permafrostablagerungen in der nordostsibirischen Arktis. In drei Forschungsartikeln habe ich gezeigt, dass der neuartige Modellierungsansatz in From von lateral gekoppelten “Kacheln” verwendet werden kann, um die Entwicklung von eisreichen Permafrostlandschaften realistisch zu simulieren. Anhand numerischer Simulationen habe ich gezeigt, dass der kleinskalige laterale Transport von Wärme, Wasser, Schnee und Sediment die Dynamik von Permafrostlandschaften sowie die Menge des aufgetauten Permafrosts unter Klimaerwärmungsszenarien entscheidend beeinflusst. Weiterhin habe ich gezeigt, dass in Simulationen, die Thermokarstprozesse berücksichtigen, wesentlich mehr Kohlenstoff vom Auftauen des Permafrosts betroffen ist, als in solchen, in denen eisreiche Ablagerungen unberücksichtigt bleiben. Insgesamt stellt die in dieser Dissertation dargelegte Forschungsarbeit einen substantiellen Fortschritt bezüglich einer realistischeren Einschätzung der Dynamik eisreicher Permafrostlandschaften mittels numerischer Modelle dar. / Permafrost is a component of Earth's cryosphere which is of importance for ecosystems and infrastructure in the Arctic, and plays a key role in the global carbon cycle. Large-scale climate models reveal high uncertainties in projections of how much permafrost would thaw in response to climate warming scenarios, since they do not represent key complexities of permafrost environments. In particular, large-scale models do not take into account thaw processes in ice-rich permafrost which cause widespread landscape change referred to as thermokarst. For this thesis, I have developed a numerical model to investigate thaw processes in ice-rich permafrost landscapes, and I have used it to obtain improved projections of how much permafrost would thaw in response to climate warming. The focus of my research was on cold, ice- and carbon-rich permafrost deposits in the northeast Siberian Arctic, and on landscapes characterized by ice-wedge polygons. In three closely interrelated research articles, I have demonstrated that the novel modelling approach of laterally coupled ''tiles'' can be used to realistically simulate the evolution of ice-rich permafrost landscapes. The numerical simulations have revealed that small-scale lateral transport of heat, water, snow, and sediment crucially affect the dynamics of permafrost landscapes and how much permafrost would thaw under climate warming scenarios. My research revealed that substantially more permafrost carbon is affected by thaw in numerical simulations which take into account thermokarst processes, than in simulations which lack a representation of excess ice. These results suggest that conventional large-scale models used for future climate projections might considerably underestimate permafrost thaw and associated carbon-cycle feedbacks. Overall, the research presented in this thesis constitutes a major progress towards the realistic assessment of ice-rich permafrost landscape dynamics using numerical models.

Boreale Wälder in Permafrostregionen sind ein wesentlicher Bestandteil regionaler und globaler Klimamuster und machen etwa ein Drittel der weltweiten Waldfläche aus. Die Entwicklung der Waldbedeckung hat einen wichtigen Einfluss auf den Permafrost, da dieser durch die Vegetation geschützt wird. Der direkte Einfluss des Klimawandels auf die Wälder und der indirekte Effekt durch eine Veränderung der Permafrostdynamik können zu weitreichenden Ökosystemverschiebungen führen, die wiederum die Persistenz des Permafrosts beeinträchtigen und wichtige Ökosystemfunktionen destabilisieren könnten. Ziel dieser Dissertation ist es zu verstehen, wie sich die komplexen Wechselwirkungen zwischen der Vegetation, dem Permafrost und der Atmosphäre auf die Wälder und den darunterliegenden Permafrost auswirken. Im Rahmen dieser Dissertation habe ich ein eindimensionales, numerisches Landoberflächenmodell (CryoGrid), das zur Simulation der physikalischen Prozesse in Permafrostgebieten verwendet werden kann, für die Anwendung in bewaldetem Gebieten angepasst. Dazu habe ich ein detailliertes, mehrschichtiges Kronendachmodell (CLM-ml v0) und ein dynamisches Lärchenbestandsmodell gekoppelt. Dies ermöglichte den Energietransfer und das Wärmeregime welche für die komplexe Wald-Permafrost-Dynamik verantwortlich sind an verschiedenen Untersuchungsstandorten in gemischten und lärchendominierten Wäldern in Ostsibirien zu reproduzieren. Die numerischen Simulationen ergaben, dass die Wälder den thermischen und hydrologischen Zustand des Permafrosts hauptsächlich durch die Veränderung der Strahlungsbilanz und der Phänologie der Schneedecke beeinflussen und so eine stabilisierende Wirkung haben. Die Untersuchung der unterschiedlichen isolierenden Wirkung verschiedener Waldtypen und Walddichten sowie die Rückkopplungsmechanismen nach Störungen zeigen Veränderungen der thermischen und hydrologischen Bedingungen und der Tiefe der Auftauschicht. Zusammenfassend legen die Ergebnisse nahe, dass lokale, detaillierte und spezifische Landoberflächenmodelle erforderlich sind, um die komplexe Dynamik in borealen Permafrostökosystemen vollständig zu erfassen. Veränderungen der Rückkopplungen zwischen Permafrost, Klima, Wald und Störungen werden die eng gekoppelten Ökosystemfunktionen destabilisieren. Die induzierten Bodenveränderungen werden sich auf wichtige Wald- und Permafrostfunktionen, wie beispielsweise die Isolation des Permafrostbodens oder die Kohlenstoffspeicherung, und Rückkopplungsmechanismen wie Überschwemmung, Dürren, Brände, und Waldverlust, auswirken. / Boreal forests in permafrost regions make up around one-third of the global forest cover and are an essential component of regional and global climate patterns. The forests efficiently protect the underlying permafrost but the exact processes are not well understood. The direct influence of climatic change on forests and the indirect effect through a change in permafrost dynamics can lead to extensive ecosystem shifts, which will, in turn, affect permafrost persistence and potentially destabilize various ecosystem functions. The aim of this dissertation is to understand how complex interactions between the vegetation, permafrost, and the atmosphere stabilize the forests and the underlying permafrost. Within this dissertation, I have adapted a one-dimensional, numerical land surface model (CryoGrid), which can be used to simulate the physical processes in permafrost regions, for the application in vegetated areas by coupling a detailed multilayer canopy model (CLM-ml v0), and a dynamic larch stand model. An intensive validation of the model setup has allowed for the precise quantification of the heat- and water transfer processes responsible for the complex permafrost dynamics under boreal forest covers. At a variety of study sites throughout eastern Siberia, the numerical simulations revealed that the forests exert a strong control on the thermal and hydrological state of permafrost through changing the radiation balance and snow cover phenology. The forest cover has a net stabilizing effect on the permafrost ground below. The detailed physical model has furthermore enabled me to study the variation in insulation effect between different forest types and densities as well as the feedback mechanisms occurring after disturbances. In summary, the results suggest that local, detailed, and specific land surface models are required to fully comprehend the complex dynamics in boreal permafrost ecosystems. The research revealed that the feedbacks between permafrost, climate, boreal forest, and disturbances will destabilize tightly coupled ecosystem functions. The induced changes will affect key forest and permafrost functions, such as the forest's insulation capacity or the carbon budget, as well as feedback mechanisms like swamping, droughts, fires, or forest loss.

The urgent ongoing contemporary climate change is drastically changing the Earth as we know it. In the Arctic, the climate is changing more drastically than the global average, and temperatures are rising significantly more. The phenomenon, known as Arctic amplification, is believed to happen by a combination of albedo reduction, cloud-feedback, and temperature inversion. Another important, but often overlooked, factor in Arctic climate change is dust. Dust does not only cause albedo reduction but has also been found to host syngenetic permafrost in Adventdalen, Svalbard. As permafrost is both a sensitive and important carbon reserve, holding twice as much carbon as currently available in the atmosphere, it is of great importance to understand the carbon storage mechanism of it. This study shows not only a correlation between cryostructures and organic carbon content but presents aeolian sedimentation rate as a possible cause of it. The results show that for syngenetic permafrost in Adventdalen, a high sedimentation rate yields structureless permafrost with low organic content. Inversely, a low sedimentation rate yields well defined cryostructures with high organic content. This shows that aeolian dust activity and loess deposits are vital to understand, in order to properly assess the cryostratigraphy and carbon content. / Den brådskande samtida klimatförändringen omarbetar dramatiskt vår värld. Arktis klimat förändras mer drastiskt än på resten av jorden och temperaturen stiger avsevärt snabbare. Fenomenet kallas förArktis förstärkning, eller Arctic Amplification, och antas ske på grund av synergier mellan minskning av albedo, molnfeedback och temperaturinversion. Damm är en annan viktig, men ofta underskattad faktor i klimatförändrarna i Arktis. Damm bidrar inte bara till en ökad reduktion av albedo utan dammavlagringar i Adventdalen Svalbard fungerar som en viktig grogrund för syngenetisk permafrost. Kolsänkan i permafrost är lika skör som den är viktig, då permafrost förvarar dubbelt så mycket kol som för nuvarande finns i atmosfären, men samtidigt stadigt tinar. Därför är det ytterst viktigt att förstå hur permafrost fungerar, själva mekanismerna bakom förvarandet av organisk kol. Detta arbete visar inte bara ett samband mellan kryostrukturer och organiskt kol i permafrost, utan föreslår att sedimentationshastighet är orsaken till det. Resultaten av LOI (loss on ignition) och kryostratigrafi tyder på att en hög sedimentationshastighet skapar en strukturlös permafrost som endast har låga halter av organisk materia. I det omvända fallet ger en låg sedimentationshastighet välformade kryostrukturer, och en permafrost med hög andel organisk materia. Detta visar på att sedimentationshastighet i loess är en viktig aspekt för att bedöma lagring av kol i permafrost, vilket är en avsevärd kolsänka att förstå i dagens klimatförändringar.

Large amounts of carbon are stored in soils of the northern circumpolar permafrost region. High-resolution mapping of this soil organic carbon (SOC) is important to better understand and predict local to global scale carbon dynamics. In this thesis, studies from five different areas across the permafrost region indicate a pattern of generally higher SOC storage in Arctic tundra soils compared to forested sub-Arctic or Boreal taiga soils. However, much of the SOC stored in the top meter of tundra soils is permanently frozen, while the annually thawing active layer is deeper in taiga soils and more SOC may be available for turnover to ecosystem processes. The results show that significantly more carbon is stored in soils compared to vegetation, even in fully forested taiga ecosystems. This indicates that over longer timescales, the SOC potentially released from thawing permafrost cannot be offset by a greening of the Arctic. For all study areas, the SOC distribution is strongly influenced by the geomorphology, i.e. periglacial landforms and processes, at different spatial scales. These span from the cryoturbation of soil horizons, to the formation of palsas, peat plateaus and different generations of ice-wedges, to thermokarst creating kilometer scale macro environments. In study areas that have not been affected by Pleistocene glaciation, SOC distribution is highly influenced by the occurrence of ice-rich and relief-forming Yedoma deposits. This thesis investigates the use of thematic maps from highly resolved satellite imagery (&lt;6.5 m resolution). These maps reveal important information on the local distribution and variability of SOC, but their creation requires advanced classification methods including an object-based approach, modern classifiers and data-fusion. The results of statistical analyses show a clear link of land cover and geomorphology with SOC storage. Peat-formation and cryoturbation are identified as two major mechanisms to accumulate SOC. As an alternative to thematic maps, this thesis demonstrates the advantages of digital soil mapping of SOC in permafrost areas using machine-learning methods, such as support vector machines, artificial neural networks and random forests. Overall, high-resolution satellite imagery and robust spatial prediction methods allow detailed maps of SOC. This thesis significantly increases the amount of soil pedons available for the individual study areas. Yet, this information is still the limiting factor to better understand the SOC distribution in permafrost environments at local and circumpolar scale. Soil pedon information for SOC quantification should at least distinguish the surface organic layer, the mineral subsoil in the active layer compared to the permafrost and further into organic rich cryoturbated and buried soil horizons. / <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>

L’hydrologie, la géochimie et la météorologie du petit bassin versant glaciaire à pergélisol continu du glacier Austre Lovén (10 km2, Spitsberg occidental, 79°N) ont été étudiées au cours des trois années hydrologiques 2010, 2011 et 2012 en vue de mieux définir le rôle des eaux souterraines de la nappe supra-pergélisol dans les flux d’eau et de solutés en sortie de bassin.Le travail de thèse a montré que la période d’écoulement survient en moyenne sur une période de 141 jours (σ = 4,5 jours) comprise entre les 9-10 mai et 26-27 octobre. La lame d’eau moyenne est de 0,940 m.a-1 (σ = 0,156 m.a-1) et se répartie à 79 % en eau de fonte (54 % de fonte de neige et de glace sur le glacier, 18 % de neige sur les versants et 7 % de neige dans la zone proglaciaire), 18 % en hauteurs de précipitation efficace et 3 % en décharge sous-glaciaire pérenne. Les incertitudes sur la quantification des composantes de l’écoulement et de la lame d’eau écoulée elle-même ne permettent pas une quantification plus précise des flux en eau de la nappe supra-pergélisol. Cette étude montrerait donc qu’en termes de flux d’eau, la composante d’eau souterraine supra-pergélisol pourrait être négligeable et ne constituer qu’un réservoir de transit de l’eau. En effet, le suivi piézométrique montre que la nappe dégèle et regèle à des profondeurs similaires malgré la présence d’épisodes de recharge. Ces recharges qui surviennent majoritairement au profit d’épisodes pluvieux importants (hauteurs cumulées sur 2 à 8 jours supérieures à 20 mm) se déchargent lentement par une alimentation de la rivière par la nappe. Les suivis thermiques du sous-sol ont enfin permis d’établir que le toit du pergélisol supposé se situe à une profondeur de 2,50 m pour une puissance de nappe pouvant atteindre plus d’1,70 m, soit 70 % de la couche active. Par ailleurs, les données thermiques montrent des températures du sous-sol à moins de 0,5°C de la température de dégel, laissant supposer une dégradation prochaine du pergélisol avec par conséquent un accroissement de l’épaisseur de l’aquifère de la nappe supra-pergélisol (couche active).Les données de géochimie montrent une augmentation de la minéralisation des eaux de surface du bassin par des contributions d’eau souterraine le long des cours d’eau, preuve que les eaux de la nappe supra-pergélisol impactent les flux de solutés aux exutoires. Les analyses en chimie élémentaire (n = 178) conduites sur les différents composants du système hydrologique montrent que les eaux du bassin possèdent un faciès sulfaté-bicarbonaté calcique à bicarbonaté-sulfaté calcique lié à l’altération des carbonates et des sulfures des moraines récentes et dans l’altération d’aluminosilicates dans les moraines plus anciennes. Les données d’isotopie du strontium (⁸⁷Sr/⁸⁶Sr  ; n = 8) corroborent un apport du calcium dissous par les aluminosilicates de par leur signature radiogénique. Les teneurs en ¹³C du CID des eaux (n = 30) sont cohérentes aussi bien avec un système ouvert sur le CO₂ du sol (à -20 ‰) et le CO₂ atmosphérique (entre -6,5 et -8 ‰) qu’avec un système fermé sur le CO₂ où la signature de δ ¹³C des carbonates marins (à 0 ‰) peut s’imposer par dissolution. Les données d’isotopie de la molécule d’eau (n = 592) ont permis d’identifier les signatures des différentes familles d’eau composant l’hydrosystème et de proposer un modèle de mélange entre 4 pôles expliquant les signatures des eaux aux exutoires du bassin versant : eaux de fonte, précipitations estivales, eaux sous-glaciaires et eaux de la nappe supra-pergélisol. Le couplage entre les teneurs en ¹⁸O et SO²₄⁻ des eaux aux exutoires confirme ce modèle de mélange, le renforçant même en termes de variations temporelles. La mesure de ³H-³He tendrait vers un temps de séjour court tandis que les premières mesures d’activité ¹⁴C (n = 15) sont faibles, renseignant une minéralisation des eaux par un carbone ancien. / The hydrology, geochemistry and meteorology of a small, Arctic glacial watershed under continuous permafrost conditions (Austre Lovén glacier catchment area of 10 km2, western Spitsbergen, 79°N) were studied during the three hydrological years 2010, 2011 and 2012 to better define the role of suprapermafrost groundwater on both water and solute fluxes at basin outlet. The runoff period occurs on average over a 141 days period (σ = 4.5 days) between May 9-10 and October 26-27. The mean total discharge is 0.940 m a-1 (σ = 0.156 m a-1) divided into 79 % of meltwater (54 % of snowmelt and icemelt from the glacier, 18 % of snowmelt from the slopes and 7 % of snowmelt from the proglacial area), 18 % of effective summer precipitation and 3% of perennial subglacial discharge. Uncertainties in quantifying the runoff components and the total discharge itself don’t allow more precise quantification of water fluxes from the suprapermafrost groundwater by water balance. This study would so show that the suprapermafrost groundwater component would be negligible in the water balance and only constitute a transit tank for water. Indeed, the potentiometric level monitoring shows that the water-table thaws and freezes at similar depths despite recharge events occurring during summer. Those recharge events mainly occur in favor of important rain events (cumulative amounts on 2 to 8 days higher that 20 mm). The water-table discharges towards rivers. The monitoring of ground temperature indicates that the frozen ground (supposed permafrost) top is located at a maximum depth of 2.50 m for a groundwater thickness reaching up to 1.70 m, or 70 % of the active layer. Thermal data show ground temperatures between 0 and - 0.5°C, close to thaw temperature, which let suppose a permafrost degradation between 2.50 and 3.40 m deep is about to occur due to climate warming. Consequently, the suprapermafrost groundwater aquifer (active layer) is expected to thicken. Geochemical data show an increase of the basin surface water mineralization by groundwater contribution along the rivers, proof of a suprapermafrost groundwater impact on the solutes fluxes at the outlets. Elementary chemical analyses (n = 178) performed on the different components of the hydrological system show that basin waters have a sulfate-bicarbonate calcium to bicarbonate-sulfate calcium type linked to carbonates dissolution and sulfides (pyrite) oxydation in the recent moraines and to aluminosilicates weathering in older moraines. Strontium isotopic data (87Sr/86Sr; n = 8) are consistent with a contribution in dissolved calcium from aluminosilicates according to their radiogenic signature. The ¹³C contents of water DIC (n = 30) are consistent just as well with a system open on the soil CO₂ (at -20 ‰) and the atmospheric CO₂ (between -6.5 et -8 ‰) than with a system closed on the CO₂ where the δ ¹³C of marine carbonates (at 0 ‰) control the δ ¹³C signature by dissolution. Isotopic data of the water molecule (n = 592) are helpful to separate the signatures of the different water masses of the hydrosystem and to propose a 4 end-members mixing model explaining the river water signature: meltwaters, summer precipitations, subglacial water and suprapermafrost groundwater. The coupling between river water contents in ¹⁸O and SO²₄⁻ confirms this mixing model, even reinforcing it in terms of temporal variations. The unique measurement of ³H-³He tends to a short residence time while the first ¹⁴C activity data (n = 15) are low, giving a water mineralization by an old carbon.

L’océan Arctique, particulièrement sensible au changement climatique, a vu lors des dernières décennies une augmentation de sa température deux fois supérieure à la moyenne mondiale. Certains scientifiques prévoient la disparition complète de la banquise pour 2050. Du fait de la future disparition des algues de glace et de l’augmentation de la fonte du pergélisol, une réévaluation de leurs contributions respectives au stockage de CO2 est nécessaire. Dans cette étude, nous avons ainsi montré que les algues de glace possèdent une forte capacité de préservation dans les sédiments (et donc de stockage du CO2) due à l’incapacité de leurs bactéries à les reminéraliser. A l’inverse, les quantités grandissantes de pergélisol rejetées en mer sont fortement reminéralisables. L’effet conjoint de l’augmentation du rejet de CO2 lors de la dégradation du pergélisol et de la diminution de son stockage par les algues de glace devrait donc contribuer à une amplification du réchauffement climatique. / With a rise in Arctic temperatures almost twice as large as the global average in recent decades, it is at high latitude that the effects of global warming are the most evident. Thus, some scientists have already predicted the complete disappearance of sea ice for 2050. Due to the future disappearance of ice algae and the increase of permafrost thawing, a reassessment of their respective contributions to CO2 storage was required. We have shown that unlike permafrost, ice algae are highly preserved in sediments (allowing CO2 storage) due to the inability of their bacteria to remineralize them. The combined effect of increasing discharge of permafrost by Arctic rivers and decreasing storage of ice algae due to the disappearance of sea ice should thus contribute to increase the global warming.