Thermokarst and thermal erosion: Degradation of Siberian ice-rich permafrost

Current climate warming is affecting arctic regions at a faster rate than the rest of the world. This has profound effects on permafrost that underlies most of the arctic land area. Permafrost thawing can lead to the liberation of considerable amounts of greenhouse gases as well as to significant changes in the geomorphology, hydrology, and ecology of the corresponding landscapes, which may in turn act as a positive feedback to the climate system. Vast areas of the east Siberian lowlands, which are underlain by permafrost of the Yedoma-type Ice Complex, are particularly sensitive to climate warming because of the high ice content of these permafrost deposits. Thermokarst and thermal erosion are two major types of permafrost degradation in periglacial landscapes. The associated landforms are prominent indicators of climate-induced environmental variations on the regional scale. Thermokarst lakes and basins (alasses) as well as thermo-erosional valleys are widely distributed in the coastal lowlands adjacent to the Laptev Sea. This thesis investigates the spatial distribution and morphometric properties of these degradational features to reconstruct their evolutionary conditions during the Holocene and to deduce information on the potential impact of future permafrost degradation under the projected climate warming. The methodological approach is a combination of remote sensing, geoinformation, and field investigations, which integrates analyses on local to regional spatial scales. Thermokarst and thermal erosion have affected the study region to a great extent. In the Ice Complex area of the Lena River Delta, thermokarst basins cover a much larger area than do present thermokarst lakes on Yedoma uplands (20.0 and 2.2 %, respectively), which indicates that the conditions for large-area thermokarst development were more suitable in the past. This is supported by the reconstruction of the development of an individual alas in the Lena River Delta, which reveals a prolonged phase of high thermokarst activity since the Pleistocene/Holocene transition that created a large and deep basin. After the drainage of the primary thermokarst lake during the mid-Holocene, permafrost aggradation and degradation have occurred in parallel and in shorter alternating stages within the alas, resulting in a complex thermokarst landscape. Though more dynamic than during the first phase, late Holocene thermokarst activity in the alas was not capable of degrading large portions of Pleistocene Ice Complex deposits and substantially altering the Yedoma relief. Further thermokarst development in existing alasses is restricted to thin layers of Holocene ice-rich alas sediments, because the Ice Complex deposits underneath the large primary thermokarst lakes have thawed completely and the underlying deposits are ice-poor fluvial sands. Thermokarst processes on undisturbed Yedoma uplands have the highest impact on the alteration of Ice Complex deposits, but will be limited to smaller areal extents in the future because of the reduced availability of large undisturbed upland surfaces with poor drainage. On Kurungnakh Island in the central Lena River Delta, the area of Yedoma uplands available for future thermokarst development amounts to only 33.7 %. The increasing proximity of newly developing thermokarst lakes on Yedoma uplands to existing degradational features and other topographic lows decreases the possibility for thermokarst lakes to reach large sizes before drainage occurs. Drainage of thermokarst lakes due to thermal erosion is common in the study region, but thermo-erosional valleys also provide water to thermokarst lakes and alasses. Besides these direct hydrological interactions between thermokarst and thermal erosion on the local scale, an interdependence between both processes exists on the regional scale. A regional analysis of extensive networks of thermo-erosional valleys in three lowland regions of the Laptev Sea with a total study area of 5,800 km² found that these features are more common in areas with higher slopes and relief gradients, whereas thermokarst development is more pronounced in flat lowlands with lower relief gradients. The combined results of this thesis highlight the need for comprehensive analyses of both, thermokarst and thermal erosion, in order to assess past and future impacts and feedbacks of the degradation of ice-rich permafrost on hydrology and climate of a certain region

Contribution of Retrogressive Thaw Slumps to the Near Shore Carbon Budget along the Yukon Coast, Canada

The mechanism of carbon dioxide and methane release to the atmosphere in permafrost regions is not solely restricted to the progressive thawing of the upper part of the ground by warmer air temperatures. Organic carbon and nutrients are released to streams, rivers or coasts by abrupt processes such as thermokarst, thermal erosion and simply river bank or coastal erosion. Thermo-erosion, as a mechanism of rapid permafrost thaw, reshapes Arctic coasts and has a clear impact on the mobilization and distribution of carbon and nitrogen in permafrost terrains. Retrogressive thaw slumps are one specific and highly dynamic landform, which results from thermo-erosion of ice-rich permafrost and leads to the displacement of large volumes of sediments. Studies reporting on the occurrence and evolution of retrogressive thaw slumps over the Arctic show that in varied Arctic areas, slumps have increased over the last decades. While the processes responsible for the initiation of retrogressive thaw slumps are well defined, little research has been done on a regional scale to define the terrains on which they occur, and to measure the volumes of sediments eroded through their development. There are currently no estimates of the contribution of these permafrost degradation landforms to the carbon budget, therefore thermo-erosional features are not yet accounted in the carbon models. With this study, we highlight the important contribution of retrogressive thaw slumps to the nearshore carbon cycle in the eastern part of the Beaufort Sea by 1) calculating the amount of sediments eroded through the development of RTSs, 2) estimating the amount of carbon mobilized and potentially transported from the land to the nearshore zone of the Beaufort Sea. We used a large set of high-resolution multispectral satellite images from 2011 (GeoEye-1 and WorldView-2) we manually digitized coastal retrogressive thaw slumps along a 235 km coastline. We gathered additional observations during fieldwork in July and August 2015 on the current development stage of retrogressive thaw slumps and classified them between active and stable. We extrapolated the eroded surfaces using a digital elevation model. Based on available literature on carbon stocks in the area, we estimated the amounts of mobilized particulate organic carbon and nitrogen. This model allowed us to measure the contribution of retrogressive thaw slumps to the near shore carbon budget in the area

Induktion neuer Prodigiosin-derivate in Streptomycescoelicolor M145 durch Kaobaltionen-Stress

Streptomyceten sind für die Produktion diverser Sekundärmetabolite bekannt. Sie besitzen oft eine Vielzahl an Biosyntheseclustern für verschiedene Sekundärmetabolite, deren Transkription stark reguliert ist. Besonders unter ungewöhnlichen Kultivierungsbedingungen kann die Expression „schlafender“ Gencluster erreicht werden, die zur Isolation unbekannter Verbindungen führt und damit großes Potential für die Identifizierung neuer Antibiotika bietet. Bei Kultivierung von S. coelicolor unter Kobaltionen-Stress traten intensiv pigmentierte Phänotypen auf, die verschiedene Sekundärmetabolitenprofile untereinander, aber auch gegenüber dem Wildtyp aufwiesen. Einer dieser Phänotypen war intensiv rot gefärbt und produzierte neben den schon bekannten Verbindungen Undecylprodigiosin und Streptorubin B eine Reihe unbekannter Metabolite. Die Isolierung und Charakterisierung dieser Verbindungen war das Hauptziel dieser Arbeit. Es wurden zwei durch Kobaltionen-Stress neu entstandenen Verbindungen des roten Phänotyps vollständig gereinigt und ihre Struktur mittels 1D- und 2D-NMRSpektroskopie identifiziert. Außerdem konnten zwei nah verwandte Derivate, die vom roten Phänotyp nur in sehr geringen Mengen gebildet und damit nicht isoliert werden konnten, anhand von Tandemmassenspektrometrie identifiziert werden. Die Strukturen wurden anschließend anhand von Fütterungsstudien und durch biomimetische Reaktionen verifiziert. Bei allen isolierten Verbindungen handelt es sich um bisher unbekannte Derivate von Undecylprodigiosin und Streptorubin B, die zusätzliche Undecylpyrrol- oder 4-Methoxy-2,2’-bipyrrol-Einheiten aufweisen. Die Verknüpfung dieser Struktureinheiten erfolgt dabei ausschließlich am Kohlenstoffatom der Methenbrücke der bekannten Prodigiosine, weshalb die neuen Verbindungen in der neuen Strukturklasse der Coeligiosine zusammengefasst werden

Factors Influencing the Spatial and Temporal Occurrence of Thermo-erosional Landforms along the Yukon Coast, Canada

Processes associated with permafrost degradation in the arctic coastal zone are highly dynamic and account for significant amounts of organic carbon released to the Arctic Ocean. Thermo-erosion, as a mechanism of rapid permafrost thaw, reshapes arctic landscapes and has a clear impact on the mobilization and distribution of carbon and nitrogen in permafrost terrains. However, few studies report on the diversity of thermo-erosional landforms or assess the factors involved in their development. This study highlights the diversity of thermo-erosional drainage pathways -- including gullies and valleys -- and specific thermokarst features such as retrogressive thaw slumps and active layer detachments, and determines the prevailing factors accounting for their distribution and driving their expansion over the last 60 years along the Yukon coast. With the software OrthoEngine from PCI Geomatica we used a large set of high resolution satellite images from 2011 (GeoEye-1 and WorldView-2) for geocoding aerial photographs from the 1950s. The aerial photographs come from the National Air Photo Library, Canada. This dataset allowed us to manually digitize and classify thermo-erosional gullies, valleys, retrogressive thaw slumps and active layer detachments for the 1950s and 2011 using ArcGIS 10.3. We gathered additional observations during fieldwork in July and August 2015 on gully and valley morphologies, and on the current development stage of retrogressive thaw slumps. Based on remote sensing, we calculated and compared the surface area occupied by slumps in 1950s and in 2011 as well as the types, number and lengths of thermo-erosional drainage pathways over the same period. We coupled these information with additional datasets related to climate, geology and topography, and performed multivariate statistical analyses using the software R. Over this time span, we observed an important spatial heterogeneity in the landform dynamics among the different geological units. The number and the surface area of retrogressive thaw slumps increased on average. We did not detect a specific increase in the length of thermo-erosional drainage pathways over the whole area, however, in some specific geological units they decreased in length due to important coastal erosion. This dataset will be complemented by soil organic carbon data collected across several thermo-erosional landforms during fieldwork conducted in 2015 in order to understand the processes of carbon mobilization within specific thermo-erosional landforms

Référence et dialogue chez les enfants autistes Asperger

National audienceNous présentons ici les premiers résultats d’une recherche portant sur le maniement de la référence chez des enfants anglophones atteints du syndrome d’Asperger. Ce travail est le résultat d’une rencontre entre deux préoccupations différentes: - Celle de l’équipe de UCLA (Etats-Unis) dirigée par Elinor Ochs et sa collaboratrice Olga Solomon qui ont travaillé sur les enfants autistes et ont rassemblé un très grand corpus sur des enfants autistes de haut niveau et Asperger, en les suivant à l’école (vidéo), dans le trajet entre l’école et la maison (audio) et durant des repas en famille (vidéo).- Celle de notre équipe « prémices dialogiques de l’anaphore » qui travaille sur l’émergence des expressions référentielles et leur valeur anaphorique dans le dialogue. (Salazar Orvig et al. 2006, 2009) Alors qu'ils se distinguent des autres types d'enfant autistes par l'absence de retard dans l'acquisition du langage, les enfants souffrant du syndrome d'Asperger, rencontreraient cependant des difficultés avec le maniement de certains outils linguistiques.. Leur trouble semble surtout lié à des problèmes d’ordre communicationnels, socio-cognitifs et pragmatique (cela se marque par exemple par un usage particulier de la prosodie), un manque d’empathie, un discours plutôt monologique. Ils sont souvent appelés de petits savants. Or l’expression de la référence est au croisement de l’appropriation du système linguistique « formel », de la pragmatique et des compétences socio-cognitives. Le lien entre ces différentes compétences peut être mis au jour de façon différente en travaillant sur des enfants qui ont des particularités dans leur appropriation des usages du langage en dialogue. C'est pourquoi nous nous sommes proposés d’adapter notre grille d’analyse des expressions référentielles dans des interactions adulte-enfant à des interactions avec des enfants autistes Asperger. Plus spécifiquement, comme nous avions mis en évidence des compétences précoces du maniement des pronoms chez de jeunes enfants dont l'inscription dialogique n'est pas perturbée, on pouvait se demander si nous allions constater des usages similaires ou distincts chez les autistes Asperger. En effet on peut se demander pour ces enfants comment se présente en dialogue leur usage d’unités linguistiques qui présupposent des savoir pragmatiques complexes, en particuliers l’évaluation des savoirs des interlocuteurs, du déroulement du dialogue, des références indirectes ou implicites à des savoir partagés

Contribution of Coastal Retrogressive Thaw Slumps to the Nearshore Organic Carbon budget along the Yukon Coast

We describe the evolution of coastal retrogressive thaw slumps (RTSs) between 1952 and 2011 along the Yukon Coast, Canada, and provide the first estimate of the contribution of RTSs to the nearshore organic carbon budget in this area. We 1) monitor the evolution of RTSs during the periods 1952-1972 and 1972-2011; 2) calculate the volume of material eroded and stocks of organic carbon (OC) mobilized through slumping – including soil organic carbon (SOC) and dissolved organic carbon (DOC) – and 3) measure the OC fluxes mobilized through slumping between 1972 and 2011. We identified RTSs using high-resolution satellite imagery from 2011 and geocoded aerial photographs from 1952 and 1972. To estimate the volume of eroded material, we applied a spline interpolation on an airborne LiDAR dataset acquired in July 2013. We inferred the stocks of mobilized SOC and DOC from existing related literature. Our results show a 73% increase in the number of RTSs between 1952 and 2011. In the study area, RTSs displaced at least 8600*103 m^3 of material, with 53% of ice. We estimated that slumping mobilized 81900*10^3 kg of SOC and 156*10^3 kg of DOC. Since 1972, 17% of the RTSs have displaced 8.6*103 m^3/yr of material, with an average OC flux of 82.5*10^3 kg/yr. This flux represents 0.3% of the OC flux released from coastal retreat; however RTSs have a strong impact on the transformation of OC in the coastal fringe

Characteristics and recent dynamics of thermo-erosional features in small catchments of Arctic Siberia

Thermal erosion is a prominent type of permafrost degradation that can lead to rapid changes in ice-rich permafrost landscapes. The process and its resulting landforms such as thermo-erosional gullies are reported to become increasingly active and widespread. (Re-)Activation of thermal erosion impacts the hydrological regime of affected landscapes and alters the biogeochemical composition of associated surface waters. Our study aims at assessing current rates and mechanisms of thermal erosion in small ice-rich permafrost catchments of Arctic Siberia. We investigated thermoerosional features in three different areas in and around the Lena River Delta that represent differing geomorphological, lithological and geocryological settings. We used a combination of field measurements, remote sensing methods including tacheometry, DGPS, and UAV surveys and subsequent GIS analyses to 1) quantify the morphometry of thermo-erosional landforms, 2) quantify the spatial extent of current thermo-erosional activity, and 3) quantify areal changes in activation and stabilization of thermal erosion over recent years to decades. Further data on snow depth and distribution in the gullies and valleys as well as hydrological and hydrochemical data of the associated streams aided the interpretation of observed spatial differences in thermal erosion rates and the development of active versus stabilized zones as well as their impacts on headwaters

Where and Why Do Coastal Retrogressive Thaw Slumps Develop?

Retrogressive thaw slumps (RTSs) are among the most active landforms in the Arctic; their number has increased tremendously over the past decades. While processes initiating discrete RTSs are well defined, little research has been done on a regional scale to reveal the major terrain controls on their development. Our research provides new insights into the dynamics of coastal RTSs. We reveal the main geomorphic factors determining the development of RTSs along a 238 km coastal segment of the Yukon Coastal Plain, Canada. We 1) show the current extent of RTSs, 2) ascertain the factors controlling their activity and initiation, and 3) explain the differences in density and coverage of RTSs. We mapped and classified the RTSs based on high-resolution satellite images acquired in 2011. We derived the terrain characteristics for each RTS and highlighted the main terrain controls over their development using univariate regression trees. We tested the response variables (RTSs activity, initiation, density and coverage) against 16 environmental variables. We detected 287 coastal RTSs in the study area. Both the activity and the initiation of the RTSs were influenced by coastal geomorphology: active RTSs and new RTSs occurred primarily on terrain with slope angles greater than 3.9° and 5.9°, respectively. The density and coverage of RTSs within each coastal segment were constrained by the volume and thickness of massive ice bodies. Coastal erosion appears to have only an indirect effect on the development of RTSs by maintaining the best conditions for RTSs to reactivate

A high honour awarded to permafrost scientists for their contribution to Russian-German cooperation in Arctic research

Dr. Mikhail Nikolaevich Grigoriev, Deputy Director of the Melnikov Permafrost Institute SB RAS (Yakutsk, Russia) and Prof. Hans-Wolfgang Hubberten, former director of the Potsdam Unit of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (Potsdam, Germany) were awarded the Order of Merit of the Federal Republic of Germany in recognition of their outstanding contributions to the development of Russian-German cooperation in Arctic research. The ceremony of bestowal took place in the MPI’s conference hall in Yakutsk on October 6, 2021

Detection of viral sequence fragments of HIV-1 subfamilies yet unknown

<p>Abstract</p> <p>Background</p> <p>Methods of determining whether or not any particular HIV-1 sequence stems - completely or in part - from some unknown HIV-1 subtype are important for the design of vaccines and molecular detection systems, as well as for epidemiological monitoring. Nevertheless, a single algorithm only, the Branching Index (BI), has been developed for this task so far. Moving along the genome of a query sequence in a sliding window, the BI computes a ratio quantifying how closely the query sequence clusters with a subtype clade. In its current version, however, the BI does not provide predicted boundaries of unknown fragments.</p> <p>Results</p> <p>We have developed <it>Unknown Subtype Finder </it>(USF), an algorithm based on a probabilistic model, which automatically determines which parts of an input sequence originate from a subtype yet unknown. The underlying model is based on a simple profile hidden Markov model (pHMM) for each <it>known </it>subtype and an additional pHMM for an <it>unknown </it>subtype. The emission probabilities of the latter are estimated using the emission frequencies of the known subtypes by means of a (position-wise) probabilistic model for the emergence of new subtypes. We have applied USF to SIV and HIV-1 sequences formerly classified as having emerged from an unknown subtype. Moreover, we have evaluated its performance on artificial HIV-1 recombinants and non-recombinant HIV-1 sequences. The results have been compared with the corresponding results of the BI.</p> <p>Conclusions</p> <p>Our results demonstrate that USF is suitable for detecting segments in HIV-1 sequences stemming from yet unknown subtypes. Comparing USF with the BI shows that our algorithm performs as good as the BI or better.</p