@phdthesis{Feige2009, author = {Feige, Katharina}, title = {Molecular ecological analysis of methanogenic communities in terrestrial and submarine permafrost deposits of Siberian Laptev Sea area}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-37998}, school = {Universit{\"a}t Potsdam}, year = {2009}, abstract = {Despite general concern that the massive deposits of methane stored under permafrost underground and undersea could be released into the atmosphere due to rising temperatures attributed to global climate change, little is known about the methanogenic microorganisms in permafrost sediments, their role in methane emissions, and their phylogeny. The aim of this thesis was to increase knowledge of uncultivated methanogenic microorganisms in submarine and terrestrial permafrost deposits, their community composition, the role they play with regard to methane emissions, and their phylogeny. It is assumed that methanogenic communities in warmer submarine permafrost may serve as a model to anticipate the response of methanogenic communities in colder terrestrial permafrost to rising temperatures. The compositions of methanogenic communities were examined in terrestrial and submarine permafrost sediment samples. The submarine permafrost studied in this research was 10°C warmer than the terrestrial permafrost. By polymerase chain reaction (PCR), DNA was extracted from each of the samples and analyzed by molecular microbiological methods such as PCR-DGGE, RT-PCR, and cloning. Furthermore, these samples were used for in vitro experiment and FISH. The submarine permafrost analysis of the isotope composition of CH4 suggested a relationship between methane content and in situ active methanogenesis. Furthermore, active methanogenesis was proven using 13C-isotope measurements of methane in submarine permafrost sediment with a high TOC value and a high methane concentration. In the molecular-microbiological studies uncultivated lines of Methanosarcina, Methanomicrobiales, Methanobacteriacea and the Groups 1.3 and Marine Benthic from Crenarchaeota were found in all submarine and terrestrial permafrost samples. Methanosarcina was the dominant group of the Archaea in all submarine and terrestrial permafrost samples. The archaeal community composition, in particular, the methanogenic community composition showed diversity with changes in temperatures. Furthermore, cell count of methanogens in submarine permafrost was 10 times higher than in terrestrial permafrost. In vitro experiments showed that methanogens adapt quickly and well to higher temperatures. If temperatures rise due to climate change, an increase in methanogenic activity can be expected as long as organic material is sufficiently available and qualitatively adequate.}, language = {en} } @phdthesis{FrankFahle2013, author = {Frank-Fahle, B{\´e}atrice A.}, title = {Methane-cycling microbial communities in permafrost affected soils on Herschel Island and the Yukon Coast, Western Canadian Arctic}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-65345}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {Permafrost-affected ecosystems including peat wetlands are among the most obvious regions in which current microbial controls on organic matter decomposition are likely to change as a result of global warming. Wet tundra ecosystems in particular are ideal sites for increased methane production because of the waterlogged, anoxic conditions that prevail in seasonally increasing thawed layers. The following doctoral research project focused on investigating the abundance and distribution of the methane-cycling microbial communities in four different polygons on Herschel Island and the Yukon Coast. Despite the relevance of the Canadian Western Arctic in the global methane budget, the permafrost microbial communities there have thus far remained insufficiently characterized. Through the study of methanogenic and methanotrophic microbial communities involved in the decomposition of permafrost organic matter and their potential reaction to rising environmental temperatures, the overarching goal of the ensuing thesis is to fill the current gap in understanding the fate of the organic carbon currently stored in Artic environments and its implications regarding the methane cycle in permafrost environments. To attain this goal, a multiproxy approach including community fingerprinting analysis, cloning, quantitative PCR and next generation sequencing was used to describe the bacterial and archaeal community present in the active layer of four polygons and to scrutinize the diversity and distribution of methane-cycling microorganisms at different depths. These methods were combined with soil properties analyses in order to identify the main physico-chemical variables shaping these communities. In addition a climate warming simulation experiment was carried-out on intact active layer cores retrieved from Herschel Island in order to investigate the changes in the methane-cycling communities associated with an increase in soil temperature and to help better predict future methane-fluxes from polygonal wet tundra environments in the context of climate change. Results showed that the microbial community found in the water-saturated and carbon-rich polygons on Herschel Island and the Yukon Coast was diverse and showed a similar distribution with depth in all four polygons sampled. Specifically, the methanogenic community identified resembled the communities found in other similar Arctic study sites and showed comparable potential methane production rates, whereas the methane oxidizing bacterial community differed from what has been found so far, being dominated by type-II rather than type-I methanotrophs. After being subjected to strong increases in soil temperature, the active-layer microbial community demonstrated the ability to quickly adapt and as a result shifts in community composition could be observed. These results contribute to the understanding of carbon dynamics in Arctic permafrost regions and allow an assessment of the potential impact of climate change on methane-cycling microbial communities. This thesis constitutes the first in-depth study of methane-cycling communities in the Canadian Western Arctic, striving to advance our understanding of these communities in degrading permafrost environments by establishing an important new observatory in the Circum-Arctic.}, language = {en} } @article{FritzUnkelLenzetal.2018, author = {Fritz, Michael and Unkel, Ingmar and Lenz, Josefine and Gajewski, Konrad and Frenzel, Peter and Paquette, Nathalie and Lantuit, Hugues and K{\"o}rte, Lisa and Wetterich, Sebastian}, title = {Regional environmental change versus local signal preservation in Holocene thermokarst lake sediments}, series = {Journal of paleolimnolog}, volume = {60}, journal = {Journal of paleolimnolog}, number = {1}, publisher = {Springer}, address = {Dordrecht}, issn = {0921-2728}, doi = {10.1007/s10933-018-0025-0}, pages = {77 -- 96}, year = {2018}, abstract = {Thermokarst lakes cover nearly one fourth of ice-rich permafrost lowlands in the Arctic. Sediments from an athalassic subsaline thermokarst lake on Herschel Island (69°36′N; 139°04′W, Canadian Arctic) were used to understand regional changes in climate and in sediment transport, hydrology, nutrient availability and permafrost disturbance. The sediment record spans the last ~ 11,700 years and the basal date is in good agreement with the Holocene onset of thermokarst initiation in the region. Electrical conductivity in pore water continuously decreases, thus indicating desalinization and continuous increase of lake size and water level. The inc/coh ratio of XRF scans provides a high-resolution organic-carbon proxy which correlates with TOC measurements. XRF-derived Mn/Fe ratios indicate aerobic versus anaerobic conditions which moderate the preservation potential of organic matter in lake sediments. The coexistence of marine, brackish and freshwater ostracods and foraminifera is explained by (1) oligohaline to mesohaline water chemistry of the past lake and (2) redeposition of Pleistocene specimens found within upthrusted marine sediments around the lake. Episodes of catchment disturbance are identified when calcareous fossils and allochthonous material were transported into the lake by thermokarst processes such as active-layer detachments, slumping and erosion of ice-rich shores. The pollen record does not show major variations and the pollen-based climate record does not match well with other summer air temperature reconstructions from this region. Local vegetation patterns in small catchments are strongly linked to morphology and sub-surface permafrost conditions rather than to climate. Multidisciplinary studies can identify the onset and life cycle of thermokarst lakes as they play a crucial role in Arctic freshwater ecosystems and in the global carbon cycle of the past, present and future.}, language = {en} } @phdthesis{Grosse2005, author = {Grosse, Guido}, title = {Characterisation and evolution of periglacial landscapes in Northern Siberia during the Late Quaternary : remote sensing and GIS studies}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5544}, school = {Universit{\"a}t Potsdam}, year = {2005}, abstract = {About 24 \% of the land surface in the northern hemisphere are underlayed by permafrost in various states. Permafrost aggradation occurs under special environmental conditions with overall low annual precipitation rates and very low mean annual temperatures. Because the general permafrost occurrence is mainly driven by large-scale climatic conditions, the distribution of permafrost deposits can be considered as an important climate indicator. The region with the most extensive continuous permafrost is Siberia. In northeast Siberia, the ice- and organic-rich permafrost deposits of the Ice Complex are widely distributed. These deposits consist mostly of silty to fine-grained sandy sediments that were accumulated during the Late Pleistocene in an extensive plain on the then subaerial Laptev Sea shelf. One important precondition for the Ice Complex sedimentation was, that the Laptev Sea shelf was not glaciated during the Late Pleistocene, resulting in a mostly continuous accumulation of permafrost sediments for at least this period. This shelf landscape became inundated and eroded in large parts by the Holocene marine transgression after the Last Glacial Maximum. Remnants of this landscape are preserved only in the present day coastal areas. Because the Ice Complex deposits contain a wide variety of palaeo-environmental proxies, it is an excellent palaeo-climate archive for the Late Quaternary in the region. Furthermore, the ice-rich Ice Complex deposits are sensible to climatic change, i.e. climate warming. Because of the large-scale climatic changes at the transition from the Pleistocene to the Holocene, the Ice Complex was subject to extensive thermokarst processes since the Early Holocene. Permafrost deposits are not only an environmental indicator, but also an important climate factor. Tundra wetlands, which have developed in environments with aggrading permafrost, are considered a net sink for carbon, as organic matter is stored in peat or is syn-sedimentary frozen with permafrost aggradation. Contrary, the Holocene thermokarst development resulted in permafrost degradation and thus the release of formerly stored organic carbon. Modern tundra wetlands are also considered an important source for the climate-driving gas methane, originating mainly from microbial activity in the seasonal active layer. Most scenarios for future global climate development predict a strong warming trend especially in the Arctic. Consequently, for the understanding of how permafrost deposits will react and contribute to such scenarios, it is necessary to investigate and evaluate ice-rich permafrost deposits like the widespread Ice Complex as climate indicator and climate factor during the Late Quaternary. Such investigations are a pre-condition for the precise modelling of future developments in permafrost distribution and the influence of permafrost degradation on global climate. The focus of this work, which was conducted within the frame of the multi-disciplinary joint German-Russian research projects "Laptev Sea 2000" (1998-2002) and "Dynamics of Permafrost" (2003-2005), was twofold. First, the possibilities of using remote sensing and terrain modelling techniques for the observation of periglacial landscapes in Northeast Siberia in their present state was evaluated and applied to key sites in the Laptev Sea coastal lowlands. The key sites were situated in the eastern Laptev Sea (Bykovsky Peninsula and Khorogor Valley) and the western Laptev Sea (Cape Mamontovy Klyk region). For this task, techniques using CORONA satellite imagery, Landsat-7 satellite imagery, and digital elevation models were developed for the mapping of periglacial structures, which are especially indicative of permafrost degradation. The major goals were to quantify the extent of permafrost degradation structures and their distribution in the investigated key areas, and to establish techniques, which can be used also for the investigation of other regions with thermokarst occurrence. Geographical information systems were employed for the mapping, the spatial analysis, and the enhancement of classification results by rule-based stratification. The results from the key sites show, that thermokarst, and related processes and structures, completely re-shaped the former accumulation plain to a strongly degraded landscape, which is characterised by extensive deep depressions and erosional remnants of the Late Pleistocene surface. As a results of this rapid process, which in large parts happened within a short period during the Early Holocene, the hydrological and sedimentological regime was completely changed on a large scale. These events resulted also in a release of large amounts of organic carbon. Thermokarst is now the major component in the modern periglacial landscapes in terms of spatial extent, but also in its influence on hydrology, sedimentation and the development of vegetation assemblages. Second, the possibilities of using remote sensing and terrain modelling as a supplementary tool for palaeo-environmental reconstructions in the investigated regions were explored. For this task additionally a comprehensive cryolithological field database was developed for the Bykovsky Peninsula and the Khorogor Valley, which contains previously published data from boreholes, outcrops sections, subsurface samples, and subsurface samples, as well as additional own field data. The period covered by this database is mainly the Late Pleistocene and the Holocene, but also the basal deposits of the sedimentary sequence, interpreted as Pliocene to Early Pleistocene, are contained. Remote sensing was applied for the observation of periglacial strucures, which then were successfully related to distinct landscape development stages or time intervals in the investigation area. Terrain modelling was used for providing a general context of the landscape development. Finally, a scheme was developed describing mainly the Late Quaternary landscape evolution in this area. A major finding was the possibility of connecting periglacial surface structures to distinct landscape development stages, and thus use them as additional palaeo-environmental indicator together with other proxies for area-related palaeo-environmental reconstructions. In the landscape evolution scheme, i.e. of the genesis of the Late Pleistocene Ice Complex and the Holocene thermokarst development, some new aspects are presented in terms of sediment source and general sedimentation conditions. This findings apply also for other sites in the Laptev Sea region.}, subject = {Dauerfrostboden}, language = {en} } @article{HeslopAnthonyGrosseetal.2019, author = {Heslop, J. K. and Anthony, K. M. Walter and Grosse, Guido and Liebner, Susanne and Winkel, Matthias}, title = {Century-scale time since permafrost thaw affects temperature sensitivity of net methane production in thermokarst-lake and talik sediments}, series = {The science of the total environment : an international journal for scientific research into the environment and its relationship with man}, volume = {691}, journal = {The science of the total environment : an international journal for scientific research into the environment and its relationship with man}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0048-9697}, doi = {10.1016/j.scitotenv.2019.06.402}, pages = {124 -- 134}, year = {2019}, abstract = {Permafrost thaw subjects previously frozen soil organic carbon (SOC) to microbial degradation to the greenhouse gases carbon dioxide (CO2) and methane (CH4). Emission of these gases constitutes a positive feedback to climate warming. Among numerous uncertainties in estimating the strength of this permafrost carbon feedback (PCF), two are: (i) how mineralization of permafrost SOC thawed in saturated anaerobic conditions responds to changes in temperature and (ii) how microbial communities and temperature sensitivities change over time since thaw. To address these uncertainties, we utilized a thermokarst-lake sediment core as a natural chronosequence where SOC thawed and incubated in situ under saturated anaerobic conditions for up to 400 years following permafrost thaw. Initial microbial communities were characterized, and sediments were anaerobically incubated in the lab at four temperatures (0 °C, 3 °C, 10 °C, and 25 °C) bracketing those observed in the lake's talik. Net CH4 production in freshly-thawed sediments near the downward-expanding thaw boundary at the base of the talik were most sensitive to warming at the lower incubation temperatures (0 °C to 3 °C), while the overlying sediments which had been thawed for centuries had initial low abundant methanogenic communities (< 0.02\%) and did not experience statistically significant increases in net CH4 production potentials until higher incubation temperatures (10 °C to 25 °C). We propose these observed differences in temperature sensitivities are due to differences in SOM quality and functional microbial community composition that evolve over time; however further research is necessary to better constrain the roles of these factors in determining temperature controls on anaerobic C mineralization.}, language = {en} } @phdthesis{Lantuit2008, author = {Lantuit, Hugues}, title = {The modification of arctic permafrost coastlines}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-19732}, school = {Universit{\"a}t Potsdam}, year = {2008}, abstract = {The arctic region is undergoing the most rapid environmental change experienced on Earth, and the rate of change is expected to increase over the coming decades. Arctic coasts are particularly vulnerable because they lie at the interface between terrestrial systems dominated by permafrost and marine systems dominated by sea ice. An increased rise in sea level and degradation of sea-ice as predicted by the Intergovernmental Panel on Climate Change in its most recent report and as observed recently in the Arctic will likely result in greater rates of coastal retreat. An increase in coastal erosion would result in dramatic increases in the volume of sediment, organic carbon and contaminants to the Arctic Ocean. These in turn have the potential to create dramatic changes in the geochemistry and biodiversity of the nearshore zone and affect the Arctic Ocean carbon cycle. To calculate estimates of organic carbon input from coastal erosion to the Arctic Ocean, current methods rely on the length of the coastline in the form of non self-similar line datasets. This thesis however emphasizes that using shorelines drawn at different scales can induce changes in the amount of sediment released by 30\% in some cases. It proposes a substitute method of computations of erosion based on areas instead of lengths (i.e. buffers instead of shoreline lengths) which can be easily implemented at the circum-Arctic scale. Using this method, variations in quantities of eroded sediment are, on average, 70\% less affected by scale changes and are therefore a more reliable method of calculation. Current estimates of coastal erosion rates in the Arctic are scarce and long-term datasets are a handful, which complicates assessment and prognosis of coastal processes, in particular the occurrence of coastal hazards. This thesis aims at filling the gap by providing the first long-term dataset (1951-2006) of coastal erosion on the Bykovsky Peninsula, North-East Siberia. This study shows that the coastline, which is made of ice-rich permafrost, retreated at a mean annual rate of 0.59 m/yr between 1951and 2006. Rates were highly variable: 97.0 \% of the rates observed were less than 2 m/yr and 81.6\% were less than 1m/yr. However, no significant trend in erosion could be recorded despite the study of five temporal subperiods within 1951-2006. The juxtaposition of wind records could not help to explain erosion records either and this thesis emphasizes the local controls on erosion, in particular the cryostratigraphy, the proximity of the Peninsula to the Lena River Delta freshwater plume and the local topographical constraints on swell development. On ice-rich coastal stretches of the Artic, the interaction of coastal dynamics and permafrost leads to the occurrence of spectacular "C-shaped" depressions termed retrogressive thaw slumps which can reach lengths of up to 650 m. On Herschel Island and at King Point (Yukon Coastal Plain, northern Canada), topographical, sedimentological and biogeochemical surveys were conducted to investigate the present and past activity of these landforms. In particular, undisturbed tundra areas were compared with zones of former slump activity, now stabilized and re-vegetated. This thesis shows that stabilized areas are drier and less prone to plant growth than undisturbed areas and feature fundamentally different geotechnical properties. Radiocarbon dating and topographical surveys indicated until up to 300 BP a likely period of dramatic slump activity on Herschel Island, similar to the one currently observed, which led to the creation of these surfaces. This thesis hypothesizes the occurrence of a ~250 years cycle of slump activity on the Herschel Island shoreline based on the surveyed topography and cryostratigraphy and anticipates higher frequency of slump activity in the future. The variety of processes described in this thesis highlights the changing nature of the intensity and frequency of physical processes acting upon the arctic coast. It also challenges current perceptions of the threats to existing industry and community infrastructure in the Arctic. The increasing presence of humans on Artic coasts coupled with the expected development of shipping will drive an increase in economical and industrial activity on these coasts which remains to be addressed scientifically.}, language = {en} } @article{MasyaginaEvgrafovaBugaenkoetal.2018, author = {Masyagina, Oxana. V. and Evgrafova, S. Yu and Bugaenko, T. N. and Kholodilova, V. V. and Krivobokov, L. and Korets, M. A. and Wagner, Dirk}, title = {Permafrost landslides promote soil CO2 emission and hinder C accumulation}, series = {The science of the total environment : an international journal for scientific research into the environment and its relationship with man}, volume = {657}, journal = {The science of the total environment : an international journal for scientific research into the environment and its relationship with man}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0048-9697}, doi = {10.1016/j.scitotenv.2018.11.468}, pages = {351 -- 364}, year = {2018}, abstract = {Landslides arc common in high-latitude forest ecosystems that have developed on permafrost. The most vulnerable areas in the permafrost territories of Siberia occur on the south-facing slopes of northern rivers, where they arc observed on about 20\% of the total area of river slopes. Landslide disturbances will likely increase with climate change especially due to increasing summer-autumn precipitation. These processes are the most destructive natural disturbance agent and lead to the complete removal of pre-slide forest ecosystems (vegetation cover and soil). To evaluate postsliding ecosystem succession, we undertook integrated ecological research at landslides of different age classes along the Nizhnyaya Tunguska River and the Kochechum River (Tura, Krasnoyarsk region, Russia). Just after the event (at the one-year-old site), we registered a drop in soil respiration, a threefold lower microbial respiration rate, and a fourfold smaller mineral soil carbon and nitrogen stock at bare soil (melkozem) plots at the middle location of the site as compared with the non affected control site. The recovery of disturbed areas began with the re-establishment of plant cover and the following accumulation of an organic soil layer. During the 35-year succession (L1972), the accumulated layer (0 layer)at the oldest site contained similar C- and N stocks to those found at the control sites. However, the mineral soil C- and N stocks and the microbial biomass even of the oldest landslide area- did not reach the value of these parameters in control plots. Later, the soil respiration level and the eco-physiological status of soil microbiota also recovered due to these changes. This study demonstrates that the recovery after landslides in permafrost forests takes several decades. In addition, the degradation of permafrost due to landslides clearly hinders the accumulation of soil organic matter in the mineral soil. (C) 2018 Elsevier B.v. All rights reserved.}, language = {en} } @article{PalagushkinaWetterichBiskabornetal.2017, author = {Palagushkina, Olga and Wetterich, Sebastian and Biskaborn, Boris K. and Nazarova, Larisa B. and Schirrmeister, Lutz and Lenz, Josefine and Schwamborn, Georg and Grosse, Guido}, title = {Diatom records and tephra mineralogy in pingo deposits of Seward Peninsula, Alaska}, series = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, volume = {479}, journal = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0031-0182}, doi = {10.1016/j.palaeo.2017.04.006}, pages = {1 -- 15}, year = {2017}, abstract = {Vast areas of the terrestrial Subarctic and Arctic are underlain by permafrost. Landscape evolution is therefore largely controlled by climate-driven periglacial processes. The response of the frozen ground to late Quaternary warm and cold stages is preserved in permafrost sequences, and deducible by multi-proxy palaeoenvironmental approaches. Here, we analyse radiocarbon-dated mid-Wisconsin Interstadial and Holocene lacustrine deposits preserved in the Kit-1 pingo permafrost sequence combined with water and surface sediment samples from nine modern water bodies on Seward Peninsula (NW Alaska) to reconstruct thermokarst dynamics and determine major abiotic factors that controlled the aquatic ecosystem variability. Our methods comprise taxonomical diatom analyses as well as Detrended Correspondence Analysis (DCA) and Redundancy Analysis (RDA). Our results show, that the fossil diatom record reflects thermokarst lake succession since about 42 C-14 kyr BP. Different thermolcarst lake stages during the mid-Wisconsin Interstadial, the late Wisconsin and the early Holocene are mirrored by changes in diatom abundance, diversity, and ecology. We interpret the taxonomical changes in the fossil diatom assemblages in combination with both modern diatom data from surrounding ponds and existing micropalaeontological, sedimentological and mineralogical data from the pingo sequence. A diatom based quantitative reconstruction of lake water pH indicates changing lake environments during mid-Wisconsin to early Holocene stages. Mineralogical analyses indicate presence of tephra fallout and its impact on fossil diatom communities. Our comparison of modern and fossil diatom communities shows the highest floristic similarity of modern polygon ponds to the corresponding initial (shallow water) development stages of thermolcarst lakes. We conclude, that mid-Wisconsin thermokarst processes in the study area could establish during relatively warm interstadial climate conditions accompanied by increased precipitation due to approaching coasts, while still high continentality and hence high seasonal temperature gradients led to warm summers in the central part of Beringia. (C) 2017 Elsevier B.V. All rights reserved.}, language = {en} } @phdthesis{Ramage2018, author = {Ramage, Justine Lucille}, title = {Impact of Hillslope Thermokarst on the Nearshore Carbon Budget Along the Yukon Coast, Canada}, doi = {10.25932/publishup-42186}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-421867}, school = {Universit{\"a}t Potsdam}, pages = {xvii, 103}, year = {2018}, abstract = {In ice-rich permafrost regions, changes in the permafrost thermal regime cause surface disturbances. These changes are amplified by the increase in air temperatures recorded in the Arctic in the past decades. Thermokarst is a process that leads to surface subsidence and formation of characteristic landforms following thawing of ice-rich permafrost or melting of massive ice. Thermokarst is widespread on hillslopes and the number of associated landforms is increasing in the Arctic. Through this process large amounts of material are eroded and transported to the sea or accumulate along hillslopes. While hillslope thermokarst modifies terrestrial and aquatic ecosystems, there is limited understanding of its environmental impact at a regional scale. In this thesis we quantify the environmental impacts of hillslope thermokarst on the valley and nearshore ecosystems along the Yukon Coast, Canada. Using supervised machine learning, we identified geomorphic factors that favour the development of coastal retrogressive thaw slump (RTS), one of the most dynamic hillslope thermokarst landform. Coastal geomorphology and ground ice type and content play a major role in RTS occurrence. Using aerial photographs and satellite imagery, we traced the evolution of RTSs between 1952 and 2011. During this time, the number and areal coverage of RTSs increased by 73\%. RTSs eroded and partly released to the nearshore zone organic carbon contained in millions of cubic meters of material. Our results show that 56\% of the RTSs identified along the coast in 2011 have eroded 16.6 × 10^6 m3 of material; a large part (45\%) was transported alongshore due to coastal processes. Moreover, we show that RTSs are a major contributor to the carbon budget in the nearshore ecosystem: 17\% of the coastal RTSs identified in 2011 contributed annually up to 0.6\% of the organic carbon released by coastal retreat along the Yukon Coast. To assess the impact of hillslope thermokarst on the terrestrial ecosystem, we measured the spatial distribution of soil organic carbon (SOC) and total nitrogen (TN) along hillslopes in three Arctic valleys. We highlight the high spatial variability in the distribution of SOC and TN in the valleys. This distribution is caused by complex soil processes occurring along the hillslopes. Hillslope thermokarst impacts the degradation of organic matter and affects the storage of SOC and TN.}, language = {de} } @article{SchirrmeisterBobrovRaschkeetal.2018, author = {Schirrmeister, Lutz and Bobrov, Anatoly and Raschke, Elena and Herzschuh, Ulrike and Strauss, Jens and Pestryakova, Luidmila Agafyevna and Wetterich, Sebastian}, title = {Late Holocene ice-wedge polygon dynamics in northeastern Siberian coastal lowlands}, series = {Arctic, antarctic, and alpine research : an interdisciplinary journal}, volume = {50}, journal = {Arctic, antarctic, and alpine research : an interdisciplinary journal}, number = {1}, publisher = {Institute of Arctic and Alpine Research, University of Colorado}, address = {Boulder}, issn = {1523-0430}, doi = {10.1080/15230430.2018.1462595}, pages = {18}, year = {2018}, abstract = {Ice-wedge polygons are common features of northeastern Siberian lowland periglacial tundra landscapes. To deduce the formation and alternation of ice-wedge polygons in the Kolyma Delta and in the Indigirka Lowland, we studied shallow cores, up to 1.3 m deep, from polygon center and rim locations. The formation of well-developed low-center polygons with elevated rims and wet centers is shown by the beginning of peat accumulation, increased organic matter contents, and changes in vegetation cover from Poaceae-, Alnus-, and Betula-dominated pollen spectra to dominating Cyperaceae and Botryoccocus presence, and Carex and Drepanocladus revolvens macro-fossils. Tecamoebae data support such a change from wetland to open-water conditions in polygon centers by changes from dominating eurybiontic and sphagnobiontic to hydrobiontic species assemblages. The peat accumulation indicates low-center polygon formation and started between 2380 +/- 30 and 1676 +/- 32 years before present (BP) in the Kolyma Delta. We recorded an opposite change from open-water to wetland conditions because of rim degradation and consecutive high-center polygon formation in the Indigirka Lowland between 2144 +/- 33 and 1632 +/- 32 years BP. The late Holocene records of polygon landscape development reveal changes in local hydrology and soil moisture.}, language = {en} }