@article{FritzHerzschuhWetterichetal.2012, author = {Fritz, Michael and Herzschuh, Ulrike and Wetterich, Sebastian and Lantuit, Hugues and De Pascale, Gregory P. and Pollard, Wayne H. and Schirrmeister, Lutz}, title = {Late glacial and holocene sedimentation, vegetation, and climate history from easternmost Beringia (northern Yukon Territory, Canada)}, series = {Quaternary research : an interdisciplinary journal}, volume = {78}, journal = {Quaternary research : an interdisciplinary journal}, number = {3}, publisher = {Elsevier}, address = {San Diego}, issn = {0033-5894}, doi = {10.1016/j.yqres.2012.07.007}, pages = {549 -- 560}, year = {2012}, abstract = {Beringian climate and environmental history are poorly characterized at its easternmost edge. Lake sediments from the northern Yukon Territory have recorded sedimentation, vegetation, summer temperature and precipitation changes since similar to 16 cal ka BP. Herb-dominated tundra persisted until similar to 14.7 cal ka BP with mean July air temperatures <= 5 degrees C colder and annual precipitation 50 to 120 mm lower than today. Temperatures rapidly increased during the Bolling/Allerod interstadial towards modern conditions, favoring establishment of Betula-Salix shrub tundra. Pollen-inferred temperature reconstructions recorded a pronounced Younger Dryas stadial in east Beringia with a temperature drop of similar to 1.5 degrees C (similar to 2.5 to 3.0 degrees C below modern conditions) and low net precipitation (90 to 170 mm) but show little evidence of an early Holocene thermal maximum in the pollen record. Sustained low net precipitation and increased evaporation during early Holocene warming suggest a moisture-limited spread of vegetation and an obscured summer temperature maximum. Northern Yukon Holocene moisture availability increased in response to a retreating Laurentide Ice Sheet, postglacial sea level rise, and decreasing summer insolation that in turn led to establishment of Alnus-Berula shrub tundra from similar to 5 cal ka BP until present, and conversion of a continental climate into a coastal-maritime climate near the Beaufort Sea.}, 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} } @article{FritzWolterRudayaetal.2016, author = {Fritz, Michael and Wolter, Juliane and Rudaya, Natalia and Palagushkina, Olga and Nazarova, Larisa B. and Obu, Jaroslav and Rethemeyer, Janet and Lantuit, Hugues and Wetterich, Sebastian}, title = {Holocene ice-wedge polygon development in northern Yukon permafrost peatlands (Canada)}, series = {Quaternary science reviews : the international multidisciplinary research and review journal}, volume = {147}, journal = {Quaternary science reviews : the international multidisciplinary research and review journal}, publisher = {Elsevier}, address = {Oxford}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2016.02.008}, pages = {279 -- 297}, year = {2016}, abstract = {Ice-wedge polygon (IWP) peatlands in the Arctic and Subarctic are extremely vulnerable to climatic and environmental change. We present the results of a multidisciplinary paleoenvironmental study on IWPs in the northern Yukon, Canada. High-resolution laboratory analyses were carried out on a permafrost core and the overlying seasonally thawed (active) layer, from an IWP located in a drained lake basin on Herschel Island. In relation to 14 Accelerator Mass Spectrometry (AMS) radiocarbon dates spanning the last 5000 years, we report sedimentary data including grain size distribution and biogeochemical parameters (organic carbon, nitrogen, C/N ratio, delta C-13), stable water isotopes (delta O-18, delta D), as well as fossil pollen, plant macrofossil and diatom assemblages. Three sediment units (SUS) correspond to the main stages of deposition (1) in a thermokarst lake (SW : 4950 to 3950 cal yrs BP), (2) during transition from lacustrine to palustrine conditions after lake drainage (SU2: 3950 to 3120 cal yrs BP), and (3) in palustrine conditions of the IWP field that developed after drainage (SU3: 3120 cal yrs BP to 2012 CE). The lacustrine phase (pre 3950 cal yrs BP) is characterized by planktonic-benthic and pioneer diatom species indicating circumneutral waters, and very few plant macrofossils. The pollen record has captured a regional signal of relatively stable vegetation composition and climate for the lacustrine stage of the record until 3950 cal yrs BP. Palustrine conditions with benthic and acidophilic diatom species characterize the peaty shallow-water environments of the low-centered IWP. The transition from lacustrine to palustrine conditions was accompanied by acidification and rapid revegetation of the lake bottom within about 100 years. Since the palustrine phase we consider the pollen record as a local vegetation proxy dominated by the plant communities growing in the IWP. Ice-wedge cracking in water-saturated sediments started immediately after lake drainage at about 3950 cal yrs BP and led to the formation of an IWP mire. Permafrost aggradation through downward closed-system freezing of the lake talik is indicated by the stable water isotope record. The originally submerged IWP center underwent gradual drying during the past 2000 years. This study highlights the sensitivity of permafrost landscapes to climate and environmental change throughout the Holocene. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} } @article{LenzGrosseJonesetal.2016, author = {Lenz, Josefine and Grosse, Guido and Jones, Benjamin M. and Anthony, Katey M. Walter and Bobrov, Anatoly and Wulf, Sabine and Wetterich, Sebastian}, title = {Mid-Wisconsin to Holocene Permafrost and Landscape Dynamics based on a Drained Lake Basin Core from the Northern Seward Peninsula, Northwest Alaska}, series = {Permafrost and Periglacial Processes}, volume = {27}, journal = {Permafrost and Periglacial Processes}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {1045-6740}, doi = {10.1002/ppp.1848}, pages = {56 -- 75}, year = {2016}, abstract = {Permafrost-related processes drive regional landscape dynamics in the Arctic terrestrial system. A better understanding of past periods indicative of permafrost degradation and aggradation is important for predicting the future response of Arctic landscapes to climate change. Here, we used a multi-proxy approach to analyse a4m long sediment core from a drained thermokarst lake basin on the northern Seward Peninsula in western Arctic Alaska (USA). Sedimentological, biogeochemical, geochronological, micropalaeontological (ostracoda, testate amoebae) and tephra analyses were used to determine the long-term environmental Early-Wisconsin to Holocene history preserved in our core for central Beringia. Yedoma accumulation dominated throughout the Early to Late-Wisconsin but was interrupted by wetland formation from 44.5 to 41.5ka BP. The latter was terminated by the deposition of 1m of volcanic tephra, most likely originating from the South Killeak Maar eruption at about 42ka BP. Yedoma deposition continued until 22.5ka BP and was followed by a depositional hiatus in the sediment core between 22.5 and 0.23ka BP. We interpret this hiatus as due to intense thermokarst activity in the areas surrounding the site, which served as a sediment source during the Late-Wisconsin to Holocene climate transition. The lake forming the modern basin on the upland initiated around 0.23ka BP and drained catastrophically in spring 2005. The present study emphasises that Arctic lake systems and periglacial landscapes are highly dynamic and that permafrost formation as well as degradation in central Beringia was controlled by regional to global climate patterns as well as by local disturbances. Copyright (c) 2015 John Wiley \& Sons, Ltd.}, language = {en} } @article{LenzWetterichJonesetal.2016, author = {Lenz, Josefine and Wetterich, Sebastian and Jones, Benjamin M. and Meyer, Hanno and Bobrov, Anatoly and Grosse, Guido}, title = {Evidence of multiple thermokarst lake generations from an 11800-year-old permafrost core on the northern Seward Peninsula, Alaska}, series = {Boreas}, volume = {45}, journal = {Boreas}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0300-9483}, doi = {10.1111/bor.12186}, pages = {584 -- 603}, year = {2016}, abstract = {Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site-specific palaeo-records are needed. Here we present a multi-proxy study of a 350-cm-long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial toHolocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain-size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, C-13(org)) and stable water isotopes (O-18, D, dexcess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre-lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22800 +/- 280cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11800cal. a BP (Unit B). At about 9000cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1060cal. a BP, including post-drainage sediment freezing from the top down to 154cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core-based reconstruction of multiple thermokarst lake generations since 11800cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice-rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in thermokarst-affected regions of the Arctic.}, language = {en} } @article{OpelMurtonWetterichetal.2019, author = {Opel, Thomas and Murton, Julian B. and Wetterich, Sebastian and Meyer, Hanno and Ashastina, Kseniia and G{\"u}nther, Frank and Grotheer, Hendrik and Mollenhauer, Gesine and Danilov, Petr P. and Boeskorov, Vasily and Savvinov, Grigoriy N. and Schirrmeister, Lutz}, title = {Past climate and continentality inferred from ice wedges at Batagay Highlands, interior Yakutia}, series = {Climate of the past : an interactive open access journal of the European Geosciences Union}, volume = {15}, journal = {Climate of the past : an interactive open access journal of the European Geosciences Union}, number = {4}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1814-9324}, doi = {10.5194/cp-15-1443-2019}, pages = {1443 -- 1461}, year = {2019}, abstract = {Ice wedges in the Yana Highlands of interior Yakutia - the most continental region of the Northern Hemisphere - were investigated to elucidate changes in winter climate and continentality that have taken place since the Middle Pleistocene. The Batagay megaslump exposes ice wedges and composite wedges that were sampled from three cryostratigraphic units: the lower ice complex of likely pre-Marine Isotope Stage (MIS) 6 age, the upper ice complex (Yedoma) and the upper sand unit (both MIS 3 to 2). A terrace of the nearby Adycha River provides a Late Holocene (MIS 1) ice wedge that serves as a modern reference for interpretation. The stable-isotope composition of ice wedges in the MIS 3 upper ice complex at Batagay is more depleted (mean delta O-18 about -35 parts per thousand) than those from 17 other ice-wedge study sites across coastal and central Yakutia. This observation points to lower winter temperatures and therefore higher continentality in the Yana Highlands during MIS 3. Likewise, more depleted isotope values are found in Holocene wedge ice (mean delta O-18 about -29 parts per thousand) compared to other sites in Yakutia. Ice-wedge isotopic signatures of the lower ice complex mean delta O-18 about -33 parts per thousand) and of the MIS 3-2 upper sand unit (mean delta O-18 from about -33 parts per thousand to -30 parts per thousand) are less distinctive regionally. The latter unit preserves traces of fast formation in rapidly accumulating sand sheets and of post-depositional isotopic fractionation.}, language = {en} } @article{OverduinWestermannYoshikawaetal.2012, author = {Overduin, Pier Paul and Westermann, Sebastian and Yoshikawa, Kenji and Haberlau, Thomas and Romanovsky, Vladimir E. and Wetterich, Sebastian}, title = {Geoelectric observations of the degradation of nearshore submarine permafrost at Barrow (Alaskan Beaufort Sea)}, series = {Journal of geophysical research : Earth surface}, volume = {117}, journal = {Journal of geophysical research : Earth surface}, number = {14}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0148-0227}, doi = {10.1029/2011JF002088}, pages = {9}, year = {2012}, abstract = {Submarine permafrost degradation rates may be determined by a number of interacting processes, including rates of sea level rise and coastal erosion, sea bottom temperature and salinity regimes, geothermal heat flux and heat and mass diffusion within the sediment column. Observations of ice-bearing permafrost in shelf sediments are necessary in order to determine its spatial distribution and to quantify its degradation rate. We tested the use of direct current electrical resistivity to ice-bearing permafrost in Elson Lagoon northeast of Barrow, Alaska (Beaufort Sea). A sharp increase in electrical resistivity was observed in profiles collected perpendicular to and along the coastline and is interpreted to be the boundary between ice-free sediment and underlying ice-bearing submarine permafrost. The depth to the interpreted ice-bearing permafrost increases from <2 m below sea level to over 12 m below sea level with increasing distance from the coastline. The dependence of the saline sediment electrical resistivity on temperature and freezing was measured in the laboratory to provide validation for the field measurements. Electrical resistivity was shown to be effective for detection of shallow ice-bearing permafrost in the coastal zone. Historical coastal retreat rates were combined with the inclination of the top of the ice-bearing permafrost to calculate mean vertical permafrost degradation rates of 1 to 4 cm yr(-1).}, language = {en} } @article{PalagushkinaWetterichSchirrmeisteretal.2017, author = {Palagushkina, Olga V. and Wetterich, Sebastian and Schirrmeister, Lutz and Nazarova, Larisa B.}, title = {Modern and fossil diatom assemblages from Bol'shoy Lyakhovsky Island (New Siberian Archipelago, Arctic Siberia)}, series = {Contemporary Problems of Ecology}, volume = {10}, journal = {Contemporary Problems of Ecology}, publisher = {Pleiades Publ.}, address = {New York}, issn = {1995-4255}, doi = {10.1134/S1995425517040060}, pages = {380 -- 394}, year = {2017}, abstract = {This article discusses the results of a taxonomic and ecological investigation of diatoms from polygonal ponds and Quaternary permafrost deposits of Bol'shoy Lyakhovsky Island (New Siberian Archipelago) and the reconstruction of climatic changes on the Island during late Pleistocene/Holocene transition using fossil diatom assemblages from the permafrost deposits. The taxonomic list of diatoms includes 159 diatom species. The main ecological factors that determine the distribution of diatoms in the investigated data set are mean July air temperature, рН, electrical conductivity, water depth, and concentrations of Si4+ and Al3+. An increase in water depth and stable lacustrine conditions in the Lateglacial-Holocene in the ancient thermokarst lake relate to Lateglacial warming before 11860 ± 160 years BP and during the early Holocene between 11210 ± 160 and 7095 ± 60 years BP.}, 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} } @article{PestryakovaHerzschuhGorodnichevetal.2018, author = {Pestryakova, Luidmila Agafyevna and Herzschuh, Ulrike and Gorodnichev, Ruslan and Wetterich, Sebastian}, title = {The sensitivity of diatom taxa from Yakutian lakes (north-eastern Siberia) to electrical conductivity and other environmental variables}, series = {Polar research : a Norwegian journal of Polar research}, volume = {37}, journal = {Polar research : a Norwegian journal of Polar research}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0800-0395}, doi = {10.1080/17518369.2018.1485625}, pages = {16}, year = {2018}, abstract = {Relative abundances of 157 diatom taxa from Yakutian lake surface-sediments were investigated for their potential to indicate certain environmental conditions. Data from 206 sites from Arctic, sub-Arctic and boreal environments were included. Redundancy analyses were performed to assess the explanatory power of mean July temperature (T-July), conductivity, pH, dissolved silica concentration, phosphate concentration, lake depth and vegetation type on diatom species composition. Boosted regression tree analyses were performed to infer the most relevant environmental variables for abundances of individual taxa and weighted average regression was applied to infer their respective optimum and tolerance. Electrical conductivity was best indicated by diatom taxa. In contrast, only few taxa were indicative of Si and water depth. Few taxa were related to specific pH values. Although T-July, explained the highest proportion of variance in the diatom spectra and was, after conductivity, the second-most selected splitting variable, we a priori decided not to present indicator taxa because of the poorly understood relationship between diatom occurrences and T-July. In total, 92 diatom taxa were reliable indicators of a certain vegetation type or a combination of several types. The high numbers of indicative species for open vegetation sites and for forested sites suggest that the principal turnover is the transition from forest-tundra to northern taiga. Overall, our results reveal that preference ranges of diatom taxa for environmental variables are mostly broad, and the use of indicator taxa for the purposes of environmental reconstruction or environmental monitoring is therefore restricted to marked rather than subtle environmental transitions.}, language = {en} }