TY - JOUR A1 - Palagushkina, Olga A1 - Wetterich, Sebastian A1 - Biskaborn, Boris K. A1 - Nazarova, Larisa B. A1 - Schirrmeister, Lutz A1 - Lenz, Josefine A1 - Schwamborn, Georg A1 - Grosse, Guido T1 - Diatom records and tephra mineralogy in pingo deposits of Seward Peninsula, Alaska JF - Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences N2 - 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. KW - Microalgae assemblages KW - Palaeoenvironments KW - Thermokarst KW - Late Quaternary KW - Permafrost Y1 - 2017 U6 - https://doi.org/10.1016/j.palaeo.2017.04.006 SN - 0031-0182 SN - 1872-616X VL - 479 SP - 1 EP - 15 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Nazarova, Larisa B. A1 - Grebennikova, Tatiana A. A1 - Razjigaeva, Nadezhda G. A1 - Ganzey, Larisa A. A1 - Belyanina, Nina I. A1 - Arslanov, Khikmat A. A1 - Kaistrenko, Victor M. A1 - Gorbunov, Aleksey O. A1 - Kharlamov, Andrey A. A1 - Rudaya, Natalia A1 - Palagushkina, Olga A1 - Biskaborn, Boris K. A1 - Diekmann, Bernhard T1 - Reconstruction of Holocene environmental changes in Southern Kurils (North-Western Pacific) based on palaeolake sediment proxies from Shikotan Island JF - Global and planetary change N2 - We investigated a well-dated sediment section of a palaeolake situated in the coastal zone of Shikotan Island (Lesser Kurils) for organic sediment-geochemistry and biotic components (diatoms, chironomids, pollen) in order to provide a reconstruction of the palaeoenvironmental changes and palaeo-events (tsunamis, sea-level fluctuations and landslides) in Holocene. During the ca 8000 years of sedimentation the changes in organic sediment-geochemistry and in composition of the diatoms and chironomids as well as the shifts in composition of terrestrial vegetation suggest that the period until ca 5800 cal yr BP was characterized by a warm and humid climate (corresponds to middle Holocene optimum) with climate cooling thereafter. A warm period reconstructed from ca 900 to at least ca 580 cal yr BP corresponds to a transition to a Nara-Heian-Kamakura warm stage and can be correlated to a Medieval Warm Period. After 580 cal yr PB, the lake gradually dried out and climatic signals could not be obtained from the declining lacustrine biological communities, but the increasing role of spruce and disappearance of the oak from the vegetation give evidences of the climate cooling that can be correlated with the LIA. The marine regression stages at the investigated site are identified for ca 6200-5900 (at the end of the middle Holocene transgression), ca 5500-5100 (Middle Jomon regression or Kemigawa regression), and ca 1070-360 cal yr BP (at the end of Heian transgression). The lithological structure of sediments and the diatom compositions give evidences for the multiple tsunami events of different strengths in the Island. Most remarkable of them can be dated at around ca 7000, 6460, 5750, 4800, 950 cal yr BP. The new results help to understand the Holocene environmental history of the Southern Kurils as a part of the Kuril-Kamchatka and Aleutian Marginal Sea-Island Arc Systems in the North-Western Pacific region. KW - Kurils KW - North-Western Pacific KW - Palaeoclimate KW - Sea level KW - Diatoms KW - Chironomids KW - Pollen Y1 - 2017 U6 - https://doi.org/10.1016/j.gloplacha.2017.10.005 SN - 0921-8181 SN - 1872-6364 VL - 159 SP - 25 EP - 36 PB - Elsevier CY - Amsterdam ER -