Lateglacial environmental and climatic changes at the Maloja Pass,Central Swiss Alps,as recorded by chironomids and pollen |
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| Authors: | Boris Ilyashuk Erika Gobet Oliver Heiri André F Lotter Jacqueline FN van Leeuwen Willem O van der Knaap Elena Ilyashuk Florencia Oberli Brigitta Ammann |
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| Institution: | 1. Institute of Archaeology and Ethnography SB RAS, Ak. Lavrentieva Str. 17, 630090 Novosibirsk, Russia;2. Novosibirsk State University, Pirogova Str. 2, 630090 Novosibirsk, Russia;3. Altai State University, Dimitrova Str. 66, 656049 Barnaul, Russia;4. Kazan Federal University, Kremlevskaya Str. 18, 420008 Kazan, Russia;5. University of Potsdam, Institute of Earth and Environmental Science, Karl Liebknecht Str. 24-25, 14476 Potsdam, Germany;6. Department of Geography, Moscow State University, Vorobievy Gory 1, 119991 Moscow, Russia;7. Institute of Geography Russian Academy of Science, Staromonetny lane, 29, 119017 Moscow, Russia;8. Institute for Geology and Mineralogy, University of Cologne, Zülpicher Str. 49a, 50674 Cologne, Germany;9. Sobolev Institute of Geology and Mineralogy SB RAS, Ak. Koptyuga Str. 3, 630090 Novosibirsk, Russia;10. Department of Geosciences, National Taiwan University, Taipei 106, Taiwan, ROC;1. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Research Unit Potsdam, Telegrafenberg A43, 14473 Potsdam, Germany;2. Kazan Federal University, Kremlyovskaya str., 18, 420018 Kazan, Russia;3. Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK;4. Geography and Environment Department, University of Southampton, University Road, Southampton SO17 1BJ, UK |
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| Abstract: | Chironomids and pollen were studied in a radiocarbon-dated sediment sequence obtained from a former lake near the Maloja Pass in the Central Swiss Alps (1865 m a.s.l.) to reconstruct the Lateglacial environment. Pollen assemblages imply a vegetation development around the Maloja Pass from shrub tundra at the beginning of the Allerød to coniferous forest during the early Holocene with a lowering of the timberline during the Younger Dryas. Chironomid assemblages are characterized by several abrupt shifts in dominant taxa through the Lateglacial. The occurrence of taxa able to survive hypoxia in the second part of the Allerød and during the Preboreal, and their disappearance at the onset of the Younger Dryas cold phase suggest summer thermal stratification and unfavourable hypolimnetic oxygen conditions in the palaeo-lake during the warmer periods of the Lateglacial interstadial and early Holocene. Mean July air temperatures were reconstructed using a chironomid-temperature transfer function from the Alpine region. The pattern of reconstructed temperature changes agrees well with the Greenland δ18O record and other Lateglacial temperature inferences from Central Europe. The inferred July temperatures of ca 10.0 °C during most of the Allerød were slightly lower than modern values (10.8 °C) and increased up to ca 11.7 °C (i.e., above present-day values) at the end of the Allerød. The first part of the Younger Dryas was colder (ca 8.8 °C) than the second part (ca 9.8 °C). During most of the Preboreal, the temperatures persisted within the limits of 13.5–14.5 °C (i.e., ca 3 °C above present-day values). The amplitudes of temperature changes at the Allerød–Younger Dryas–Preboreal transitions were ca 3.5–4.0 °C. The temperature reconstruction also shows three short-lived cooling events of ca 1.5–2.0 °C, which may be attributed to the centennial-scale Greenland Interstadial events GI-1d and GI-1b, and the Preboreal Oscillation. |
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