Vegetation reconstruction during the last millennium – derived by a lacustrine pollen record from Northern Siberia (Chatanga, Russia)


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ulrike.herzschuh [ at ] awi.de

Abstract

Northern Central Siberia is sparsely investigated even the area is provides many suitable archives for palaeoenvironmental studies. Studies are needed to understand the reaction of the highly sensible ecosystem to environmental dynamics and build the basic for ongoing research. The objective of this thesis is to reconstruct the vegetation development at 72°N in Arctic Siberia and to deduce environmental reasons for the changes in the vegetation cover. Sediment samples from a small lake in the vicinity of Chatanga on the Taimyr Peninsula were prepared for light microscopy and pollen analyses were conducted at the Alfred-Wegener-Institute for Polar and Marine Research in Potsdam. The ages of the upper samples were determined by the Environmental Radioactivity Research Centre at the University of Liverpool and deductively ascertained for the rest of the core. The dataset of the pollen count was used to generate highly resolved pollen diagrams of the last millennium: one entire pollen diagram for all taxa, which have been counted throughout the short core, and the other pollen diagram, pollen influx diagram and Iversendiagram for the primary taxa. Statistical analyses were performed to verify significant pollen assemblage zones and to construct synthetic environmental gradients. The pollen assemblages are reflecting three phases of vegetation development during the last millennium, which correspond to the termination of the Medieval Warm Period to the subsequent Little Ice Age and to the Recent Warming period. The Medieval Warm Period reaches till 1308 AD and is predominantly characterized by the regression of Alnus pollen, whereby the percentages of Cyperaceae pollen are increasing. Betula and the herb species do not show comparably trends. The mild climate of the Medieval Warm Period became cooler and drier, which is reflected by the decrease of Alnus pollen so that the dense canopy of the shrub tundra became more lightly and sedges established the light places during the termination of the Medieval Warm Period to the Little Ice Age. The percentages of Salix, Artemisia and Potentilla mainly increased, next to other herbs in general, between 1308 AD and the beginning of the Recent Warming in the middle of the 20th century. Alnus and Betula present lower pollen content during the period of the Little Ice Age, so that Salix could have established on the favorable places, where Alnus and Betula grew once before. Larix displays the northernmost tree species and is known for its heavy and large pollen. Due to the increase of Larix pollen content over that time period, it is likely that the vegetation cover was more lightly than during the Medieval Warm Period so that Larix had less competition or stress to produce pollen and the pollen could have been accumulated easier due to the scare vegetation cover around the lake. The vegetation consisted mainly of herbs and grasses, shrubs were growing on well exposed places, because the climate during the Little Ice Age was cooler and drier than today. Since the second half of the 20th century, the percentage content of Alnus and Betula pollen increased markedly, whereby Salix and Larix regressed next to Cyperaceae, Poaceae and also Artemisia. The flowering herb species produce less pollen than wind pollinated plants like Betula, Alnus, Salix or all grasses. However the percentages of the herb taxa became less abundant, their pollen has been increasingly accumulated since the second half of the 20th century, which reflects that the climate became warmer and moister in the recent decades.Larch is underrepresented in the lake accumulations too, because single trees and groups of Larix gmelinii were documented at the study site. Either Larix gmelinii is under competition or stress to produce pollen in the study area or the pollen doesn´t get representatively accumulated within the lake.



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Thesis (Master)
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42129
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Schreiber, X. (2014): Vegetation reconstruction during the last millennium – derived by a lacustrine pollen record from Northern Siberia (Chatanga, Russia) , Master thesis, Fakultät für Umweltwissenschaften.


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