Reconstruction of vegetation during the last 1100 years in northern Central Siberia (Russia) from pollen and geochemical analyses of lake sediments


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Liv.Heinecke [ at ] awi.de

Abstract

The northern Central Siberian Arctic provides many suitable archives for climate reconstructions and presents a highly sensitive eco-region with scarce human disturbance. The objective of this study was to identify and interpret changes in the vegetation cover during the last 1100 year, by means of a short core, which was cored in 2007 from a lake in the catchment of the Popigai river, Northern Siberia. In order to achieve reliable results, a multi-proxy approach was used to identify alterations in the lake system and its vicinity. In this study a pollen record was generated and analyzed with statistical means. Further measurements include sedimentary parameters, namely grain size, biogeochemistry (TN, TC, TOC) and stable isotopes (δ13C and δ15N). The results of the statistical analyses were used to divide the pollen record into five zones. Each pollen assemblage zone (PAZ) is showing a rather specific pollen composition and is indicating changes in the vegetation cover in the lake’s vicinity. The relationships among samples and species were investigated using a principal component analysis, revealing a clear treeline signal. The lower part of the core is reflecting the Medieval Warm Period (MWP), reaching from about 900 AD to 1300 AD. The pollen composition comprises of a rather mixed signal, including tree taxa as well as shrub and herb taxa, yet not displaying a pronounced trend. However, internal sedimentological lake signals, e.g. TOC, TN and δ13C show a clear decrease during this time. From approx. 1300 AD to 1550 AD a rather unspecific pollen assemblage was reconstructed. Starting around 1550 AD and lasting until the early 18th century, the vegetation signal showed a clear decrease in tree pollen accompanied by a strong increase in shrub pollen, thereby indicating to the Little Ice Age (LIA). This coincides with the results of the TOC and the TN measurements, which display here their lowest values within this study. Another transition zone, which lasts until the 1970s, separates the LIA from the Global Warming period. This recent warming trend is clearly reflected in the pollen composition of the upper samples, where a pronounced increase of tree pollen as well as a decrease in herb pollen becomes apparent. Biogeochemical results match this trend by displaying the highest values throughout the core in the upper samples. The stable isotope ratios are showing more variability, although the δ15N ratios are presenting a slightly positive trend. Since proxies, especially sedimentary ones, can be reflecting different parameters, the multi-proxy approach proved very useful. The combination of biogeochemistry and stable isotope ratios is used to indicate the source of organic matter in the sediment, identifying a clearly lacustrine dominated signal in this study. Furthermore, it is possible to draw conclusions concerning the bioproductivity in the lake system from the determined parameters. The findings presented here are indicating that the major climate phases in the last 1100 years are also reflected in the vegetation and sediment signals in the investigated lake. The end of the Medieval Warm Period as well as the Little Ice Age and modern day Global Warming are well distinguishable in the pollen record. This study queues well into the ongoing research to understand the reaction and feedbacks of the high latitudes in relation to global climate change and can thereby contribute to a higher resolution as well as a better understanding of the Siberian Arctic.



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Thesis (Diplom)
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Not peer-reviewed
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Published
Eprint ID
40399
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Heinecke, L. (2011): Reconstruction of vegetation during the last 1100 years in northern Central Siberia (Russia) from pollen and geochemical analyses of lake sediments , Diplom thesis, Institut für Erd- und Umweltwissenschaften.


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