A Holocene high-resolution record of aquatic productivity,seasonal anoxia and meromixis from varved sediments of Lake Łazduny,North-Eastern Poland: insight from a novel multi-proxy approach |
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| Authors: | Andrea Sanchini Sönke Szidat Wojciech Tylmann Hendrik Vogel Agnieszka Wacnik Martin Grosjean |
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| Institution: | 1. Institute of Geography & Oeschger Centre for Climate Change Research, University of Bern, Switzerland;2. Department of Chemistry and Biochemistry & Oeschger Centre for Climate Change Research, University of Bern, Switzerland;3. Faculty of Oceanography and Geography, University of Gdansk, Poland;4. Institute of Geological Sciences & Oeschger Centre for Climate Change Research, University of Bern, Switzerland;5. W. Szafer Institute of Botany, Polish Academy of Sciences, Kraków, Poland |
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| Abstract: | Anthropogenic eutrophication and spreading anoxia in freshwater systems is a global concern. Little is known about anoxia in earlier historic times under weaker human impact, or under prehistoric natural conditions with different trophic, land cover and climatic regimes. We use a novel approach that combines high-resolution hyperspectral imaging with µ-XRF and HPLC-pigment data, which allows us to assess chloropigments (productivity) and bacteriopigments (anoxia) at seasonal subvarve-scale resolution. Our ~9700 cal a bp varved sediment record from NE Poland suggests that productivity increased stepwise from oligotrophic Early Holocene conditions (until ~9200 cal a bp ) to mesotrophic conditions in the Mid- and Late Holocene. Natural eutrophication was mainly a function of progressing landscape evolution with intense weathering under dense forest and warm-moist climatic conditions. Generally, anoxia increased with increasing productivity. Seasonal anoxia and some multi-decadal periods of meromixis were the common mixing patterns throughout the Holocene except for a period of persisting meromixis between ~5200 and 2000 cal a bp. Anthropogenic deforestation around 400 cal a bp resulted in substantially better lake oxygenation despite high productivity. In this small lake, aquatic productivity and lakeshore forest cover (wind shield) were more important factors controlling oxic/anoxic conditions than Holocene temperature variability. |
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| Keywords: | anoxia aquatic productivity high-resolution record Holocene Poland |
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