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| Titel |
Development of anoxia during the last 90 years in Lake Tiefer See, NE Germany |
| VerfasserIn |
Miriam Groß-Schmölders, Nadine Dräger, Ulrike Kienel, Achim Brauer |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250101217
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| Publikation (Nr.) |
 EGU/EGU2015-322.pdf |
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| Zusammenfassung |
| The sediments from the deepest part of the lake basin (62 m) of Lake Tiefer See, an elongated
lake formed in a sub-glacial channel during the last glaciation in NE Germany, have
been proven to be annually laminated (calcite varves) since AD 1924 (KIENEL
ET AL. 2013). Possible explanations for the onset of varve formation are either
eutrophication caused by increased nutrient influx through the use of fertilizers in
agriculture and/or the modern climatic warming. Since varves can only form under
predominantly anoxic conditions it is hypothesized that the development of the
anoxic water body in Lake Tiefer See can be reconstructed by determining the
onset of varve formation in different parts and at different water depths of the lake
basin.
Therefore, we investigated: eleven short cores (length from 49 cm (TSK 14 S 2) to 121
cm (TSK 13 QP5)) from a depth of 19, 4 m up to 62 m water depth, mainly along a N-S and a
W-E transect. The onset of varve preservation was investigated on all cores by varve
counting. Counting and characterization of varves has been obtained by micro-facies analyses
of large-scale thin sections μXRF-element scanning.
In result we found a good correlation between the onset of varve formation/preservation
and water depth. Whereas varves at the deepest point of Lake Tiefer See are developed since
1924 the onset of varve formation began successively later at more shallow water depths. The
latest development of varves since 1981 occurs in the northern part of the basin at a water
depth of 30 meters and in the East in a depth of 19 meters. In addition to the onset of varve
formation, further differences between deep and shallow water cores have been
observed. (1) The number of sub-layers per year: two or three layers in the shallow
areas in the east, up to seven layers in the deeper part. (2) Better preservation of
varves in the northern than in the eastern part of the basin. (3) Different diatom
assemblages related to the water depth: Stephanodiscus medius in all water depths
detectable; Asterionella, Fragilaria, Navicula, Stephanodiscus parvus, Synedra, Tabellaria
in larger abundances only in the deeper parts; Aulacoseira mainly in the shallow
areas. (4) Missing single varves have been only traced in the eastern part of the
basin.
Possible reasons for the observed differences including wind and wave activity near the
shore-line and in shallow water, water circulation and lake bathymetry are discussed in this
paper.
The varves of Lake Tiefer See are part of an integrated multi-proxy study including
high-resolution sediment analyses and monitoring of modern deposition processes within the
Virtual Institute of Integrated Climate and Landscape Evolution Analysis –ICLEA– of the
Helmholtz Association, grant number VH-VI-415.
Reference
KIENEL, U.; DULSKI, P.; OTT, F.; LORENZ, S.; BRAUER, A. (2013): Recently
induced anoxia leading to the preservation of seasonal laminae in two NE-Germany lakes.
Journal of Paleolimnology 50:535 – 544 |
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