The first dated preglacial diatom record in Lake Ladoga: long-term marine influence or redeposition story?
Preglacial environments in Lake Ladoga, the largest European lake, located within the limits of the Scandinavian glaciations, are very poorly investigated compared to postglacial ones. The only existed preglacial record containing marine sediments below the Weichselian till was obtained by deep geol...
| Published in: | Journal of Paleolimnology |
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| Main Authors: | , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | unknown |
| Published: |
2021
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| Subjects: | |
| Online Access: | https://epic.awi.de/id/eprint/53495/ https://doi.org/10.1007/s10933-020-00150-0 https://hdl.handle.net/10013/epic.67a9b0cc-0475-4454-a730-b2c6b26a002f |
| Summary: | Preglacial environments in Lake Ladoga, the largest European lake, located within the limits of the Scandinavian glaciations, are very poorly investigated compared to postglacial ones. The only existed preglacial record containing marine sediments below the Weichselian till was obtained by deep geological drilling in 1930s. Environmental conditions in Lake Ladoga prior to the Last Glacial Maximum were primarily reconstructed based on the studies of terrestrial boreholes and outcrops. The studied records suggest that in the Last Interglacial, during the Eemian marine transgression, the Ladoga basin became a part of the marine Baltic-White Sea connection, and turned fresh when the Eemian Sea regressed by the onset of the Weichselian glacial epoch. However, these records, often incomplete and poorly dated, leave major uncertainties on the environment established in Lake Ladoga after the Eemian Sea regression and its evolution throughout the Weichselian. This article presents the first Early Weichselian (MIS5, ~118-80 ka) diatom record in Lake Ladoga, based on the study of a sediment core Co1309 retrieved from Lake Ladoga within the frame of the Russian-German research project PLOT. Mixed occurrence of ecologically incompatible marine/brackish-marine and freshwater species, selective preservation and low diatom concentrations provide an interpretation for our record as a result of reworking of the previously accumulated marine Eemian sediments and redeposition of marine diatoms, rather than the direct marine influence. The new diatom record also suggests unstable high-energy environments prevailed at the coring site during the Early Weichselian. Similar trends in total diatoms and total fragments concentrations indicate changing sediment supply or reworking intensity. The preglacial diatom record substantially differs from the Holocene ones in Lake Ladoga indicating different paleoenvironmental settings in the lake basin prior to and after the last glaciation. Its close similarity to other Early Weichselian diatom records in the Ladoga region, characterized with mixed diatom-poor assemblages, in turn, suggest their formation under similar conditions. Lower concentrations of diatoms, diatom fragments, and other siliceous microfossils ~118-113 ka and ~90-80 ka might reflect the Early Weichselian cooling stages, while their increase between ~113 and 90 ka is likely attributed to the some climate amelioration and related environmental changes. |
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