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system prevailed, the basin was dominated by a basin-to-basin transport after
the gates to the North Sea opened during the Littorina transgression(s).
(b) The basin-to-basin transport from the Bornholm to the Gotland Basin resulted
in the accumulation of the “Stolpe Foredelta” in front of the “mouth” of the
Stolpe Channel within the southern Eastern Gotland Basin. The latter estuarine
inflow dynamics driven by the atmospheric circulation varies obviously on cen-
tennial time scales. The resulting laminated sediments of zones B1, B3, and B5
alternate with more homogeneous sediments of zones B2, B4, and B6.
(c) According to diatom analysis the facies types stand for different paleosalinities.
Whereas laminated sediments have been deposited under brackish-marine con-
ditions, the more homogeneous sediments are mainly bound to a fresher water
depositional environment.
(d) We relate the periodical facies shifts to changes of the NAO on centennial time
scales. During phases of a predominantly maritime NAO mode, westerly winds
drive more saline water to the Baltic Basin. The effect is a permanent halo-
cline precluding vertical water mixing and oxygen supply to the bottom water.
The poorly ventilated bottom water leads to the accumulation of laminated
sediments not disturbed by bioturbation. During phases of a predominantly con-
tinental NAO the influence of westerlies to the Baltic Basin is reduced, the
salinity drops, and a weak (or none) halocline allows the transport of oxygen
from the surface to the bottom by vertical mixing. A benthic fauna, due to the
bioturbation, results in homogeneous sediments.
(e) Time series analysis of sediment physical and chemical proxies of the depo-
sitional environment reveals remarkable periodicities of about 900 and 1500
years. Similar periods are reported from marine sediments from the Northern
Atlantic and the Greenland ice cores. According to our hypothesis, these
periodicities in Baltic Sea sediments stand for global climate signals.
Acknowledgements The study has been supported by the German Federal Ministry of Education
and Research. The authors express their gratitude to the captain and the crew of the R/V “Poseidon”
for the excellent co-operation during the expedition in June 2005.
We thank Dr. Torsten Seifert from the Leibniz-Institute for Baltic Sea Research Warnemünde,
Germany, who provided results from numerical modelling of the current system in the central
Baltic Sea.
We also thank Dorota Kaulbarsz, Polish Geological Institute Gdansk, and Irina Taranenko,
St. Petersburg State University, for her co-operation within the frame of this project.
References
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Alvi K, Winterhalter B (2001) Authigenic mineralisation in the temporally anoxic Gotland Deep,
the Baltic Sea. Baltica 14:74-83
Andrén E (1999) Holocene environmental changes recorded by diatom stratigraphy in the southern
Baltic Sea. Meddelanden fran Stockholms Universitets Institution foer Geologi och Geokemi
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