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terrigenous discharge by storms inducing coastal erosion and increasing coast-to-
basin transport. In contrast, the brackish-marine phases are characterized mainly by
pelagic deposition and basin-to-basin transport. The diatom record and the recon-
support the interpretation of warmer sea water temperature during brackish phases
B1, B3, and B5 whereas during the deposition of the more lacustrine phases of zones
B2, B4, and B6 colder water masses prevailed. By dating, zone B5 can be allocated
to the Medieval Climate Anomaly (MCA), whereas B6 mirrors the Little Ice Age
have shown that the MUC sediment succession reflects the change of climatic con-
ditions fromMCA through LIA to MWP. Within that core sediments from the MCA
and the MWP are represented by dark laminated sediments interrupted by a layer of
30 cm homogeneous grey (bioturbated) sediments of the LIA. Paleosalinity prox-
ies identify the laminated MCA and MWP sediments as brackish-marine, while the
homogeneous LIA sediments have been deposited in a fresher water. This change in
the sediment texture makes the MUC core analogue to the B zones deposited within
the eastern Gotland Basin after the Littorina transgression. In order to identify the
driving force of the changing depositional environment we compared the sedimen-
tary facies with a reconstruction of the NAO oscillation mode reconstructed by a
this study, the NAO mode was positive (maritime) for the MCA. It shifted to pre-
dominantly negative values for the time span from the beginning of the fifteenth to
middle of the nineteenth century (LIA) before it returned to positive values for the
modern warm period (with a negative excursion within the last third of the twentieth
century). According to these results we have to assume that during the MCA, warm
winters with westerly winds reduced ice coverage, dominated the meteorological
and hydrographic regime, whereas during the LIA easterly winds with extended ice
coverage during winter time prevailed. These differences have consequences on the
supply of saline water to the central basins of the Baltic Sea (Baltic Proper). We have
to assume that the baroclinic and barotropic inflows from the North Sea are the main
reasons for “renewing” of the saline bottom water of the Baltic Sea basins (Matthäus
more coupled to strong westerly winds (winter half). Time series analyses of major
Baltic inflows from 1880 to today, which represents the modern warm period, prove
the exceptional importance of strong barotropic inflows for central Baltic deepwa-
summer time and during calm periods. It means that under a general negative NAO
situation (cold periods), at least barotropic inflows and therefore the supply of saline
water to the Baltic Basin is reduced whereas at positive NAO and forced baro-
clinic inflow the salinity would increase. This assumption seems to yield for the last
parison to the investigation of the MUC from the Eastern Gotland Basin (Leipe et al.
sis and numerical process modelling hydrographic and meteorological processes of