The Development of the Baltic Sea Basin During the Last 130 ka - The Baltic Sea Basin - page 90

4.3.6 Salinity
The outlets/inlets at Öresund and Great Belt widened and became deeper until ca.
6 ka BP, resulting in increasing and maximum postglacial salinities (e.g., Westman
and Sohlenius 1999 ) . Based on model calculations, Gustafsson and Westman ( 2002 )
suggest that changes in the morphology and depths of the sills in the inlet area only
partly explain the salinity variations during the last ca. 8 ka BP. They found that
a major cause of the salinity changes was variations in the freshwater input to the
basin. The latter study demonstrated that the freshwater supply to the basin may
have been 15-60% lower than at present during the phase of maximum salinity
around 6 ka BP (Fig. 4.8 ) . In addition, climate-driven long-term freshwater dis-
charge variability may have been an important factor controlling the salinity and the
stratification in the Baltic Sea during the last ca. 8 ka BP (Zillén et al. 2008 ) .
The eustatic sea level rise ceased sometime between 6 and 5 ka BP. The remain-
ing, though slow, rebound resulted in shallower Öresund and Great Belt straits and
decreased salinities. An estimate of the Baltic basin paleosalinity was presented by
Gustafsson and Westman ( 2002 ) . They used presence or absence of mollusks and
a silicoflagellate to infer different salinity intervals of the last 8 ka. Emeis et al.
( 2003 ) reconstructed Baltic salinity fluctuations throughout Holocene using stable
carbon isotopes. A comparison of these two salinity reconstructions (Zillén et al.
2008 ) shows great discrepancies: Gustafsson and Westman ( 2002 ) show a decrease
in salinity from the maximum value between 5 and 6 ka BP, while Emeis et al.
( 2003 ) infer increased salinity during the last 2 ka years. Another method to infer
Fig. 4.8 Paleogeographic
map showing the Littorina
Sea during the most saline
phase at ca. 6.5 ka BP