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of the BIL and the sea gradually rose. It has been estimated that this difference at
13 ka BP was in the order of 10 m (Björck 2008 ) , and around this time there are
strong indications that a first drainage of the BIL occurred (Björck 1981 , 1995 ) .
This is thought to have been the consequence of ice recession north of the south
Swedish highlands and Mt. Billingen, situated between Lake Vättern and Lake
Vänern (Björck and Digerfeldt 1984 ) . This deglaciation uncovered parts of the
middle Swedish lowlands and opened up a contact between the sea in the west,
occupying, e.g., Lake Vänern, and the BIL. Due to a later ice readvance and erosion
of the deglaciated terrain, the proofs for this drainage are more of circumstantial
character, though the circumstantial evidences are many (cf. Björck 1995 ) , than
concrete drainage deposits. It may have been recorded in the Arkona basin as basin-
wide sandy layer (Moros et al. 2002 ) . There is, however, no evidence that marine
water entered the Baltic basin.
When the Younger Dryas cooling set in at ca. 12.8 ka BP, the ice sheet advanced
south over the previously deglaciated areas and once again blocked the northern
drainage of the BIL at Mt. Billingen. This ponding effect might have been a gradual
process but must have led to a more or less rapid transgression, depending on how
long the updamming took, until the Öresund outlet functioned again. Complex
Younger Dryas sediment lithologies in lakes in Blekinge (Björck 1981 ) , in more or
less contact with the BIL during Younger Dryas, imply that the BIL experienced a
complex water level history during this time period. It has been shown that during
this phase the BIL reached as far southwest as into the Kiel Bay (Jensen et al. 1997 ,
2002 ) .
Fig. 4.4 Paleogeographic
map showing the Baltic Ice
Lake just prior to the
maximum extension and final
drainage at ca. 11.7 ka BP
 
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