Geoscience Reference
In-Depth Information
4.3 Late and Postglacial History of the Baltic Sea
4.3.1 16,0-11,7 ka BP
While the development of the Baltic Sea during the last glacial period is only frag-
mentarily known, its history since the last deglaciation is better understood. It is
based on studies of numerous sediment cores from different parts of the basin as well
as on analyses of the mechanisms behind the geodynamic history of the Baltic Sea
the water level changes in different parts of the Baltic basin and with comparisons
to the relative sea level changes seen in parts of Denmark and on the Swedish west
coast.
The complexities of the post-LGM history of the southern parts of the
Scandinavian ice sheet (SIS) have been summarized by Houmark-Nielsen and Kjær
Ice Lake (BIL), should have an age of ca. 16 ka BP. Lower valleys in Denmark as
well as the Öresund area between Sweden and Denmark were possibly the main
drainage pathways for the glacial melt water, and the Store Belt and Öresund straits
were most likely formed as a consequence of gradual erosion by these rivers as the
area rebounded above base level (sea level). While the southernmost parts of the
basin were filled up with glacial deposits formed at the margin of the ice sheet, the
deeper parts, such as the Arkona Basin and Bornholm Basin, later on constituted a
glacial lake as the deglaciation continued.
During the initial stage of the BIL, it was most likely at level with the sea.
However, as the isostatic rebound of the outlet in the Öresund threshold area
between Copenhagen and Malmö - made up by glacial deposits on top of chalk
bedrock - was greater than the sea level rise, the Öresund outlet river eroded its bed
in pace with the emerging land. In fact, the island of Ven with its complex glacial
the fluvial downcutting reached the flint-rich chalk bedrock, the erosion must have
ceased more or less completely. This is possibly an important turning point in the
BIL development: the uplift of the threshold lifted the BIL above sea level and the
updamming (ponding) of this large glacial lake started. Based on the apparent sud-
den changing rate of shore displacement in Blekinge this seems to have occurred at
ca. 14 ka BP.
The deglaciation of the central Baltic led to the formation of the so-called highest
shoreline since the deglaciation of the coastal areas was followed by rapid isostatic
rebound. Because of the deglaciation, the sedimentation in the BIL was predomi-
nantly of a glaciolacustrine character resulting in either glacial varved clay or more
homogenous glacial clay: as the ice sheet retreated north the BIL grew in size with
varved clay forming in proximal areas of the ice sheet, while homogeneous clay was
deposited in more distal areas. Organic productivity was very low and even diatoms
were rare.
Due to the fact that the isostatic uplift of the outlet area in Öresund was more
rapid than the eustatic sea level rise, the altitudinal difference between the level
