|A review of the history of the Baltic Sea, 13.0-8.0 ka BP|
Björck, S. (1995). A review of the history of the Baltic Sea, 13.0-8.0 ka BP. Quaternary International 27: 19-40
In: Quaternary International. Elsevier: Oxford. ISSN 1040-6182, more
Marine; Brackish water; Fresh water
The dynamic history of the Baltic Sea during the millennia following the last deglaciation has been one of the main topics for many generations of Quaternary geologists around the Baltic Sea. Based on the present-state-of-knowledge and certain hypotheses, a model for the development during the Baltic Ice Lake, Yoldia Sea, and Ancylus Lake stages are presented. The Öresund Strait was the threshold of the initial stage of the Baltic Ice Lake and was eroded down to bedrock as a result of the isostatic uplift. The emerging threshold forced the Baltic Ice Lake to rise above sea level at ca. 12.0 ka BP. This gradual up-damming ended at ca. 11.2 ka BP when the large glacial lake was lowered 5–10m by possible subglacial drainage at Mt. Billingen. A glacial readvance during the Younger Dryas ended a ca. 400 year long land-bridge between Sweden and the continent, by blocking the former drainage route. Once again the Baltic Ice Lake had to rise above sea level to be drained over the öresund Strait. At ca. 10.5 ka BP a gradual ice recession began, and 200 years later, when the receding ice sheet could not withhold the up-dammed water masses, the final drainage of the Baltic Ice Lake occurred, which rapidly lowered the water level within the Baltic basin with ca. 25 m and ended the Baltic Ice Lake stage. The next stage, the Yoldia sea, was characterized by a complex pattern of relative sea level changes with large differences within the Baltic basin, a very restricted Baltic Sea in the south, and thus an extensive landbridge. At ca. 9.9 ka BP a short (100–200 years) saline ingression is seen in the Baltic sediment records from Stockholm in the north to the southernmost parts of the Yoldia sea. The gradually shallower strait in south central Sweden (The Närke Strait) ended the saline influence. 300–400 years later the two remaining outlets west of Lake Vänern, Göta Älv and Otteid-Steinselva, had become too shallow to ‘swallow’ the outflowing Yoldia Sea waters. At this stage the Baltic/Lake Vänern level could thus not fall in pace with the relative sea level fall outside the outlet areas. This was the isolation of Lake Vänern and the Baltic from the sea and the beginning of the Ancylus Lake. Since the water depth of the (larger) Göta Älv outlet had to be more or less maintained, the Ancylus Lake level had to rise in pace with the uplift of the outlet region. This caused a significant and rapid transgression (10–30 m in ca. 300 years) in the southern Baltic, which flooded large areas with recently immigrated (pine) forests. Since the Öresund Strait, during the Yoldia Sea stage, had been uplifted more than southerly areas, the Ancylus transgression ended with a new drainage pathway at ca. 9.2 ka BP: through the Darss Sill area in the southern Baltic and northwards through the Store Belt Strait. This so-called Dana River had cut off the former large land-bridge. The Quaternary deposits of this new threshold were eroded and a fairly rapid regression set in. At ca. 9.0 ka BP the Dana River had eroded down to the sea level, which isolated Lake Vänern from the Ancylus Lake and created a land-bridge between southern Sweden and northwards. Ca. 800 years later, when the sea level rose above the Öresund threshold, marine water could enter the Baltic, and at ca. 8.0 ka BP brackish water characterized the southern Baltic. This marks the end of the Ancylus Lake.