Ancylus Lake

Ancylus Lake is a name given by geologists to a large freshwater lake that existed in northern Europe approximately from 9500 to 8000 years BC being in effect one of various predecessors to the modern Baltic Sea. Origin, evolution and demise The Ancylus Lake replaced the Yoldia Sea after the latter had been severed from its saline intake across a seaway along the Central Swedish lowland, roughly between Gothenburg and Stockholm. The cutoff was the result of isostatic rise being faster than the concurrent post-glacial sea level rise. In the words of Svante Björck the Ancylus Lake "is perhaps the most enigmatic (and discussed) of the many Baltic stages". The lake's outlet and elevation relative to sea-level was for long time surrounded by controversy. It is now known that the lake was above sea level, included Lake Vänern, and drained westward through three outlets at Göta Älv, Uddevalla and Otteid. As result of the continued isostatic uplift of Sweden, the outlets in central Sweden were severed. In turn this resulted in the lake tipping over a till substrate at what is now the Great Belt in Denmark. Being located no less than 10 m above sea level the lake began thus to drain to the sea through the Dana River between 9000 and 8900 years B.C. The formation of the Dana River is thought to have caused a dramatic erosion of sediments, peatlands and forests along its path. This led initially to a relatively rapid fall in the lake level over hundreds of years, which then continued at a slower pace. Another consequence of the lowering of the lake and isostatic uplift was that a north-south land bridge formed between Lake Vänern and the Ancylus Lake effectively making Lake Vänern a separate basin. The Ancylus Lake existed from approximately 9500 to 8000 years B.C. calibrated, during the Boreal period. The lake became the Littorina Sea when rising sea levels broke through the Dana River forming the Great Belt. This transformation was gradual as salt-water had begun to enter the Ancylus Lake 8800 years B.P. The salt-water that entered the lake resulted in episodic brackish water pulses. The final end of the Ancylus Lake, however, came 7800–7200 year B.C. when Øresund was flooded causing a massive inflow of salt-water.