| Evolution of the Baltic Sea |
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| Pleistocene |
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Eemian Sea (130,000–115,000 BC) Ice sheets and seas (115,000–12,600 BC) |
| Holocene |
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Baltic Ice Lake (12,600–10,300 BC) Yoldia Sea (10,300–9,500 BC) Ancylus Lake (9,500–8,000 BC) Mastogloia Sea (8,000–7,500 BC) Littorina Sea (7,500–4,000 BC) Modern Baltic Sea (4,000 BC–present) |
Yoldia Sea is a name given by geologists to a variable brackish water stage in the Baltic Sea basin that prevailed after the Baltic Ice Lake was drained to sea level during the Weichselian glaciation. Dates for the Yoldia sea are obtained mainly by radiocarbon dating material from ancient sediments and shore lines and from clay-varve chronology. They tend to vary by as much as a thousand years, but a good estimate is 10,300 – 9500 radiocarbon years BC, equivalent to ca 11,700–10,700 calendar years BC. The sea ended gradually when isostatic rise of Scandinavia closed or nearly closed its effluents, altering the balance between saline and fresh water. The Yoldia Sea became Ancylus Lake. The Yoldia Sea stage had three phases of which only the middle phase had brackish water.
The name of the sea is adapted from the obsolete name of the bivalve, Portlandia arctica (previously known as Yoldia arctica), found around Stockholm. This bivalve requires cold saline water. It characterizes the middle phase of the Yoldia Sea, during which saline water poured into the Baltic, before the acceleration of glacial melting.