Yoldia Sea

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 Weichsel 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 BP, equivalent to ca 11,700-10,700 calendar years BP. 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 . 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.

The Baltic Ice Lake, the Yoldia Sea, the Ancylus Lake and the Littorina Sea are four recognized stages in the postglacial progression of the Baltic basin – there are also transition periods which can be considered as substages. From earliest to most recent they run:

The Baltic Ice Lake came to an end when it overflowed through central Sweden and drained, a process complete by about 10,300 BP (radiocarbon years). The straits through the present Stockholm region (via Lake Vänern and the Strait of Närke) to the Atlantic were the only outlet at that time. When lake level reached sea level the difference in salinity caused a backflow from the North Sea, creating saline regions in which the marine bivalve Yoldia flourished. This phase lasted until about 10,000 BP.

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