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. Description 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 – fresh water proglacial lake with level greater than sea level – dammed by glacial ice until the ice dam broke free at the north slope of Billingen uplands – the lake level then dropped ~ 26 meters to sea level - ~ 10,000 years before the present (B.C.). Transition period - Between the Baltic Ice Lake and the Yoldia Sea there was a transient lake stage before the ingression of salt water. This lasted ~300 years (292 - 309 annual deposition varves are seen in the geologic record, depending on where measured). The Yoldia Sea – a short lived connection with the sea across south-central Sweden over the Närke strait – approximately 10,000 to 9,600 B.C.. The Ancylus Lake – creation of a fresh water lake through uplift, which blocked the Närke strait- 9,600 to 7,800 ΒP. The Littorina Sea – with the rise in sea level and the submergence of the Øresund strait, the Baltic again communicated with the North Sea beginning ~ 7,800