ΒP to present. This is sometimes split into substages: The Mastogloia Sea - a substage sometimes used to distinguish the period between 8000 and 7000 years ago when the Baltic became distinctly brackish - during this period the English Channel and the Danish straits circulation was established, increasing Atlantic water inflow. The Limnea Sea – a substage sometimes used to distinguish the transition of the Baltic Sea to a more stagnant phase, which currently exists – about 2,500 B.C. The Baltic Ice Lake came to an end when it overflowed through central Sweden and drained, a process complete by about 10,300 B.C. (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 B.C.. Subsequently, increased melting of the glacier provided additional fresh water and the lake became stratified (meromictic), with salt water on the bottom and fresh on top. Over the life of the sea and from location to location the salinity was a variable. Whether it is possible to speak of stages of salinity that would apply uniformly to the whole sea is debatable. At about 10,000 B.C., the exit continued to rise and the lake/sea broke through Denmark creating the first Great Belt channels. The total opening was less than 1 km wide and included two channels at the northern end. The Great Belt channels was blocked again by rising land from the post-glacial rebound that created Ancylus Lake. Geographically, the Gulf of Bothnia remained under the ice. The Gulf of Finland was open but most of Finland was an archipelago, over which debris carried by glacial streams gradually spread. A land bridge joined Germany to southern Sweden through Denmark. Relieved of its weight of ice, Finland rose gradually and unevenly from the sea. Parts of the Yoldia shoreline are above sea level today while other parts remain below. The Yoldia Sea toward its end was about 30m below current sea level. A channel at the location of the Neva River connected Yoldia Sea to Lake Ladoga. The Yoldia Sea existed entirely within the Boreal Blytt–Sernander period. The forests and species lining its shores were boreal. Mesolithic cultures