Baltic Ice Lake

The Baltic ice lake is a name given by geologists to a freshwater lake that gradually formed in the Baltic Sea basin as glaciation retreated from that region at the end of the Pleistocene. The lake, dated to 12,600-10,300 BP, is roughly contemporaneous with the three Pleistocene Blytt-Sernander periods. The lake followed a period of massive glaciation in the region, which followed the end of the Eemian Sea. The post-glacial Yoldia Sea was immediately subsequent to the Baltic ice lake.

Evidence and Factors

The term lake is used to mean a body of primarily fresh water. A sea is filled with brackish or salt water. In the history of the Baltic Sea, the distinction is not always clear. Salinity has varied with location, depth and time.

The main factors are the advance or recession of the Scandinavian glacier and the sinking of the landforms due to the weight of ice or springing back when relieved of it. The glacier provides a massive flow of fresh water. Salt water enters from the North Sea through straits. When the straits are blocked or nearly blocked fresh water prevails and a lake exists. The same condition exists when the waters are substantially higher than sea level, even though the straits are not blocked. The release of fresh water depends on climate.

Several methods are used to determine the quality (temperature, salinity, solids content) of ancient sea water. The main one is the type of diatoms found in the sediment. Some species require salt water, while others require fresh. Other invertebrates serve as marker species as well. Also, periods of maximum supply from melt water are marked by low organic carbon in the sediment. Higher carbon content causes greater deposition of iron sulfide, which appears as a black varve.

Formation

The edge of the retreating Weichselian glacier departed from the Gardno end-moraines of northern Poland at around 14,000 BP and reached the southern shore of the Baltic sea in the time window, 13,500/13,000 BP. In the next several hundred years, closed fresh water pools formed in the southern Baltic region from melt water as the ice retreated northward. These were about 40 m above the current sea level.

By 12,000 BP the edge of the glacier was at a line across southern Sweden to the northern shore of the Baltic countries. A connected body of water, the Ramsay Sea, stretched from the Danish islands region to the shores of Estonia. The Gulfs of Bothnia and Finland were still glaciated. In the Allerød, rising land in the Denmark region created the Baltic ice lake. It egressed through a small channel in the Strait of Oresund. The lake was higher than sea level (which was lower than our sea level) by some tens of meters. Lake Ladoga was part of it.

Emergence of the land then closed the channel through the Strait of Oresund. The lake rose until at about 11,200 BP it broke through central Sweden in the Mount Billingen region. By 10,800, the lake had dropped 55 meters. At that time, during the Younger Dryas, the glacier advanced again over the central Sweden exit, the lake rose about 25 m and broke through the Strait of Oresund again. By now the Gulf of Finland was deglaciated.

At the peak of this high water phase, most of Finland was under water, including Helsinki, at a depth of 115 meters. Only southern Sweden was free of ice. The Danish islands were all connected on the other side of the Strait of Oresund. Around 10,500, the climate became warmer, the ice retreated to the north of Mount Billingen, and the waters broke through central Sweden again, providing a second egress. Water level dropped 25 m to then sea level.

ummary

At about 14000 BC the retreating ice had reached the southern shores of the present Baltic. Melt water formed extensive lacustrine systems still seen in north Russia, Poland and Germany. By 12,600 BC the Baltic ice lake had come into existence. Beyond it only southern Sweden was habitable, and it was an island. It is well known that Scandinavia means 'the island of Scandza' or 'Scandia', which cannot be accounted for by today's map, and is generally assumed to be an inadvertent misrepresentation by ancient geographers. However, the first Scandinavia was an island, and was identical to southern Sweden.

Several carbon-dated sites in Estonia indicate that human habitation of the shores of the Baltic ice lake began in the Boreal, in the time window 11,200 - 10,200 BP. Charcoal, animal bones, and artifacts from Mesolithic temporary settlements have been found at Pulli and in the Lake Ladoga region. The diet included roe deer, red deer, marten, otter, wolf, bear and ringed seal. An open pine-birch forest covered the region. Pollen from Pinus, Betula, Alnus, Rosaceae, Cyperaceae and Artemisia have been found.

Around 10,300 BP, the ice lake discharged through channels that opened in central Sweden (near Mount Billingen) until it reached the ocean level. The Yoldia Sea phase began (10,300-9500 BP).

External links

* [http://www.pgi.gov.pl/pgi_en/index.php?option=news&task=viewarticle&sid=4&Itemid=2 Polish Geological Institute, The Baltic Ice Lake]

* [http://www.helsinki.fi/maantiede/geofi/fennia/demo/pages/oksanen.htm FENNIA 2002 180:1-2 Late Weichselian and Holocene shore displacement history of the Baltic Sea in Finland]

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