Short History of Baltic sea
Wednesday, 19. August 2009, 18:55:37
Reading a thesis is not done in half an hour. Struggling my way through a new interesting thesis by Christin Eriksson at the Department of Earth Sciences, University of Gothenburg, on the "Characterizing and Reconstructing 500 years of Climate in the Baltic Sea Basin” I got stuck during the paragraph about the geologic history of the Baltic Sea (reminding me of some of the material I read 30-40 years ago. To refresh my memory I have dived into some of the articles on Wikipedia and a few of my old books to refresh my memory.
Before the Baltic sea there was the Eemian sea, a body of water located approximately where the Baltic sea is now during the last or Eemian Stage (of the Ice Age), roughly 130,000 to 115,000.
The not-so-long history of the Baltic Sea starts, however, about 15,000 years ago with the formation of the Baltic Ice Lake, 15,000–11,600 years ago - so The Baltic Sea is one of the youngest on the Earth. During each ice-sheet advance, the Baltic area was strongly eroded. It resulted in the formation of a vast depression, occupied today by the Baltic Sea.
Large ice sheets that had been dominating the region for several thousand years were now retreating rapidly, leaving behind suppressed land and discharging large amounts of freshwater. The map shows Late Baltic Ice Lake around 10,300 years ago, with a channel near Mount Billingen through what is now central Sweden. (Map of the Early Baltic Ice Lake, about 13,000 years ago is found here).
Clays, deposited in the Baltic Ice Lake, are conspicuous by alternating light-coloured coarser-grained layers and darker finer-grained layers. The former were deposited in summers, the latter – in winters. These deposits contain small amount of organic matter.
The Baltic Ice Lake was soon replaced by the Yoldia Sea, which lasted for approximately 900 years. At this stage, a connection with the outside ocean was established near Närke and Vänern, situated just south of the retreating ice sheet. 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. In the initial phase of the Yoldia Sea saline water poured into the Baltic, before the acceleration of glacial melting.
The connection with the ocean later closed as the Yoldia Sea was replaced by the Ancylus Lake, and a freshwater system now came into being. The map shows the Ancylus Lake around 8,700 years ago. The relic of Scandinavian Glacier in white. The river Svea älv formed an outlet to the Atlantic Sea. Salt water did not enter the lake, which became entirely fresh as the lake rose above sea level. The ancylus lake is named after the freshwater limpet Ancylus fluviatilis.
Deeper parts of the Yoldia Sea and Ancylus Sea were areas of fine-grained clay deposition with infrequent faunal fragments.
Towards the end of its history the level of the Ancylus Lake was falling following the formation of a new outlet at the Great Belt. The Ancylus Lake reached the level of the sea ca. 8500 years ago, marking the beginning of the Mastogloia Sea. Many researchers have been unwilling to recognize the Mastogloia Sea as a separate stage in the development of the Baltic Sea, favouring including it in either the Ancylus Lake stage or the Littorina Sea stage. The transitional Mastogloia Sea was so named because it was inhabited by characteristic diatoms of the genus Mastogloia.
The Littorina Sea (also Litorina Sea) later followed, when a connection with the outside ocean was reopened approximately 8500 years ago, due to the great sea level rise resulting from melting ice sheets. The wide and deep straits in the south (the so-called “Dana Elv” which as one of Europe’s water-richest rivers flew through the deep channel of the Great Belt) allowed for extensive water exchange with the North Atlantic, and the salinity of the Littorina Sea was higher than the Baltic Sea as we know it today. It existed around 7500–4000 years ago and followed the Mastogloia Sea. The Littorina Sea was a period of transgression and maximum salinity during the warmer Atlantic period of European climatology. At the optimum, approximately 4500 years ago, the sea contained twice the volume of water and covered 26.5% more surface area than it does today. The map shows the Littorina Sea around 7000 years ago.
Silt deposits, accumulated at that time in deeper waters, contain abundant fragments of marine microfauna and microflora. Shallow water sand deposits are abound in marine bivalves of Cardium sp. and Macoma balthica.
The transgression phase of the Littorina Sea continued for approximately 3000 years in its southern parts, caused by a rapid sea level change that dominated the isostatic uplift (following the Ice Age). When the sea level rise ended, the land uplift in Sweden and areas north of Lithuania caused regression of the Baltic Sea, resulting in shallower sills and thereby reduced Atlantic inflows. Even today, the land is still recovering from the last glaciation, and isostatic maps indicate that Sweden is experiencing isostatic uplift in the north and isostatic depression in the south.
Now if you want to know more about the latest 500 years of the Baltic Sea you may read the interesting thesis (I still haven’t got to the end of it!).
In Swedish:
Before the Baltic sea there was the Eemian sea, a body of water located approximately where the Baltic sea is now during the last or Eemian Stage (of the Ice Age), roughly 130,000 to 115,000.
The not-so-long history of the Baltic Sea starts, however, about 15,000 years ago with the formation of the Baltic Ice Lake, 15,000–11,600 years ago - so The Baltic Sea is one of the youngest on the Earth. During each ice-sheet advance, the Baltic area was strongly eroded. It resulted in the formation of a vast depression, occupied today by the Baltic Sea.
Large ice sheets that had been dominating the region for several thousand years were now retreating rapidly, leaving behind suppressed land and discharging large amounts of freshwater. The map shows Late Baltic Ice Lake around 10,300 years ago, with a channel near Mount Billingen through what is now central Sweden. (Map of the Early Baltic Ice Lake, about 13,000 years ago is found here).Clays, deposited in the Baltic Ice Lake, are conspicuous by alternating light-coloured coarser-grained layers and darker finer-grained layers. The former were deposited in summers, the latter – in winters. These deposits contain small amount of organic matter.
The Baltic Ice Lake was soon replaced by the Yoldia Sea, which lasted for approximately 900 years. At this stage, a connection with the outside ocean was established near Närke and Vänern, situated just south of the retreating ice sheet. 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. In the initial phase of the Yoldia Sea saline water poured into the Baltic, before the acceleration of glacial melting. The connection with the ocean later closed as the Yoldia Sea was replaced by the Ancylus Lake, and a freshwater system now came into being. The map shows the Ancylus Lake around 8,700 years ago. The relic of Scandinavian Glacier in white. The river Svea älv formed an outlet to the Atlantic Sea. Salt water did not enter the lake, which became entirely fresh as the lake rose above sea level. The ancylus lake is named after the freshwater limpet Ancylus fluviatilis.Deeper parts of the Yoldia Sea and Ancylus Sea were areas of fine-grained clay deposition with infrequent faunal fragments.
Towards the end of its history the level of the Ancylus Lake was falling following the formation of a new outlet at the Great Belt. The Ancylus Lake reached the level of the sea ca. 8500 years ago, marking the beginning of the Mastogloia Sea. Many researchers have been unwilling to recognize the Mastogloia Sea as a separate stage in the development of the Baltic Sea, favouring including it in either the Ancylus Lake stage or the Littorina Sea stage. The transitional Mastogloia Sea was so named because it was inhabited by characteristic diatoms of the genus Mastogloia.The Littorina Sea (also Litorina Sea) later followed, when a connection with the outside ocean was reopened approximately 8500 years ago, due to the great sea level rise resulting from melting ice sheets. The wide and deep straits in the south (the so-called “Dana Elv” which as one of Europe’s water-richest rivers flew through the deep channel of the Great Belt) allowed for extensive water exchange with the North Atlantic, and the salinity of the Littorina Sea was higher than the Baltic Sea as we know it today. It existed around 7500–4000 years ago and followed the Mastogloia Sea. The Littorina Sea was a period of transgression and maximum salinity during the warmer Atlantic period of European climatology. At the optimum, approximately 4500 years ago, the sea contained twice the volume of water and covered 26.5% more surface area than it does today. The map shows the Littorina Sea around 7000 years ago.Silt deposits, accumulated at that time in deeper waters, contain abundant fragments of marine microfauna and microflora. Shallow water sand deposits are abound in marine bivalves of Cardium sp. and Macoma balthica.
The transgression phase of the Littorina Sea continued for approximately 3000 years in its southern parts, caused by a rapid sea level change that dominated the isostatic uplift (following the Ice Age). When the sea level rise ended, the land uplift in Sweden and areas north of Lithuania caused regression of the Baltic Sea, resulting in shallower sills and thereby reduced Atlantic inflows. Even today, the land is still recovering from the last glaciation, and isostatic maps indicate that Sweden is experiencing isostatic uplift in the north and isostatic depression in the south.
Now if you want to know more about the latest 500 years of the Baltic Sea you may read the interesting thesis (I still haven’t got to the end of it!).
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http://www.sciencedaily.com/releases/2009/08/090812092817.htm
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http://www.pgi.gov.pl/pgi_en/index.php?option=news&task=viewarticle&sid=4&Itemid=2
In Swedish:
WIDGETIZE