Ancylus Lake
Encyclopedia
Ancylus lake is a name given by geologists to the body of fresh water that replaced the Yoldia Sea
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...

 after the latter had been severed from its saline intake across central Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

 (with the eastern end of the channel near present Stockholm) by the isostatic rise of south Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...

n landforms. The dates are approximately 9500-8000 BP
Before Present
Before Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...

 calibrated, during the full Boreal period
Boreal (period)
In paleoclimatology of the Holocene, the Boreal was the first of the Blytt-Sernander sequence of north European climatic phases that were originally based on the study of Danish peat bogs, named for Axel Blytt and Rutger Sernander, who first established the sequence. In peat bog sediments, the...

. The lake became Littorina Sea
Littorina Sea
Littorina Sea is a geological brackish-water stage of the Baltic Sea, which existed around 7500–4000 BP and followed the Mastogloia Sea, transitional stage of the Ancylus Lake...

 when rising oceanic levels broke through the Great Belt
Great Belt
The Great Belt is a strait between the main Danish islands of Zealand and Funen . Effectively dividing Denmark in two, the Belt was served by the Great Belt ferries from the late 19th century until the islands were connected by the Great Belt Fixed Link in 1997–98.-Geography:The Great Belt is the...

.

The lake was named by Gerard de Geer
Gerard De Geer
Baron Gerard Jacob De Geer was a Swedish geologist who made significant contributions to Quaternary geology, particularly geomorphology and geochronology. De Geer is best known for his discovery of varves.- Early life and family :...

 after Ancylus fluviatilis
Ancylus fluviatilis
Ancylus fluviatilis is a species of very small, freshwater, air-breathing limpet, an aquatic pulmonate gastropod mollusk in the tribe Ancylini within the family Planorbidae, the ram's horn snails and their allies.-Distribution and conservation status:...

, a gastropod found in its sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

s.

Description

The elevation of southern Sweden did not entirely block the flow across central Sweden. Some egress continued from the lake through the Göta
Göta älv
The Göta is a river that drains lake Vänern into the Kattegat at the city of Gothenburg on the western coast of Sweden. It is located in Götaland, with the river itself being a site of early Geatish settlement. The length is 93 km. Often the combination of Göta älv and Klarälven is mentioned...

 and Steinselva rivers, which exit Lake Vänern to the Kattegat
Kattegat
The Kattegat , or Kattegatt is a sea area bounded by the Jutland peninsula and the Straits islands of Denmark on the west and south, and the provinces of Västergötland, Scania, Halland and Bohuslän in Sweden on the east. The Baltic Sea drains into the Kattegat through the Øresund and the Danish...

. Salt water did not enter the lake, however, which became entirely fresh as the lake rose above sea level. The date at which the flow was certainly blocked is about 8000 BP, when nearby Lake Vättern
Vättern
Vättern is the second largest lake in Sweden, after Lake Vänern and the sixth largest lake in Europe. It is a long, finger-shaped body of fresh water in south central Sweden to the southeast of Vänern pointing at the tip of Scandinavia....

 (part of the waterway system) became dissevered from Ancylus lake.

The result of increasing lake levels was the Ancylus transgression, a general flooding around its shores, 9500-9200 BP. By this time a somewhat larger Gulf of Bothnia
Gulf of Bothnia
The Gulf of Bothnia is the northernmost arm of the Baltic Sea. It is situated between Finland's west coast and Sweden's east coast. In the south of the gulf lie the Åland Islands, between the Sea of Åland and the Archipelago Sea.-Name:...

 and parts of Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

 were free of ice, while the Rovaniemi
Rovaniemi
Rovaniemi is a city and municipality of Finland. It is the administrative capital and commercial centre of Finland's northernmost province, Lapland. It is situated close to the Arctic Circle and is between the hills of Ounasvaara and Korkalovaara, at the confluence of the Kemijoki River and its...

 region of Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...

 appeared no later than 9000 BP, despite the new flooding.

Accelerated melting and landforms rebounding at different rates in different locations led to some instability. By 9200 BP the lake rose over the Dars sill and cut a new channel in the vicinity of what is now the "Great Belt
Great Belt
The Great Belt is a strait between the main Danish islands of Zealand and Funen . Effectively dividing Denmark in two, the Belt was served by the Great Belt ferries from the late 19th century until the islands were connected by the Great Belt Fixed Link in 1997–98.-Geography:The Great Belt is the...

" (the channel between the Danish islands Zealand and Funen), which some geologists call the Dana River. For a time, Skåne, or southern Sweden, was an island once more, from about 9200 to no later than 8000 BP. The lake level began to drop.

North Scandinavia

By 9000 BP the northern channel ceased functioning, joining Skåne to Sweden rather than to Denmark. However, only an isthmus connected Skåne to the new northern lands. If Skåne acquired its designation as an island on a geographic basis, it must have been no later than the Ancylus lake phase. At that time Mesolithic
Mesolithic
The Mesolithic is an archaeological concept used to refer to certain groups of archaeological cultures defined as falling between the Paleolithic and the Neolithic....

 cultures moved into newly released land around the shores of the Gulf of Bothnia
Gulf of Bothnia
The Gulf of Bothnia is the northernmost arm of the Baltic Sea. It is situated between Finland's west coast and Sweden's east coast. In the south of the gulf lie the Åland Islands, between the Sea of Åland and the Archipelago Sea.-Name:...

. They were fishing along the shores, hunting seals and following the reindeer into their new ranges.

In Lapland Mesolithic fishers, hunters and probably herders found pine-birch forest with tundra-like open spaces. In addition to pinus and betula were aspen
Aspen
Populus section Populus, of the Populus genus, includes the aspen trees and the white poplar Populus alba. The five typical aspens are all native to cold regions with cool summers, in the north of the Northern Hemisphere, extending south at high altitudes in the mountains. The White Poplar, by...

, alder
Alder
Alder is the common name of a genus of flowering plants belonging to the birch family . The genus comprises about 30 species of monoecious trees and shrubs, few reaching large size, distributed throughout the North Temperate Zone and in the Americas along the Andes southwards to...

, willow
Willow
Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...

, crowberries
Crowberry
Crowberry is a small genus of dwarf evergreen shrubs that bear edible fruit. They are commonly found in the northern hemisphere, from temperate to subarctic climates, and also in the Southern Andes of South America and on the South Atlantic islands of South Georgia, the Falklands and Tristan da...

, grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...

 and sedge
Cyperaceae
Cyperaceae are a family of monocotyledonous graminoid flowering plants known as sedges, which superficially resemble grasses or rushes. The family is large, with some 5,500 species described in about 109 genera. These species are widely distributed, with the centers of diversity for the group...

. Much of the new Finnish land was covered by mire
Poor fen
A poor fen is a natural wetland habitat, consisting of dense low growth of small sedges and other plants...

. Moraine
Moraine
A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...

 ridges and drumlin
Drumlin
A drumlin, from the Irish word droimnín , first recorded in 1833, is an elongated whale-shaped hill formed by glacial ice acting on underlying unconsolidated till or ground moraine.-Drumlin formation:...

s formed an extensive island system. The shores around the lake were stony ground.
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