Older Dryas
The Older Dryas is in Earth's history the name of a cool period between the Bolling interstadial and interstadial Alleröd the late Weichsel ice age ( Quaternary ). The Older Dryas began Warvenjahren 13,540 BP and ended at 13,350 Warvenjahren vh (after Warvenchronologie in Meerfelder ). The period was marked by a renewed, strong chilling with a relapse into a shrub tundra or been exposed birch forest.
Naming and conceptual history
The name Older Dryas, Older Dryas often, even tundra Mean Time or Dryas 2, was coined by Johannes Iversen in 1942. Dryas, the genus name of the White Mountain Avens ( Dryas octopetala ), which was frequently throughout Germany and Scandinavia during this time.
Definition
The Older Dryas was defined by John Iversen in type profile Bølling Sø. In general, this interval is characterized by a sharp decrease in the ( Tree ) birch pollen and an increase of non- arboreal pollen.
Stratigraphy
The Older Dryas, known in the North Atlantic region as well as inter- Allerød Cold Period I ( IACP I), is the cool middle part of the tripartite Greenland Interstadial 1c (GI -1c) and therefore corresponds to the Greenland interstadial 1c2 (GI - 1c2 ). It follows that already at Bolling interstadial belonging, relatively warm Greenland Interstadial 1c3 (GI - 1c3 ). The beginning of the Alleröd interstadial fine, warm Greenland interstadial 1c1 (GI - 1c1 ) joins her.
In North America and the North Atlantic region, the Oldest Dryas and the Aegelsee fluctuation 400 years older - Greenland Interstadial 1d (GI -1d) - referred to as the Older Dryas. Because of stratigraphic confusion therefore Older Dryas, caution is advised in the use of the term.
Dating
The Older Dryas has now demonstrated widespread in northern Germany. It is dated after the Warvenchronologie in Meerfelder on Warvenjahre 13,540 BP to about 13,350 Warvenjahre vh, ie it is converted 11590-11400 BC The Geozentrum Hanover dated the Older Dryas, however, with 13480-13350 cal BP Recently, Van Raden (2012 ) and the slightly older period 11674-11572 BC considered.
Environmental parameters
Oxygen isotopes
While the older Dryas, the δ18O values experienced a decrease of 2.5 ‰ SMOW, they fell from - 37.5 to nearly - 40 ‰ SMOW. The minimum comes to lie at approximately 11,600 BC.
Paleogeography
In northwest Europe, the Baltic Ice Lake was, which was cut off from Eisschildrand. Denmark and southern Sweden were ice-free and therefore could be colonized by pioneer plants. The northern Scandinavia was completely iced over, and the largest part of Finland was buried under ice and the Baltic countries were flooded by the Ice Lake. Between the British Isles and mainland Europe, which were still connected to each other due to the low sea levels, was the so-called Doggerland, a very rich wildlife, rolling hills; hundreds of tons of bone material were recovered here from the bottom of the North Sea.
Vegetation
Depending on the permafrost and latitude northern Europe was covered by steppe or tundra vegetation. Wetlands to lakes and rivers were densely covered with dwarf birch, willow, buckthorn and juniper. In river plains and high altitudes further south grew bright birch forests.
As the first birch and pine had immigrated during the Bolling Interstadial in northern Europe. Due to the slowdown in the older Dryas, there was a new initiative of the ice masses. Consequently, the forests moved back to the south and were replaced by open grassland with alpine, cold-resistant plants. A comparable, arctic tundra Park can be found today in Siberia in the transition zone between taiga and tundra. In the older Dryas, however, it extended in an almost continuous band of Siberia to the UK.
An alpine indicator plants to lead:
- Dryas octopetala
- Oxyria digyna (Alpine sorrel )
Among the trees are found:
- Pines ( Pinaceae ), predominantly in Poland
- Betula pubescens ( downy birch ) in Central Europe
- Salix herbacea ( dwarf willow)
At Graslandtaxa should be mentioned:
- Artemisia
- Ephedra ( Ephedra )
- Hippophae ( sea buckthorn )
Cultural History
The humans (Homo sapiens sapiens Cro -Magnon type ) were located during the older Dryas still in the late Upper Paleolithic. They were organized into groups and survived on the plains of Eurasia by hunting reindeer ( Northern Europe ) or woolly mammoths (Ukraine). On their hunting expeditions they already put a dog (Canis familiaris). The culture of the late Upper Paleolithic was not uniform, but rather several regional traditions had emerged. For example, the Azilian ( 12300-9600 BC) in France, the penknife groups ( 12000-10800 BC) in the north-western Central Europe, the Bromme culture ( 11400-10500 BC ) in southern Scandinavia, the Creswellien ( 12500-8000 BC) in southern England and Wales and the Swiderien ( 13000-9500 BC) in Poland and Hungary.