Boreal (period)
The Preboreal (also: Vorwärmezeit ) is in Earth's history the oldest period of the Holocene. He took 11560-10640 cal BP, which corresponds to 9610-8690 BC
- 4.1 Greenhouse gas carbon dioxide
- 4.2 Oxygen isotopes
- 4.3 Radiocarbon
- 6.1 Baltic Sea Region
Definition and stratigraphic position
The term Preboreal (ie the Boreal upstream) is derived from Latin pre - before, before, and the Greek god of the north wind Βορέας - boreas.
The Preboreal joined the subarctic time of the Younger Dryas at ( 10850-9610 BC) with its treeless tundra. It in turn was replaced by the Boreal.
Preboreal the corresponding zone of the pollen IV Firbas Franz (1949 ) or the pollen of zone I Zagwijn WH (1986 ) and Litt et al. (2001).
Klimastratigraphisch can Preboreal be divided into three parts ( from young to old):
- Late Preboreal (9200-8690 BC)
- Präboreale fluctuation or Rammelbeek phase (9350-9200 BC)
- Friesland phase (9610-9350 BC)
According to this threefold distinction WZ Hoek (1997), the three pollen zones 4a (Friesland phase), 4b ( Rammelbeek phase) and 4c ( Late Preboreal ).
Investigations Russian Moore divide the Preboreal in a PB -1 ( 10000-9800 radiocarbon years, or 9600-9270 BC) and in a PB -2 ( 9800-9300 radiocarbon years, or 9270-8541 BC).
The Preboreal together with the Boreal Alt- Holocene.
Culture History corresponds to the Preboreal the beginning of the Mesolithic.
Temporal classification
Note: Only the fields marked with a black dividing line boundaries are more or less exactly; they are based on annual layers in lake sediments in north-central Europe and are, strictly speaking, only for air levels. The other boundaries are determined unsafe and not rigid. In particular, the boundary between Central and Jungholozän is highly variable. In the stages of culture the different regional development is observed.
Dating
The beginning of the Holocene, and thus the Preboreal is usually expressed with the period 9700-9610 BC. In a recalibration, the period 9530-9500 is taken BC in the eye. The end of the Preboreal comes to rest in 8690 BC.
Historical Climate History
The average temperatures rose at the beginning of Friesland phase in the northern hemisphere very fast: within only 20 to 40 years to six degrees Celsius. The temperature increase related primarily to the winter average temperatures for the summer average temperatures found Bos et al (2007 ) on the basis of plant communities only an increase up to 3 ° C. Similar sharp increases in temperature had occurred several times towards the end of the Weichsel glaciation ( Dansgaard -Oeschger & events ).
The Präboreale fluctuation from 9350 BC brought an abrupt climatic deterioration, from 9300 BC then established themselves largely humid, wet and cold conditions. Towards the end of Präborealen fluctuations, the climate recovered again abruptly and the temperatures rose again at 4 ± 1.5 ° C.
The temperatures maintained during the Late Preboreal with slight variations in their level at approximately, from 8900 BC, however, continued an upward trend for a Boreal back.
Environmental parameters
Greenhouse gas carbon dioxide
The carbon dioxide concentration was rocketed towards the end of Friesland phase of around 260 ppmv to 330 ppmv in the altitude. During the Rammelbeek phase showed no significant change. In Late Preboreal they fell back to 300 ppmv from the beginning to be leveling then ppmv at par with the already high value of 350.
Oxygen isotopes
The δ18O values indicate the beginning of the Friesland - phase parallel to the temperature gradient a dramatic increase by 5 ‰ from - 41 ‰ to - 36% ( SMOW ). During the cool - phase Rammelbeek they fall by 3 ‰. After a further increase at the beginning of the Late Preboreal they eventually stabilize at - 37 ‰ ( SMOW ).
Radiocarbon
The Δ 14 C values are typical during the early Preboreal no drastic fluctuations. After a slight increase at the beginning of Friesland phase - but 5 ‰, the trend is to more negative values around - 20 ‰. During the Rammelbeek phase stabilization occurs at - 22 ‰ a. At the beginning of the Late Preboreal a rapid increase takes place from - 15 ‰ to positive values with a maximum of 15 ‰ to 9000 BC to the output of Preboreal then 10 ‰ be registered.
Vegetation history development
Birch, pine and hazel spread from southern refugia (eg Upper Rhine, Rhone Valley, Central Danube ) further north, and it emerged birch or birch - pine forests. The rapid spread of hazel, but mainly only from the beginning of the Boreal is brought into connection with the immigration of people. The dominant taxon präborealen forest was the birch (Betula pubescens and Betula pendula), which was supplanted only towards the end of the late Preboreal of the jaw. Companion plants were rowan (Sorbus aucuparia ) and aspen (Populus tremula ), and also the heat-sensitive species juniper Juniperus communis and Juniperus nana.
The birch had gained during the Friesland phase very rapidly in importance, however, was greatly decreased during the cool Präborealen fluctuation. The heather -like ( Ericales ) disappeared at the beginning of the Preboreal and herb plants at higher altitudes sites were generally declining. Open grasslands with grasses ( Poaceae ) had been able to temporarily re-establish during Präborealen fluctuation.
The Preboreal follows in the Boreal immigration of mixed oak forests in Central Europe which existed preferably of oak, elm, lime and ash.
Sea level
Sea level rise during the Preboreal was around 9 meters ( 63 feet below sea level to 54 feet below sea level). However, he was not homogeneous, but the rate was until 9100 BC still relatively low ( 5 mm / year), then in the Late Preboreal vigorously to attract ( 15 mm / year).
Baltic Sea Region
The Preboreal in the Baltic region is characterized by the development of draining across the Öresund Baltic Ice, which was created after the melting of the Fennoscandian ice sheet about 10,600 BC, before the beginning of Preboreal. To 9200 BC, the Ice Lake experienced a decrease by five to ten yards through the formation of a new effluent at Billingen in central Sweden. This outflow was prevented by 8800 BC by a Eisvorstoß, after which the water level rose again in the Ice Lake. The Ice Lake remained until the early Boreal exist (8300 BC).
Volcanic eruption
The situation created by a volcanic eruption in Iceland tephra from Saksunarvatn represents a major stratigraphic marker horizon in Preboreal; they will in Greenland at 8230 ± 60, in lake sediments from Krakenes in Norway in 8060-8040 and in north-western Germany lakes dates back to 8140 years BC.
Cultural and Historical Development
With the Preboreal correlates the Frühmesolithikum whose beginning but it is sometimes recognized only to 9000 BC. Carrier cultures are the Beuronian in southern Germany ( 9600-7000 BC), the Maglemosian culture from 9000 BC in Denmark and the Creswellien in England ( 12500-8000 BC). In Belgium, the Neerharen group that Ourlaine group and the Verrebroek group shall be given. However, the level in Haltern, North Rhine -Westphalia began in the Boreal (from 7400 BC).
The Epipalaeolithic ( 12000-9500 BC) enough with the cultures of Iberomaurusien ( North Africa - 20000-8000 BC), the Azilian (Southern Europe - 12300-9600 BC) and the Swiderien (Eastern Europe - 13,000 to 9500 BC), just to Preboreal. In the Levant the Neolithic period had already begun, represented by the Preceramic Neolithic A ( 9500-8800 BC) and Early Preceramic Neolithic B ( 8800-7000 BC). Against 9000 BC was settled in the Middle East Jericho for the first time, probably the oldest permanent settlement site in the world. Also in northern central Europe settlements of Preboreal were discovered, such as in Friesack in Brandenburg. Discovered network fragments refer here to the importance of fishing.
In North America, established himself from 9000 BC frühpaläoindianische the Clovis culture ( 9000-8800 BC). This was followed from 8900 BC, the medium-to spätpaläoindianische, based on the bison hunt Folsom culture ( 8900-8200 BC).