Allerød oscillation
The Alleröd interstadial, also Allerød interstadial or Alleröd fluctuation, is the last warm phase ( interstadial ) just before the end of the last ice age ( Quaternary ). It lasted 13350-12680 Warvenjahren v. h, corresponding to 11400-10730 BC.
Naming and conceptual history
The name was suggested by Nikolaj Hartz and Vilhelm Milthers 1901 spätweichselglaziale, interstadial deposits. The interstadial conditions were developed on the basis of plant remains large. This warm phase was named after the type locality Allerød in Zealand (Denmark), northwest of Copenhagen. John Iversen could capture these warmer phase based on pollen and named it Alleröd period oscillation or Alleröd.
Definition
The beginning of the Alleröd interstadial is defined by the spread of birch forests. At the end of Alleröd interstadial (and thus the beginning of the Younger Dryas ) they disappeared and were replaced by a shrub tundra.
Regional correspondences are the Windermere interstadial in the UK ( 11900-11150 BC), the Woodgrange Interstadial in Ireland ( 11800-11000 BC) and the Two Creeks interstadial in North America ( 11350-10050 BC ).
The original type profile at Allerød ( Sealand, Denmark ) no longer exists. As a para- stratotype therefore Bølling Sø ( Jutland, Denmark) applies.
Stratigraphy
The onset and duration of Alleröd interstadial may vary somewhat regionally well. It was preceded by the Older Dryas, while then came the Younger Dryas. With the Younger Dryas the Pleistocene and the Holocene began ended.
According to Rasmussen et al 2006 Alleröd interstadial includes the periods ( from young to old):
- GS-1 Greenland stadial - 10946-9753 BC: Younger Dryas
- GI -1a Greenland interstadial 1a - 11149-10946 BC - warm: warm-up period before the onset of the Younger Dryas
- GI -1b Greenland interstadial 1b - 11361-11149 BC - cool: Gerzensee fluctuation
- GI -1c Greenland interstadial 1c - 12004-11361 BC - warm: Alleröd Biozone
1c can the Greenland interstadial also be further subdivided ( from young to old):
- GI - 1c1 - 11572-11324 BC - hot
- GI - 1c2 - 11674-11572 BC - cold: Aegelsee fluctuation or Older Dryas
- GI - 1c3 - 11958-11674 BC - hot
The Alleröd interstadial usually follows the Older Dryas period with the GI - 1c1. Occasionally, its duration is, however, understood longer; so it is, for example, in southern Germany, in Switzerland, in North America and the North Atlantic region immediately after the Oldest Dryas period with the GI - 1c3 one.
For a detailed stratigraphy see Van Raden et al, 2012.
Dating
The dating is validated with the aid of dendrochronology and is hinged Warvenchronologie. After Warvenchronologie the Alleröd interstadial 13350-12680 Warvenjahre lasted v. h This translates into 11400-10730 BC The Geozentrum Hanover dated this interval 13350-12700 v. h.
However, the evaluation of the annual layers in the Greenland ice yielded for the Alleröd interstadial a much longer period of 971 ± 31 years for GRIP and 1091 ± 29 years for NGRIP. The GISP2 core can be even close to 1,120 ± 56 years. This discrepancy in the duration of the Alleröds explained by its above- mentioned extension to the Oldest Dryas.
In Scandinavia Mangerud had, inter alia, the 1974 Alleröd interstadial still with the period 11800-11000 radiocarbon years defined (corresponding to 11757-10973 BC).
Volcanic eruption
The eruption of the Laacher See volcano ( Laacher See) is also an outstanding geological event ( large-area deposition of Bimstuff, to Northern Europe detectable), which took place in this time interval. He is surrounded by the Gerzensee variation (GI -1b). The far transported over by the wind volcanic ash allows the correlation over long distance within Western, Central and Northern Europe. After the dating of the eruption was 12,880 Warvenjahre v. h (relative to 1950), ie in the year 10,930 BC
Vegetation history development
In Alleröd, which was very similar to today's climate already existed in Eurasia and Central Europe, the first scale reforestation after the last ice age ( Weichsel glacial = ). It installed itself Laub-/Nadel-Mischwälder mainly, in southern regions dominated deciduous forests. The first section of Alleröds was characterized by clear birch forests, later there was indeed a closed, but not too dense forest, where the pine -dominated (pine maximum around 11,000 BC). In addition there were aspen, spruce, larch, juniper mixed with oak, willow and hazel. Clearings and open areas were colonized by grasses ( Poaceae ), pigweed family ( Chenopodiaceae ) and Artemisia. Against 11,000 BC in northern Italy, the so-called jaw drop occurred, that is, the hitherto dominant pine forests thinned noticeably. Benefited from the birch, which again took over dominance. The birch summit, however, was only in the beginning of the Younger Dryas reached (around 10,300 BC).
Environmental parameters
Temperatures
According to Johnsen et al 1995, temperatures were 5 to 12 K colder than today during the Alleröd interstadial in Greenland, Ireland arise towards the end of Alleröds 4 to 5 K.
After the temperature maximum in the Bolling interstadial began a general, gradual cooling trend, which continued unbroken through in Alleröd interstadial. Documents, for example, the average summer temperatures (July) for Ireland at the beginning of Alleröds still at 13 ° C, so they had cooled down until the beginning of the Younger Dryas at around 10 ° C.
The to 11,950 BC incipient Alleröd Biozone (GI -1c) was warm, but showed a slight temperature oscillations under several decline. The Gerzensee variation (GI -1b), English Intra Allerød Cold Period, brought from 11,300 BC a significant cooling of up to 2 K. from 11,100 BC starting warming up before the start of the Younger Dryas (GI -1a ), English younger Dryas pre Warming, with 2 K also presented the prevailing towards the end of Alleröd Biozone temperature conditions to restore the settings then be reconciled with a significant temperature drop of nearly 3 K to the younger Dryas.
Oxygen isotopes
The δ18O values range up to 11,000 BC steadily and in a significant way by 12% (from - 36 ‰ to - 41 ‰), and then up towards the end of Alleröd interstadial ( the GI -1a) back on - 38 ‰ to rise.
Carbon isotopes
The δ13C values range during the Alleröds steadily to 57% back ( from 3.5 to 1.5 ‰ ), the Gerzensee fluctuation brakes this is something.
Cultural History
At the type locality in Allerød, Denmark, north-west of Copenhagen ( Denmark) archaeological remains from that for residential development of Europe in the late Paleolithic ( Upper Paleolithic ) significant period were found in the late 19th century for the first time. The increasing forest cover in Central Europe the great herds of the open land were displaced as livelihood of the Raiders of the Magdalenian. As a result, settlements and hunting camps were smaller; archaeological legacies of Alleröds are called penknife groups in northern Germany after the typical stone tool form. In southern Germany there is a contact zone late Magdalenian. In about the same time developed the Bromme culture in southern Scandinavia ( 11400-10500 BC) and the Swiderien in Poland and Hungary ( 13000-9500 BC). The Ahrensburg culture began towards the end of Alleröd interstadial ( 10760-9650 BC). In the southeastern Mediterranean Neolithic times had already begun.