8.2 kiloyear event
The Misox variation (called the Anglo-American 8.2 kilo year event) was a sharply defined, relatively short-term climate change around 6200 years BC In the mesolithic central Europe it came within a few decades to a cooling of about 2 ° C. The reheating took place in less than 100 years just as fast.
Definition
The temperature fluctuation was detected by palynological investigations on the mires of Misoxtals in the Swiss canton of Graubünden for the Alpine region. The discovery was already in 1960 by Heinrich Zoller ( 1923-2009 ), Professor of Botany at the University of Basle, has been made.
The Misox fluctuation is 5 equivalent to the Bond event.
Dating
According to the English names of the start of the Misox fluctuation is given as 8200 years BP or with 6250 years BC. In Greenland 6225 years are recognized BC. The variation thus falls into the Older Atlantic period.
Dissemination
As in the Greenland ice cores GRIP ( " Greenland Ice Core Project") and the GISP ( " Greenland Ice Sheet Project"), a variation at the time around 6200 years BC can be determined, is the thesis that these climate change globally or was widespread, at least in the northern hemisphere, occupied. Already in the 1960s, a hemispheric this variation was discussed. Studies on Soppensee ( Switzerland ) and in Schleinsee ( Southern Germany ) showed that the layered sediments have a similar change in the pollen distribution. About a layer of tephra, which occurred in the sediments of both lakes, the data could be correlated and absolutely dated. It was also for the montane altitudinal zone, a rapid change of the vegetation at the time of Misox fluctuation.
In Norwegian lakes, the profiles of sediments were also correlated with the found in the ice cores anomaly 8200 years ago. The confirmed by these investigations cooling is called in Norway Finse event.
Causes
The Misox variation was most likely passed through the final breakup of the Laurentian ice sheet in the way, which drew a gigantic meltwater pulse by itself. So broke the huge meltwater lakes Agassiz and Ojibway and drained abruptly in the North Atlantic. The huge amount of freshwater released in turn affected the thermohaline circulation of the North Atlantic by the north-facing reduced heat transport.
Effects
Estimates of the cooling achieved depend upon the interpretation of the proxy data. The values vary between 1 and 5 ° C. In Greenland, the temperature drop was 3.3 ° C, which here took place quite rapidly ( in less than 20 years ); the variation took a total of 150 years, the maximum cold stretched his hand over 60 Jahre.Tropische records from ancient coral reefs in Indonesia indicate a cooling of 3 ° C. At the same time carbon dioxide concentrations decreased over a period of about 300 years back by about 25 ppm.
Sea level
The original meltwater pulse led to a sea level rise of 0.5 to 4 meters. Solely on the basis of estimates of the volume of the two lakes Agassiz and Ojibway, and the magnitude of the decaying ice sheet values of 0.4 to 1.2 meters can be achieved. However, sea level data from today's Delta regions contain a signal for a rapid rise 2-4 meters, that is superimposed on the general, postpleistozänen sea level rise. The meltwater signal reached because of isostatic effects which deplazierenden melt water masses at its full strength only far away from the origin (Hudson Bay). So only about 20%, in North-West Europe and 70% in Asia, for example, achieved 105% of the global average value in the Mississippi Delta. The cooling during Misox fluctuation was temporary, however, caused by the meltwater pulse sea level rise was permanent in nature.
Vegetation
Proof of cooling within the hitherto regarded as climatically stable Frühholozäns led to the rapid recognition and dissemination of pollen analysis in the presentation paleoclimatic contexts. In a cooling such occurs within a period of a few decades in the higher levels of the Alps to the decline of silver fir (Abies alba), Norway spruce ( Picea abies), larch (Larix decidua), Mountain Pine ( Pinus mugo ) and their replacement by shrubs such as juniper (Juniperus communis), buckthorn ( Hippophae rhamnoides ), willow (Salix sp.), green alder ( Alnus viridis), heather family ( Ericaceae ), heather (Calluna vulgaris) and crowberry ( Empetrum nigrum). This change in species composition is also reflected in the pollen that were preserved in the sediments of lakes and bogs.
Cultural History
The extending over several centuries, climatic and hence cultural and historical changes of the early Atlantic period are to be correlated only with difficulty with the very abrupt running Misox fluctuation. In North Africa at this time, drier conditions had been established and in East Africa, there was even more than five centuries of drought. In western Asia, especially in Mesopotamia, the climate had cooled at the same time Aridifikation over three centuries. This may have provided the driving force for the development of irrigation agriculture in Mesopotamia - by its overproduction was only able to provide the basis for the developed there forming urban civilization with great social organization.