Tardiglaciaire
In Paleoclimatology, the term Tardiglaciaire indicates the last phase of the Pléistocène, preceding the current time by the Holocène. Tardiglaciaire corresponds to the ultimate subdivision of the last Glaciation (Glaciation of Würm in the Alps), during which the Climat is heated overall even if it is marked by cold oscillations. It precedes the period current Interglaciaire (one still speaks about postglacial), overall heat, which is the Holocène.
The chronological limits of Tardiglaciaire vary according to the authors but the majority consider that it lasts of the end of the last glacial maximum (around approximately 18.000 years BP) to the last called cold oscillation recent Dryas (around 11.650 years BP gauged around 9700 years front J is. - C.).
A total phenomenon
The illustration above represents the variations of the average total temperatures for the 40.000 last years, reconstituted starting from the rate of the isotope 18O of oxygen present in taken icicles at the Greenland and in the Antarctic. For all the curves, a rise in the temperatures is perceptible starting from approximately 18.000 BP to approximately 10.000 BP. Tardiglaciaire corresponds to this phase of slow total radoucissement, marked by important relatively abrupt fluctuations.
Regional variations
In Europe and North Atlantic
Tardiglaciaire is one period of slow radoucissement intersected with cold chill resulting in teeth of saw on the general curve. The importance and the duration of these fluctuations depend on the hemisphere and the area considered. In Europe, the study of the alpine Palynozone S made it possible to identify five under-periods or Chronozone S:
- old Dryas or Dryas I
- Bölling or Bølling (13000 at 12000 BP).
- average Dryas or Dryas II (12000 at 11800 BP);
- Alleröd or Allerød (11800 at 11000 BP);
- recent Dryas or Dryas III (11000 at 10000 BP).
The red curve of the illustration above corresponds to the zone of the Greenland: it shows an abrupt rise of temperature towards 14.500 BP corresponding to the hot episodes of Bølling - Allerød before an abrupt fall towards 12.500 BP (recent Dryas). An explanation advanced for this phenomenon, circumscribed with the Atlantic northern and the Europe, is that the cast iron of the European Inlandsis then makes it possible the hot oceanic currents of the North Atlantic (Gulf Stream) to go up until the Iceland, the warming reaches then an average rate of 4° C per century and the marine level goes up of 28 Mr. C' is Bølling. This abrupt warming supports the cast iron of the glaciers of the Greenland, releasing consequently from great quantities of fresh water in the ocean and stopping the increase of the marine hot currents temporarily. The temperature relapses then, it is the recent Dryas. Finally, the currents grow blurred leaving the marine currents and the temperature to go up in a final way. The period tardiglaciaire is completed then and one returns in the postglacial one (Holocene) whose first chronozone in Europe is called Préboréal.
In North America
In the internal areas of the continent of North America, Tardiglaciaire is marked by a rain crisis involving the formation of temporary lakes such as the Lac Bonneville, with the site of the Big lake Salted.
In Africa
The period corresponds to a increased Aridité of the continent, more marked than today: the deserts such as the the Sahara then were extended and the tropical forests were reduced to some small islands along the Golfe of Guinea and in central Africa. Thus one notes a sedimentary gap in the human occupations of West Africa (the Sahel) between 25.000 years and 11.000 years BP, which would tend to show that the men of the time would have deserted this zone for southernmost areas close to the remaining forest small islands. However at the end of the period around 15.000 years BP, a climatic transition marked by a strong instability settles, before leaving room to a wet phase at the beginning of the Holocène, favorable to the geographical extension of the vegetation and the Man.
Correlation with the prehistoric cultures
From an archaeological point of view, Tardiglaciaire corresponds in Western Europe to the Magdalénien and the Épipaléolithique. The slow warming and the cast iron of the ices allow the magdaléniens groups occupying the South-west of France to migrate towards the territories formerly covered by the ice, that it is towards North (Belgium, Germany, Petite Poland) or towards high-altitudes (the Pyrenees, alpine arc).
It is during Tardiglaciaire that takes place the first Domestication of an animal specie by the man, that of the Chien.