Concept information
Terme préférentiel
Younger Dryas
Définition
- The Younger Dryas, which occurred circa 12,900 to 11,700 years BP, was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum, which lasted from circa 27,000 to 20,000 years BP. The Younger Dryas was the last stage of the Pleistocene epoch that spanned from 2,580,000 to 11,700 years BP and it preceded the current, warmer Holocene epoch. The Younger Dryas was the most severe and longest lasting of several interruptions to the warming of the Earth's climate, and it was preceded by the Late Glacial Interstadial (also called the Bølling–Allerød interstadial), an interval of relative warmth that lasted from 14,670 to 12,900 BP. The change was relatively sudden, took place over decades, and resulted in a decline of temperatures in Greenland by 4~10 °C (7.2~18 °F), and advances of glaciers and drier conditions over much of the temperate Northern Hemisphere. A number of theories have been put forward about the cause, and the hypothesis historically most supported by scientists is that the Atlantic meridional overturning circulation, which transports warm water from the Equator towards the North Pole, was interrupted by an influx of fresh, cold water from North America into the Atlantic. However, several issues do exist with this hypothesis, one of which is the lack of a clear geomorphological route for the meltwater. In fact, the originator of the meltwater hypothesis, Wallace Broecker, stated in 2010 that "The long-held scenario that the Younger Dryas was a one-time outlier triggered by a flood of water stored in proglacial Lake Agassiz has fallen from favor due to lack of a clear geomorphic signature at the correct time and place on the landscape". A volcanic trigger has been proposed more recently, and the presence of anomalously high levels of volcanism immediately preceding the onset of the Younger Dryas has been confirmed in both ice cores and cave deposits. The Younger Dryas did not affect the climate equally worldwide, but the average worldwide temperature changed drastically. For example, in the Southern Hemisphere and some areas of the Northern Hemisphere, such as southeastern North America, a slight warming occurred. The Younger Dryas is the youngest and longest of three stadials, which resulted from typically abrupt climatic changes that took place over the last 16,000 years. Within the Blytt–Sernander classification of north European climatic phases, the prefix "Younger" refers to the recognition that this original "Dryas" period was preceded by a warmer stage, the Allerød oscillation, which, in turn, was preceded by the Older Dryas, around 14,000 calibrated years BP. That is not securely dated, and estimates vary by 400 years, but it is generally accepted to have lasted around 200 years. In northern Scotland, the glaciers were thicker and more extensive than during the Younger Dryas. (Adapted from: https://en.wikipedia.org/wiki/Younger_Dryas#Effects_on_agriculture)
Concept générique
Synonyme(s)
- Dryas III
- last Dryas
- Last Dryas
- Recent Dryas
- Young Dryas
Traductions
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français
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Dryas III
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Dryas Récent
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Younger Dryas
URI
http://data.loterre.fr/ark:/67375/QX8-B0DCHJM3-V
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