Analyses of stable isotopes from Greenland ice cores provide estimates for the start and end of the Younger Dryas period.
Since 1916 and the onset and later refinement of pollen analytical techniques and a steadily growing number of pollen diagrams, palynologists have concluded that the Younger Dryas represented a distinct period of vegetational change in large parts of Europe during which warmer climate vegetation was replaced by that of a generally cold climate, a glacial plant succession that often contained Dryas octopetala.
This drastic change in vegetation is typically interpreted to be an effect of a sudden decrease in (annual) temperature, unfavorable for the previously rapidly northward-spreading forest vegetation.
The Oldest Dryas occurred approximately 1,770 calendar years before the Younger Dryas and lasted about 400 calendar years.
According to the GISP2 ice core from Greenland, the Oldest Dryas occurred between about 15,070 and 14,670 calendar years BP.
The Older Dryas, in turn, is preceded by another warmer stage, the Bølling oscillation that separates it from a third and even older stadial.
This stadial is often, but not always, known as the Oldest Dryas.
In the Greenland Summit ice core chronology, the Younger Dryas corresponds to Greenland Stadial 1 (GS-1).
The preceding Allerød warm period (interstadial) is subdivided into three events: Greenland Interstadial-1c to 1a (GI-1c to GI-1a).
Various paleoclimatic records from ice cores, deep sea sediments, speleothems, continental paleobotanical data, and loesses show similar abrupt climate events, which are consistent with Younger Dryas events, during the terminations of the last four glacial periods.
They argue that Younger Dryas events might be an intrinsic feature of deglaciations that occur at the end of glacial periods.
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