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... > geologic time scale > geological age > Phanerozoic > Cenozoic > Quaternary > Dansgaard-Oeschger event
scientific discipline > stratigraphy > climatostratigraphy > climatostratigraphic period > Dansgaard-Oeschger event

Terme préférentiel

Dansgaard-Oeschger event  

Définition

  • Dansgaard–Oeschger events (often abbreviated D–O events) are rapid climate fluctuations that occurred 25 times during the last glacial period. Some scientists say that the events occur quasi-periodically with a recurrence time being a multiple of 1,470 years, but this is debated. The comparable climate cyclicity during the Holocene is referred to as Bond events. The best evidence for Dansgaard–Oeschger events remains in the Greenland ice cores, which only go back to the end of the last interglacial, the Eemian interglacial (about 115,000 years ago). Ice core evidence from Antarctic cores suggests that the Dansgaard–Oeschger events are related to the so-called Antarctic Isotope Maxima by means of a coupling of the climate of the two hemispheres, the Polar see-saw. In the Northern Hemisphere, they take the form of rapid warming episodes, typically in a matter of decades, each followed by gradual cooling over a longer period. For example, about 11,500 years ago, averaged annual temperatures on the Greenland ice sheet increased by around 8 °C over 40 years, in three steps of five years, where a 5 °C change over 30–40 years is more common. Warming resulting from D-O events extended farther south into central North America as well, as indicated by speleothem oxygen isotope excursions chronologically corresponding to D-O events recorded in Greenland ice cores. The course of a D-O event sees a rapid warming, followed by a cool period lasting a few hundred years. This cold period sees an expansion of the polar front, with ice floating further south across the North Atlantic Ocean. D-O events are also believed to cause minor increases in atmospheric carbon dioxide concentrations on the order of around 5 ppm. The events appear to reflect changes in the North Atlantic Ocean circulation, perhaps triggered by an influx of fresh water or rain. The events may be caused by an amplification of solar forcings, or by a cause internal to the earth system – either a "binge-purge" cycle of ice sheets accumulating so much mass they become unstable, as postulated for Heinrich events, or an oscillation in deep ocean currents. These events have been attributed to changes in the size of the ice sheets and atmospheric carbon dioxide. The former determines the strength of the Atlantic Ocean circulation via altering the northern hemisphere westerly winds, gulf stream, and sea-ice systems. The latter modulates atmospheric inter-basin freshwater transport across central North America, which changes the freshwater budget in the North Atlantic and thus the circulation. These studies corroborate the previously suggested existence of a "D-O window" of AMOC bistability ('sweet spot' for abrupt climate changes) associated with ice volume and atmospheric CO2, accounting for the occurrences of D-O type events under intermediate glacial conditions in the late Pleistocene. (Adapted from: https://en.wikipedia.org/wiki/Dansgaard%E2%80%93Oeschger_event)

Concept générique

Synonyme(s)

  • Dansgaard Oeschger event
  • D-O event

Traductions

  • événement de Dansgaard-Oeschger

    français

  • événement D-O
  • événement Dansgaard Oeschger
  • évènement Dansgaard Oeschger
  • événement Dansgaard-Oeschger
  • évènement Dansgaard-Oeschger
  • évènement de Dansgaard Oeschger
  • évènement de Dansgaard-Oeschger

URI

http://data.loterre.fr/ark:/67375/QX8-FQ1FZPJN-T

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