"The Younger Dryas – One-time event or intrinsic feature of late Pleistocene climate change?"

The Younger-Dryas cold spell is one of the most prominent abrupt climate-change events in the past and a key feature of the last deglaciation. It is an intermittent, 1300-year long return to almost glacial conditions within a general warming trend. Although the climatic impact of the Younger Dryas was largest in the North-Atlantic realm, it affected climate at a global scale. Paleoceanographic reconstructions revealed that this event was associated with a significant reduction in the production rate of North Atlantic Deep Water. Recently, it has been proposed that the Younger Dryas was a unique event and should be regarded as an "accident" during the last deglaciation.

Here, the Younger Dryas is considered in the framework of climate change at millennial timescales during the late Pleistocene (i.e., Dansgaard-Oeschger events). A box model of the North Atlantic Ocean exhibits self-sustained oscillations of the large-scale ocean circulation, which are reminiscent of Dansgaard-Oeschger-style oscillations. The freshwater forcing of this ocean model depends on mean climate state, represented by global ice volume. When forced with modeled ice-volume evolution over the last 800 thousand years, the model predicts Younger-Dryas-type cooling events for each major deglaciation. Accordingly, Younger-Dryas-type events are an expected response of the climate system during deglaciations and can be conceived as Dansgaard-Oeschger-stadials, overprinted by rapidly changing boundary conditions. Hence, the Younger Dryas appears to be an intrinsic feature of late Pleistocene climate variability. In addition to the conceptual climate model, experiments with a coupled climate model will be presented to highlight the potential of the climate system to vary at millennial timescales.




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