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Arctic freshwater forcing of the Younger Dryas cold reversal


The last deglaciation was abruptly interrupted by a millennial-scale reversal to glacial conditions1, the Younger Dryas cold event. This cold interval has been connected to a decrease in the rate of North Atlantic Deep Water formation and to a resulting weakening of the meridional overturning circulation2,3,4 owing to surface water freshening. In contrast, an earlier input of fresh water (meltwater pulse 1a), whose origin is disputed5,6, apparently did not lead to a reduction of the meridional overturning circulation4. Here we analyse an ensemble of simulations of the drainage chronology of the North American ice sheet in order to identify the geographical release points of freshwater forcing during deglaciation. According to the simulations with our calibrated glacial systems model, the North American ice sheet contributed about half the fresh water of meltwater pulse 1a. During the onset of the Younger Dryas, we find that the largest combined meltwater/iceberg discharge was directed into the Arctic Ocean. Given that the only drainage outlet from the Arctic Ocean was via the Fram Strait into the Greenland–Iceland–Norwegian seas7, where North Atlantic Deep Water is formed today, we hypothesize that it was this Arctic freshwater flux that triggered the Younger Dryas cold reversal.

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Figure 1: Major deglacial drainage outlets for North America, along with approximate positions of proglacial Lake Agassiz and Keewatin dome just before the onset of the YD.
Figure 2: Eustatic sea-level chronologies.
Figure 3: Computed regional drainage chronologies and the inferred regional temperature change chronology.

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This paper is a contribution to the Polar Climate Stability Research Network, which is funded by the Canadian Foundation for Climate and Atmospheric Sciences and a consortium of Canadian universities. We thank W. Broecker, A. Dyke, T. Fisher, C. Hillaire-Marcel and J. Teller for discussions.

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Correspondence to Lev Tarasov.

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Reprints and permissions information is available at The authors declare no competing financial interests.

Supplementary information

Supplementary Discussion

Two fluid dynamical issues concerning large meltwater discharge into the mid-Altantic or Gulf of Mexico are discussed. It is argued that it is unlikely for a large surface freshwater plume to be formed and/or advected intact to the sites of North Atlantic Deep Water Formation. This file also includes a supplementary discussion concerning the uncertainties pertaining to and the dynamical source of the spike in Arctic discharge during Younger Dryas onset, and Supplementary Figures S1-S3. (PDF 211 kb)

Supplementary_Figures S4-S6

Supplementary Figures S4-S6 detail computed -12.8 kyr drainage basins and surface topography for 3 good-fit ensemble runs. (PDF 366 kb)

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Tarasov, L., Peltier, W. Arctic freshwater forcing of the Younger Dryas cold reversal. Nature 435, 662–665 (2005).

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