A period of cooling about 13,000 years ago interrupted about 2,000 years of deglacial warming. Known as the Younger Dryas (YD), the event is thought to have resulted from a slowdown of the Atlantic meridional overturning circulation in response to a sudden flood of Laurentide Ice Sheet meltwater that reached the Nordic Seas. Oxygen isotope evidence for a local source of meltwater to the open western North Atlantic from the Gulf of St Lawrence has been lacking. Here we report that the eastern Beaufort Sea contains the long-sought signal of 18O-depleted water. Beginning at ~12.94 ± 0.15 thousand years ago, oxygen isotopes in the planktonic foraminifera from two sediment cores as well as sediment and seismic data indicate a flood of meltwater, ice and sediment to the Arctic via the Mackenzie River that lasted about 700 years. The minimum in the oxygen isotope ratios lasted ~130 years. We suggest that the floodwater travelled north along the Canadian Archipelago and then through the Fram Strait to the Nordic Seas, where freshening and freezing near sites of deep-water formation would have suppressed convection and caused the YD cooling by reducing the meridional overturning.
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We thank the officers and crew of USCGC Healy for making this project a success. We are also indebted to M. Carman for help processing core samples, A. McNichol for helpful discussions of 14C in the Arctic, A. Gagnon for the stable isotope measurements, the NOSAMS staff for providing 14C data and M. McCarthy, C. Moser, C. Griner and C. Mayo for leading the coring effort. S. Nielsen helped with translation of Hartz and Milthers14. The manuscript benefited from help from M. Blaauw and B. Keigwin with the Bayesian age model. This research was funded by NSF grants ARC 1204045 to L.D.K. and ARC 1203944 to N.W.D.