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The Younger Dryas stadial (Greenland Stadial 1) has long been recognized in proxy records throughout the North Atlantic region as a stable, cool period that started and ended abruptly. However, modeling experiments in which the Younger Dryas cooling was forced by meltwater predict much more unstable climatic conditions compared to the proxy records. Here we present evidence of a climatically unstable Younger Dryas based on a decadal-resolution marine proxy record from the Norwegian continental shelf. This record shows that the North Atlantic was characterized in the early Younger Dryas by Arctic Water and an increasing accumulation of fresh surface water that peaked at 12,500 calendar yr B.P. For ϳ300 yr during the late Younger Dryas, the sea-surface temperatures fluctuated between glacial values (ϳ2 ؇C) and interglacial values (ϳ10 ؇C) on a subdecadal to multidecadal time scale. This period of extreme instability preceded the more stable and warm Holocene, starting ca. 11,500 calendar yr B.P. These results are consistent with modeling experiments that link the Younger Dryas climate changes to fluctuations of the North Atlantic thermohaline circulation.

Publisher's copyright statement: NOTICE: this is the author's version of a work that was accepted for publication in Palaeogeography, Palaeoclimatology, Palaeoecology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be re ected in this document. Changes may have been made to this work since it was submitted for publication. A de nitive version was subsequently published in Palaeogeography, Palaeoclimatology, Palaeoecology, 2012, 31, , Part A, 10.1016/j.palaeo.2012 Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. prior to 8,600 cal. yr BP and ended at about 7,700-7,500 cal. yr BP, when the GIS margin had 25 withdrawn from the fjords and become mainly land-based. The benthic foraminiferal record from 26 one of the coastal sites mainly reflects West Greenland Current (WGC) subsurface water properties 27 and to a minor degree surface productivity. The most significant feature in this record is an abrupt 28 shift to a higher-productivity regime around ~7,700 cal. yr BP. We suggest that the cessation of a 29 widespread GIS meltwater discharge at that time favoured an increased influence of (sub)surface 30 water of Atlantic origin and initiation of modern subpolar gyre circulation enabling Labrador Sea 31 deep convection. Further offshore, a record of planktonic foraminiferal assemblages shows an 32 oceanographic change at ca. 9,500 cal. yr BP, while a gradual but marked change in the planktonic 33 foraminiferal assemblage between 8,800-7,000 cal. yr BP may be related to a narrowing of the 34 WGC low-salinity surface water belt. The oceanic regime off West Greenland prior to ~7,800 cal.