Funding was provided by US National Science Foundation (NSF) awards OPP-1205196 and PLR-1418256 to S.B.D., ARC-1205062 to B.E.S. and OPP-1205008 to M.J.E. L.D.T. acknowledges institutional support from Rowan University and the Doherty Postdoctoral Scholarship at Woods Hole Oceanographic Institution. M.B.O. acknowledges support from the Department of Defense Office of Naval Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a. Collection, analysis and interpretation of core D5 was supported by NSF grant 0352511 to J.R.McC. B.P.Y.N. and M.R.v.d.B. acknowledge support from the Polar Program of the Netherlands Organization for Scientific Research (NWO/NPP) and the Netherlands Earth System Science Centre (NESSC). For running the MAR model, computational resources have been provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifique de Belgique (FRS–FNRS) under grant number 2.5020.11 and the Tier-1 supercomputer (Zenobe) of the Fédération Wallonie Bruxelles infrastructure funded by the Walloon Region under grant agreement number 1117545. We thank M. Waszkiewicz and IDPO/IDDO for ice core drilling support. We thank the NSF Ice Core Facility (formerly NICL), A. York, M. Bingham, M. Hatch, S. Zarfos, Z. Li, and Milton Academy students for ice core sampling and processing support. We thank R. Banta for help with the D5 core, and A. Arienzo and N. Chellman for help in analysing the NU core. We thank M. Tedesco for providing the satellite melt duration data used in Fig. 3d. Maps in Figs. 1a, 3 and Extended Data Figs. 3, 4 were created with the NCAR Command Language (https://www.ncl.ucar.edu), and maps in Fig. 1b and Extended Data Fig. 6 were created with Esri ArcGIS. We acknowledge the use of Rapid Response imagery in Fig. 1b from the Land, Atmosphere Near real-time Capability for EOS (LANCE) system operated by the NASA/GSFC/Earth Science Data and Information System (ESDIS) with funding provided by NASA/HQ.

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Nature thanks J. Briner and B. Vinther for their contribution to the peer review of this work.