The last glacial period exhibited abrupt Dansgaard-Oeschger climatic oscillations, evidence of which is preserved in a variety of Northern Hemisphere palaeoclimate archives. Ice cores show that Antarctica cooled during the warm phases of the Greenland Dansgaard-Oeschger cycle and vice versa, suggesting an interhemispheric redistribution of heat through a mechanism called the bipolar seesaw. Variations in the Atlantic meridional overturning circulation (AMOC) strength are thought to have been important, but much uncertainty remains regarding the dynamics and trigger of these abrupt events. Key information is contained in the relative phasing of hemispheric climate variations, yet the large, poorly constrained difference between gas age and ice age and the relatively low resolution of methane records from Antarctic ice cores have so far precluded methane-based synchronization at the required sub-centennial precision. Here we use a recently drilled high-accumulation Antarctic ice core to show that, on average, abrupt Greenland warming leads the corresponding Antarctic cooling onset by 218 ± 92 years (2Ï) for Dansgaard-Oeschger events, including the Bølling event; Greenland cooling leads the corresponding onset of Antarctic warming by 208 ± 96 years. Our results demonstrate a north-to-south directionality of the abrupt climatic signal, which is propagated to the Southern Hemisphere high latitudes by oceanic rather than atmospheric processes. The similar interpolar phasing of warming and cooling transitions suggests that the transfer time of the climatic signal is independent of the AMOC background state. Our findings confirm a central role for ocean circulation in the bipolar seesaw and provide clear criteria for assessing hypotheses and model simulations of Dansgaard-Oeschger dynamics.
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Acknowledgements We thank the WAIS Divide Drilling Team (2006–2013) (E. Morton, P. Cassidy, M. Jayred, J. Robinson, S. Polishinski, J. Koehler, L. Albershardt, J. Goetz, B. Gross, R. Kulin, S. Haman, W. Neumeister, C. Zander, J. Kyne, L. Augustin, B. Folmer, S. B. Hansen, E. Alexander and J. Fowler) and the dozens of core handlers who processed the ice core in the field and at the National Ice Core Laboratory (NICL). This work isfundedthrough the USNationalScience foundationgrants 0944078,0841308 (to M.A.), 1043528 (to R.B.A., D.E.V. and J.M.F.), 1142173 (to R.B.), 1204172, 1142041, 1043518 (to E.J.B.), 0839066 (to J.C.-D.), 0087345, 0944191 (to H.C. and E.D.W.), 0539232, 0537661 (to K.M.C.), 1142069, 1142115 (to N.W.D.), 0841135 (to IDDO), 0839093, 1142166 (to J.R.M.), 0440819, 1142164 (to K.C.M.), 1142178 (to P.B.P.), 0538657 (to J.P.S.), 1043500, 0944584 (to T.A.S.), 1043313 (to M.K.S), 0537930, 1043092 (to E.J.S.), 0230149, 0230396, 0440817, 0440819, 0944191, 0944348 (to K.C.T.), 0944266 (to M.S.T.), 0839137 (to K.C.W. and K.N.), 0537593 and 1043167 (to J.W.C.W.); the USGS Climate and Land Use Change Program (to G.D.C. and J.J.F.); the NOAA Climate and Global Change Fellowship Program, administered by the University Corporation for Atmospheric Research (to C.B.); the Villum Foundation (to M.W.); the Joint Institute for the Study of the Atmosphere and Ocean (to J.B.P., JISAO contribution no.2343); and the KoreaPolarResearchInstitute,grant PE15010(to J.A.).The National Science Foundation Office of Polar Programs also funded the WAIS Divide Science Coordination Office at the Desert Research Institute of Nevada and University of New Hampshire for the collection and distribution of the WAIS Divide ice core and related tasks; the Ice Drilling Program Office and Ice Drilling Design and Operations group for coring activities; the NICL for curation of the core; Raytheon Polar Services for logistics support in Antarctica; and the 109th New York Air National Guard for airlift in Antarctica.
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