Water isotope records from the EPICA Dronning Maud Land (EDML) and the NorthGRIP ice cores have revealed a one to one coupling between Antarctic Isotope Maxima (AIM) and Greenland Dansgaard-Oeschger (DO) events back to 50 kyr. In order to explore if this north–south coupling is persistent over Marine Isotopic Stage 5 (MIS 5), a common timescale must first be constructed.Here, we present new records of d18O of O2 (d18Oatm) and methane (CH4) measured in the air trapped in ice from the EDML (68–147 kyr) and NorthGRIP (70–123 kyr) ice cores. We demonstrate that, through the period of interest, CH4 records alone are not sufficient to construct a common gas timescale between the two cores. Millennial-scale variations of d18Oatm are evidenced over MIS 5 both on the Antarctic and Greenland ice cores and are coupled to CH4 profiles to synchronise the NorthGRIP and EDML records. They are shown to be a precious tool for ice core synchronisation.With this new dating strategy, we produce the first continuous and accurate sequence of the north–south climatic dynamics on a common ice timescale for the last glacial inception and the first DO events of MIS 5, reducing relative dating uncertainties to an accuracy of a few centuries at the onset of DO events 24 to 20. This EDML-NorthGRIP synchronisation provides new firm evidence that the bipolar seesaw is a pervasive pattern from the beginning of the glacial period. The relationship between Antarctic warming amplitudes and their concurrent Greenland stadial duration highlights the particularity of DO event 21 and its Antarctic counterpart. Our results suggest a smaller Southern Ocean warming rate for this long DO event compared to DO events of MIS 3.

Gas tie points used to correlate NorthGRIP and EDML (EPICA Dronning Maud Land, Latitude: -75.002, Longitude: 0.068) records by minimizing the area between the NorthGRIP and EDML d18Oatm and CH4 records and associated uncertainties. Note that synchronisation uncertainties are minimal for DO events 19, 20 and 21 thanks to the use of d15N. Data extracted in the frame of a joint ICSTI/PANGAEA IPY effort, see http://doi.pangaea.de/10.1594/PANGAEA.150150

Supplement to: Capron, Emilie; Landais, Amaëlle; Lemieux-Dudon, Bénédicte; Schilt, Adrian; Masson-Delmotte, Valerie; Buiron, Daphné; Chappellaz, Jérôme A; Dahl-Jensen, Dorthe; Johnsen, Sigfús Jóhann; Leuenberger, Markus Christian; Loulergue, Laetitia; Oerter, Hans (2010): Synchronising EDML and NorthGRIP ice cores using d18O of atmospheric oxygen (d18Oatm) and CH4 measurements over MIS5 (80-123 kyr). Quaternary Science Reviews, 29(1-2), 222-234