%0 Journal Article %T Phase relationships between orbital forcing and the composition of air trapped in Antarctic ice cores %A Bazin %A Lucie %A Capron %A Emilie %A Dumont %A Marie %A Jouzel %A Jean %A Landais %A Amaelle %A Leuenberger %A Markus %A Masson-Delmotte %A Val谷rie %A Picard %A Ghislain %A Pri谷 %A Fr谷d谷ric %A Ritz %A Catherine %J - %D 2016 %R https://doi.org/10.5194/cp-12-729-2016 %X

Abstract. Orbital tuning is central for ice core chronologies beyond annual layer counting, available back to 60 ka (i.e. thousands of years before 1950) for Greenland ice cores. While several complementary orbital tuning tools have recently been developed using 汛¹⁸O_atm, 汛O₂⁄N₂ and air content with different orbital targets, quantifying their uncertainties remains a challenge. Indeed, the exact processes linking variations of these parameters, measured in the air trapped in ice, to their orbital targets are not yet fully understood. Here, we provide new series of 汛O₂決N₂ and 汛¹⁸O_atm data encompassing Marine Isotopic Stage (MIS) 5 (between 100 and 160 ka) and the oldest part (340–800 ka) of the East Antarctic EPICA DomeˋC (EDC) ice core. For the first time, the measurements over MISˋ5 allow an inter-comparison of 汛O₂決N₂ and 汛¹⁸O_atm records from three East Antarctic ice core sites (EDC, Vostok and DomeˋF). This comparison highlights some site-specific 汛O₂決N₂ variations. Such an observation, the evidence of a 100 ka periodicity in the 汛O₂決N₂ signal and the difficulty to identify extrema and mid-slopes in 汛O₂決N₂ increase the uncertainty associated with the use of 汛O₂決N₂ as an orbital tuning tool, now calculated to be 3–4 ka. When combining records of 汛¹⁸O_atm and 汛O₂決N₂ from Vostok and EDC, we find a loss of orbital signature for these two parameters during periods of minimum eccentricity (‵ 400 ka,ˋ‵ 720–800 ka). Our data set reveals a time-varying offset between 汛O₂決N₂ and 汛¹⁸O_atm records over the last 800 ka that we interpret as variations in the lagged response of 汛¹⁸O_atm to precession. The largest offsets are identified during Terminations II, MISˋ8 and MISˋ16, corresponding to periods of destabilization of the Northern polar ice sheets. We therefore suggest that the occurrence of Heinrich每like events influences the response of 汛¹⁸O_atm to precession.