On the Limits of Orbital Dating Using EPICA Dome C δO2/N2

We present here the first δO2/N2 record of trapped air from the EPICA Dome C (EDC) ice core, covering the period between 300 and 800 ka, which includes two periods of low orbital eccentricity. This record is a composite of several measurement series performed on ice samples stored at -25°C or -50°C. The samples stored at -25°C show clear gas loss on the order of 6.5‰. Two different gas loss corrections are proposed to account for this effect, with both corrections preserving the strong spectral powers at orbital frequencies of δO2/N2, in particular the antiphase relationship with local summer insolation. Although the exact mechanism underlying this relationship remains unclear, previous studies have proposed a link between surface insolation and ice grain properties at close-off and have used δO2/N2 to orbitally date the Vostok and Dome Fuji ice core records over the last 400 ka. Unlike previous studies, we find the strongest correlation between δO2/N2 and an integrated summer insolation (21st of December to 21st of March). Choice of tuning target and data filtering are shown to add at least 2 ka of uncertainty to the orbital tuning method. Moreover, we show that over periods of low eccentricity, the correlation between δO2/N2 and the different insolation curves is ambiguous because some peaks in the insolation curves cannot be identified in the δO2/N2 record (or vice versa). Recognizing these limitations of this dating method for the period 300-800 ka on the EDC ice core, we use the δO2/N2 signal to test the accuracy of the recommended EDC age scale (EDC3). From the comparison between the summer insolation curves, we reveal that the EDC3 age scale is generally correct within its published uncertainty (6 ky) over the 300-800 ka period except over the following periods corresponding to minima in eccentricity: 360-450 ka and 720-760 ka (and possibly 520-560 ka). The link between δ18Oatm and precession confirms that these periods are problematic periods in the EDC3 chronology. Finally, we use the δO2/N2 signal to propose the minimal and maximal durations of MIS 11: 21.5 ka and 37.9 ka.