Towards orbital dating of the EPICA Dome C ice core using δO₂/N₂

Abstract. Based on a composite of several measurement series performed on ice samples stored at −25 °C or −50 °C, we present and discuss the first δO₂/N₂ record of trapped air from the EPICA Dome C (EDC) ice core covering the period between 300 and 800 ka (thousands of years before present). The samples stored at −25 °C show clear gas loss affecting the precision and mean level of the δO₂/N₂ record. Two different gas loss corrections are proposed to account for this effect, without altering the spectral properties of the original datasets. Although processes at play remain to be fully understood, previous studies have proposed a link between surface insolation, ice grain properties at close-off, and δO₂/N₂ in air bubbles, from which orbitally tuned chronologies of the Vostok and Dome Fuji ice core records have been derived over the last four climatic cycles. Here, we show that limitations caused by data quality and resolution, data filtering, and uncertainties in the orbital tuning target limit the precision of this tuning method for EDC. Moreover, our extended record includes two periods of low eccentricity. During these intervals (around 400 ka and 750 ka), the matching between δO₂/N₂ and the different insolation curves is ambiguous because some local insolation maxima cannot be identified in the δO₂/N₂ record (and vice versa). Recognizing these limitations, we restrict the use of our δO₂/N₂ record to show that the EDC3 age scale is generally correct within its published uncertainty (6 kyr) over the 300–800 ka period.