On the potential of coupling air content and O2/N2 from trapped airfor establishing an ice core chronology tuned on local insolation

The potential to access an ice core chronology tuned on local insolation has been demonstrated for the first time in the work of M. Bender (2002) linking the variations of O2/N2 ratios in the air trapped in the Vostok ice with local (78°S) summertime insolation. More recently, it has been shown that the long-term changes in air content, V, recorded in ice from the high Antarctic plateau are also dominantly imprinted by the local summer insolation ( Raynaud et al., 2007). This paper presents a new V record from Vostok, which is compared with the published Vostok O2/N2 record for the same period of time (160–390 ka BP) by using the same spectral analysis methods. The spectral differences between the two properties and the possible mechanisms linking them with insolation through the surface snow structure and the close-off processes are discussed. The main result of our study is that the two experimentally independent local insolation proxies lead to absolute (orbital) timescales, which agree together within less than 1 ka on average. This result strongly adds credibility to the total content and the O2 to N2 ratio of the air trapped in ice as reliable and complementary tools for accurate dating of existing and future deep ice cores.