δ¹⁵N of N₂ in air trapped in polar ice: a tracer of gas transport in the firn and a possible constraint on ice age-gas age differences

We use records of surface temperature and CO₂ at Byrd and Vostok, along with their respective chronologies, to constrain the ice age-gas age difference (Δage) throughout the section of the Vostok ice core corresponding to the last glacial termination. In principle, Δage values calculated from these data can be used to discriminate whether gas in the firn mixes to the bubble close-off depth or to a depth equivalent to the diffusive column height. In practice, however, uncertainties in the chronology of Byrd and Vostok are too great to allow us to distinguish between these two possibilities. One can only say that at the time of the last termination, Δ for Vostok was between three and 10.6 kyr. Previous estimates fall within this range. -from Authors