Fractionation of O<sub>2</sub>∕N<sub>2</sub> and Ar∕N<sub>2</sub> in the Antarctic ice sheet during bubble formation and bubble–clathrate hydrate transition from precise gas measurements of the Dome Fuji ice core

Abstract. The variations of δO2/N2 and δAr/N2 in the Dome Fuji ice core were measured from 112 m (bubbly ice) to 2001 (clathrate hydrate ice). Our method, combined with low storage temperature samples (−50 ∘C), successfully excludes post-coring gas-loss fractionation signals our data. From bubbly middle bubble–clathrate transition zone (BCTZ) (112–800 m) below BCTZ (>1200 m), data exhibit orbital-scale similar local summer insolation. lower (800–1200 have large scatter, which may be caused by millimeter-scale inhomogeneity air composition finite sample lengths. insolation signal originally recorded at bubble close-off remains through BCTZ, reconstructed analyzing long (more than 50 cm for core). In clathrate zone, scatter around variability decreases depth, indicating diffusive smoothing δAr/N2. A simple gas diffusion model was used reproduce thus constrain their permeation coefficients. relationship between is markedly different datasets representing (slope ∼ 0.5), transformation (∼1), loss (∼0.2), suggesting that contributions mass-independent mass-dependent processes are those cases. method presented here useful improving orbital dating deep cores over multiple glacial cycles further studying non-insolation-driven (e.g., atmospheric composition) these gases.