[A-CC26] Ice cores and paleoenvironmental modeling

[ACC26-01] Fractionation of O₂/N₂ and Ar/N₂ in polar ice cores during bubble formation, bubble-clathrate hydrate transition, and gas loss during storage from precise gas measurements of the Dome Fuji ice core, Antarctica

★Invited Papers

*Ikumi Oyabu¹, Kenji Kawamura^1,2,3, Tsutomu Uchida⁴, Shuji Fujita^1,2, Kyotaro Kitamura¹, Motohiro Hirabayashi¹, Jeffrey Severinghaus⁵, Morgan Jacob⁵ (1.National Institute of Polar Research, Research Organization of Information and Systems, 2.The Graduate University of Advanced Studies (SOKENDAI), 3.Japan Agency for Marine Science and Technology (JAMSTEC), 4.Hokkaido University, 5.Scripps Institution of Oceanography)

Keywords:ice core, ice sheet, Dome Fuji, fractionation, O2/N2, Ar/N2

The variations of δΟ₂/Ν₂ and δΑr/N₂ in the Dome Fuji ice core were measured from 112 m (bubbly ice) to 2000 m (clathrate hydrate ice) at high precision. Our method combined with low storage temperature (-50 °C) successfully remove post-coring gas-loss fractionation signals from our data. From bubbly ice to the middle of bubble-clathrate transition zone (BCTZ) (112 – 800 m) and below the BCTZ (>1200 m), the δΟ₂/Ν₂ and δΑr/N₂ data exhibit orbital-scale variations similar to local summer insolation. The data in the lower BCTZ (800 – 1200 m) have large scatters, which may be caused by mm-scale inhomogeneity of air composition combined with finite sample lengths. In the clathrate hydrate zone, the scatters around the orbital-scale variability decrease with depth, indicating diffusive smoothing of δΟ₂/Ν₂ and δΑr/N₂. A simple gas diffusion model was used to reproduce the smoothing and thus constrain permeation coefficients of the gases. Relationship between δAr/Ν₂ and δΟ₂/Ν₂ is markedly different for the datasets representing bubble close-off (slope ~0.5), diffusion within the ice sheet (~1), and post-coring gas-loss (~0.2), suggesting that the dominant fractionation processes are different for those cases. The method and data presented here may be useful for improving the orbital dating of deep ice cores over the multiple glacial cycles, and for further studying non-insolation-driven signals (e.g., atmospheric composition) of these gases.