[A-CC26] アイスコアと古環境モデリング

[ACC26-01] ドームふじ氷床コアにおけるO₂/N₂とAr/N₂の分別

★招待講演

*大藪 幾美¹、川村 賢二^1,2,3、内田 努⁴、藤田 秀二^1,2、北村 享太郎¹、平林 幹啓¹、Severinghaus Jeffrey⁵、Morgan Jacob⁵ (1.情報・システム研究機構　国立極地研究所、2.総合研究大学院大学、3.海洋研究開発機構、4.北海道大学、5.スクリップス海洋研究所)

キーワード：アイスコア、氷床、ドームふじ、分別、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.