Preprints
https://doi.org/10.5194/tc-2021-147
https://doi.org/10.5194/tc-2021-147

  15 Jun 2021

15 Jun 2021

Review status: this preprint is currently under review for the journal TC.

Fractionation of O2/N2 and Ar/N2 in the Antarctic ice sheet during bubble formation and bubble-clathrate hydrate transition from precise gas measurements of the Dome Fuji ice core

Ikumi Oyabu1, Kenji Kawamura1,2,3, Tsutomu Uchida4, Shuji Fujita1,2, Kyotaro Kitamura1, Motohiro Hirabayashi1, Shuji Aoki5, Shinji Morimoto5, Takakiyo Nakazawa5, Jeffrey P. Severinghaus6, and Jacob Morgan6 Ikumi Oyabu et al.
  • 1National Institute of Polar Research, Tokyo 190-8518, Japan
  • 2Department of Polar Science, The Graduate University of Advanced Studies (SOKENDAI), Tokyo 190-8518, Japan
  • 3Japan Agency for Marine Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan
  • 4Division of Applied Physics, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan
  • 5Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
  • 6Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA

Abstract. The variations of δO2/N2 and δAr/N2 in the Dome Fuji ice core were measured from 112 m (bubbly ice) to 2001 m (clathrate hydrate ice) at high precision. Our method, combined with the low storage temperature of the samples (−50 °C), successfully excludes post-coring gas-loss fractionation signals from our data. From the bubbly ice to the middle of the bubble-clathrate transition zone (BCTZ) (112–800 m) and below the BCTZ (> 1200 m), the δO2/N2 and δAr/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. The insolation signal originally recorded at the bubble close-off remains through the BCTZ, and the insolation signal may be reconstructed by analyzing long ice samples. In the clathrate hydrate zone, the scatters around the orbital-scale variability decrease with depth, indicating diffusive smoothing of δO2/N2 and δAr/N2. A simple gas diffusion model was used to reproduce the smoothing and thus constrain their permeation coefficients. The relationship between δAr/Ν2 and δO2/N2 is markedly different for the datasets representing bubble close-off (slope ~0.5), bubble-clathrate hydrate transformation (~1), and post-coring gas-loss (~0.2), suggesting that the contribution of the mass-independent and mass-dependent 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 further studying non-insolation-driven signals (e.g., atmospheric composition) of these gases.

Ikumi Oyabu et al.

Status: open (until 31 Aug 2021)

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  • RC1: 'Comment on tc-2021-147', Anonymous Referee #1, 05 Jul 2021 reply

Ikumi Oyabu et al.

Ikumi Oyabu et al.

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Short summary
We present O2/N2 and Ar/N2 records from Dome Fuji ice core through the bubbly ice, bubble-clathrate transition, and clathrate ice zones without gas-loss fractionation. The insolation signal is preserved through the clathrate formation. The relationship between Ar/Ν2 and Ο22 suggests that the fractionation for bubble-clathrate transition is mass-independent, while the bubble close-off process involves a combination of mass-independent and mass-dependent fractionation for O2 and Ar.