Preprints
https://doi.org/10.5194/tc-2021-196
https://doi.org/10.5194/tc-2021-196

  22 Jul 2021

22 Jul 2021

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

Effective coefficient of diffusion and permeability of firn at Dome C and Lock In, Antarctica – Estimates over the 100–850 kg m−3 density range

Neige Calonne1, Alexis Burr2,3, Armelle Philip2, Frédéric Flin1, and Christian Geindreau4 Neige Calonne et al.
  • 1Univ. Grenoble Alpes, Université de Toulouse, Météo-France, CNRS, CNRM, Centre d’Études de la Neige, Grenoble, France
  • 2Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, Grenoble, France
  • 3Univ. Grenoble Alpes, CNRS, Grenoble INP, SIMaP, Grenoble, France
  • 4Univ. Grenoble Alpes, CNRS, Grenoble INP, 3SR, Grenoble, France

Abstract. Modeling air transport through the entire ice sheet column is needed to interpret climate archives. To this end, different regressions were proposed to estimate the effective coefficient of diffusion and permeability of firn. Such regressions are often valid for specific depth or porosity ranges and were little evaluated as data of these properties are scarce. To contribute with a new dataset, this study presents the effective coefficient of diffusion and the permeability at Dome C and Lock In, Antarctica, from the near-surface to the close-off (23 to 133 m depth). Also, microstructure is characterized based on density, specific surface area, closed porosity ratio, connectivity index and structural anisotropy through the correlation lengths. All properties were estimated based on pore-scale computations on 3D tomographic images of firn samples. Normalized diffusion coefficient ranges from 1.9 × 10−1 to 8.3 × 10−5 and permeability ranges from 1.2 × 10−9 to 1.1 × 10−12 m2, for densities between 565 and 888 kg m−3. No or little anisotropy is reported. Next, we investigate the relationship of the transport properties with density over the firn density range as well as over the entire density range encountered in ice sheets by including snow data. Classical analytical models and regressions from literature are evaluated. For firn (550–850 kg m−3), good agreements are found for permeability and diffusion coefficient with the regressions based on the open porosity of Freitag et al. (2002) and Adolph and Albert (2014), despite the rather different site conditions (Greenland). Over the entire 100–850 kg m−3 density range, permeability is accurately reproduced by the Carman-Kozeny and Self-Consistent (spherical bi-composite) model when expressed in terms of a rescaled porosity ϕres = (ϕ–ϕoff) / (1–ϕoff) to account for pore closure, with ϕoff the close-off porosity. For the normalized diffusion coefficient, none of the evaluated formulas were satisfactory so we propose a new regression based on the rescaled porosity that reads D/Dair = (ϕres)1.61.

Neige Calonne et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-196', Johannes Freitag, 04 Oct 2021
  • RC2: 'Comment on tc-2021-196', Zoe Courville, 10 Oct 2021

Neige Calonne et al.

Neige Calonne et al.

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Short summary
Modeling gas transport in ice sheets from surface to close-off is key to interpret climate archives. Estimates of diffusion coefficient and permeability of snow and firn are required but remain a large source of uncertainty. We present a new dataset of diffusion coefficient and permeability from 20 to 120 m depth at two Antarctic sites. We suggest predictive formulas to estimate both properties over the entire 100–850 kg m−3 density range, i.e. anywhere within the ice sheet column.