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Volume 11, issue 6 | Copyright
Geosci. Model Dev., 11, 2393-2418, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model description paper 20 Jun 2018

Model description paper | 20 Jun 2018

Numerical experiments on vapor diffusion in polar snow and firn and its impact on isotopes using the multi-layer energy balance model Crocus in SURFEX v8.0

Alexandra Touzeau1, Amaëlle Landais1, Samuel Morin2, Laurent Arnaud3, and Ghislain Picard3 Alexandra Touzeau et al.
  • 1LSCE, CNRS UMR8212, UVSQ, Université Paris-Saclay, Gif-sur-Yvette, 91191, France
  • 2Météo-France – CNRS, CNRM UMR3589, Centre d'Etudes de la Neige, Grenoble, France
  • 3Univ. Grenoble Alpes, CNRS, IGE, 38000 Grenoble, France

Abstract. To evaluate the impact of vapor diffusion on isotopic composition variations in snow pits and then in ice cores, we introduced water isotopes in the detailed snowpack model Crocus. At each step and for each snow layer, (1) the initial isotopic composition of vapor is taken at equilibrium with the solid phase, (2) a kinetic fractionation is applied during transport, and (3) vapor is condensed or snow is sublimated to compensate for deviation to vapor pressure at saturation.

We study the different effects of temperature gradient, compaction, wind compaction, and precipitation on the final vertical isotopic profiles. We also run complete simulations of vapor diffusion along isotopic gradients and of vapor diffusion driven by temperature gradients at GRIP, Greenland and at Dome C, Antarctica over periods of 1 or 10 years. The vapor diffusion tends to smooth the original seasonal signal, with an attenuation of 7 to 12% of the original signal over 10 years at GRIP. This is smaller than the observed attenuation in ice cores, indicating that the model attenuation due to diffusion is underestimated or that other processes, such as ventilation, influence attenuation. At Dome C, the attenuation is stronger (18%), probably because of the lower accumulation and stronger δ18O gradients.

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Short summary
We introduced a new module of water vapor diffusion into the snowpack model Crocus. Vapor transport locally modifies the density of snow layers, possibly influencing compaction. It also affects the original isotopic signature of snow layers. We also introduced water isotopes (𝛿18O) in the model. Over 10 years, the modeled attenuation of isotopic variations due to vapor diffusion is 7–18 % lower than the observations. Thus, other processes are required to explain the total attenuation.
We introduced a new module of water vapor diffusion into the snowpack model Crocus. Vapor...