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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/gmd-2017-217
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Model description paper
26 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).
Numerical experiments on isotopic diffusion in polar snow and firn using a multi-layer energy balance model
Alexandra Touzeau1, Amaëlle Landais1, Samuel Morin2, Laurent Arnaud3, and Ghislain Picard3 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
3LGGE, CNRS UMR5183, Université Grenoble Alpes, Grenoble, France
Abstract. To evaluate the impact of vapor diffusion onto isotopic composition variations in the snow pits and then in ice cores, we introduced water isotopes in the detailed snowpack model Crocus. The isotopes routine is run with a 1 s resolution. At each step and for each snow layer, 1) the initial isotopic composition of vapor is taken at equilibrium with solid phase, 2) kinetic fractionation is applied during transport, and 3) condensation is realized.

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 and isotopic diffusion 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 9.5 % of the original signal over 10 years at GRIP. This is smaller than the observed attenuation in ice cores, indicating that the model underestimates attenuation due to diffusion or that other processes, such as ventilation, also contribute to the observed attenuation. At Dome C, the attenuation is stronger (14 %), probably because of the lower accumulation and stronger δ18O gradients.

Because vapor diffusion is not the only process responsible of the signal attenuation, it would be useful to implement in the model ventilation of the snowpack and exchanges with the atmosphere to evaluate their contribution.


Citation: Touzeau, A., Landais, A., Morin, S., Arnaud, L., and Picard, G.: Numerical experiments on isotopic diffusion in polar snow and firn using a multi-layer energy balance model, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2017-217, in review, 2017.
Alexandra Touzeau et al.
Alexandra Touzeau et al.
Alexandra Touzeau et al.

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Short summary
We introduced a new module of water vapor diffusion into the snowpack model Crocus. Indeed, 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 ten years, the modelled attenuation of isotopic variations due to vapor diffusion is 8–14 %, 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. Indeed,...
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