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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/tc-2019-89
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-89
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Jun 2019

Research article | 25 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Multi-tracer study of gas trapping in an East Antarctic ice core

Kévin Fourteau1, Patricia Martinerie1, Xavier Faïn1, Christoph F. Schaller2, Rebecca J. Tuckwell2, Henning Löwe4, Laurent Arnaud1, Olivier Magand1, Elizabeth R. Thomas3, Johannes Freitag2, Robert Mulvaney3, Martin Schneebeli4, and Vladimir Ya. Lipenkov5 Kévin Fourteau et al.
  • 1Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, F-38000 Grenoble, France
  • 2Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, 27568 Bremerhaven, Germany
  • 3British Antarctic Survey, Natural Environment Research Council, Cambridge, UK
  • 4WSL Institute for Snow and Avalanche Research (SLF), CH-7260 Davos Dorf, Switzerland
  • 5Climate and Environmental Research Laboratory, Arctic and Antarctic Research Institute, St. Petersburg, 199397, Russia

Abstract. We study a firn and ice core drilled at the new "Lock-In" site in East Antarctica, located 136 km away from Concordia station towards Durmont d'Urville. High resolution chemical and physical measurements were performed on the core, with a particular focus on the trapping zone of the firn where air bubbles are formed. We measured the air content in the ice, closed and open porous volumes in the firn, firn density, firn liquid conductivity and major ion concentrations, as well as methane concentrations in the ice. The closed and open porosity volumes of firn samples were obtained by the two independent methods of pycnometry and tomography, that yield similar results. The measured increase of the closed porosity with density is used to estimate the air content trapped in the ice with the aid of a simple gas trapping model. Results show a discrepancy, with the model trapping too much air. Experimental errors have been considered but do not explain the discrepancy between the model and the observations. The model and data can be reconciled with the introduction of a reduced compression of the closed porosity compared to the open porosity. Yet, it is not clear if this limited compression of closed pores is the actual mechanism responsible for the low amount of air in the ice. High resolution density measurements reveal the presence of a strong layering, manifesting itself as centimeter scale variations. Despite this heterogeneous stratification, all layers, including the ones that are especially dense or less dense compared to their surroundings, display similar pore morphology and closed porosity as function of density. This implies that all layers close in a similar way, even though some close in advance or later compared to the bulk firn. Investigation of the chemistry data suggests that in the trapping zone, the observed stratification is partly related to the presence of chemical impurities.

Kévin Fourteau et al.
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Short summary
Understanding gas trapping in polar ice is essential to study the relationship between greenhouse gases and past climates. New data of bubble closure, used in a simple gas trapping model, show inconsistency with the final air content in ice. It suggests gas trapping is not fully understood. We also use a combination of high-resolution measurements to investigate the effect of polar snow stratification on gas trapping and find that all strata have similar pores, but that some close in advance.
Understanding gas trapping in polar ice is essential to study the relationship between...
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