Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/cp-2017-94
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
31 Jul 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).
Gas enclosure in polar firn follows universal law
Christoph Florian Schaller1, Johannes Freitag1, and Olaf Eisen1,2 1Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, 27568 Bremerhaven, Germany
2Department of Geosciences, University of Bremen, 28359 Bremen, Germany
Abstract. In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it is crucial to understand the fundamental lock-in process. Within the porous firn, bubbles are sealed continuously until the respective horizontal layer reaches a critical porosity. Present-day firn models use a postulated temperature dependence of this value as the only parameter to adjust to the surrounding conditions of individual sites. However, no direct measurements of the firn microstructure could confirm these assumptions. Here we show that the critical porosity is a universal constant by providing a statistically solid data set of μm-resolution 3D X-ray computer tomographic measurements for ice cores representing different extremes of the temperature and accumulation ranges. We demonstrate why indirect measurements yield misleading data and substantiate our observations by applying percolation theory as a theoretical framework for bubble trapping. Incorporation of our results does significantly influence the dating of trace gas records, changing gas age–ice age differences by up to more than 1000 years. This will help resolve inconsistencies, such as differences between East Antarctic δ15N records (as a proxy for firn height) and model results. We expect our findings to be the basis for improved firn air and densification models, leading to lower dating uncertainties. The reduced coupling of proxies and surrounding conditions may allow for more sophisticated reinterpretations of trace gas records in terms of paleoclimatic changes and will foster the development of new proxies, such as the air content as a marker of local insolation.

Citation: Schaller, C. F., Freitag, J., and Eisen, O.: Gas enclosure in polar firn follows universal law, Clim. Past Discuss., https://doi.org/10.5194/cp-2017-94, in review, 2017.
Christoph Florian Schaller et al.
Christoph Florian Schaller et al.

Data sets

Supplement to: Schaller, C. F. et al. (2017): Gas enclosure in polar firn follows universal law
Christoph Florian Schaller, Johannes Freitag, and Olaf Eisen
https://doi.org/10.1594/PANGAEA.879577
Christoph Florian Schaller et al.

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Short summary
In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it is crucial to understand the fundamental lock-in process. In our study, we conduct the first direct and statistically solid measurements of firn microstructure in the lock-in zone. We show that the critical porosity of bubble trapping is a universal constant, which leads to significant changes in dating and interpretation of ice core gas records.
In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it...
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