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Climate of the Past An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/cp-2017-78
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
04 Jul 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Climate of the Past (CP).
Analytical constraints on layered gas trapping and smoothing of atmospheric variability in ice under low accumulation conditions
Kévin Fourteau1, Xavier Faïn1, Patricia Martinerie1, Amaëlle Landais2, Alexey A. Ekaykin3, Vladimir Ya. Lipenkov3, and Jérôme Chappellaz1 1Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, F-38000 Grenoble, France
2Laboratoire des Sciences du Climat et de l’Environnement, UMR8212, CEA-CNRS-UVSQ-UPS/IPSL, Gif-sur-Yvette, France
3Climate and Environmental Research Laboratory, Arctic and Antarctic Research Institute, St. Petersburg, 199397, Russia
Abstract. We investigate for the first time through continuous measurements the loss and alteration of past atmospheric information from air trapping mechanisms under low accumulation conditions. Methane concentration changes were measured over the Dansgaard-Oeschger event 17 (D0-17, ~ 60,000 yrBP) in the Antarctic Vostok 4G-2 ice core. Measurements were performed using continuous-flow analysis combined with laser spectroscopy. The results highlight many anomalous layers at the centimeter scale, unevenly distributed along the ice core. The anomalous methane mixing ratios differ from those in the immediate surrounding layers by up to 50 ppbv. This phenomenon can be theoretically reproduced by a simple layered trapping model, creating very localized gas age scale inversions. We propose a method for cleaning the record of anomalous values which aims at minimizing the bias in the overall signal. Once the layered-trapping induced anomalies are removed from the record, the DO-17 appears to be smoother than its equivalent record from the high accumulation WAIS Divide ice core. This is expected due to the slower sinking and densification speeds of firn layers at lower accumulation. However and surprisingly, the degree of smoothing appears similar between modern and DO-17 conditions at Vostok. This suggests that glacial records of trace gases from low accumulation sites in the East Antarctic plateau can provide a better time resolution of past atmospheric composition changes than usually expected. We also developed a method to extract the gas age distributions in ice layers that can be applied even for sites without firn-air measurements. It is particularly adapted for the conditions of the East Antarctic plateau, as it helps to characterize smoothing for a large range of very low temperature and accumulation conditions.

Citation: Fourteau, K., Faïn, X., Martinerie, P., Landais, A., Ekaykin, A. A., Lipenkov, V. Ya., and Chappellaz, J.: Analytical constraints on layered gas trapping and smoothing of atmospheric variability in ice under low accumulation conditions, Clim. Past Discuss., https://doi.org/10.5194/cp-2017-78, in review, 2017.
Kévin Fourteau et al.
Kévin Fourteau et al.
Kévin Fourteau et al.

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Short summary
We measured methane concentrations from a polar ice core to quantify the differences between the ice record and the past true atmospheric conditions. Two effects were investigated by combining data analysis and modeling: the stratification of polar snow before gas enclosure driving chronological hiatuses in the record, and the gradual formation of bubbles in the ice attenuating fast atmospheric variations. Thus study will contribute at improving future climatic interpretations from ice archives.
We measured methane concentrations from a polar ice core to quantify the differences between the...
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