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The Cryosphere An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/tc-2017-35
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
05 Apr 2017
Review status
This discussion paper is under review for the journal The Cryosphere (TC).
Constraints on post-depositional isotope modifications in East Antarctic firn from analysing temporal changes of isotope profiles
Thomas Münch1,2, Sepp Kipfstuhl3, Johannes Freitag3, Hanno Meyer1, and Thomas Laepple1 1Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Telegrafenberg A43, 14473 Potsdam, Germany
2Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
3Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, 27568 Bremerhaven, Germany
Abstract. Stable water isotopes in firn and ice cores are extensively used to infer past climate changes. In low-accumulation regions their interpretation is however challenged by poorly constrained effects that may influence the initial isotope signal during and after deposition. This is reflected in snow-pit isotope data from Kohnen Station, Antarctica, which exhibit a clear seasonal cycle but also strong inter-annual variations that contradict local temperature observations. These inconsistencies persist even after averaging many profiles and are thus not explained by local stratigraphic noise. Previous studies have suggested that post-depositional processes may significantly influence the isotopic composition of East Antarctic firn. Here, we reject the hypothesis of post-depositional change within the open-porous firn beyond diffusion and densification. To this end, we analyse 22 stable water isotope profiles obtained from two snow trenches at Kohnen Station and examine the temporal isotope modifications by comparing the new with published trench data extracted 2 years earlier. The initial isotope profiles undergo changes over time due to downward-advection, firn diffusion and densification in magnitudes consistent with independent estimates. Beyond that, we find no evidence for additional modification of the original isotope record. These results show that the discrepancy between local temperatures and isotopes most likely originates from spatially coherent processes prior to or during deposition, such as precipitation intermittency or systematic isotope modifications acting on drifting or loose surface snow.

Citation: Münch, T., Kipfstuhl, S., Freitag, J., Meyer, H., and Laepple, T.: Constraints on post-depositional isotope modifications in East Antarctic firn from analysing temporal changes of isotope profiles, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-35, in review, 2017.
Thomas Münch et al.
Thomas Münch et al.
Thomas Münch et al.

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The importance of post-depositional changes for the temperature interpretation of water isotopes is poorly constrained by observations. Here, for the first time, temporal isotope changes in the open-porous firn are directly analysed using a large array of shallow isotope profiles. By this, we can reject the possibility of post-depositional change beyond diffusion and densification as the cause of the discrepancy between isotope and local temperature variations at Kohnen Station, East Antarctica.
The importance of post-depositional changes for the temperature interpretation of water isotopes...
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