Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/tc-2017-199
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
11 Sep 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal The Cryosphere (TC).
On the similarity and apparent cycles of isotopic variations in East Antarctic snow-pits
Thomas Laepple1, Thomas Münch1,2, Mathieu Casado3, Maria Hoerhold4, Amaelle Landais3, and Sepp Kipfstuhl4 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
3Laboratoire des Sciences du Climat et de l’Environnement - IPSL, UMR 8212, CEA-CNRS-UVSQ, Gif sur Yvette, France
4Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, 27568 Bremerhaven, Germany
Abstract. Stable water isotopes in polar ice provide a wealth of information about past climate evolution. Snow pit studies allow us to relate observed weather and climate conditions to the measured isotope variations in the snow. They therefore offer the possibility to test our understanding of how isotope signals are formed and stored in firn and ice. As stable water isotopes in the snowfall are strongly correlated to air temperature, isotopes in the near surface snow are supposed to depict the seasonal cycle at a given site. Accordingly, variation between sites in accumulation rate is expected to be matched by variation in the number of seasonal cycles. However, snowpit studies from different accumulation conditions in East Antarctica reported similar isotopic variability and comparable apparent cycles in the δ18O and δD profiles with typical wavelengths of ∼ 20 cm. These observations are unexpected as the accumulation rates strongly differ between the sites, ranging from 20 to 80 mm w.e. yr−1 (∼ 5–25 cm of snow per year). Various mechanism have been proposed to explain the isotopic variations individually at each site; however, none of these is consistent with the similarity of the different profiles independent of the local accumulation conditions.

Here, we systematically analyze the properties and origins of isotopic variations in high-resolution firn profiles from eight East Antarctic sites. First, we confirm the suggested cycle length (mean distance between peaks) of ∼ 20 cm by counting the isotopic maxima. Spectral analysis further shows a strong similarity between the sites but indicates no dominant periodic features. Finally, the apparent cycle length increases with depth for most East Antarctic sites, which is inconsistent with burial and compression of a regular seasonal cycle. We show that these results can be explained by isotopic diffusion acting on a noise dominated isotope signal. The firn diffusion length is rather stable across the East Antarctic and thus leads to similar power spectral densities of the isotopic variations. This in turn implies a similar distance between isotopic maxima in the firn profiles.

Our results explain a large set of observations discussed in the literature, providing a simple explanation for the interpretation of apparent cycles in shallow isotope records, without invoking complex mechanisms. Finally, the results underline previous suggestions that isotopic signals in single ice cores from low-accumulation regions have a small signal-to-noise ratio and thus likely do not allow the reconstruction of interannual to decadal climate variations.


Citation: Laepple, T., Münch, T., Casado, M., Hoerhold, M., Landais, A., and Kipfstuhl, S.: On the similarity and apparent cycles of isotopic variations in East Antarctic snow-pits, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-199, in review, 2017.
Thomas Laepple et al.
Thomas Laepple et al.
Thomas Laepple et al.

Viewed

Total article views: 388 (including HTML, PDF, and XML)

HTML PDF XML Total BibTeX EndNote
296 87 5 388 4 6

Views and downloads (calculated since 11 Sep 2017)

Cumulative views and downloads (calculated since 11 Sep 2017)

Viewed (geographical distribution)

Total article views: 388 (including HTML, PDF, and XML)

Thereof 385 with geography defined and 3 with unknown origin.

Country # Views %
  • 1

Saved

Discussed

Latest update: 22 Nov 2017
Publications Copernicus
Download
Short summary
We explain why snow pits across different sites in East Antarctica show visually similar variations in water isotopes. We argue that the similarity and the apparent cycles of around 20 cm in the isotopic variations are the result of a seasonal cycle in isotopes, noise, for example from precipitation intermittency, and diffusion. The near constancy of the diffusion length across many ice-coring sites explains why the structure and cycle length is largely independent of the accumulation conditions.
We explain why snow pits across different sites in East Antarctica show visually similar...
Share