Preprints
https://doi.org/10.5194/egusphere-2023-2462
https://doi.org/10.5194/egusphere-2023-2462
03 Jan 2024
 | 03 Jan 2024

Post-depositional modification on seasonal-to-interannual timescales alters the deuterium excess signals in summer snow layers in Greenland

Michael Town, Hans Christian Steen-Larsen, Sonja Wahl, Anne-Katrine Faber, Melanie Behrens, Tyler Jones, and Arny Sveinbjornsdottir

Abstract. We document the isotopic evolution of near-surface snow at the EastGRIP ice core site in the Northeast Greenland National Park using a time-resolved array of 1-m deep isotope (δ18O, δD) profiles. The snow profiles were taken from May–August during the 2017–2019 summer seasons. An age-depth model was developed and applied to each profile mitigating the impacts of stratigraphic noise on isotope signals. Significant changes in deuterium excess (d) are observed in surface snow and near-surface snow as the snow ages. Decreases in d of up to 5 ‰ occurs during summer seasons after deposition during two of the three summer seasons observed. The d always experiences a 3–5 ‰ increase in d after aging one year in the snow due to a broadening of the autumn d maximum. Models of idealized scenarios coupled with prior work (Wahl et al., 2022) indicate that the summertime post-depostional changes in dd) can be explained with surface sublimation, forced ventilation of the near-surface snow down to 20–30 cm, and isotope-gradient-driven (IGD) diffusion throughout the column. The interannual Δd is also partly explained with IGD diffusion, but other mechanisms are at work that leave a bias in the d record. Thus, d does not just carry information about source region conditions and transport history as is commonly assumed, but also integrates local conditions into summer snow layers as the snow ages. Finally, we observe a dramatic increase in the seasonal isotope-to-temperature sensitivity occurs, which can be explained solely by IGD diffusion. Our results are dependent on the site characteristics (e.g. wind, temperature, accumulation rate), but indicate that more process-based research is necessary to understand water isotopes as climate proxies. Recommendations for monitoring and physical modeling are given, with special attention to the d parameter.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Michael Town, Hans Christian Steen-Larsen, Sonja Wahl, Anne-Katrine Faber, Melanie Behrens, Tyler Jones, and Arny Sveinbjornsdottir

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2462', Anonymous Referee #1, 30 Jan 2024
    • AC2: 'Reply on RC1', Michael Town, 27 May 2024
  • RC2: 'Comment on egusphere-2023-2462', Mathieu Casado, 15 Apr 2024
    • AC1: 'Reply on RC2', Michael Town, 27 May 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2462', Anonymous Referee #1, 30 Jan 2024
    • AC2: 'Reply on RC1', Michael Town, 27 May 2024
  • RC2: 'Comment on egusphere-2023-2462', Mathieu Casado, 15 Apr 2024
    • AC1: 'Reply on RC2', Michael Town, 27 May 2024
Michael Town, Hans Christian Steen-Larsen, Sonja Wahl, Anne-Katrine Faber, Melanie Behrens, Tyler Jones, and Arny Sveinbjornsdottir
Michael Town, Hans Christian Steen-Larsen, Sonja Wahl, Anne-Katrine Faber, Melanie Behrens, Tyler Jones, and Arny Sveinbjornsdottir

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Short summary
A polar snow isotope data from Northeast Greenland shows the snow changes after deposition. Summer snow sometimes enriches in oxygen-18, making it seem warmer than it actually was. Deuterium excess signals sometimes change after deposition making it seem that the snow came from warmer, closer, or more humid places. After a year of aging, summer layer deuterium excess always increases. Some reinterpretation of the deuterium-excess signals used to tune isotope-enabled models is necessary.