Preprints
https://doi.org/10.5194/tc-2021-87
https://doi.org/10.5194/tc-2021-87

  14 Apr 2021

14 Apr 2021

Review status: this preprint is currently under review for the journal TC.

The role of sublimation as a driver of climate signals in the water isotope content of surface snow: Laboratory and field experimental results

Abigail G. Hughes1, Sonja Wahl2, Tyler R. Jones1, Alexandra Zuhr3,4, Maria Hörhold5, James W. C. White1, and Hans Christian Steen-Larsen2 Abigail G. Hughes et al.
  • 1Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, Colorado, USA
  • 2Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway
  • 3Alfred-Wegener-Institut Helmholtz Zentrum für Polar- und Meeresforschung, Research Unit Potsdam, Telegrafenberg A45, 14473 Potsdam, Germany
  • 4University of Potsdam, Institute of Geosciences, Karl-Liebknecht-Str. 24-25, 14476 Potsdam-Golm, Germany
  • 5Alfred-Wegener-Institut Helmholtz Zentrum für Polar- und Meeresforschung, Research Unit Bremerhaven, 27568 Bremerhaven, Germany

Abstract. Ice core water isotope records from Greenland and Antarctica are a valuable proxy for paleoclimate reconstruction, yet the processes influencing the climate signal stored in the isotopic composition of the snow are being revisited. Apart from precipitation input, post-depositional processes such as wind-driven redistribution and vapor-snow exchange processes at and below the surface are hypothesized to contribute to the isotope climate signal. Recent field studies have shown that surface snow isotopes vary between precipitation events and co-vary with vapor isotopes, which demonstrates that vapor- snow exchange is an important driving mechanism. Here we investigate how vapor-snow exchange and sublimation processes influence the isotopic composition of the snowpack. Controlled laboratory experiments under dry air flow show an increase of snow isotopic composition of up to 8 ‰ δ18O in the uppermost layer, with an attenuated signal down to 3 cm snow depth over the course of 4–6 days. This enrichment is accompanied by a decrease in the second-order parameter d-excess, indicating kinetic fractionation processes. Using a simple mass-balance and diffusion box model in conjunction with our observed laboratory vapor isotope signals, we are able to reproduce the observed changes in the snow. This confirms that sublimation alone can lead to a strong enrichment of stable water isotopes in surface snow and subsequent enrichment in the layers below. To compare laboratory experiments with realistic polar conditions, we completed four 2–3 day field experiments at the East Greenland Ice Core Project site (Northeast Greenland) in summer 2019. High-resolution temporal sampling of both natural and isolated snow was conducted under clear-sky conditions, and demonstrated that the snow isotopic composition changes on hourly timescales. A change of snow isotope content associated with sublimation is currently not implemented in isotope-enabled climate models and is not taken into account when interpreting ice core isotopic records. However, our results demonstrate that post-depositional processes such as sublimation play a role in creating the climate signal recorded in the water isotopes in surface snow. This suggests that the ice core water isotope signal may effectively integrate across multiple parameters, and the ice core climate record should be interpreted as such.

Abigail G. Hughes et al.

Status: open (until 09 Jun 2021)

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Abigail G. Hughes et al.

Abigail G. Hughes et al.

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Short summary
Water isotope records in Greenland and Antarctic ice cores are a valuable proxy for paleoclimate reconstruction, and are traditionally thought to primarily reflect precipitation input. However, post-depositional processes are hypothesized to contribute to the isotope climate signal. In this study we use laboratory experiments, field experiments, and modeling to show that sublimation and vapor-snow isotope exchange can rapidly influence the isotopic composition of the snowpack.