Preprints
https://doi.org/10.5194/tc-2021-188
https://doi.org/10.5194/tc-2021-188

  06 Jul 2021

06 Jul 2021

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

Microstructure, Micro-inclusions and Mineralogy along the EGRIP ice core – Part 1: Localisation of inclusions and deformation patterns

Nicolas Stoll1, Jan Eichler1, Maria Hörhold1, Tobias Erhardt1,2, Camilla Jensen2, and Ilka Weikusat1,3 Nicolas Stoll et al.
  • 1Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 2Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 3Department of Geosciences, Eberhard Karls University, Tübingen, Germany

Abstract. Impurities deposited in polar ice allow the reconstruction of the atmospheric aerosol concentration of the past. At the same time they impact the physical properties of the ice itself such as its deformation behaviour. Impurities are thought to enhance ice deformation, but observations are ambiguous due to a shortage of comprehensive microstructural analyses. For the first time, we systematically analyse micro-inclusions in polar fast flowing ice, i.e. from the East Greenland Ice Core Project ice core drilled trough the Northeast Greenland Ice Stream. In direct relation to the inclusions we derive the crystal-preferred orientation, fabric, grain size, and microstructural features at ten depths, covering the Holocene and Late Glacial. We use optical microscopy to create microstructure maps to analyse the in situ locations of inclusions in the polycrystalline, solid ice samples. Micro-inclusions are more variable in spatial distribution than previously observed, and show various distributional patterns ranging from centimetre-thick layers to clusters and solitary particles, independent of depth. Analysing the area occupied by grain boundaries in the respective samples shows that micro-inclusions are slightly more often located at or close to grain boundaries in half of all samples. Throughout all samples we find strong indications of dynamic recrystallisation, such as grain islands, bulging grains and different types of subgrain boundaries. We discuss the spatial variability of micro-inclusions, the link between spatial variability and mineralogy, and possible effects on the microstructure and deformation behaviour of the ice. Our results emphasise the need for holistic approaches in future studies, combining microstructure and impurity analysis.

Nicolas Stoll et al.

Status: open (until 31 Aug 2021)

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Nicolas Stoll et al.

Nicolas Stoll et al.

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Short summary
We did a systematic analysis of the location of inclusions in the EGRIP ice core, the first ice core from an ice stream. We combine this with crystal orientation and grain size data enabling the first overview about the microstructure of this unique ice core. Micro-inclusions show a strong spatial variability, patterns (clusters or horizontal layers) and roughly one third is located at grain boundaries. More holistic approaches are needed to understand deformation processes in the ice better.