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

• Main Authors: Stoll, Nicolas, Eichler, Jan, Hörhold, Maria, Erhardt, Tobias, Jensen, Camilla, Weikusat, Ilka
• Format: Text
• Language: English
• Published: 2021
• Subjects: Greenland; East Greenland; East Greenland Ice-core Project; Greenland ice core; Greenland Ice core Project; ice core
• Online Access: https://doi.org/10.5194/tc-2021-188; https://tc.copernicus.org/preprints/tc-2021-188/

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.