Preprints
https://doi.org/10.5194/egusphere-2023-3146
https://doi.org/10.5194/egusphere-2023-3146
05 Jan 2024
 | 05 Jan 2024

Development of deformational regimes and microstructures in the deep sections and overall layered structures of the Dome Fuji ice core, Antarctica

Tomotaka Saruya, Atsushi Miyamoto, Shuji Fujita, Kumiko Goto-Azuma, Motohiro Hirabayashi, Akira Hori, Makoto Igarashi, Yoshinori Iizuka, Takao Kameda, Hiroshi Ohno, Wataru Shigeyama, and Shun Tsutaki

Abstract. An in-depth examination of rheology within the deep sections of polar ice sheets is essential for enhancing our understanding of glacial flow. In this study, we investigate the crystalline textural properties of the 3035-m-long Antarctic deep ice core, with a particular emphasis on its lowermost 20 %. We examine the crystal orientation fabric (COF) and compare it with various other properties from the ice core. In the uppermost approximately 80 % thickness zone (UP80%), the clustering strength of single pole COF steadily increased, reaching its possible maximum at the bottom of the UP80%. Below 1800 m in the UP80%, layers with more or fewer dusty impurities exhibit slower or faster growth of cluster strength. This situation continued until 2650 m. In the remaining lowermost approximately 20 % thickness zone (LO20%), the trend of the COF clustering strength changed around 2650 m and exhibited substantial fluctuations below this depth. In more impurity-rich layers, stronger clustering is maintained. In impurity-poor layers, relaxation of the COF clustering occurred due to the emergence of new crystal grains with c-axis orientation distinctly offset from the existing cluster, and dynamic recrystallization related to this emergence. The less impure layers show apparent features of bulging and migrating grain boundaries. We argue that the substantial deformational regime of polar ice sheets involves dislocation creep in both UP80% and LO20%, with dynamic recrystallization playing a critical role in the LO20%, particularly in impurity-poor layers, to recover a potential of COF available for the continuation of dislocation-creep-based deformation. Furthermore, we observe that layers and cluster axes of COF rotate meridionally due to rigid-body rotation caused by simple shear strain above subglacial slopes. These features provide vital clues for the development of the 3D structure of polar ice sheets in the deeper part, leading to inhomogeneous deformation between layers in various thickness scales, and the formation of folds, faults and mixing depending on the layers.

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Tomotaka Saruya, Atsushi Miyamoto, Shuji Fujita, Kumiko Goto-Azuma, Motohiro Hirabayashi, Akira Hori, Makoto Igarashi, Yoshinori Iizuka, Takao Kameda, Hiroshi Ohno, Wataru Shigeyama, and Shun Tsutaki

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • AC1: 'Comment on egusphere-2023-3146', Tomotaka Saruya, 09 Jan 2024
  • RC1: 'Comment on egusphere-2023-3146', Maurine Montagnat, 13 Feb 2024
    • AC2: 'Reply on RC1', Tomotaka Saruya, 10 Apr 2024
  • RC2: 'Comment on egusphere-2023-3146', David Prior, 15 Apr 2024
    • AC3: 'Reply on RC2', Tomotaka Saruya, 21 May 2024
Tomotaka Saruya, Atsushi Miyamoto, Shuji Fujita, Kumiko Goto-Azuma, Motohiro Hirabayashi, Akira Hori, Makoto Igarashi, Yoshinori Iizuka, Takao Kameda, Hiroshi Ohno, Wataru Shigeyama, and Shun Tsutaki
Tomotaka Saruya, Atsushi Miyamoto, Shuji Fujita, Kumiko Goto-Azuma, Motohiro Hirabayashi, Akira Hori, Makoto Igarashi, Yoshinori Iizuka, Takao Kameda, Hiroshi Ohno, Wataru Shigeyama, and Shun Tsutaki

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Short summary
Crystal orientation fabrics (COF) and microstructures in the deep sections of the Dome Fuji ice core were investigated using innovative methods with unprecedentedly high statistical significance and dense depth coverage. Together with our previous studies, we have obtained a whole layer profile of the COF and physical properties of the Dome Fuji ice core. COF profile and its fluctuation were found to be highly dependent on impurities concentrations and recrystallization processes.