Development of crystal orientation fabric in the Dome Fuji ice core in East Antarctica: implications for the deformation regime in ice sheets

Saruya, Tomotaka; Fujita, Shuji; Iizuka, Yoshinori; Miyamoto, Atsushi; Ohno, Hiroshi; Hori, Akira; Shigeyama, Wataru; Hirabayashi, Motohiro; Goto-Azuma, Kumiko

doi:https://doi.org/10.5194/tc-2021-336

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https://doi.org/10.5194/tc-2021-336

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30 Nov 2021

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

Development of crystal orientation fabric in the Dome Fuji ice core in East Antarctica: implications for the deformation regime in ice sheets

Tomotaka Saruya¹, Shuji Fujita^1,2, Yoshinori Iizuka³, Atsushi Miyamoto⁴, Hiroshi Ohno⁵, Akira Hori⁵, Wataru Shigeyama^2,a, Motohiro Hirabayashi¹, and Kumiko Goto-Azuma^1,2 Tomotaka Saruya et al.

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¹National Institute of Polar Research, Tokyo 190-8518, Japan
²Department of Polar Science, The Graduate University for Advanced Studies, SOKENDAI, Tokyo 190-8518, Japan
³Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan
⁴Institute for the Advancement of Higher Education, Hokkaido University, Sapporo 060-0817, Japan
⁵Kitami Institute of Technology, Kitami 090-8507, Japan
^anow at: JEOL Ltd., Tokyo 196-8558, Japan

Received: 25 Oct 2021 – Accepted for review: 26 Nov 2021 – Discussion started: 30 Nov 2021

Abstract. The crystal orientation fabric (COF) of a polar ice sheet has a significant effect on the rheology of the sheet. With the aim of better understanding the deformation regime of ice sheets, the present work investigated the COF in the upper 80 % of the depth within the 3035 m long Dome Fuji Station ice core drilled at one of the dome summits in East Antarctica. Dielectric anisotropy (∆ε) data were acquired as a novel indicator of the vertical clustering of COF resulting from vertical compressional strain within the dome, at which the ice cover has an age of approximately 300 kyrs BP. The ∆ε values were found to exhibit a general increase moving in the depth direction, but with fluctuations over distances on the order of 10–10² m. In addition, significant decreases in ∆ε were found to be associated with depths corresponding to three major glacial to interglacial transitions. These changes in ∆ε are ascribed to variations in the deformational history caused by dislocation motion occurring from near-surface depths to deeper layers. Fluctuations in ∆ε over distances of less than 0.5 m exhibited a strong inverse correlation with at depths greater than approximately 1200 m, indicating that they were enhanced during the glacial/interglacial transitions. The ∆ε data also exhibited a positive correlation with the concentration of chloride ions together with an inverse correlation with the amount of dust particles in the ice core at greater depths corresponding to decreases in the degree of c-axis clustering. Finally, we found that fluctuations in ∆ε persisted to approximately 80 % of the total depth of the ice sheet. These data suggest that the factors determining the deformation of ice include the concentration of chloride ions and amount of dust particles, and that the layered contrast associated with the COF is preserved all the way from the near-surface to a depth corresponding to approximately 80 % of the thickness of the ice sheet. These findings provide important implications regarding further development of the COF under the various stress-strain configurations that the ice will experience in the deepest region, approximately 20 % of the total depth from the ice/bed interface.

Tomotaka Saruya et al.

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RC1: 'Comment on tc-2021-336', Anonymous Referee #1, 24 Jan 2022 reply

Dear editor,

This paper investigates the crystal orientation fabric of the Dome Fuji Station ice core using a novel methodology as the dielectric anisotropy (from the dielectric permittivity tensor). Dielectric anisotropy is revealed as a good indicator of the vertical clustering of the crystal orientation fabric, also exhibiting a correlation with the concentration of chloride ions and with the amount of dust particles in the ice core. From the results, the authors conclude that the COF clustering is therefore affected by the presence of chloride irons, which increase the dislocation density, promote dislocation creep and enhance the COF clustering, while the presence of dust impedes it. The results show a COF layering in the upper 80% of the ice sheet, where the COF contrast amplitude increases at deeper layers. The conclusion is sound regarding the lowest 20% of the ice sheet, as layers will behave differently under stress depending on the COF cluster strength.

This well-written and well-organised manuscript presents a very useful methodology to be further evaluated in the future. We could obtain the COF contrast from the permittivity contrast obtained in VHF/UHF radar sounding. This will allow comparing deep COF layers avoiding areas with layers with heterogeneous thickness. This heterogeneity can lead to layer disturbances and folding due simple shear close to the bedrock.

The detailed description of the presence of soluble impurities and particles and its correlation with the COF is very useful for the understanding on the effect of them on ice rheology, which is currently unknown.

The manuscript is relevant for and thus can be a valuable contribution once some important issues are addressed. Thus, I recommend that the paper is accepted after minor revisions.

Suggestions for improvement:

Line 50: this statement “requires a reference.

Line 80: I would give details of the physicochemical properties obtained.

Table 1: Could you explain in the text why the thickness at the EDC samples (Durand) are not indicated?

Line 110: the authors do not explain why this study focuses on the upper 80% and not in the whole ice core. What are the difficulties to apply it in the bottom 20%? A discussion on this aspect will be useful.

Figure 2. Colouring in red and blue the lines is not necessary as they do not provide extra information.

Line 150: the detrended Ae value is a key parameter used in this work. It is mathematically defined in the text, but it would be very useful for readers to be able to see an explanation of what it value means, in practical terms.

Line 186. has the value of 0.0334 for the single ice crystal been determined in this study or does it come from the literature? In this case, a citation would be needed.

Line 213. Would it be possible to briefly explain the relationship between the permittivity value and the normalized eigenvalues? (here or in the caption of figure 6). I find the reference to Saruya et al. 2021 not enough, as this data is relevant for the conclusions.

Figures 4 and 5: I suggest including the references at the legend, as in figure 7.

In general: please, check the graphics in all figures. Box and axis markers do not match (as in figure 7).

Line 384: the reason why the presence of HCl has a stronger effect on dislocation migration than NaCl is explained later, in line 387. I suggest moving line 384 there to make the paragraph more understandable.

Line 444: In general: It should be explained with a bit more detail, what the positive or negative feedback mechanism referred to Azuma (1994) does mean (Relationship between CPO and deformation conditions).

Line 499: Regarding the alteration of layers in the deep parts in ice sheets, here I miss some discussion with observations already done in ice cores (as in Faria et al., 2010; Jansen et al., 2016, etc…).

Conclusion and chapter 4.5 : both texts are very similar. I would modify the conclusion part in bullet points or in a more synthetised way, because as it is now it reads as a repetition of the explanation given in the previous section 4.5.

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Citation: https://doi.org/10.5194/tc-2021-336-RC1

Tomotaka Saruya et al.

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Short summary

Crystal orientation fabrics (COF) of the Dome Fuji ice core was investigated with an innovative method with unprecedentedly high statistical significance and dense depth coverage. COF profile and its fluctuation were found to be highly dependent on concentration of chloride ion and dust. The data suggest deformation of ice at the deepest zone will be highly influenced by COF fluctuations that progressively develop from the near-surface firn toward the deepest zone within ice sheets.


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