Full crystallographic orientation (<i>c</i> and <i>a</i> axes) of warm, coarse-grained ice in a shear-dominated setting: a case study, Storglaciären, Sweden

Monz, Morgan E.; Hudleston, Peter J.; Prior, David J.; Michels, Zachary; Fan, Sheng; Negrini, Marianne; Langhorne, Pat J.; Qi, Chao

doi:https://doi.org/10.5194/tc-15-303-2021

Articles | Volume 15, issue 1

https://doi.org/10.5194/tc-15-303-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/tc-15-303-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 15, issue 1

Research article

|

22 Jan 2021

Research article |

| 22 Jan 2021

Full crystallographic orientation (c and a axes) of warm, coarse-grained ice in a shear-dominated setting: a case study, Storglaciären, Sweden

Morgan E. Monz, Peter J. Hudleston, David J. Prior, Zachary Michels, Sheng Fan, Marianne Negrini, Pat J. Langhorne, and Chao Qi

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Final revised paper (published on 22 Jan 2021)
Preprint (discussion started on 08 Jun 2020)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of paper by Monz and co-authors', Maurine Montagnat, 02 Jul 2020
- AC1: 'Authors Response to Reviewer 1', Morgan Monz, 28 Aug 2020
RC2: 'Review of the ms. Electron backscatter diffraction (EBSD) based determination of crystallographic preferred orientation (CPO) in warm, coarse-grained ice: a case study, Storglaciären, Sweden', Andrea Tommasi, 10 Jul 2020
- AC2: 'Authors Response to Reviewer 2', Morgan Monz, 28 Aug 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by editor and referees) (03 Sep 2020) by Olivier Gagliardini

AR by Svenja Lange on behalf of the Authors (15 Oct 2020) Author's response

ED: Referee Nomination & Report Request started (15 Oct 2020) by Olivier Gagliardini

RR by Andrea Tommasi (26 Oct 2020)

Suggestions for revision or reasons for rejection

The authors have revised the ms accordingly to the reviewers reccommendations answering most comments, in particular those concerning the technique.
The statement in the conclusion and discussion that at low strain rates, dynamic recrystallization should be more effective deserves, however, some clarification.
Dynamic recrystallization depends on the work rate, which is usually higher at high strain rates, and on finite strain. So I would guess that the reason for a stronger effect of dynamic recrystallization on the CPO evolution in the studied natural setting is rather the higher finite strain.
Similarly for statement in l. 583 "Dynamic recrystallization and grain growth are enhanced at low strain rates". Dynamic recrystallization involves two processes: nucleation and growth. Neither are really favored by low strain rates. Because grain growth depends more strongly on diffusion than deformation, relative grain growth rates (relative to deformation rates) are higher at lower strain rates and higher temperatures, allowing for coarser recrystallized grain sizes. However, absolute recrystallization rates are not faster.
A point that was already highlighted in the first reviews is the comparison with experimental results: The authors acknowledge that there are two datasets, but compare their data only to those obtained by their group. Why? This gives the impression that the present data is only consistent with this one, what is not true, since the general features of the two preexisting datasets are coherent.
Last, concerning line 529: if in many cases, splitting of the <c> axis distribution in two maxima alligned in the plane normal to the shear direction is observed in absence of transpression, transpression cannot be the clearest explanation for this observation. In the conclusion of this paragraph, it would be better to clearly state which are the conditions you think better explain the splitting of the c-axis maxima in the studied case. It would also be interesting to discuss the processes that allow for dynamic recrystallization to produce such a change in the c-axis distribution.
Minor comments:
- The statement lines 187-188 is rather harsh. Are you really sure that none of these previous studies gave enough consideration to this important and rather first-order limitation of the observations?
- line 210, "that" is missing before "recrystallization"
- line 235: there are other groups that perform routine EBSD analyses on ice
- lines 440-441: Words missing: The composite pattern has one c-axis maximum ROUGHLY perpendicular to the shear plane, that is elongateD or split in TWO MAXIMA ALLIGNED a plane normal to the shear direction

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ED: Publish subject to minor revisions (review by editor) (02 Nov 2020) by Olivier Gagliardini

AR by Morgan Monz on behalf of the Authors (11 Nov 2020) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (17 Nov 2020) by Olivier Gagliardini

Dear Morgan,

Thanks for the revised version of your paper. Based on this new version and your reply to the last review, I think that your paper can now be accepted for publication in The Cryosphere.

I have nevertheless a last remark regarding plotting pole figures using orientations of pixels or grains. Just before the results section, you have a paragraph which discuss this as well as the Appendix material. I feel that your conclusion that "If the sample does not contain a representative number of grains, as is often the case with coarse-grained ice, then using one-point-per-grain provides a more representative fabric" is a bit weak and not really supported by any references or objective arguments of what should be a more representative fabric? Some years ago (Gagliardini et al., 2003), I conducted a modeling work to study the influence of accounting for the grain area when evaluating statistic parameters used to describe polycrystal fabric. The conclusion was that accounting for the grain area greatly improve the fabric description, in opposition with your current affirmation. I should have mentioned this publication before in the review process, but I am always reluctant because it is not the role of an editor to promote his own work. Nevertheless, I think in this particular case, and because they have not been that much work on that very specific subject, I would be interested to know how our findings based on synthetical fabrics (for which we know what is the real fabric) can support or not your statement about pixel versus grain orientations.

Best regards,
Olivier Gagliardini

Gagliardini O., G. Durand and Y. Wang, 2004 Grain area as a statistical weight for polycrystal constituents. J. of Glaciol ., 50 (168), p. 87-95.

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AR by Morgan Monz on behalf of the Authors (21 Nov 2020) Author's response Manuscript

ED: Publish as is (02 Dec 2020) by Olivier Gagliardini

Short summary

We present full crystallographic orientations of warm, coarse-grained ice deformed in a shear setting, enabling better characterization of how crystals in glacial ice preferentially align as ice flows. A commonly noted c-axis pattern, with several favored orientations, may result from bias due to overcounting large crystals with complex 3D shapes. A new sample preparation method effectively increases the sample size and reduces bias, resulting in a simpler pattern consistent with the ice flow.