Revisiting the role of vertical shear in analytic ice shelf models
Abstract. Analytic modeling of ice shelf flow began when Weertman derived an expression for the strain rates within an unconfined shelf, of uniform thickness, extending only in one direction. Nearly two decades later, Thomas generalized Weertman's analysis to ice shelves of nonuniform thickness, deriving one of the most well-known analytic models in glaciology: . However, despite the prevalence of this model in both historical and contemporary texts, there remain persistent miscommunications regarding the role of vertical shear in its construction. In Thomas' original approach, vertical shear stress was considered negligible in the stress balance; in a significant contrast, the same model is typically derived in contemporary texts by the neglect of basal resistance. These two approaches are not equivalent, and yet, it remains common to misinterpret vertical shear stress as typically neglected in current ice shelf modeling studies. This manuscript provides clarification on this pervasive misconception. We emphasize that vertical shear stress should not be interpreted as negligible in the construction of general shallow shelf models. However, we also demonstrate that the vertical shear stress inherent in Thomas' expression does not give rise to a well-defined vertical shear strain rate. For situations in which vertical shear stress in shallow ice shelf models is of interest, we provide guidance on how to best calculate it.
Chris Miele et al.
Status: final response (author comments only)
RC1: 'Comment on egusphere-2022-1310', Anonymous Referee #1, 26 Jan 2023
- AC1: 'Reply on RC1', Chris Miele, 27 Jan 2023
RC2: 'Review of “Revisiting the role of vertical shear in analytic ice shelf models” by C. Miele et al.', Anonymous Referee #2, 16 Mar 2023
- AC2: 'Reply on RC2', Chris Miele, 16 Mar 2023
RC3: 'Comment on egusphere-2022-1310', Josefin Ahlkrona, 21 Mar 2023
- AC3: 'Reply on RC3', Chris Miele, 21 Mar 2023
RC4: 'Comment on egusphere-2022-1310', Anonymous Referee #4, 21 Mar 2023
- AC4: 'Reply on RC4', Chris Miele, 21 Mar 2023
- EC1: 'Editor Comment on egusphere-2022-1310', Reinhard Drews, 23 Mar 2023
Chris Miele et al.
Chris Miele et al.
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I think that I reviewed this manuscript for another journal, and if so, I was supportive of its publication at that time, and still am. I do note some relatively minor, but important corrections to the “narrative” being presented, and I describe them now:
The abstract uses the words “miscommunications”, “misinterpretation” and “misconception”. I think that these words are sort of unfair to the early scientists who developed the initial modes of thinking about, doing analysis with and modeling ice shelves. These early scientists were well aware of the fact that shear stress in the vertical was prevalent in ice shelves at amplitudes that could be large (e.g., at an ice front or when there are large thickness gradients); however, their intention was to develop strategic simplifications and approximations which would allow glaciological science to make progress. Their pioneering work leading to the “shallow shelf approximation” was fundamental to the progress of glaciology through the 1960’s onward to the present day. It is thus not only unfair to their legacy to imply that they were “misleading”, but it is a kind of cheap writer’s trick to introduce the substance of the present paper. I strongly object to this tone and think that it detracts from the paper by setting up a false “combative” tone that completely misleads the reader.
I see that this tone that I object to is not present in the Introduction, and the authors very correctly laud the initial development of one of the most effective approximations in glaciological history (the shallow shelf approximation). This is important. And I compliment the authors for having done so. But again: I see words like (line 65) “persistent mischaracterizations”. This is a false and incorrect statement: approximation is not a mischaracterization.
A challenge: After recently attending the AGU and also reading a paper by Catherine Walker:
Walker, C. C. and Gardner, A. S. (2019). Evolution of ice shelf rifts: Implications for formation mechanics and morphological controls, Earth and Planetary Science Letters, 526,115764, doi:10.1016/j.epsl.2019.115764.
I became aware of the fact that many rifts on the Antarctic ice shelves are not vertical, but slightly offset from vertical, and that they have an interesting, not-fully-understood asymmetry of the rift shoulders associated with bending moments. I wonder if this phenomena (also described in one of Walker’s papers on ice shelled planets) is an observable phenomena that is directly related to the subject of this paper. If the authors think that it is, then they might find that their paper is made even stronger by including references to the Walker study, and also to (not sure if this is as relevant):
Walker, C. C., J. N. Bassis, J. N. and Schmidt, B. E. (2021). Propagation of vertical fractures through planetary ice shells: The role of basal fractures at the ice-ocean interface and proximal cracks. The Planetary Science Journal, Vol. 2, No. 4, doi:10.3847/PSJ/ac01ee.
line 2 of abstract “…, extending in only one direction,…”. I’m pretty sure that Weertman’s 1957 paper also gives the solution for spreading in two horizontal directions.
I was not able to find other errors or edits to make, and I commend the authors for doing a fine job of proof reading.