Dynamic response of Antarctic Peninsula Ice Sheet to potential collapse of Larsen C and George VI ice shelves

Schannwell, Clemens; Cornford, Stephen; Pollard, David; Barrand, Nicholas E.

doi:https://doi.org/10.5194/tc-12-2307-2018

Articles | Volume 12, issue 7

https://doi.org/10.5194/tc-12-2307-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/tc-12-2307-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 12, issue 7

Research article

| Highlight paper

|

19 Jul 2018

Research article | Highlight paper |

| 19 Jul 2018

Dynamic response of Antarctic Peninsula Ice Sheet to potential collapse of Larsen C and George VI ice shelves

Clemens Schannwell, Stephen Cornford, David Pollard, and Nicholas E. Barrand

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Final revised paper (published on 19 Jul 2018)
Preprint (discussion started on 06 Feb 2018)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of ""Dynamic response of Antarctic Peninsula Ice Sheet to collapse of Larsen C and George VI ice shelves''', Anonymous Referee #1, 15 Mar 2018
- AC1: 'Final response to reviews', Clemens Schannwell, 09 May 2018
RC2: 'Review of "Dynamic response of Antarctic Peninsula Ice Sheet to collapse of Larsen C and George VI ice shelves" by Clemens Schannwell and his colleagues', Lionel Favier, 12 Apr 2018
- AC1: 'Final response to reviews', Clemens Schannwell, 09 May 2018

Peer-review completion

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

AR by Clemens Schannwell on behalf of the Authors (09 May 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 May 2018) by Olivier Gagliardini

RR by Anonymous Referee #1 (25 May 2018)

Suggestions for revision or reasons for rejection

Review of “Dynamic response of Antarctic Peninsula Ice Sheet to collapse of Larsen C and George VI ice shelves”

1 Summary statement

The revised manuscript by C. Schannwell and co-authors addresses most of the points raised by both reviewers. The new version is clear and the authors tried to present a more detailed analysis of the results and an improved discussion. There is one thing that remains unclear and not really discussed: it concerns the similarity of the results between experiments 1 and 2 for the PSU3D model but not for the BISICLES model. The BISICLES results show a much larger grounding line retreat and ice loss in ex- periment 2 than experiment 1 for George VI ice shelf, while one would expect a larger response for experiment as the changes are more extreme (removal of all the ice shelf).

Note that the page and line numbers refer to the version of the manuscript including the highlighted changes.

2 Major comments

There is no real discussion on the differences between experiments 1 and 2. For Larsen, results are similar for the two experiments and for both PSU3D and BISICLES models. For George VI, the results are similar between experiments 1 and 2 for PSU3D but significantly different for BISICLES. The thinning rates and grounding retreat (Fig. 6 and 8) as well as the ice loss (Fig.4 and Fig.7) show a much larger response in for experiment 2 than for experiment 1, which is unlike one would expect as experiment 1 represents a much more radical change (removal of all the ice shelf). There is not much explanation about this, and the authors should at least discuss why the behavior of PSU3D is similar why the behavior of BISICLES is different for the two experiments, and also explain why the changes are larger for experiment 2 than experiment 1 in BISCICLES.

Another relatively minor point relates to the tables that were in the first version of this manuscript and disappeared into a supplementary material. As mentioned by both reviewers, the tables were not clear and needed some clarification, which does not mean to hide them. It would be best to put them in the Appendix with the supplemental figures, and make sure they are easy to understand.

3 Specific comments

p.1 l.4: “in future” → “in the future”

p.1 l.11: “relative importance to sea level of the large ...“ → “ relative importance of the large ... of collapse on sea level rise.”

p.5 l.2: “A is the depth averaged rheological exponent” → “A is the depth averaged rheological coefficient”

p.5 l.12: “the thickness” → “the ice thickness”

p.7 l.1: I still think this is confusing. You want the model to represent “reality”, or the version we know of reality provided by observations. So the models “should” only be as close as possible to that. I understand the argument of being close to equilibrium to simplify the comparison between models and assess the impact of the ice shelf collapse, but the first sentence is really misleading and not accurate, and should be at least rephrased.

p.10 Tab.1: Add the default sliding on BISICLES Experiment 1 (third line of the table). Also add “zero melt” or something along this line for Experiment 2 (lines 8 and 9).

p.12 Figure 4 caption: How is the uncertainty in BAS-APISM computed?

p.12 Figure 4 caption: “Upper panels show” and “Lower panels show”

p.16 l.23: “scenario” → “reason/explanation”

p.16 l.25: “sticky” → “high friction”

p.18 l.14-20: This paragraph is not really convincing, the arguments should be more detailed.

p.29 Figure A4 caption: “distribtution” → “distribution”

p.31 Figure A6 caption: should be “Upper panels show” and “Lower panels show”

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RR by Anonymous Referee #2 (05 Jun 2018)

ED: Publish subject to minor revisions (review by editor) (05 Jun 2018) by Olivier Gagliardini

AR by Clemens Schannwell on behalf of the Authors (18 Jun 2018) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (21 Jun 2018) by Olivier Gagliardini

Dear Clemens,

Thanks for this new version of your paper that I have carefully re-read. I have still some minor points that should be corrected before publication. See the list below.

Regards,
Olivier Gagliardini

- caption Fig 1: the red inset are not only used by Fig 8, but also Fig 2 (and others?)? Should be corrected. Also, what are the model domains should be specified (not here, but in the text)? Whole Antarctica? Same for all 3 models?
- page 5, line 2: by surface liquid, you mean water? Why not water then?
- page 5, line 25: "is to (Pollard et al., 2O15)." -> "is to (Pollard et al., 2O15):". Also, R in Eq. 11 is not defined (at least its definition is not clear from line 25.
- caption Fig. 3: Give in words what is dV/dt
- caption Fig. 4: "Note different" -> "Note the different" (?)
- Figure 7: In the y-axis label, missing a space after loss and (%); and loss and (km2). Also, there should be 4 curves in panels e and f as in the 4 other panels? It seems that there is only 3?
- page 15, line 8: "Tables A3,A4" -> "Tables A3 and A4"
- page 16, line 21: "this boundary condition results..." it is not clear what did you change? Is it the bed DEM? Then it should be specificaly mentioned instead of using "boundary condition" which can also refer to sliding, etc... Same line 24 for boundary input dataset. Is it the bed DEM dataset that you are refereeing to?
- page 17, line 5: an analysis using the five drainage basins is not really done in section 3.4, as given number stay general. To justify the introduction of these 5 basins at the stage of the paper, I would expect that the discussion in this section is really focussed on the differences observed from one to an other basin. On the same line, dh/dt presented in Fig. 8 are not really discussed, especially the differences between one basin to an other. Only the tables in the Annex give explicit number for each individual basin. Fig 8 and Tables A1 to A4 should be commented a bit more in this section?
- page 17, line 9: "8fold speed up" -> "8 fold speed up"
- page 17, line 12: each of this mass loss rates number should be put in context of the maximal potential sea level contribution of each sector? The same apply at other place of the paper, especially in the predicted contribution of Larsen C relative to George VI?
- page 17, line 15: what does 6.4 km represents? retreat rate of what, the grounding line? It should be mentioned. Also, with the units of km, it is not a rate of retreat. I guess it should be : "the simulated retreat of the GL over XX years is 6.4 km in ..."?
- page 19, line 3: give at which date these sea level projections apply.
- page 19, line 5: I don't understand the "only" 55% as it seems already a large number if you have loss 55% of the total potential contribution to sea level rise? As in my previous remarks, this is an interesting number that should be given also for Larsen C?
- Figures A1 and A2 could be smaller (one column)
- caption Table A1: for dGL_15, it is not really averaged over 15 years but it gives the total retreat over 15 years?
- captions of Tables A2 to A4 could be simplified : "Same as Table A1 but for George VI embayment.

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AR by Lorena Grabowski on behalf of the Authors (26 Jun 2018) Author's response

ED: Publish subject to technical corrections (26 Jun 2018) by Olivier Gagliardini

Short summary

Despite the speculation on the state and fate of Larsen C Ice Shelf, a key unknown factor remains: what would be the effects of ice-shelf collapse on upstream drainage basins and thus global sea levels? In our paper three state-of-the-art numerical ice-sheet models were used to simulate the volume evolution of the inland ice sheet to ice-shelf collapse at Larsen C and George VI ice shelves. Our results suggest sea-level rise of up to ~ 4 mm for Larsen C ice shelf and ~ 22 for George VI ice shelf.