LCice 1.0 – a generalized Ice Sheet System Model coupler for LOVECLIM version 1.3: description, sensitivities, and validation with the Glacial Systems Model (GSM version D2017.aug17)

Bahadory, Taimaz; Tarasov, Lev

doi:https://doi.org/10.5194/gmd-11-3883-2018

Articles | Volume 11, issue 9

https://doi.org/10.5194/gmd-11-3883-2018

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

https://doi.org/10.5194/gmd-11-3883-2018

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

Articles | Volume 11, issue 9

Development and technical paper

|

27 Sep 2018

Development and technical paper |

| 27 Sep 2018

LCice 1.0 – a generalized Ice Sheet System Model coupler for LOVECLIM version 1.3: description, sensitivities, and validation with the Glacial Systems Model (GSM version D2017.aug17)

Taimaz Bahadory and Lev Tarasov

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Final revised paper (published on 27 Sep 2018)
Supplement to the final revised paper
Preprint (discussion started on 02 Jan 2018)

Interactive discussion

Status: closed

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

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- Supplement

SC1: 'Executive Editor comment on "Coupling the Glacial System Model (GSM) to LOVECLIM: description, sensitivities, and validation"', Astrid Kerkweg, 31 Jan 2018
RC1: 'Review / comments', Anonymous Referee #1, 16 Feb 2018
RC2: 'Good manuscript but needs some restructuring and a more detailed description of the model', Irina Rogozhina, 26 Feb 2018
EC1: 'editor comment', Dan Goldberg, 06 Mar 2018
AC1: 'Response to reviewer/editor comments and revised manuscript', Lev Tarasov, 17 Jul 2018

Peer-review completion

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

AR by Lev Tarasov on behalf of the Authors (17 Jul 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Jul 2018) by Dan Goldberg

RR by Anonymous Referee #1 (09 Aug 2018)

Suggestions for revision or reasons for rejection

The manuscript has been greatly improved. Most importantly 1) the description of the dynamic meltwater routing and the selection of temperature profiles for sub-shelf melting is much clearer now, thanks to the revised text, modified figures and extra information in the supplementary material, and 2) the conclusion that the four new parameterisations have an effect on the ice sheet evolution is now supported by the presented results.

Code availability has been improved by providing the coupling routines and modified LOVECLIM code in a repository. The provided temporary link to the code unfortunately did not work for me (access not permitted), so I cannot comment on the code.

The authors clarified in their response why they perform glacial inception / 110ka sensitivity experiments before the modern ensemble simulations. Still, I think the paper could be more concise, if it would focus on the coupling scheme and new parameterisations and on the sensitivity of the ice sheet evolution during the inception to the different coupling parameterisations and parameters only. The subsequent ensemble parameter sensitivity analysis (Section 4) may be more suitable in the author’s other manuscript, where the presented result (the subset of parameters) is actually used to calibrate the coupled model for glacial inception ensemble simulations, if I understand correctly.
If the authors do decide to keep the ensemble simulations in this manuscript, then I would suggest to further improve the motivation / connection between the two parts. For example, the workflow/computational efficiency-argument that the authors give in their response to Dr. Rogozhina’s comment could be added to the manuscript (individual sensitivity tests are cheap, and therefore were performed prior to including the tested parameter or parameterisation in the ensemble simulations). Furthermore, the necessity of the ensemble simulations or the necessity to validate a newly developed model could be pointed out more clearly to connect the two parts of the manuscript.

Regarding my suggestion to include a more detailed analysis of the sensitivity simulations, I appreciate that the authors identify and describe the role that the AMOC weakening and sea-ice growth has on the enhanced ice sheet growth during the inception when meltwater runoff routing is dynamic. However, I disagree with their argument that all other feedbacks are either too trivial or too complicated to discuss. To revisit the author’s example of dynamic lapse rates: It may be clear that “large differences in lapse rates cause large temperature differences over regions with high elevation gradients”; but it is not evident to me why the dynamic lapse rate computation then leads to thinner ice in most of North America and Greenland (Fig. 3c). Here, maybe a plot of the lapse rate deviations from 6.5K/km rather than of the absolute lapse rate (Fig.3a-b) would be more helpful to understand what is happening — possibly combined with a plot of the difference between the GSM high-resolution surface height and the LOVECLIM surface height?

Minor comments:
+++++++++++++++++

Abstract, lines 5-7: “…interactions …that are often neglected: …, novel downscaling…”
I don’t think the authors mean that the novel downscaling is often neglected, but that the redistribution of precipitation due to fine-scale ice-sheet topography that is not resolved by the atmospheric model is neglected. To my understanding, the *novel* downscaling is not the neglected process, but the solution to the problem. Please rephrase accordingly for clarity. Similarly, I would replace “ocean temperatures for sub-shelf melt” by “sub-shelf melting based on ocean temperatures”, since the neglected interaction is the sub-shelf melting and not the ocean temperature.

page 7, line 7:
remove “during the retreat phase”. It looks like the divergence occurs also during the inception (Fig. 2), which is in line with the argument given in lines 8-9, namely, that a weaker response is expected for longer time intervals between coupling.

page 11, line 24:
Fig.6 => should be Fig.4

page 13, line 12:
add reference to Fig.6

page 26, line 5:
“shown directly or via changes in temperature and/or precip” can be omitted now

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ED: Publish as is (29 Aug 2018) by Dan Goldberg

AR by Lev Tarasov on behalf of the Authors (05 Sep 2018)

Short summary

We describe a new coupling between the Glacial Systems Model and the LOVECLIM intermediate complexity climate model. The coupling is distinguished from that of previous studies by greater completeness and accuracy, with the intent of capturing the major feedbacks between ice sheets and climate on glacial cycle timescales. The fully coupled model will be used to examine the ice/climate phase space of past glacial cycles.