Ocean-driven millennial-scale variability of the Eurasian ice sheet during the last glacial period simulated with a hybrid ice-sheet–shelf model

Alvarez-Solas, Jorge; Banderas, Rubén; Robinson, Alexander; Montoya, Marisa

doi:https://doi.org/10.5194/cp-15-957-2019

Articles | Volume 15, issue 3

https://doi.org/10.5194/cp-15-957-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/cp-15-957-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 15, issue 3

Research article

|

04 Jun 2019

Research article |

| 04 Jun 2019

Ocean-driven millennial-scale variability of the Eurasian ice sheet during the last glacial period simulated with a hybrid ice-sheet–shelf model

Jorge Alvarez-Solas, Rubén Banderas, Alexander Robinson, and Marisa Montoya

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Final revised paper (published on 04 Jun 2019)
Supplement to the final revised paper
Preprint (discussion started on 09 Oct 2018)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC1: 'Review of Alvarez-Solas et al.', Anonymous Referee #1, 22 Oct 2018
- AC1: 'Response to all referees', Jorge Alvarez-Solas, 08 Mar 2019
RC2: 'Review of Alvarez et al.', Anonymous Referee #2, 08 Nov 2018
- AC1: 'Response to all referees', Jorge Alvarez-Solas, 08 Mar 2019
RC3: 'Review of Alvarez-Solas et al.', Anonymous Referee #3, 12 Nov 2018
- AC1: 'Response to all referees', Jorge Alvarez-Solas, 08 Mar 2019

Peer-review completion

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

ED: Reconsider after major revisions (12 Mar 2019) by Hugues Goosse

AR by Jorge Alvarez-Solas on behalf of the Authors (13 Mar 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (19 Mar 2019) by Hugues Goosse

RR by Anonymous Referee #2 (15 Apr 2019)

Suggestions for revision or reasons for rejection

I thank the authors for their thorough answers. They have notably included a few important points in the discussion. I still have some minor suggestions to make the paper more convincing.

- 1) The simulated ice sheets in the course of the simulations show a negative trend in ice volume, leading to a ~40-50% ice loss from their initial value. I previously pointed out that such transient response may raise doubt in the experiment setup: is the imposed forcing too strong to maintain an ice sheet?
The authors put forward three points that can explain this trend: i- ice volume hysteresis; ii- orbital variability and iii- refreezing / sub-shelf ice accretion.
The two first points are indeed expected. A simple way to close the debate, and thus to reinforce your conclusions, would be to present the results of your ice reconstructions when the orbital forcing is also included, following the setup of a previous paper in your group (Banderas et al., 2018). In doing so and showing that your setup can broadly reproduce the expected Eurasian ice sheet volume change (e.g. a maximum ice volume between 26 to 21 k), readers will be definitively convinced of the validity of your setup, strengthening your conclusions.
Finally, refreezing does occur below the grounded and floating ice. Refreezing is by definition melt water that turns back to ice under certain conditions. I agree that locally this refreezing can lead to ice accretion. On a larger scale however, refreezing leads, at best, to a net zero mass balance. In order to have model grid-size scale (40km) ice accretion, it means that ocean waters turn into ice. This might happen but I doubt that a substantial ice-sheet scale ice growth (i.e. a few metres of SLE per millenia) can be due to this phenomenon.

- 2) I appreciate the discussion on the limitations of the model on the grounding line migration, although you only discuss the role of resolution. You should also mention that there are ways to cope with coarse resolution models such as flux adjustment derived from analytical formulations (e.g. Schoof, 2007) or subgrid grounding line computations and basal friction scaling (e.g. Winkelmann et al., 2011).

- 3) I previously asked for a 2D map of the imposed forcing changes, i.e. SMB and sub-shelf basal melting rate, around an idealised DO event (for example a change from beta=-1. to beta=1. On top of your initial topography). This allows the reader to have a grasp of what the ice sheet is actually experiencing. In your answer you point me to Fig. 1 and 3 which show the absolute temperature and precipitation and their changes. However: i- Fig. 1 and 3 are the direct outputs from CLIMBER3 (not scaled to NGRIP) and thus it is not what you actually use as a forcing; and ii- it is not straightforward to convert a summer temperature to a SMB.
I agree that the paper is already long but this kind of figure seems to me even more important than Fig. 3 which shows climatic fields that are not directly used by the ice sheet model.

As a side note: I do not understand what is depicted in the figure of your answer R2 SC3b. I assume it is interstadial minus stadial since you have a more negative SMB at the margins. Also, there is no indication on which beta change this figure is based on, nor if it is computed after the atmospheric scaling. In any case, this kind of figure along with the sub-shelf melting anomaly (or potential melt if there is no ice shelf) would be an important addition to the paper.

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ED: Publish subject to minor revisions (review by editor) (23 Apr 2019) by Hugues Goosse

AR by Jorge Alvarez-Solas on behalf of the Authors (30 Apr 2019) Author's response Manuscript

ED: Publish as is (06 May 2019) by Hugues Goosse

AR by Jorge Alvarez-Solas on behalf of the Authors (07 May 2019)

Short summary

The last glacial period was marked by the existence of of abrupt climatic changes; it is generally accepted that the presence of ice sheets played an important role in their occurrence. While an important effort has been made to investigate the dynamics and evolution of the Laurentide ice sheet during this period, the Eurasian ice sheet (EIS) has not received much attention. Here we investigate the response of the EIS to millennial-scale climate variability using a hybrid 3-D ice-sheet model.