The impact of the North American glacial topography on the evolution of  the Eurasian ice sheet over the last glacial cycle

Liakka, Johan; Löfverström, Marcus; Colleoni, Florence

doi:https://doi.org/10.5194/cp-12-1225-2016

Articles | Volume 12, issue 5

https://doi.org/10.5194/cp-12-1225-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/cp-12-1225-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 5

Research article

|

25 May 2016

Research article |

| 25 May 2016

The impact of the North American glacial topography on the evolution of the Eurasian ice sheet over the last glacial cycle

Johan Liakka, Marcus Löfverström, and Florence Colleoni

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Final revised paper (published on 25 May 2016)
Supplement to the final revised paper
Preprint (discussion started on 10 Nov 2015)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC C2615: 'Review of Liakka et al.', Anonymous Referee #1, 10 Dec 2015
- AC C2983: 'Response to Referee 1', Johan Liakka, 20 Jan 2016
RC C2703: 'Review of Liakka et al.', Anonymous Referee #2, 19 Dec 2015
- AC C2997: 'Response to Referee 2', Johan Liakka, 20 Jan 2016

Peer-review completion

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

ED: Reconsider after major revisions (02 Feb 2016) by Volker Rath

AR by Johan Liakka on behalf of the Authors (14 Mar 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (15 Mar 2016) by Volker Rath

RR by Anonymous Referee #1 (08 Apr 2016)

Suggestions for revision or reasons for rejection

The authors have addressed most of my comments adequately, and I find that the manuscript has improved considerably. However, there are a few remaining issues that have to be taken into account before publication.

1) The rationale for using a PI OHT is discussed in much more detail. In my opinion this discussion and the new Figure 2 makes the study more convincing. There are however two additional suggestions that I would like to make.

In Figure 2 a rather wide colour scale is used, ranging between -26°C and 0°C, while the MARGO anomalies do not exceed -12°C. The figure would be a lot more informative if a more narrow scaling range would be applied (i.e. between -12°C and 0°C).

I agree that using "BO2009 OHT" is much less confusing than the term "LGM OHT". However, I find the discussion of the simulated LGM SSTs still confusing. For instance, on line 148: "We find that the annual mean LGM SST response in CAM3 using PI OHT is in better agreement with the response in CSSM4". When discussing the SSTs simulated with CAM3, I would suggest making a distinction between LGM[PI subscript] SSTs and LGM[BO subscript] SSTs.

2) In my previous review, I proposed to include a flow diagram to explain the full, sequential experimental setup. Although the authors have considerably improved Section 2.1, I still think this could make the methodology easier to understand.

3) The authors have added a sentence to explain the applied modern mixed-layer depth. "Aside from areas covered by perennial sea ice, simulated changes of the LGM mixed-layer depth are small compared to PI (of order 10 m; Brandefelt and Otto-Bliesner, 2009); following Löfverström et al. (2014) we therefore use a modern annual mean mixed-layer depth in all simulations". As explained by the authors in their reply to the reviewers, the simulated mixed layer depths from the LGM experiments were not saved on the CCSM3 data server. I suggest to simply mention this in the manuscript as well, since I consider the small difference between LGM and PI mixed-layer depths not a good argument to take the PI mixed-layer depth if the LGM mixed-layer depth is also available.

4) The statistical significance of the simulated anomalies is now tested using a Student t-test. However, if I look at the figures, it is not entirely clear what results are not statistically significant. For instance, in Figures 3d, f and h, the simulated temperature anomalies are presented. The caption explains that all results shown in coloured shading are statistically significant at a 95% level. But what about the white areas on the map? Are they all statistically not significant, or do they also include grid cells with small anomalies between -0.1 and 0.1 that are statistically significant?

Textual comments
Line 134: typo, "the the"
Line 365: should be "of Beghin"

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RR by Anonymous Referee #2 (08 Apr 2016)

ED: Publish subject to minor revisions (review by Editor) (16 Apr 2016) by Volker Rath

AR by Johan Liakka on behalf of the Authors (25 Apr 2016) Author's response Manuscript

ED: Publish subject to technical corrections (05 May 2016) by Volker Rath

AR by Johan Liakka on behalf of the Authors (06 May 2016) Manuscript

Short summary

The present study explains why Scandinavia was ice-covered 20 000 years ago, while Siberia was mostly ice free. The authors show that the ice-sheet extent in Eurasia was to a large extent controlled by atmospheric circulation changes due to the ice sheet in North America. As the North American ice sheet becomes larger, it induces a cooling in Europe and a warming in Siberia: this climatic pattern forces the Eurasian ice sheet to migrate westward until it is centered over Scandinavia.