A 120&thinsp;000-year record of sea ice in the North Atlantic?

Maffezzoli, Niccolò; Vallelonga, Paul; Edwards, Ross; Saiz-Lopez, Alfonso; Turetta, Clara; Kjær, Helle Astrid; Barbante, Carlo; Vinther, Bo; Spolaor, Andrea

doi:https://doi.org/10.5194/cp-15-2031-2019

Articles | Volume 15, issue 6

https://doi.org/10.5194/cp-15-2031-2019

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

https://doi.org/10.5194/cp-15-2031-2019

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

Articles | Volume 15, issue 6

Research article

|

19 Dec 2019

Research article |

| 19 Dec 2019

A 120 000-year record of sea ice in the North Atlantic?

Niccolò Maffezzoli, Paul Vallelonga, Ross Edwards, Alfonso Saiz-Lopez, Clara Turetta, Helle Astrid Kjær, Carlo Barbante, Bo Vinther, and Andrea Spolaor

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Final revised paper (published on 19 Dec 2019)
Preprint (discussion started on 17 Jul 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 Maffezzoli et al', Anonymous Referee #1, 10 Aug 2018
- AC1: 'Answers to Reviewer#1', Niccolò Maffezzoli, 30 Jul 2019
RC2: 'review of Maffezzoli et al. "120,000 year record of sea ice in the North Atlantic"', Anonymous Referee #2, 10 Aug 2018
- AC2: 'Answers to Reviewer#2', Niccolò Maffezzoli, 30 Jul 2019
RC3: 'review', Anonymous Referee #3, 22 Aug 2018
- AC3: 'Answers to Reviewer#3', Niccolò Maffezzoli, 30 Jul 2019

Peer-review completion

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

ED: Reconsider after major revisions (31 Jul 2019) by Amaelle Landais

AR by Niccolò Maffezzoli on behalf of the Authors (05 Sep 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (16 Sep 2019) by Amaelle Landais

RR by Anonymous Referee #1 (02 Oct 2019)

Suggestions for revision or reasons for rejection

The authors have really done a very major revision of this paper and have acted on all the main comments made by the reviewers including me. In particular they have:
• Made it much clearer that their interpretation of Br_enr is not yet confirmed
• Done a complete revision of the calculation of the nss components with multiple options to show the sensitivity to different methods
• Revised the way they present the FYSI/OW and FYSI/MYSI discussion, removing the previous transformation

I cannot say I agree with every last sentence of their interpretation now, but it is a very much sounder scientific paper that presents the data but allows the reader to assess the viability of the interpretation. I have some minor suggestions (and even more minor typos) for the authors to consider. However overall, I thank them for being open to so many changes to their presentation and believe the paper is now almost ready for publication.

Abstract: I appreciate the caveats added here. I would suggest two extra changes that I think will better represent the way the findings are now presented.
line 8 Instead of “We find that”, I propose “Our interpretation implies that”
line 11 “as supported by sea ice records…”. I think it might be more helpful to instead say “Our interpretation is consistent with sea ice records…”

Page 2, Line 33. Spolaor didn’t really show opposite results, rather they tried to explain their data by assuming the opposite in their model. Perhaps better “a model run by Spolaor assumed the opposite”.

Page 3, line 4, you mean “shed light” not “shade light”.

Page 4, line 25 “1.1 ppb (Na)”

Page 7, line 7 Asian should have capital A
line 21 sulfate not sufate

Page 8, line 27 “for the” not “for the for”

Fig 7. It’s really hard to see the details of the Br_enr plots, including the colour changes. I would suggest that this figure presents as a large plot just one version (logically with Tbar) and then shows the 4 alternatives in the supplement, perhaps as another figure in appendix B. This would be clearer. Obviously it would also require changes in the text to reference the different parts of the figure.

Figure 6. I notice that Muller and Stein have some intermediate PIP values again at 24 ka which don’t seem to be represented by an increase in your Br data and which are just off the edge of this figure. Worth a comment?

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RR by Anonymous Referee #4 (18 Oct 2019)

RR by Anonymous Referee #5 (18 Oct 2019)

Suggestions for revision or reasons for rejection

Building on previous efforts by the same group, this paper adds another interesting element to the possibility to use Br enrichment as a proxy for the extent of FYSI. Initial reviews were critical yet highly constructive and the authors have reacted positively and humbly, making major changes to their paper and their efforts are laudable.

The current revised version reads well, does explain the limits and caveats of the approach and I have to say almost adds a convincing touch to the hypothesis. Thus, FYSI extent variations could indeed be determined from Br enrichment, and lower values would be indicative of either MYSI or OW (open water).

Given that the hypothesis is still being tested, numberless details could be discussed further. However, my main impression is that the paper is interesting, for the most part the interpretations are logical and the data and discussion represent a useful contribution to the topic, so that I am happy to recommend publication of the paper in CP.

I however have a question that disturbs me a bit, and I am not sure whether I or the authors missed something. From the data of Figure 6, the authors used the NGRIP temperature during the YD as the threshold for a change in regimes between MYSI/FYSI and FYSI/OW. But that same temperature was prevalent during 16-18 kyr, just before the OD, and no change in regime took place then. According to the authors, during the YD, temperature seasonality and fresh water input were different, which explains why, despite the cold temperature, a maximum in FYSI was reached. But then, since obviously temperature is not the only intervening variable, and since during the YD conditions were arguably particular and not representative of what took place during glacial epochs, why apply this threshold to the whole 120 kyr record? I guess I will not be the only reader to wonder, and some explanation is in order. By the way, why is the one low Br data point around 12.5 kyr never discussed? There are just 3 points with a high Br value during the YD, so one point, i.e. 25% of the data during or near the YD, certainly cannot be ignored and the difficulty swept under the rug. Likewise, is the high Br point at 13.8 kyr meaningful or just noise in the data? Perhaps some more detailed investigation would yield more clues about the interactions between the Br signal and climate variables.

One minor style comment: normally, equations are produced at their first mention in the text. This is not the case for equations 1 and 7. I am not sure this can be easily fixed without altering the flow of the text, but please give it a thought.

In summary, it is inevitable that this paper will leave some unanswered questions, and the present work seems to me as worthy of publication in CP. I however recommend that the authors think of addressing the points I raised when submitting a final version.

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ED: Publish subject to minor revisions (review by editor) (23 Oct 2019) by Amaelle Landais

AR by Niccolò Maffezzoli on behalf of the Authors (02 Nov 2019) Author's response Manuscript

ED: Publish as is (15 Nov 2019) by Amaelle Landais

Short summary

This study provides the first ice-core-based history of sea ice in the North Atlantic Ocean, reaching 120 000 years back in time. This record was obtained from bromine and sodium measurements in the RECAP ice core, drilled in east Greenland. We found that, during the last deglaciation, sea ice started to melt ~ 17 500 years ago. Over the 120 000 years of the last glacial cycle, sea ice extent was maximal during MIS2, while minimum sea ice extent exists for the Holocene.