Younger Dryas ice margin retreat in Greenland: new evidence from southwestern Greenland

Funder, Svend; Sørensen, Anita H. L.; Larsen, Nicolaj K.; Bjørk, Anders A.; Briner, Jason P.; Olsen, Jesper; Schomacker, Anders; Levy, Laura B.; Kjær, Kurt H.

doi:https://doi.org/10.5194/cp-17-587-2021

Articles | Volume 17, issue 2

https://doi.org/10.5194/cp-17-587-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/cp-17-587-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 2

Research article

|

04 Mar 2021

Research article |

| 04 Mar 2021

Younger Dryas ice margin retreat in Greenland: new evidence from southwestern Greenland

Svend Funder, Anita H. L. Sørensen, Nicolaj K. Larsen, Anders A. Bjørk, Jason P. Briner, Jesper Olsen, Anders Schomacker, Laura B. Levy, and Kurt H. Kjær

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Final revised paper (published on 04 Mar 2021)
Preprint (discussion started on 08 May 2020)

Interactive discussion

Status: closed

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

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SC1: 'Great paper, but with a suggestion', R.B. Alley, 17 May 2020
- AC1: 'Response to Richard Alley', Svend Funder, 14 Aug 2020
SC2: 'Interpreting 10Be ages from bedrock samples', Nicolas Young, 19 May 2020
- AC2: 'Response to Nicolas Young', Svend Funder, 14 Aug 2020
RC1: 'Review of manuscript by Funder et al.', David Ullman, 20 Jun 2020
- AC3: 'Response to David Ullman', Svend Funder, 15 Aug 2020
RC2: 'Younger Dryas ice-margin retreat in Greenland, new evidence from Southwest Greenland', David Roberts, 25 Jun 2020
- AC4: 'Response to David Roberts', Svend Funder, 16 Aug 2020

Peer-review completion

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

ED: Reconsider after major revisions (01 Sep 2020) by Alberto Reyes

AR by Svend Funder on behalf of the Authors (13 Nov 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (03 Dec 2020) by Alberto Reyes

RR by Nicolas Young (17 Dec 2020)

Suggestions for revision or reasons for rejection

Funder et al present a revised manuscript based off a number of reviews/comments made on the initial submission. One of the primary concerns raised by not only me, but a few of the reviewers had to do with the issue of isotopic inheritance in bedrock samples. The main issue being that if you only have a few samples from one location, they are all from bedrock, and they yield consistent ages, one still cannot rule out the possibility that minor amounts of inheritance has influenced all the samples and the deglaciation age is slightly too old. This concept of minor “baseline” inheritance appears to exist within the literature. As it applies to this study, the concern is that if you take the 10Be ages at face value in a few locations then, yes, deglaciation of the outer coast could have happened early/mid Younger Dryas and then one can say the ice margin retreated through the Younger Dryas. If by chance, however, there is a small amount of inheritance and the “true” deglaciation age is younger (e.g., end of YD or later), then you cannot really say anything about ice-margin behavior during the YD because the ice margin was still in the ocean.

My primary criticism of version 1 was that the authors took the bedrock 10Be ages at face value and didn’t really consider the alternative (inheritance), and then spun their dataset to argue for YD retreat at their sites with new 10Be ages. The argument in this revision is still the same, but I am pleased to see that the authors at least acknowledge the possibility of isotopic inheritance. For example, the topic of inheritance appears in the abstract, introduction, and at the start of section 4, no complaints on my end. I think really what we have here is a difference of interpretation. The authors default is to say these bedrock 10Be ages are “real” and then interpret those ages within the context of YD ice-margin behavior while, based on personal experience working in SW Greenland, I probably would have framed this study from the assumption that the bedrock samples might indeed be influenced by a slight amount of isotopic inheritance considering what else we know about regional deglaciation. Without a lot more measurements, there is no way say who is right here. Just a difference of scientific opinion, which should in no way hold up publication. The publication of the 10Be ages themselves is a contribution.

Moving beyond the inheritance issue, a few minor things I noticed that the authors should clean up:

- take another thorough look for typos and check where you have placed paragraph breaks.
- Might just be the version I have in front of me, but double check the photo resolution for images in Figure 2.
- I still advocate for up in the Sisimiut region, based on the recent 10Be ages from the coast, you can conclude 1) ice margin was out in the ocean until ~11.6 ka, and 2) the Fiskebanke moraines have to be >11.6 ka (Young et al, 2020). As it is, they place a line on a figure marking the “Preboreal” ice-margin position in the region, but I think that glosses over the level of detail we actually know about the ice-margin history in that region based off recent 10Be ages.
- On Fig.4, shouldn’t there also be a blue arrow in the Disko region as well since there is a well-constrained ice-margin advance in the early/middle YD, followed by retreat through the remained of the YD. Maybe touching upon Richard’s point, but interpreting Greenland ice cores as a direct proxy for ice-margin behavior, one might expect an early/mid YD advance followed by retreat….which is what the chronology implies in Disko Bugt.
- Lastly, I encourage these authors to place their 10Be sample information in the ICE-D database (http://ice-d.org/). I personally think the community should be embracing this database as its more tailored towards the needs of cosmogenic isotope users versus some of the more generic repositories, and I think it is pretty user friendly. The authors cannot upload their dataset themselves, but if they contact me, I’d be happy to do it.

Referee Report: PDF

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ED: Publish subject to minor revisions (review by editor) (06 Jan 2021) by Alberto Reyes

AR by Svend Funder on behalf of the Authors (15 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (28 Jan 2021) by Alberto Reyes

AR by Svend Funder on behalf of the Authors (31 Jan 2021) Manuscript

Short summary

Cosmogenic ¹⁰Be exposure dates from outlying islets along 300 km of the SW Greenland coast indicate that, although affected by inherited ¹⁰Be, the ice margin here was retreating during the Younger Dryas. These results seem to be corroborated by recent studies elsewhere in Greenland. The apparent mismatch between temperatures and ice margin behaviour may be explained by the advection of warm water to the ice margin on the shelf and by increased seasonality, both caused by a weakened AMOC.