Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model

Crichton, Katherine A.; Ridgwell, Andy; Lunt, Daniel J.; Farnsworth, Alex; Pearson, Paul N.

doi:https://doi.org/10.5194/cp-17-2223-2021

Articles | Volume 17, issue 5

https://doi.org/10.5194/cp-17-2223-2021

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

https://doi.org/10.5194/cp-17-2223-2021

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

Articles | Volume 17, issue 5

Research article

|

21 Oct 2021

Research article |

| 21 Oct 2021

Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model

Katherine A. Crichton, Andy Ridgwell, Daniel J. Lunt, Alex Farnsworth, and Paul N. Pearson

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Final revised paper (published on 21 Oct 2021)
Supplement to the final revised paper
Preprint (discussion started on 14 Jan 2020)
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Interactive discussion

Status: closed

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

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RC1: 'Review for "Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model"', Anonymous Referee #1, 17 Feb 2020
- AC1: 'Authors response to reviewer 1', Katherine Crichton, 05 Aug 2020
RC2: 'Review', Anonymous Referee #2, 17 Feb 2020
- AC2: 'Authors response to reviewer 2', Katherine Crichton, 05 Aug 2020
RC3: 'review of "Data-constrained assessment... since the middle Miocene...', Anonymous Referee #3, 20 Feb 2020
- AC3: 'Authors response to reviewer 3', Katherine Crichton, 05 Aug 2020

Peer-review completion

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

ED: Reconsider after major revisions (18 Sep 2020) by Yannick Donnadieu

Dear Dr. Crichton

Thank you for submitting your manuscript entitled «Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model» to Climate of the Past.

I think in it's present form the manuscript is not always well written and well structured, but has generally appropriate figures, text, and referencing. The reviewers have several suggestions for improving the paper to make it more impactful and accurate. I will want to see all this done before publishing the manuscript.

The paper has been reviewed by two paleoclimate modelers and one paleo-proxy expert and both have given it substantive and major reviews which I concur with. While the three reviewers recognize the importance of your work, they also ask for substantial modifications of your manuscript with some similarities. The reviewers 1 and 2 ranked the paper as requiring a major round of revisions while the third one choose minor revisions.

As editor, I liked the general philosophy of the paper and found it smart to try to constrain the MOC evolution over the last 15 Ma using the cGENIE model and available data. However, the paper is a bit messy and will benefit for a re-writing keeping in mind that the general goal should be to shorten it to focus on the essential results. There are many places where the level of details is too high and also where as a reader I felt a bit lost (i.e. don’t discuss too much previous results if they don’t bring something to put forward your main ideas). You also have to be aware that the group of Heather Stoll suggested that CO2 may be higher than the Sosdian’s estimates (2019, QSR). So please, be more balanced on that specific point, there are other proxies than Boron isotopes for reconstructing pCO2 and in any cases, these proxies are still required many work to be done before the community can rely on it. About the oceanic circulation, did you try to compare your results with previous reconstructions of the evolution of the NADW. Are they any proxies such as Nd to be compared with ? Indeed, there are some recent papers claiming an early onset of the NADW like during the EOT (work of Hutchinson, Coxall and co) in stark contrast with the old paradigm stating that the NADW appeared during the Miocene. Last but not least, can you provide the reader with regression coefficients for figures 2, 9-10.

Please submit a revised version of your manuscript taking into account as much as possible reviewer assessments (as you already did in your answers). I will send back the revised manuscript to reviewers.

I look forward to receiving your revised manuscript. If you have any questions, please contact the editorial office at editorial@copernicus.org
.

Sincerely,

Yannick Donnadieu

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AR by Katherine Crichton on behalf of the Authors (10 May 2021) Author's response Manuscript

ED: Referee Nomination & Report Request started (12 Jul 2021) by Yannick Donnadieu

RR by Anta-Clarisse Sarr (23 Jul 2021)

Suggestions for revision or reasons for rejection

« Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model » by Crichton et al.

Revised version of the manuscript by Crichton et al. has been largely improved since the original one. Details on model and experiments setup have been moved to appendix, which is a good point. I appreciate the introduction of new simulations with closed CAS so conclusions are better justified. I also acknowledge the effort that have been done to make the manuscript clearer especially in the results and discussion parts. I therefore believe that the manuscript is ready for publication. I however still have minor comment on one point that I feel might still be made clearer for the reader.

Paragraph referring to CO2 concentration (l. 41 and following) during the Miocene in the Introduction is not clear.
First, is not straightforward to understand about which part of the Miocene the authors are referring to when stating “Climate modelling studies have tended to apply a forcing of around 400ppm, based on later estimates (Londoño et al 2018 references therein) » (l. 41-42) as they do not provide references for such modeling studies and also because multiple paleoclimate simulations have been performed both for the late and the middle Miocene for which most of the groups used different pCO2 concentration (see Burls et al., 2021, https://doi.org/10.1029/2020PA004054 for compilation).
I addition, I do not really understand the few lines on pCO2 that seems to focus on the mid-Miocene, while the paper provide simulation from 15 Ma onward. I do not think this part is really needed, because the authors then discuss pCO2 concentration needed to reproduce Miocene climate state in the discussion and compare it with the same references. I feel like one sentence on pCO2 decrease since MMCT providing appropriate reference(s) (in which the recent review by Rae et al., 2021, https://doi.org/10.1146/annurev-earth-082420-063026 could be cited for example) would probably have been enough and would make the introduction more synthetic and clearer.

List of specific comment :

l.56 : I do not think Hamon et al. (2013) is the appropriate reference as they "only" test the impact of closing the eastern Tehtys seaway on climate/ocean. As there are many references focusing on eastern Tethys seaway closure it would be better to cite paleogeography paper such as Rögl et al. 1999 (or the many others that studies on the paleogeographic evolution of the region during the Miocene) or at least papers suggesting switch off of the Mediterranean / Atlantic connection based on geochemistry (such Bialik et al. 2019 or others).

l. 110 “ noting that these proxies, like any proxy, are subject to uncertainties and limitations” is a pretty vague statement and do not help the reader to identify potential weakness of the model-data comparison. I still think that kind of point is very important to clarified especially when the paper target a broad audience from both modeling and data researchers. Short sentence listing mains limitations of such proxies would be more useful.

Fig 9-11 - I think you should provide de regression coefficients.

Technical correction :

l. 37-38 « Marine data also indicate a significantly warmer-than-present Miocene climate with global surface ocean temperatures 6 °C warmer than present (Stewart et al., 2004; Herbert et al., 2016), global deep ocean temperature 4 to 6 °C warmer (Cramer et al., 2011). » — This sentence sounds grammatically incorrect.

l. 51 Correct reference is Sepulchre et al. 2014 (as in the reference list)

l. 475 & 481 - Modestou (as in the reference list) or Modestu (as in the Text) ?

l. 514 : Tethyan instead of Tethian ?

l.538 ‘Bell et al. (2015) found that an early Pliocene (4.7 to 4.2 Ma) shoaling of CAS was had no profound impact’

Mid-Miocene or mid-Miocene ? Please keep in consistent in the paper

Overuse of brackets make some part of the paper difficult to read and most of the time they can be removed as the text content within the brackets perfectly fits within the sentence.

In paragraph 3.4 you start using ‘benthic T’ instead of ‘benthic temperature’ but the T abbreviation is never defined in the paper and I am not sure it is very useful. It might be bette to keep using ‘benthic temperature’ everywhere

References
Burls et al., 2021, https://doi.org/10.1029/2020PA004054
Rae et al., 2021, https://doi.org/10.1146/annurev-earth-082420-063026
Rögl et al. 1999 - Mediterranean and Paratethys. Facts and hypotheses of an Oligocene to Miocene paleogeography (short overview). Geologica carpathica, 50(4), 339-349.
Bialik et al. 2019, https://doi.org/10.1038/s41598-019-45308-7

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ED: Publish subject to technical corrections (27 Aug 2021) by Yannick Donnadieu

AR by Katherine Crichton on behalf of the Authors (10 Sep 2021) Author's response Manuscript

Short summary

The middle Miocene (15 Ma) was a period of global warmth up to 8 °C warmer than present. We investigate changes in ocean circulation and heat distribution since the middle Miocene and the cooling to the present using the cGENIE Earth system model. We create seven time slices at ~2.5 Myr intervals, constrained with paleo-proxy data, showing a progressive reduction in atmospheric CO₂ and a strengthening of the Atlantic Meridional Overturning Circulation.