Deep ocean temperatures through time

Valdes, Paul J.; Scotese, Christopher R.; Lunt, Daniel J.

doi:https://doi.org/10.5194/cp-17-1483-2021

Articles | Volume 17, issue 4

https://doi.org/10.5194/cp-17-1483-2021

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

Special issue:

Publications by EGU Medallists

https://doi.org/10.5194/cp-17-1483-2021

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

Articles | Volume 17, issue 4

Research article

|

19 Jul 2021

Research article |

| 19 Jul 2021

Deep ocean temperatures through time

Paul J. Valdes, Christopher R. Scotese, and Daniel J. Lunt

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Final revised paper (published on 19 Jul 2021)
Supplement to the final revised paper
Preprint (discussion started on 06 Jul 2020)

Interactive discussion

Status: closed

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

- Printer-friendly version

- Supplement

RC1: 'review', Anonymous Referee #1, 31 Jul 2020
- AC1: 'Response to Reviewers 1 and 2', Paul Valdes, 13 Nov 2020
RC2: 'Review', Anonymous Referee #2, 11 Aug 2020
- AC1: 'Response to Reviewers 1 and 2', Paul Valdes, 13 Nov 2020
- AC2: 'Response to Reviewers 1 and 2', Paul Valdes, 13 Nov 2020

Peer-review completion

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

ED: Reconsider after major revisions (14 Dec 2020) by Yannick Donnadieu

Dear Prof. Valdes:

Thank you for submitting your manuscript entitled « Deep Ocean Temperatures through Time» to Climate of the Past.

Your manuscript has been read by two anonymous reviewers. They ranked the paper as requiring a major round of revisions. While both reviewers recognize the importance of your work, they also ask for additional diagnostics and for more in depth description of the limitations of your modeling approach. Other specific points are the representation of tropical deep-water formations in GCMs, the site by site comparison to proxies records.
On a personal note, I appreciated you’d modified the water scheme in HadCM3 in order to conserve water as it wasn’t the case in Farnsworth’s simulations. It would have been great to compare your results with those of Farnsworth after having applied this correction. What are the main changes if any, in particular in terms of mixed layer depths and MOC ? You may consider doing it for two or three cases being particularly affected by salinity drift. About the meridional heat transport, while I do agree that compensation exists between the atmosphere and the ocean; papers have been published by people from the MIT (including David Ferreira) showing that a change in heat transport does not affect the same processes and same climate feedbacks if it occurs in the ocean or in the atmosphere.

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 probably send back the revised manuscript to one of the reviewers given that both ranked it with a major revision.

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

Sincerely,

Yannick Donnadieu

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AR by Paul Valdes on behalf of the Authors (10 Mar 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (15 Mar 2021) by Yannick Donnadieu

RR by Anonymous Referee #2 (04 Apr 2021)

Suggestions for revision or reasons for rejection

The authors generally do a good job of responding to my previous comments and concerns. There are still a few minor points that I would like addressed before publication.

“We have also examined the temperatures timeseries at 2731m (the deepest layer for which we have time series data) and it shows the same trends (see supplementary figures).”
The supplemental figures are very helpful for understand the responses. I agree that global and 2731m ocean temperatures generally show the same trends. However, global and 2731m ocean temperature do not have a consistent offset between time periods, which is very interesting and important for comparing models with proxies. Hopefully these differences will be explored in great detail in future works. By the way, there are some formatting issues and inconsistencies in the supplemental figures. Please fix before publication.

“Except for the very coldest temperatures, the residuals of the linear fit are near Gaussian suggesting that there is no systematic evidence for non-linear variations. Moreover when studies use deep ocean temperatures to estimate global surface temperatures, they always assume linearity.”
That’s my point. You would not expect a linear relationship at low temperatures. I thought previous works distinguished between warm and cold climates.

The ocean initial conditions are still not clear. “we initialized the ocean temperatures and salinity with the values from previous model simulations from similar time periods” does not say much. From the supplemental, some simulations start cold, and some simulations start warm. Is initial salinity the same for all simulations? Are the initial conditions to blame for the unusual jumps in ocean temperature in some simulations (e.g. preindustrial)?

I thought HadCM3 requires a piece of land at the poles, is this not the case? It does not appear in the supplemental land mask figures.

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ED: Publish subject to minor revisions (review by editor) (28 Apr 2021) by Yannick Donnadieu

AR by Paul Valdes on behalf of the Authors (08 May 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (10 May 2021) by Yannick Donnadieu

AR by Paul Valdes on behalf of the Authors (17 May 2021) Manuscript

Short summary

Deep ocean temperatures are widely used as a proxy for global mean surface temperature in the past, but the underlying assumptions have not been tested. We use two unique sets of 109 climate model simulations for the last 545 million years to show that the relationship is valid for approximately the last 100 million years but breaks down for older time periods when the continents (and hence ocean circulation) are in very different positions.