Dynamics of sediment flux to a bathyal continental margin section through the Paleocene–Eocene Thermal Maximum

Dunkley Jones, Tom; Manners, Hayley R.; Hoggett, Murray; Kirtland Turner, Sandra; Westerhold, Thomas; Leng, Melanie J.; Pancost, Richard D.; Ridgwell, Andy; Alegret, Laia; Duller, Rob; Grimes, Stephen T.

doi:https://doi.org/10.5194/cp-14-1035-2018

Articles | Volume 14, issue 7

https://doi.org/10.5194/cp-14-1035-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/cp-14-1035-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 14, issue 7

Research article

|

11 Jul 2018

Research article |

| 11 Jul 2018

Dynamics of sediment flux to a bathyal continental margin section through the Paleocene–Eocene Thermal Maximum

Tom Dunkley Jones, Hayley R. Manners, Murray Hoggett, Sandra Kirtland Turner, Thomas Westerhold, Melanie J. Leng, Richard D. Pancost, Andy Ridgwell, Laia Alegret, Rob Duller, and Stephen T. Grimes

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Final revised paper (published on 11 Jul 2018)
Supplement to the final revised paper
Preprint (discussion started on 16 Nov 2017)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC1: 'Orbital forcing of terrestrial hydrology, weathering and carbon sequestration during the Palaeocene-Eocene Thermal Maximum', Anonymous Referee #1, 14 Dec 2017
- AC1: 'Author Comment to Anonymous Referee 1', Tom Dunkley Jones, 05 Jan 2018
  - RC3: 'Reply to Reply on my review comment', Anonymous Referee #1, 06 Jan 2018
RC2: 'Review', Victoriano Pujalte, 15 Dec 2017
- AC2: 'Author Comment to Victoriano Pujalte (Referee 2)', Tom Dunkley Jones, 05 Jan 2018
  - RC4: 'New Comment to the Replay of Tom Dunkley Jones et al.', Victoriano Pujalte, 09 Jan 2018
    - AC4: 'Author Comment to Victoriano Pujalte (Referee 2) Second Comment', Tom Dunkley Jones, 10 Jan 2018
SC1: 'Review comment on: “Orbital forcing of terrestrial hydrology, weathering and carbon sequestration during the Palaeocene-Eocene Thermal Maximum”', Michael Clare, 03 Jan 2018
- AC3: 'Reply to Short Comment of Mike Clare', Tom Dunkley Jones, 05 Jan 2018
  - SC2: 'Response to Reply by Dunkley Jones', Michael Clare, 06 Jan 2018
RC5: 'Comment 3', Victoriano Pujalte, 11 Jan 2018

Peer-review completion

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

ED: Reconsider after major revisions (18 Jan 2018) by Laurie Menviel

AR by Tom Dunkley Jones on behalf of the Authors (31 Mar 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (05 Apr 2018) by Laurie Menviel

RR by Michael Clare (12 Apr 2018)

Suggestions for revision or reasons for rejection

Review of “Dynamics of sediment flux to a bathyal continental margin section through the Paleocene-Eocene Thermal Maximum” by Mike Clare

I am pleased to have been invited to provide a follow up review to my previous two rounds of open comments on the manuscript of Dunkley-Jones et al. “Dynamics of sediment flux to a bathyal continental margin section through the Paleocene-Eocene Thermal Maximum”. This manuscript presents an interesting, well–conceived and novel study of the Zumaia section of the PETM that analyses new high-resolution bulk sediment stable isotope and major element data with an aim to better understand the roles of hinterland hydrology and carbon sequestration due to variable sediment accumulation rates. Previous studies have demonstrated that this section is an expanded, well-preserved and continuous section; hence, it is an excellent location for the study of these aspects. Previous studies have also demonstrated an increase in detrital accumulation during the PETM (as shown here), but did not do so with such a high-temporal resolution that accumulation rates could be precisely tied to specific phases of the PETM (as achieved by Dunkley-Jones et al.) A new finding presented here is that peak values of detrital accumulation were reached during the recovery phase of the PETM isotopic excursion (and not prior to or coincident with it). The second key finding is that the peak in detrital accumulation corresponds to the period of maximum organic carbon sequestration. This has not been documented before, and it is suggested by the authors that organic carbon sequestration may explain the recovery of the PETM carbon isotopic excursion, as it cannot be accounted for by silicate weathering alone. This important new finding may have a wider impact on our understanding of the global system recovery from other climate hyperthermals, but to my knowledge has been under-appreciated or not referenced at all in many other studies. To this end, this study presents exciting new findings to add significant scientific value to a classic PETM type section as well as to better understand how our planet may recover from dramatic periods of rapid warming. I am largely happy with the modifications made to the previous manuscript, in particular the change in focus of the new version that reduces emphasis on some more contentious aspects (with respect to previous open reviews). With regard to some of the open review comments by other reviewers on allochthonous interruptions in the PETM (as indicated in the marked up manuscript), from my personal experience at the outcrop I can vouch for the lack of [at least visually discernable] turbidites within the PETM succession (indeed that was the focus of our 2016 paper) and believe the authors have done as thorough a job as required to discount this potential bias from their analysis. I outline some relatively minor comments in the attached marked up .pdf manuscript and also have some specific comments below, but am very supportive of its publication and consider that the authors will have no issues with addressing my comments.

1) “Results” are not distinctly separated from “Discussion”. This is my main issue with the manuscript as it stands. I suspect that due to the need to touch on a number of aspects of the study (and reference previous work at this already well-studied site), the flow of the paper does not necessarily read like a conventional scientific manuscript. There are not clear Results and Discussion sections, which sometimes makes it difficult for the reader (at least for me) to see where the original study-specific observations are being made, and then where interpretations or wider implications are discussed. For instance, in section 3 new results are presented alongside discussion of previous literature. The least that needs to be done is to differentiate clearly to the reader where new facts end and interpretations begin. I have no strong preference for how this is done as I recognise the flow of the manuscript needs to dip in and out of the different aspects of the study, but it could be simply achieved by use of sub-headings, or slight restructuring.
2) Recognise previous studies (re. age model): While the authors present a new “robust age model” for the section (line 34 page 5), I suggest that they make sure to reference the seminal and outstanding work done by many previous authors (i.e. not to suggest that previous age models were not robust). Any work on this section builds on a significant body of research, so I would simply suggest tempering the language and ensuring that the previous efforts are more clearly recognised.
3) Significant threshold for spectral analysis is not explained or justified: The spectral analysis is a valuable and neatly quantified aspect of the study to demonstrate temporal clustering of enhanced Si (relative to Fe). What I was unclear on was what significance threshold was used for that analysis? This was not clear to me. For instance, the 0.45 m peak is only just significant at 90th percentile confidence interval – how is that discerned from other “peaks” that occur at a similar threshold? This should be explained more clearly to avoid suspicion of author bias.
4) Provide context for comparative studies: Reference is made to the Big Horn Basin throughout the text (and then Polecat Bench in Figure 6), but these sites are never introduced properly. What is their setting? Where are they in the world? Why is it worth comparing Zumaia to this site/these sites? The authors should bear in mind that readers of this article may not be au fait with the global PETM literature.

Referee Report: PDF

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RR by Anonymous Referee #1 (14 Apr 2018)

ED: Publish subject to minor revisions (review by editor) (20 May 2018) by Laurie Menviel

AR by Tom Dunkley Jones on behalf of the Authors (04 Jun 2018) Author's response Manuscript

ED: Publish subject to technical corrections (07 Jun 2018) by Laurie Menviel

AR by Tom Dunkley Jones on behalf of the Authors (15 Jun 2018) Author's response Manuscript

Short summary

The Paleocene–Eocene Thermal Maximum (PETM) is a transient global warming event associated with a doubling of atmospheric carbon dioxide concentrations. Here we document a major increase in sediment accumulation rates on a subtropical continental margin during the PETM, likely due to marked changes in hydro-climates and sediment transport. These high sedimentation rates persist through the event and may play a key role in the removal of carbon from the atmosphere by the burial of organic carbon.