A global scavenging and circulation ocean model of thorium-230 and protactinium-231 with improved particle dynamics (NEMO–ProThorP 0.1)

van Hulten, Marco; Dutay, Jean-Claude; Roy-Barman, Matthieu

doi:https://doi.org/10.5194/gmd-11-3537-2018

Articles | Volume 11, issue 9

https://doi.org/10.5194/gmd-11-3537-2018

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

Special issue:

Nucleus for European Modelling of the Ocean - NEMO

https://doi.org/10.5194/gmd-11-3537-2018

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

Articles | Volume 11, issue 9

Model description paper

|

31 Aug 2018

Model description paper |

| 31 Aug 2018

A global scavenging and circulation ocean model of thorium-230 and protactinium-231 with improved particle dynamics (NEMO–ProThorP 0.1)

Marco van Hulten, Jean-Claude Dutay, and Matthieu Roy-Barman

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Final revised paper (published on 31 Aug 2018)
Supplement to the final revised paper
Preprint (discussion started on 08 Dec 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of "A global scavenging and circulation ocean model of thorium-230 and protactinium-231 with realistic particle dynamics (NEMO–ProThorP 0.1) *"', Peter Santschi, 28 Dec 2017
- AC1: 'Response to reviewers', Marco van Hulten, 23 Feb 2018
RC2: 'A global scavenging and circulation ocean model of thorium-230 and protactinium-231 with realistic particle dynamics (NEMO–ProThorP 0.1)', Anonymous Referee #2, 30 Dec 2017
- AC1: 'Response to reviewers', Marco van Hulten, 23 Feb 2018
RC3: 'Review: A global scavenging and circulation ocean model of thorium-230 and protactinium-231 with realistic particle dynamics', Anonymous Referee #3, 07 Jan 2018
- AC1: 'Response to reviewers', Marco van Hulten, 23 Feb 2018

Peer-review completion

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

AR by Marco van Hulten on behalf of the Authors (09 Mar 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (26 Mar 2018) by Andrew Yool

RR by Anonymous Referee #3 (30 Apr 2018)

Suggestions for revision or reasons for rejection

The presentation of the article is much improved and the authors have provided a good supplementary document with much need details. However, I do not find the explanation they have provided, of why the instantaneous equilibrium is an appropriate approximation, convincing. In my first review I showed that the adsorption and desorption terms were not as fast as the sinking rate for large particles.

After carefully reading the authors response, I returned to this issue and using a single large and single small particle class for Thorium derived 1-D vertical profile solutions. I chose the numbers based on the dominate sinking flux (CaCO3 for large) and POC for small, their Table 4 and numbers from the supplementary materials. I considered the solutions in the absence of mixing and advection. I chose a very large dissociation value of 4/yr (Note: smaller values will make the problems discussed worse, not better). The profiles obtained are attached.

We see that the large particles are falling so fast, they do not reach equilibrium until at least 2000 m. This means they transport far less Th than estimated by the authors. The dissolved Th and the Th on the small particles are much larger than estimated by the authors.

As expressed by the authors in their response, these ratios can be changed by changing the equilibrium constants, kappa. However, the other difference the full solution shows is that the dissolved and particulate phases are not straight lines with origins at zero depth. In particular, the dissolved phase has a distinct curvature and intercept. This curvature means, compared with the authors solution, the real difference in the upper waters (0-2000m) and the lower waters (2000-4000m) is much less than occurs for a straight line with origin at zero depth.

On the other hand, observed profiles do not have such a large intercept. This result must mean that particles falling as fast as 50 m/d cannot play as large a role as the authors suggest.

It can not be expected that the results from a model that gets the 1-D profiles incorrect, would be accurate in 3-D. The interpretation of the results, due to the tuning required to correct this model deficit, is uncertain.

Other issues noticed:

Opal is still used at least once
Figure 5c: caption says uM, color bar says nM

Referee Report: PDF

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RR by Anonymous Referee #4 (05 Jun 2018)

ED: Reconsider after major revisions (13 Jun 2018) by Andrew Yool

AR by Marco van Hulten on behalf of the Authors (18 Jul 2018) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (15 Aug 2018) by Andrew Yool

AR by Marco van Hulten on behalf of the Authors (16 Aug 2018) Author's response Manuscript

ED: Publish as is (20 Aug 2018) by Andrew Yool

AR by Marco van Hulten on behalf of the Authors (20 Aug 2018)

Short summary

We present an ocean model of the natural radioactive isotopes thorium-230 and protactinium-231. These isotopes are often used to investigate past ocean circulation and particle transport. They are removed by particles produced by plankton and from uplifted desert dust that is deposited into the ocean. We approach observed dissolved and adsorbed Th-230 and Pa-231 activities. The Pa-231 / Th-230 sedimentation ratio is reproduced as well; this quantity can be used as a proxy for ocean circulation.