Vertical distribution of planktic foraminifera through an oxygen minimum zone: how assemblages and test morphology reflect oxygen concentrations

Davis, Catherine V.; Wishner, Karen; Renema, Willem; Hull, Pincelli M.

doi:https://doi.org/10.5194/bg-18-977-2021

Articles | Volume 18, issue 3

https://doi.org/10.5194/bg-18-977-2021

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

https://doi.org/10.5194/bg-18-977-2021

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

Articles | Volume 18, issue 3

Research article

|

10 Feb 2021

Research article |

| 10 Feb 2021

Vertical distribution of planktic foraminifera through an oxygen minimum zone: how assemblages and test morphology reflect oxygen concentrations

Catherine V. Davis, Karen Wishner, Willem Renema, and Pincelli M. Hull

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Final revised paper (published on 10 Feb 2021)
Supplement to the final revised paper
Preprint (discussion started on 03 Aug 2020)
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: 'Review of the manuscript on Vertical distribution of planktic foraminifera through an Oxygen Minimum Zone: how assemblages and shell morphology reflect oxygen concentrations, by Davis and coauthors', Ralf Schiebel, 09 Sep 2020
- AC1: 'Response to Reviewer 1', Catherine Davis, 05 Oct 2020
RC2: 'Review on „Vertical distribution of planktic foraminifera through an Oxygen Minimum Zone: how assemblages and shell morphology reflect oxygen concentrations“', Anonymous Referee #2, 09 Sep 2020
- AC2: 'Response to Reviewer 2', Catherine Davis, 05 Oct 2020

Peer-review completion

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

ED: Reconsider after major revisions (08 Oct 2020) by Markus Kienast

AR by Katja Gänger on behalf of the Authors (22 Oct 2020) Author's response

ED: Referee Nomination & Report Request started (01 Nov 2020) by Markus Kienast

RR by Anonymous Referee #2 (13 Nov 2020)

Suggestions for revision or reasons for rejection

The authors present a revised version of the paper „Vertical distribution of planktic foraminifera through an Oxygen Minimum Zone: how assemblages and shell morphology reflect oxygen concentrations“. In their response letter, the authors satisfactory addressed all my comments to the original manuscript in detail and changed the manuscript accordingly. Find some thoughts about the revised manuscript below:

The new CT-Scan images in figure 10 are indeed very helpful.

Despite thinking, that a comparison of the optical and CT imaging with electron microscopy would be beneficial for this study, I understand that the amount of sample material is limited for this approach. Since the presented work is more a pilot study, the SEM comparison should rather be the focus of future research.

The authors now added a short part about different survival strategies of benthic foraminifera to oxygen depletion to the introduction (i.e. denitrification, dormancy, and specialized morphology). This is okay but it might have been beneficial for the manuscript to discuss these strategies directly in context with their own data and findings.

I have only two minor points of revision that should be included into the manuscript before publication:

About the comparison between CT and light microscopy: The authors now included the equation of the linear regression. For the sake of completeness it would be great if the authors can add the statistical errors of the (i.e. the error of the slope and the intercept).

One comment about the following sentence of the authors within the response letter:
“The reviewer raises a very good point. Unfortunately, all of these analyses were carried out on plankton tow specimens which may have been at different stages of (late) ontogeny, which complicates the meaning of a “last” chamber.”

In this case, using the term “last” chamber without further explanation might be misleading. Please clarify directly, that not all individuals were in the same ontogenetic stage.

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RR by Ralf Schiebel (19 Nov 2020)

Suggestions for revision or reasons for rejection

The new version of the paper of Catherine Davis and coauthors on “Vertical distribution of planktic foraminifera through an Oxygen Minimum Zone: how assemblages and test morphology reflect oxygen concentrations” reads better than the 1st version, and I agree to most of the points made in the reply to the reviewer’s comments and the revised manuscript. However, there is one issue that may need rethinking, and some minor points they want to be addressed before final publication of the paper.

I understand that new data on the molecular genetics of G. hexagonus are not easy to get on short notice. I also understand that Davis and coauthors may have the feeling that G. hexagonus is a normal component of Atlantic assemblages of modern planktic foraminifers. However, I know the specimens presented by Smart et al. (2018) by heart; the specimens really look like G. hexagonus, but they are not numerous. Therefore, we could not get data on the genotypes. Also, the G. hexagonus found in sediment assemblages are not numerous, and may have been transported into the Atlantic Ocean by currents (if these are G. hexagonus at all; I did not have a look at them). Therefore, I would suggest to be careful with stating that G. hexagonus is present in all modern oceans; this would need proof of an entire life cycle of G. hexagonus, including reproduction, in Atlantic water masses. Having said all this, Section “4.2 Globorotaloides hexagonus as an OMZ Indicator Species” reads better than before. The authors may still add that "final proof of the presence of G. hexagonus in the Atlantic may be provided by molecular genetics", which I would regard as a good way to solve the issue.

Minor points:
Line 44: Breitburg et al., 2108 should possibly read 2018
Line 196: “extremely oxygen depleted OMZ” is not a term defined below in this paper. I would suggest to drop “extremely”. Along the same lines, the paper would benefit from dropping a number of adjectives in places, which would make reading more scientific.
Line 211: change “transitional (nets sampling between these two extremes)“ to “between these two concentrations”.
Line 213: I would suggest to change “the densest population“ to „highest standing stock”, which is possibly more correct in a scientific way. In general, densities may be changed for standing stock throughout the paper.
Lines 244-252: I would suggest to add the numbers of empty tests to the Table 1.
Line 273: better change “interaction” to “relationship”; interaction insinuates determination, which is possibly not the case.
Line 287: “Globorotaloides hexagonus tests were light for their size“, relates to something that is not mentioned. “Light” compared to what?
Line 299: Please briefly describe what is meant by “compactness” and “aspect ratio”.
Line 337-339: „It is more likely that cytoplasm-bearing tests of T. sacculifer found below the
photic zone are a consequence of their very high abundance in the surface ocean and
reflected premature mortality and/or the retention of cytoplasm following reproduction.“ Did these specimens still have their spines? If yes, they may not have reproduced.
Line 358: Predation may be another reason to be taken into account.
Line 427 of the 1st version of manuscript: Sorry, this should have read Buchwald. Lines 441-442 in the new version of manuscript does still contain the same transposed digits: “Buchwald et al., 2105”, which may be changed to 2015.
Lines 456-464 presents a repetition of statements presented above, and may be rewritten or removed.
Final paragraph, lines 465-480: Another explanation for larger test sizes may be that G. hexagonus continuously grew larger under less optimal environmental conditions, i.e., lack of oxygen, and only reproduced with a delay when the environmental conditions had improved to support survival of the offspring (see Mojtahid et al., 2015 for G. ruber) and Schiebel and Hemleben (2017) for a more general explanation of the phenomenon.
Figure 1: O2 concentration larger than 7.5 ml L-2 are not presented in the map, and may be cut from the scale. By doing so, the relevant part of the scale may be more detailed.
Figure 9: The few red and yellow markers are not easy to see in the paper copy of the figure, and I would suggest to use darker color. Also, the green and blue markers would benefit from darker color.

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ED: Publish subject to minor revisions (review by editor) (07 Dec 2020) by Markus Kienast

AR by Catherine Davis on behalf of the Authors (16 Dec 2020) Author's response Author's tracked changes Manuscript

ED: Publish as is (04 Jan 2021) by Markus Kienast

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