Coupled calcium and inorganic carbon uptake suggested by magnesium and sulfur incorporation in foraminiferal calcite

van Dijk, Inge; Barras, Christine; de Nooijer, Lennart Jan; Mouret, Aurélia; Geerken, Esmee; Oron, Shai; Reichart, Gert-Jan

doi:https://doi.org/10.5194/bg-16-2115-2019

Articles | Volume 16, issue 10

https://doi.org/10.5194/bg-16-2115-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-16-2115-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 10

Research article

|

20 May 2019

Research article |

| 20 May 2019

Coupled calcium and inorganic carbon uptake suggested by magnesium and sulfur incorporation in foraminiferal calcite

Inge van Dijk, Christine Barras, Lennart Jan de Nooijer, Aurélia Mouret, Esmee Geerken, Shai Oron, and Gert-Jan Reichart

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Final revised paper (published on 20 May 2019)
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Preprint (discussion started on 12 Dec 2018)
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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 manuscript bg-2018-481', Anonymous Referee #2, 04 Jan 2019
- AC1: 'Response to referee 1', Inge van Dijk, 14 Feb 2019
- AC2: 'Response to referee 1', Inge van Dijk, 14 Feb 2019
RC2: 'Review of manuscript bg-2018-481', Anonymous Referee #1, 07 Jan 2019
- AC3: 'Response to referee 2', Inge van Dijk, 14 Feb 2019

Peer-review completion

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

ED: Publish subject to minor revisions (review by editor) (20 Feb 2019) by Hiroshi Kitazato

ED: Publish subject to minor revisions (review by editor) (06 Mar 2019) by Hiroshi Kitazato

AR by Inge van Dijk on behalf of the Authors (06 Mar 2019) Author's response Manuscript

ED: Reconsider after major revisions (07 Mar 2019) by Hiroshi Kitazato

AR by Inge van Dijk on behalf of the Authors (08 Mar 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (11 Mar 2019) by Hiroshi Kitazato

RR by Anonymous Referee #1 (08 Apr 2019)

Suggestions for revision or reasons for rejection

Re-review of manuscript bg-2018-481

The authors have addressed virtually all my previous comments and therefore I recommend publication, although I ask for further clarification on a few minor points below.

Aside from the issues raised last time (see below), my only remaining concern is the arrows that are drawn onto Fig. 9 (‘SWV-dominated’, ‘Ca transport-dominated’ etc.). The graph is interesting, but I see no basis for these simplifications either in this study or the existing literature. I agree that the calcification process in Ammonia clearly differs from the high-Mg benthics but generalising further than that is a mistake in my opinion. Consider Amphistegina, one of the few species for which we have good observational evidence about the calcification process (e.g. abundant seawater vacuoles, pH elevation). If anything, this genus should plot at or near the opposite end of these arrows. To give another specific example of why this is problematic, the authors state in their response that ‘We acknowledge that SWV also includes a small increase in pH (8.75 according to Bentov et al., 2009). However, the pH increase in the vacuoles is lower then observed inside small benthic foraminifera. Therefore, we reduced the size of the arrow, but kept the direction as it was.’, but as far as I understand the argument, this does not seem internally consistent. The authors here use the data of Bentov et al. [2009] as evidence for a distinction in the degree of pH elevation in foraminifera known to vacuolise large quantities of seawater, yet based on its Mg/Ca ratio, the species that Bentov et al. studied (A. lobifera) would plot in the ‘H+ pump-dominated’ ‘Ca transport-dominated’ area of Fig. 9. I recommend removing the arrows and labels, and caution against distinguishing between ‘SWV-dominated’ and ‘H+ pump-dominated’ based on the available pH reconstructions. Bear in mind the HPTS-pH calibration becomes challenging as pH 9 is approached (Fig. 1 in de Nooijer et al., 2008), such that there may not be a significant difference between the small and high-Mg benthics.

We tried to clear up the nomenclature used in the manuscript. We replaced coupled with coregulation and covariation.
I appreciate the author’s efforts here, and I agree that the change to covariation is an improvement. However, I would nonetheless recommend finding a different word to ‘coregulation’. E.g. at the bottom of page 1 (there are no line numbers…), ‘we observe a coregulation of S and Mg’. Yet coregulation to me implies active regulation by the organism, which I agree is the case for Mg/Ca, but this remains to be constrained in the case of sulphur.

Because in the case of SWV, you would expect the opposite, a decrease of Mg/Ca due to less efficient export of Mg.
I would argue that it does not mean that the process does not operate in all biomineralization models, rather it is overprinted by some other process. In any case, I don’t understand the logic in the TMT model. Surely what is important is how selective the channels/pumps are for Ca over Mg, so what is relevant here is the free(?)/available Mg/Ca ratio of the seawater. If I understand, you hypothesise that the free/available Mg is increased at higher temperature due to dehydration, which means that it is more readily transported. However, doesn’t this ignore that Ca will be similarly dehydrated, and so the free/available Mg/Ca ratio is not greatly temperature dependent? The same logic applies in reverse to Mg removal in the vacuolisation model.

Lastly, one comment that is new to this version (near the bottom of page 10). Bear in mind that foraminifera growth rate could be decoupled from crystal growth rate. It is not necessarily safe to assume anything about S incorporation from the foraminifera growth data as we cannot distinguish between rapid precipitation of calcite that only takes place occasionally from slow, regular precipitation.

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RR by Guillaume Paris (09 Apr 2019)

ED: Publish subject to minor revisions (review by editor) (15 Apr 2019) by Hiroshi Kitazato

AR by Inge van Dijk on behalf of the Authors (25 Apr 2019) Author's response

ED: Publish as is (26 Apr 2019) by Hiroshi Kitazato

AR by Inge van Dijk on behalf of the Authors (02 May 2019)

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Short summary

Systematics in the incorporation of different elements in shells of marine organisms can be used to test calcification models and thus processes involved in precipitation of calcium carbonates. On different scales, we observe a covariation of sulfur and magnesium incorporation in shells of foraminifera, which provides insights into the mechanics behind shell formation. The observed patterns imply that all species of foraminifera actively take up calcium and carbon in a coupled process.