Nutrient distribution and nitrogen and oxygen isotopic composition of nitrate in water masses of the subtropical southern Indian Ocean

Harms, Natalie C.; Lahajnar, Niko; Gaye, Birgit; Rixen, Tim; Dähnke, Kirstin; Ankele, Markus; Schwarz-Schampera, Ulrich; Emeis, Kay-Christian

doi:https://doi.org/10.5194/bg-16-2715-2019

Articles | Volume 16, issue 13

https://doi.org/10.5194/bg-16-2715-2019

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

https://doi.org/10.5194/bg-16-2715-2019

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

Articles | Volume 16, issue 13

Research article

|

12 Jul 2019

Research article |

| 12 Jul 2019

Nutrient distribution and nitrogen and oxygen isotopic composition of nitrate in water masses of the subtropical southern Indian Ocean

Natalie C. Harms, Niko Lahajnar, Birgit Gaye, Tim Rixen, Kirstin Dähnke, Markus Ankele, Ulrich Schwarz-Schampera, and Kay-Christian Emeis

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Final revised paper (published on 12 Jul 2019)
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Preprint (discussion started on 03 Jan 2019)
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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 of Harms et al.', Annie Bourbonnais, 30 Jan 2019
- AC1: 'Reply to the Review of the Referee #1 (Bourbonnais)', Natalie Carina Harms, 22 Feb 2019
RC2: 'Referee Comment for Harms et al', Anonymous Referee #2, 11 Feb 2019
- AC2: 'Reply to the Review of the Referee #2 (Anonymous)', Natalie Carina Harms, 22 Feb 2019

Peer-review completion

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

ED: Reconsider after major revisions (07 Mar 2019) by Markus Kienast

AR by Natalie Carina Harms on behalf of the Authors (05 Apr 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (15 Apr 2019) by Markus Kienast

RR by Anonymous Referee #2 (20 May 2019)

Suggestions for revision or reasons for rejection

The authors have done a good job of revising the manuscript. They have addressed most of my comments and concerns, though I have a few new ones arising from the material added to the manuscript in the revision process, in addition to a few minor typographic corrections to note.

P. 2, Line 28: This equation for N*, including the constant 2.9 is in units of umol/kg

P. 3, line 15: Typo on δ15N-NO3-

P. 16, line 8: You could also compare your results to Martin and Casciotti, 2017: Paired N and O isotopic analysis of nitrate and nitrite in the Arabian Sea oxygen deficient zone.

P. 16, line 16: Typo on δ15N-NO3-

P. 17, lines 4-6: This is certainly one possibility. In this region, I think the authors should also discuss the potential for oxygen minimum zone processes to alter Δ(15-18), since this is an idea that is out there in the literature. If they don’t think that is important here, they could say so, but I think some mention is warranted.

P. 18, lines 13-16: This sentence construction doesn’t quite make logical sense. I would suggest clarification.

P. 19, line 13: Should this be “…the influx of nutrient enriched mineral aerosols…”?

P. 19, line 14: I’d suggest “…neglect this factor in our further discussion.”

P. 20: I found this whole section somewhat confusing, and potentially problematic, starting with equation 1. I think this section would be much clearer if they started with an N mass balance, which includes uptake and remineralization. Perhaps in your P mass balance, you can bring in the N/P ratios, but using it from the start is extremely confusing. It’s not obvious in these equations where the remineralized N and P are, though that is where the N2 fixation signal should reside.

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RR by Annie Bourbonnais (13 Jun 2019)

ED: Publish subject to minor revisions (review by editor) (18 Jun 2019) by Markus Kienast

AR by Natalie Carina Harms on behalf of the Authors (21 Jun 2019) Author's response Manuscript

ED: Publish as is (25 Jun 2019) by Markus Kienast

AR by Natalie Carina Harms on behalf of the Authors (25 Jun 2019) Manuscript

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Short summary

The Indian Ocean subtropical gyre is a large oligotrophic area that is likely to adjust to continued warming by increasing stratification, reduced nutrient supply and decreasing biological production. In this study, we investigated concentrations of nutrients and stable isotopes of nitrate. We determine the lateral influence of water masses entering the gyre from the northern Indian Ocean and from the Southern Ocean and quantify the input of nitrogen by N₂ fixation into the surface layer.