Remote and local drivers of oxygen and nitrate variability in the shallow oxygen minimum zone off Mauritania in June 2014

Thomsen, Soeren; Karstensen, Johannes; Kiko, Rainer; Krahmann, Gerd; Dengler, Marcus; Engel, Anja

doi:https://doi.org/10.5194/bg-16-979-2019

Articles | Volume 16, issue 5

https://doi.org/10.5194/bg-16-979-2019

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

https://doi.org/10.5194/bg-16-979-2019

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

Articles | Volume 16, issue 5

Research article

|

13 Mar 2019

Research article |

| 13 Mar 2019

Remote and local drivers of oxygen and nitrate variability in the shallow oxygen minimum zone off Mauritania in June 2014

Soeren Thomsen, Johannes Karstensen, Rainer Kiko, Gerd Krahmann, Marcus Dengler, and Anja Engel

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Final revised paper (published on 13 Mar 2019)
Preprint (discussion started on 15 Jun 2018)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'REVIEW of “Remote and local drivers of oxygen and nitrate variability in the shallow oxygen minimum zone off Mauritania in June 2014”', Anonymous Referee #1, 24 Aug 2018
- AC3: 'AC1 final response', Soeren Thomsen, 27 Nov 2018
RC2: 'Review of “Remote and local drivers of oxygen and nitrate variability in the shallow oxygen minimum zone off Mauritania in June 2014” by Soren Thompsen et al.', Anonymous Referee #2, 15 Oct 2018
- AC2: 'AC2 final response', Soeren Thomsen, 27 Nov 2018
AC1: 'AR1 final response', Soeren Thomsen, 27 Nov 2018

Peer-review completion

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

ED: Reconsider after major revisions (04 Dec 2018) by Marilaure Grégoire

AR by Soeren Thomsen on behalf of the Authors (05 Dec 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (11 Dec 2018) by Marilaure Grégoire

RR by Anonymous Referee #1 (23 Dec 2018)

Suggestions for revision or reasons for rejection

\section*{Second revision of ``Remote and local drivers of oxygen and nitrate variability in the shallow oxygen minimum zone off Mauritania in June 2014'' by Soeren Thomsen et al.}

\subsection*{General Assesmemnt}
The authors have successfully addressed my comments/concerns, and they have modified the manuscript accordingly or, at least, they provided convincing explanations of why not doing so. I can now support publication. However, I still have a number of minor concerns and small corrections to the manuscript that must be might before final publication.

\subsection*{Minor comments and technical corrections}
\begin{itemize}
\item P2 – L16: suggests $\rightarrow$ suggest

\item P2 – L28-29: ``… an equatorward coastal jet whereas a surface intensified poleward flow with velocities well above 30 cm/s were* observed ...'' $\rightarrow$ was

P5 – L2-3: ``These analyses include the results of the local AOU and OMP analysis in regard to remote (transport) and local respiration and remineralization processes.''. The construction of this sentence sounds a bit odd to me, you might want to consider rephrasing it, maybe: ``These analyses include the results of the local AOU and OMP analysis in regard to remote (transport) and local (respiration and remineralization) processes.''

\item P6 – L22-25: The description of the ADCP dataset is a bit confusing. It is not clear from this description how many instruments have been used. From this paragraph it seems that more than one instrument has been used, but this is not coherent with Fig. 4 caption. Please revise this paragraph.

\item P6 – L31. Add units to the expression ($r = 1.8417 \cdot \mathrm{ESD}^{1.8}$)

\item P7 – L5. ``(Kalvelage et al., 2015)'' $\rightarrow$ Kalvelage et al. (2015).

\item In P. 8 – L22-23 you state ``In practice we fitted a {\bf 4th order polynomial function} to a group of 18 offshore AOU reference profiles using density as the independent variable'' but in L27-28 you refer to ``Moreover a smooth offshore AOU ($\sigma$) profile was 30 needed that allow for fitting a {\bf simple linear fit}''. Am I missing something or this is contradictory?

\item P9 – L 10: ``(here first guess Redfield ratio following (Karstensen and Tomczak, 1998), 8.625 = 138
O$_2$ / 16 $\sum$NO$_x$ )'' $\rightarrow$ revise the use of brackets in this sentence

\item P9 – L17: ``Mixing of water masses are* not resolved'' $\rightarrow$ is (?)

\item P9 – L23: ``respired /remineralized signal'' $\rightarrow$ respiration/remineralization signal

\item P9 – L24: ``were* regional remineralization'' $\rightarrow$ where

\item P10 – L4: ``relatively cold waters'': consider writing ``relatively cold surface waters'' for more clarity

\item P12 – L7: Delete ``(not shown)'' referring to the mixed layer depth, it is now shown in Fig. 3

\item P13 – L20: ``The along-shore circulation exhibited elevated variability during June 2014, which are* described based on two ship-based acoustic Doppler current profiler transects'' $\rightarrow$ is

\item Fig. 4 and associated description/discussion. Just for my curiosity, are the temporal changes in meridional velocity associated with changes in the wind forcing, while going towards the upwelling relaxation season? If the authors have any information about the origins of this variability, it could be useful to discuss it in the manuscript in relation to the increase in DO at the shelf break. Also, authors could add isopycnals to this figure to illustrate changes in the water mass distribution associated with the offshore shift of the poleward flow. This is just a suggestion.

\item Fig 9 caption. Please specify what filled areas represent in this figure ($\pm$ 1SD, 95$\%$ confidence intervals…)
P23 – L1: ``Cape Blance'' $\rightarrow$ ``Cape Blanc''

\item P23 – L19: ``Its difficult'' $\rightarrow$ ``It is difficult''

\item P23 – L27: ``… as the once presented ..'' $\rightarrow$ “as those presented”

\end{itemize}

Referee Report: PDF

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ED: Publish subject to minor revisions (review by editor) (30 Jan 2019) by Marilaure Grégoire

AR by Soeren Thomsen on behalf of the Authors (08 Feb 2019) Author's response Manuscript

ED: Publish as is (14 Feb 2019) by Marilaure Grégoire

AR by Soeren Thomsen on behalf of the Authors (18 Feb 2019)

Short summary

Physical and biogeochemical observations from an autonomous underwater vehicle in combination with ship-based measurements are used to investigate remote and local drivers of the oxygen and nutrient variability off Mauritania. Beside the transport of oxygen and nutrients characteristics from remote areas towards Mauritania also local remineralization of organic material close to the seabed seems to be important for the distribution of oxygen and nutrients.