Dissolved iron in the North Atlantic Ocean and Labrador Sea along the GEOVIDE section (GEOTRACES section GA01)

Tonnard, Manon; Planquette, Hélène; Bowie, Andrew R.; van der Merwe, Pier; Gallinari, Morgane; Desprez de Gésincourt, Floriane; Germain, Yoan; Gourain, Arthur; Benetti, Marion; Reverdin, Gilles; Tréguer, Paul; Boutorh, Julia; Cheize, Marie; Lacan, François; Menzel Barraqueta, Jan-Lukas; Pereira-Contreira, Leonardo; Shelley, Rachel; Lherminier, Pascale; Sarthou, Géraldine

doi:https://doi.org/10.5194/bg-17-917-2020

Articles | Volume 17, issue 4

https://doi.org/10.5194/bg-17-917-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

GEOVIDE, an international GEOTRACES study along the OVIDE...

https://doi.org/10.5194/bg-17-917-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 4

Research article

|

21 Feb 2020

Research article |

| 21 Feb 2020

Dissolved iron in the North Atlantic Ocean and Labrador Sea along the GEOVIDE section (GEOTRACES section GA01)

Manon Tonnard, Hélène Planquette, Andrew R. Bowie, Pier van der Merwe, Morgane Gallinari, Floriane Desprez de Gésincourt, Yoan Germain, Arthur Gourain, Marion Benetti, Gilles Reverdin, Paul Tréguer, Julia Boutorh, Marie Cheize, François Lacan, Jan-Lukas Menzel Barraqueta, Leonardo Pereira-Contreira, Rachel Shelley, Pascale Lherminier, and Géraldine Sarthou

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Final revised paper (published on 21 Feb 2020)
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Preprint (discussion started on 04 Apr 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 of the manuscript “Dissolved iron in the North Atlantic Ocean and Labrador Sea long the GEOVIDE section (GEOTRACES section GA01)” submitted by M. Tonnard et al.', Christian Schlosser, 16 May 2018
- AC1: 'Response', Manon Tonnard, 17 Aug 2018
- AC3: 'Response to Christian Schlosser: good version', Manon Tonnard, 19 Sep 2018
- AC4: 'Response to Christian Schlosser: new version of the manuscript', Manon Tonnard, 19 Sep 2018
- AC5: 'Response to Christian Schlosser: new version of the supplementary material of the manuscript', Manon Tonnard, 19 Sep 2018
RC2: 'Review of Tonnard et al.', Anonymous Referee #2, 26 Jun 2018
- AC2: 'Response', Manon Tonnard, 17 Aug 2018
- AC6: 'Response to Referee#2: good version', Manon Tonnard, 19 Sep 2018
- AC7: 'Response to Referee#2: new version of the manuscript', Manon Tonnard, 19 Sep 2018
- AC8: 'Response to Referee#2: new version of the supplementary material of the manuscript', Manon Tonnard, 19 Sep 2018

Peer-review completion

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

ED: Publish subject to minor revisions (review by editor) (25 Sep 2018) by Catherine Jeandel

ED: Reconsider after major revisions (27 Sep 2018) by Catherine Jeandel

AR by Manon Tonnard on behalf of the Authors (02 Oct 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Oct 2018) by Catherine Jeandel

RR by Anonymous Referee #2 (09 Nov 2018)

Suggestions for revision or reasons for rejection

Review comments of the resubmitted version of Tonnard et al.
To start I would like to comment on some practicalities. Continuous line numbers throughout the text (and not restarting at every page) would have made life much easier for the reviewers. In addition, responses to reviewers’ comments in underlined red very hard to read in this pdf-converted tracked changes file! I am aware this is the first experience publishing but please consider giving responses in a well-organised way next time. You can highlight text in other smoother colours or in bold that are easier to read than red underlined text with hundreds of text boxes attached on the side. You should also consider that when giving response to reviews it is important to include the new line numbers of the new text. This was done sometimes, but most of the time (for the short responses) the reviewer had to find its way around the text. Things like this considerably increase the revision time, especially for such long papers.
I appreciate the amount of effort that has gone into making the requested changes. Even though the paper has considerably improved, it still needs a few changes before publication. Apart from the minor corrections below, there are a few more important points below:
1) some of your discussion is based on the expectation to see “DFe fingerprints” in specific water masses. Realistically, I do not think that the DFe residence time is long enough to persist along the flow path of a water mass, and I therefore would like to motivate you to compare the residence time of DFe in a certain region to the time it takes for this DFe to travel from the “source” region (i.e., surface ocean, sediments, hydrothermal ridge, river) along the flow path of the water mass in question considering its flow velocity. I believe you will find that these times are not compatible to see a DFe fingerprint and that internal processes along these flow paths are much more important. I encourage you to include these calculations in your paper when you discuss DFe signatures in water masses.
2) Include some important descriptions in your methods section: Chl-a sampling and measurement techniques, fluorometer measurements, how the fluorometer is calibrated with the Chl-a measurements; describe why you used the sensor data from the stainless steel CTD; include the interclibration plots, even though they are different they are important for the GEOTRACES community, and explain the likely reasons why they are different; more detail on the different filtration techniques, including information on which samples are filtered through which size fraction (table S1); use the correct density values to make the conversion of units
3) Figures should be “cited” much more often in the text to support the discussion. Some figures are missing to explain correlations (see below). Some Figure do not correspond to what is said in the text (see below). Please revise the entire text on how it is supported by the Figures and the supplementary material. Some of the figures in the supplementary material are not even mentioned in the main text. Are they really necessary?
Specific comments:
Page1, Line 31: remove cause of “enhanced se-air interactions”. Suggestion: Deep winter convection occurring the previous winter provided iron-to-nitrate ratios sufficient to sustain phytoplankton growth and lead to relatively elevated DFe concentrations within subsurface waters of the Irminger Sea. Page 2, Line 4: delete "the production of sinking biogenic particles". POC is biogenic particles, so you don't repeat. Rather say, they are exported through "sinking and ocean currents".
Page 2, line 10: “to be able to”
Page 2, line 10: I would move the sentence mentioning specifically Fe to the paragraph starting line 30, since this is where you start properly talking about the role of trace metals in the ocean; the rest of the nutrient discussion is good
Page 3, Line 10: “throughout” instead of “along”
Page 4, line 12: You need to say that a filtration techniques were not directly compared. You can not say that you didn't observe significant differences since you have not directly compare these techniques. Change sentence: "Fe concentration differences between stations 11 and 13, and 13 and 15 were most likely due to different filtration techniques".
Page 4, Line 29: “Spectrometer”
Page 5, line 13: you've already covered calibrations beforehand so please delete the repetition
Page 5, line 16: “considering all analytical sessions”
Page 5, Line 22: I still believe it is more correct to use the actual density of each seawater sample to make this conversion. The universal 1.025 value is used for conversions when actual density is not available.
Page 5, Line 22: I think it is important to include the intercalibration plot you show in your response document in the paper in this section, with an explanation of why these profiles are so different. Just because they don't coincide, doesn't mean you should discard them. Intercalibration is important for the GEOTRACES community
Page 5, line 24: “from Sea-Ice Melt”
Page 5, line 26: “we briefly describe the principle”
Page 5, line 27: remove “the” in front of water masses and check throughout the text.
Page 5, line 27: explain in the text how you estimated the proportions of AW and PW in each sample.
Page 6, line 10: missing description of Chl-a sampling and measurements. Please include the description you have given in the reviewers response document here in this section. Also add which casts Chl-a measurements were made on and which casts fluorometer measurements were made on.
Page 6, line 11: and was fluorescence not also measured with a sensor?
Page 6, line 12: please briefly explain here why you use the data from the stainless casts and not from your trace metal rosette casts. Please include in the paper what you described in the reviewers response, that the O2 data was not calibrated on the TM CTD, etc
Page 7, line 11: put into brackets "the outliers are flagged with number 3"
Page 7, line 24: “representing 60% of the…”
Page 7, line 26: “ENACW was also…” (remove “the”)
Page 7, line 28 and line 30: “SubPolar Mode Water”
Page 7, line 24: “representing 40% of the…”
Page 8, line 2: “below ENACW up to…”
Page 8, line 4: briefly say why sea-surface salinity is lower. Ice melt?
Page 8, line 18: remove “the” in front of water masses
Page 9, line 23: Which rosette is the Chl-a data coming from? Stainless steel or TMR? A brief description has to be included in the methods section
Page 10, line 14: delete “upper” since you already say “surface”
Page 10, line 18: Fingerprinting water masses? I do not see a correlation of water masses and Fe concentrations in figure 3. I would call this section "DFe signatures in water masses" or “DFe concentrations in water masses”
Page 12, line 19: instead of low-level say low-altitude to avoid confusion with wind force.
Page 13, line 3: the fate of atmospheric Fe also depends on Fe-ligand availability.
Page 13, line 10: “remineralisation signal”
Page 13, line 14: If you insist on discussing the DFe concentrations in relation to water masses it is VERY IMPORTANT to compare residence times of DFe with the time it takes for each water mass to travel from the "source" region. I.e., for Mediterranean water how long does it take for water masses to travel from the surface Mediterranean to where there is still 60% of this water mass - station 29?; for deep water masses, how long does it take for this water mass to travel from a sediment contact region to the place where there is still 60 % of this water mass present; for intermediate water masses, how long does it take for these water masses from the moment they are in contact with the atmosphere to travel to the place where there is still 60 % of this water mass, etc. Also note that DFe residence times vary in different regions and at different concentrations.
Page 13, line 24: chlorophyllide-a
Page 14, line 21: remove “to occur”
Page 14, line 27: Why figure S4? I only see surface values in this figure but you talk about dFe at 2500 m depth!
Page 14, line 28: sediment inputs can also happen diagonally, horizontally etc, doesn’t have to be strictly vertically. Please mention that
Page 14, line 30, “during GEOVIDE”
Page 15, line 3: what is its residence time? Look for values in your study area in the published bibliography.
Page 15, line 2-4: this sentence makes no sense. Not from water masses but from lateral advection of deep waters? Are deep waters not water masses?
Page 15, line 11: “scavenging component”
Page 15, line 11: remove “the” in front of 230-Th
Page 15, line 14: briefly explain what the differences are in behaviour of Fe and Th
Page 15, line 15: “would be the presence of Fe-binding organic ligands in these samples…”
Page 15, line 16: “from the seafloor to the overlying deep waters… “
Page 15, line 17: diffusion of particles? Diffusion is a term applied for dissolved substances...
Page 15, line 20: “due to the presence of Fe-binding…”
Page 15, line 30: “transported within ISOW…” (remove “the”)
Page 16, line 3: you could put into brackets “basaltic” since at the MOR volcanic particles might be most present on the seafloor. “resuspension of (basaltic) particles…”
Page 16, line 4: which station? 40? I can't see stn 40 in figure 4! why do you cite figure 7? what is Fe* telling you about hydrothermal vents? needs to be clarified. Figure 4 focuses on surface and subsurface waters, so how can this help interpreting deep hydrothermal sources? Please cite the correct figures.
Page 16, line 4: low trasmissiometer data at which station? Please at least show a transmissiometer profile.
Page 16, line 8, line 12: remove “the” in front of water masses
Page 16, line 16: “DFe to surface waters…”
Page 16, line 27: sentence confusing, where was the atmospheric deposition higher, during GA01 or GA03?
Page 16, line 31: “, that extends through an area…”
Page 17, line 15: “extended 200 km off the Greenland stations…”
Page 17, line 22: briefly mention in brackets above which salinity values are considered "brine"
Page 17, line 23: residence time of brines? You should mention that the calculated brine and sea-ice signals are mixed in the surrounding water since salinity anomalies are not associated to those signals. If you talk about residence times, do you talk of the pure brine or the seawater mixed brines? This is confusing and should be clarified in the main text
Page 17, line 33: I can't see a salinity signal at 100 m depth..
Page 18, line 2: what does a correlation plot show dFe vs MW or Sea-ice fraction? A little hard to see correlations on vertical profiles
Page 18, line 5: “for which no DFe data was available…”
Page 18, line 11: “the surface DFe depletion is likely explained…”
Page 19, line 24: “DFe and PFe concentrations…”
Page 19, line 25: “in the samples closest to the seafloor…”
Page 19, line 27: station 2 and 4 are the same margin, so delete "different behaviour of Fe among different margins"
Page 20, line 1: “the more lithogenic sediments…”
Page 20, line 11: remove “the” in front of particulate Fe and in front of Dal and in front of AOU
Page 20, line 20: “enrichment of Fe in the particulate phase…” (since the Fe will be adsorbed, and not "within" the particle)
Page 20, line 22: “and Mn from the dissolved phase…”
Page 21, line 11: “classes are dealt with in Tonnard…”
Page 21, line 22: “from the Iceland Basin and the Irminger Sea. “
Page 21, line 33: “stations from the subpolar gyre…”
Page 22, line 22: it is hard to follow these correlations, slope and intercept values without the corresponding figures. Please add the figures
Page 22, line 3: “compared”
Page 22, line 6: “follows”
Page 22, line 13: add the reference where you got this ratio from
Page 22, line 21: how do you know the Fe:N requirement of the phytoplankton in that area? please add a reference
Page 22, line 22: “deposition to IcSPMW” (remove “the”)
Page 22, line 24-27: I can see lowest Fe* in the Iceland Basin, not the West European Basin
Page 23, line 10: remove “the” in front of ISOW.
Page 23, line 23: “in the Irminger Sea”
Page 23, line 31: “tip jet events”
Page 36, line 36: MOW not labelled in the plots
Page 38, line 4: do you mean sea-ice or sea-ice-melt?
Page 39: you forgot to add the station numbers to the graph
Supplementary material: add page numbers and add the paper info at the top of this document (title, authors, affiliations, etc).
Page3: why did you not consider station 1 and 17? Please briefly explain. what do the black dots represent? Describe the red line in the legend. What is the value of DFe meadian? Correct error on y axis title
Page 8: specify the sampling depth for these surface values
Table S1: add a column informing the filtration size for each sample (since you have not directly compared these methods on natural samples)

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ED: Publish subject to minor revisions (review by editor) (23 Nov 2018) by Catherine Jeandel

AR by Manon Tonnard on behalf of the Authors (02 Dec 2019) Author's response Manuscript

ED: Publish subject to technical corrections (09 Jan 2020) by Catherine Jeandel

AR by G. Sarthou on behalf of the Authors (15 Jan 2020) Manuscript

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Short summary

We investigated the spatial distribution of dissolved Fe during spring 2014, in order to understand the processes influencing the biogeochemical cycle in the North Atlantic. Our results highlighted elevated Fe close to riverine inputs at the Iberian Margin and glacial inputs at the Newfoundland and Greenland margins. Atmospheric deposition appeared to be a minor source of Fe. Convection was an important source of Fe in the Irminger Sea, which was depleted in Fe relative to nitrate.