Estimates of ikaite export from sea ice to the underlying seawater in a sea
ice–seawater mesocosm

Geilfus, Nicolas-Xavier; Galley, Ryan J.; Else, Brent G. T.; Campbell, Karley; Papakyriakou, Tim; Crabeck, Odile; Lemes, Marcos; Delille, Bruno; Rysgaard, Søren

doi:https://doi.org/10.5194/tc-10-2173-2016

Articles | Volume 10, issue 5

https://doi.org/10.5194/tc-10-2173-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/tc-10-2173-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 10, issue 5

Research article

|

21 Sep 2016

Research article |

| 21 Sep 2016

Estimates of ikaite export from sea ice to the underlying seawater in a sea ice–seawater mesocosm

Nicolas-Xavier Geilfus, Ryan J. Galley, Brent G. T. Else, Karley Campbell, Tim Papakyriakou, Odile Crabeck, Marcos Lemes, Bruno Delille, and Søren Rysgaard

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Final revised paper (published on 21 Sep 2016)
Preprint (discussion started on 11 Feb 2016)

Interactive discussion

Status: closed

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

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RC1: 'tc-2016-14 Comments', Anonymous Referee #1, 25 Mar 2016
- AC1: 'Response number1', Nicolas-Xavier Geilfus, 13 May 2016
RC2: 'Reviewer #2 Geilfus et al.', Anonymous Referee #2, 02 Apr 2016
- AC2: 'response 2', Nicolas-Xavier Geilfus, 13 May 2016
RC3: 'Review of Geilfus et al', Anonymous Referee #3, 11 Apr 2016
- AC3: 'Response 3', Nicolas-Xavier Geilfus, 13 May 2016

Peer-review completion

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

AR by Nicolas-Xavier Geilfus on behalf of the Authors (13 May 2016) Author's response

ED: Referee Nomination & Report Request started (18 May 2016) by Lars Kaleschke

RR by Anonymous Referee #3 (15 Jun 2016)

Suggestions for revision or reasons for rejection

I suggest adding a comment on that salinity and TA in seawater did not have the same concentrations before the experiment (t=0) and after (=end) the experiment due to remaining sea ice in the pool. That is what I mean with “closing the TA budget” (perhaps wrong wording). TA should be the same in the seawater before and after finishing the experiment, if all ice melted (and taking into account the sampled ice TA). For clarification, please just add a comment in the method section or when introducing Table 1 or Figure 2.

Lines 510-513, after comment on the study by Fransson et al 2013 “….release of brine decreased Ωaragonite by 0.8 ……related to CO2 enrichment of brine”. I suggest adding (for consistency): “Conversely, during ice melt, Ωaragonite increased by 1.4 between March and May, likely due to both CaCO3 dissolution and primary production. This contrasts….”
Line 517, after …..DOE (1994). “This shows the complexity of ikaite and its impact on the carbonate system and Ω in the underlying water.”
Line 528. Add “may” before “therefore” so that the sentence reads “…..impede the effect of ikaite rejection and may therefore lower Ωaragonite.

Table 2. Please check the significant numbers of decimals and values for all the parameters. Are two decimals significant regarding the accuracy in the measurements and calculations? I think that one or no decimal is more accurate. This is valid also for Figure 6 linear regression equations and R2.
Table 2. What parameter is in the first column (and unit?)? Date/time in decimals?

Suggested additional reference Lyakhin (1970): show evidence that sea ice can release solid CaCO3 to the underlying water
Reference:
Lyakhin, Y. I. (1970), Saturation of water of the Sea of Okhotsk with calcium carbonate, Oceanology, 10, 789–795.

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RR by Anonymous Referee #4 (29 Jun 2016)

Suggestions for revision or reasons for rejection

Review Geilfus et al., Impacts of ikaite export from sea ice to the underlying seawater in a sea ice-seawater mesocosm

The paper analyses a three week mesocosm study performed at the outdoor sea ice research facility SERF in Winnipeg with respect to the transfer of ikaite crystals to the underlying water during sea ice growth and melt, and it;’s effect on the water and ice carbon budget. The facility allows for a constrained environment which allows to analyze the full “ocean” budget, with out the uncertainty of horizontal and vertical processes in a deep ocean.

The study seems a reasonable set up and analyses performed adequately. The results provide some important additions to our understanding of the role of ikaite precipitation and dissolution during sea ice growth and melt processes.

I recommend publication with minor revisions.

Requested revisions are mostly minor clarifications with a few concerns with respect to the suitability of the set up for the analysis of specific processes. My main question is with respect to the melting procedure, i.e. does melting initiated from an underwater source provide the adequate representation for sea ice melting usually initiated by atmospheric warming and incident shortwave. This is particularly relevant when discussing release of ikaite crystals through melted channels at the bottom of the sea ice versus exchange of CO2 at the surface.

Minor comments:

Abstract

The first 1-3 sentences seem a bit disconnected and I am feeling I am missing a sentence on what ikaite is about.

sentence 1 could be

L14 rm “from open water”

L19 up to => therefrom , then rm :of the ikaite...within sea ice”

Main text:
L29 released to the atmosphere - from where?
L50 rejected from sea ice - clarify direction (where to)
L67/68 fluxes are....incorporated into water masses ….or below sea ice – something is wrong here, please clarify sentence
L70 Are you referring to the shrinking of the brine channels due to freezing ? If so please clarify
L72-74 would move the “internal ice melt” forward , since that is what increases the ibrine volume, correct?
L75 Eq 3 – should this be Equ 1?
L86 of the different processes
L90 the addition “from open water” makes the sentence a bit convoluted. I think it would be sufficient to clarify once at the befginning that the experiment starts with open water, then only write “ from initial sea ice formation to melt” ( This occurs several times in the manuscript)
L95 suggest to rm “major changes in”
L104 formulated => formed ???

L106ff How realistic is it to have an under water heat source versus an atmospheric heat source, particularly in terms of melting the ice structure and opening of brine channels from top or bottom, allowing fluxes out of the ice ???

L113 How well mixed is the underlying water – is 1.3m a representative depth?

L244 rm Therefore ( previous sentence is not the cause of this)

L 260 expected : expected based on what? ( does that refer to no ikaite interaction?)
L267 throughout the ice

section 5.2.1 Suggest to define some dTA for the difference between TA(ice)* and TA(ice), this might make the text clearer.

L279 black dots =diamonds
L280 .. highly variable ( isn’t that something that would be expected, ie. Concentration needs to become high enough for crystallization, but once it is precipitated the concentration needs to be build up again before more crystallization can happen??? - not sure, I am not a chemist...)

L282 I can’t see this in the Figure ( 7a??) please clarify. If differences are minor a zoom in and clarification might help.
L290-309 This section would profit from some streamlining, as is the message is confusing
e.g. L299 you talk about underestimation while the figure shows mostly overestimation till Jan 17. While this is addressed later it doesn’t make sense where it is stated.
L301-303 could ikaite also be redissolved with sea water infiltration?
L307-308 clarify that the message is precip is not only reduced but actual dissolution occurs
L309 can you discern this from the water column? If so state this and refer to section where this is discussed

section 5.22 could the export towards the underlying sea water be intensified by the melting from the bottom ? ( Since it already starts befor ethe melting is turned on, it might not be the case, but it might be good to discuss.

L320 one-month long – Isn’t the experiment 17 days only or is this another experiment?

L 326 started => starts
L 320-349 again, this starts to become confusing, any streamlining would help
L344 delay of reaction ??
L358 Please clarify if you were actually measuring ikaite or derived it.
L367 rm contain

5.4 This title is strange, I suggest to put the “ attempt of a CO2 budget in a separate section (from line 400 and maybe frame it as an error or uncertainty analysis...)

L399 Are you generating this kind of turbulence in the tank?
L424 Suggest: As a result several area => Several areas
L427 the annual
L428 saturation state
L440 suggest using “alleviate” instead of “hamper”
L448 month-long – 17 day?
L449 rm “from open water”
L450 suggest “direct CO2 exchange” to clarify this is released from the ice to the atmosphere
L452 estimation => estimates; rm here
L455 were missing ???? had been removed?
L470 responsible formation

Figure 2 use consistent ABCD, abcd in caption and figure

Panel d indicate blue and green, What is the black line in panel d, also the different symbols are not discernible

caption last line: profile => profiles

Fig 3 caption clarify what is indicated with * (E.g. add in brackets after “variation of salinity observed” (**).

Fig. 6 what are the green and blue lines

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ED: Publish subject to minor revisions (Editor review) (12 Jul 2016) by Lars Kaleschke

AR by Nicolas-Xavier Geilfus on behalf of the Authors (13 Jul 2016) Author's response Manuscript

ED: Publish subject to minor revisions (Editor review) (11 Aug 2016) by Lars Kaleschke

AR by Nicolas-Xavier Geilfus on behalf of the Authors (12 Aug 2016) Author's response Manuscript

ED: Publish as is (15 Aug 2016) by Lars Kaleschke

AR by Nicolas-Xavier Geilfus on behalf of the Authors (16 Aug 2016) Manuscript

Short summary

The fate of ikaite precipitation within sea ice is poorly understood. In this study, we estimated ikaite precipitation of up to 167 µmol kg^-1 within sea ice, while its export and dissolution into the underlying seawater was responsible for a TA increase of 64–66 μmol kg^-1. We estimated that more than half of the total ikaite precipitated was still contained in the ice when sea ice began to melt. The dissolution of the ikaite crystals in the water column kept the seawater pCO₂ undersaturated.