Sea ice pCO2 dynamics and air&ndash;ice CO2 fluxes during the Sea Ice Mass Balance in the Antarctic (SIMBA) experiment &ndash; Bellingshausen Sea, Antarctica

Geilfus, N.-X.; Tison, J.-L.; Ackley, S. F.; Galley, R. J.; Rysgaard, S.; Miller, L. A.; Delille, B.

doi:https://doi.org/10.5194/tc-8-2395-2014

Articles | Volume 8, issue 6

https://doi.org/10.5194/tc-8-2395-2014

© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/tc-8-2395-2014

© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 8, issue 6

Research article

|

20 Dec 2014

Research article |

| 20 Dec 2014

Sea ice pCO₂ dynamics and air–ice CO₂ fluxes during the Sea Ice Mass Balance in the Antarctic (SIMBA) experiment – Bellingshausen Sea, Antarctica

N.-X. Geilfus, J.-L. Tison, S. F. Ackley, R. J. Galley, S. Rysgaard, L. A. Miller, and B. Delille

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Final revised paper (published on 20 Dec 2014)
Preprint (discussion started on 23 Jun 2014)

Interactive discussion

Status: closed

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

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- Supplement

RC C1416: 'tc-2014-88 - Referee Comment', Sönke Maus, 28 Jul 2014
- AC C1908: 'reply_review_1', N-X. Geilfus, 25 Sep 2014
SC C1417: 'A comment on the "Impact of snow cover on CO2 dynamics in Antarctic pack ice"', Philipp Griewank, 29 Jul 2014
- AC C1907: 'Review_Griewank', N-X. Geilfus, 25 Sep 2014
RC C1679: 'Review of "Impact of snow cover on CO2 dynamics in Antarctic pack ice"', Anonymous Referee #2, 27 Aug 2014
- AC C1906: 'reply_review_2', N-X. Geilfus, 25 Sep 2014

Peer-review completion

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

AR by Nicolas-Xavier Geilfus on behalf of the Authors (26 Sep 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (26 Sep 2014) by Martin Schneebeli

RR by Sönke Maus (20 Oct 2014)

Suggestions for revision or reasons for rejection

The authors have clarified many aspects and improved the paper. However, I still find that the following points need improvements.

• The authors claim that processes related to cooling-warming of samples prior to bulk CO2 measurements likely will not affect the results; I give some more arguments and reference from field work that indicate fundamental changes in microstructure during similar cooling-warming, and suggest possible effects on the method. These should be considered a bit more critically in the text.
• One main conclusion proposed by the authors is now: Both techniques, measuring
the pCO2 within sea ice and brine, address different parts of the brine network.
However, in this connection the authors have corresponded with arguments (that
are also mentioned in the paper) that I find confusing (e.g. that the bulk pCO2
measurements include information from isolated brine pockets). Have I misunderstood something in the Geilfus et al. (2012) methodology paper? As I understand the latter, pCO2 is measured from equilibration of a standard gas with the ice samples warmed to in-situ temperatures, and it is then the connected brine pore space that the gas equilibrates with, not the isolated brine pockets. If I am correct here, then this should be corrected in the paper (e.g. Line 418), and it should be noted that both the bulk pCO2 the in situ pCO2 methods can only measure CO2 within interconnected brine networks.
Regarding the comparison of the methods, the conclusion that in situ pCO2 relates to another fraction of the brine network (the most mobile one), is acceptable, provided the critical notes on the sack-hole technique by the authors. However, a note on disadvantages of the bulk pCO2 technique, especially the possible consequences of microstructure change, brine expulsion and air space (see my comments below) need to be added.
• Fig. 10 and text: A subsection 5d is termed “comparison” between Antarctic and
Arctic. Based on Fig. 10 a difference between the reions is supposed, and written in the present text (L. 447...). In my opinion this should be tested statistically, even if the causes are unknown. Also, Fig. 10a would be, as noted, much more informative, if the y-scale would be changed.
• I still find some passages about brine convection speculative, mentioning too frequently the work by Brabant (2012) that is not per-reviewed. Also, if, as on Lines 331 ff., Rayleigh numbers estimated by Brabant (2012) are explicitely mentioned, then Ra should at least be defined. In my opinion, Brabant (2012) may be referenced, yet not in the detail given here.

Provided that the authors address these aspects, which I rate as minor improvements, I recommend the paper for publication in “The Cryosphere”.

Referee Report: PDF

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ED: Publish subject to minor revisions (Editor review) (26 Oct 2014) by Martin Schneebeli

AR by Anna Wenzel on behalf of the Authors (06 Nov 2014) Author's response Manuscript

ED: Publish as is (24 Nov 2014) by Martin Schneebeli

Short summary

Temporal evolution of pCO2 profiles in sea ice in the Bellingshausen Sea, Antarctica (Oct. 2007), shows that physical and thermodynamic processes control the CO2 system in the ice. We show that each cooling/warming event was associated with an increase/decrease in the brine salinity, TA, TCO2, and in situ brine and bulk ice pCO2. Thicker snow covers reduced the amplitude of these changes. Both brine and bulk ice pCO2 were undersaturated, causing the sea ice to act as a sink for atmospheric CO2.