Geothermal flux and basal melt rate in the Dome C region inferred from radar reflectivity and heat modelling

Passalacqua, Olivier; Ritz, Catherine; Parrenin, Frédéric; Urbini, Stefano; Frezzotti, Massimo

doi:https://doi.org/10.5194/tc-11-2231-2017

Articles | Volume 11, issue 5

https://doi.org/10.5194/tc-11-2231-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

Oldest Ice: finding and interpreting climate proxies in ice...

https://doi.org/10.5194/tc-11-2231-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 11, issue 5

Research article

|

20 Sep 2017

Research article |

| 20 Sep 2017

Geothermal flux and basal melt rate in the Dome C region inferred from radar reflectivity and heat modelling

Olivier Passalacqua, Catherine Ritz, Frédéric Parrenin, Stefano Urbini, and Massimo Frezzotti

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Final revised paper (published on 20 Sep 2017)
Preprint (discussion started on 14 Mar 2017)

Interactive discussion

Status: closed

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

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RC1: 'Review of Passalacqua et al', Anonymous Referee #1, 01 Apr 2017
- AC1: 'Answer to referee #1', Olivier Passalacqua, 19 Jun 2017
RC2: 'Review of Passalacqua et al.', Anonymous Referee #2, 10 Apr 2017
- AC2: 'Answer to referee #2', Olivier Passalacqua, 19 Jun 2017
SC1: 'comparison study', Martin Siegert, 11 Apr 2017
- AC3: 'Annswer to Martin Siegert', Olivier Passalacqua, 19 Jun 2017

Peer-review completion

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

AR by Olivier Passalacqua on behalf of the Authors (19 Jun 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Jul 2017) by Kenichi Matsuoka

RR by Anonymous Referee #2 (29 Jul 2017)

Suggestions for revision or reasons for rejection

The authors did a lot of work to address all the reviewer concerns, and I think it has improved significantly. I have just a few additional minor suggestions and edits.

The title has not been updated online, but maybe this is the case since it is still in TCD. There may be a good justification to change from “thermal modelling” to “heat modelling”, but I think that thermal modelling is more common. And, perhaps it would otherwise be “heat-flow modelling”? This may be just a matter of preference and I think that either is fine because the community should know what you mean.

There are still a few typos in the manuscript. I urge the authors to give this a very careful read before publication. I have noted the ones I found here but cannot be sure it is a complete list.

Line 8: “protected from basal melting” is awkward, would suggest “…did not experience basal melting…”

Line 9: suggest “infer” instead of “retrieve”

Most of the time you use GF after the acronym is introduced, but sometimes spell it out. Unless worth spelling out for a specific point then keep consistent throughout.

Line 43: extra “to”

Line 44: missing “it” between “chance” and “has”

Lines 47-50: Confusing at this point that the 3-D modeling is something that should be / will be done in future, but is not part of this study. “Later” could mean in this paper, or in future work outside of this study

Line 58: Given the size of Antarctica, I would say that deep boreholes are rare! I would also suggest another word to describe distribution of cores if you want to elaborate on what you mean by coverage of deep boreholes.

Line 72: Typo “pis”

And wouldn’t drawdown of layers also be a good indicator of basal melting, if it was happening for a long enough time?

Line 112: Suggest adding to end of this sentence … “using a heat model”

Line 122: Should be “letters and numbers”

Line 240: extra “a”; instead of “short” maybe “limited”, or give spatial scale you are talking about

Line 310: Not sure what you mean at the end of this sentence with “put out”

Line 347: should be “parameters”

Line 365 and elsewhere: I think it should be “Bedmap2”, no space

Line 369: Suggest “was zero” instead of “vanished”

Line 378: Suggest “was melting” instead of “melted” and specify over past 400 ka

Line 414: Suggest “constructed” instead of “built”

Line 425: Typo “par”

Line 427: Can cut out word “attributed”

Line 446: Suggest “calculated” instead of “induced”

Line 453: Typo “constrains”

Line 468: Suggest “small” instead of “tiny”

Line 473: What do you mean by assignment errors?

Line 496: word missing or extra around “physical key”

Line 497-: I am not sure I follow the points exactly as they are written, especially what “sufficient hilly bedrock to be applied” means in relation to the interpolation

Also a typo on “constrains” should be “constraints”

Line 535: Should be “has” instead of “have”

Line 536: Would use another word than “prevent”, maybe “limit”

Line 539: Should be “surveys”

Line 543: Don’t need negative in front of 800 ka

Line 560: What physical model (ice flow? Heat flow? Both?) is mentioned here

Line 565: missing “of”

Table 1 caption: First sentence doesn’t clearly introduce what is given the table, maybe there are some words missing or punctuation is incorrect?

Figure 1: Would mention that the boxes are 10 spots discussed later and/or reference these locations in later figure caption

Figure 9 is incredibly busy. Not sure the best way to handle that but would consider expanding the caption to help better guide the reader through all that is there, and you could reference back to Figure 1. Maybe you can change opacity of red/blue dots to better see what is new to show in this figure?

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ED: Publish subject to technical corrections (12 Aug 2017) by Kenichi Matsuoka

The revised manuscript is now reviewed by one referee and myself. Overall, the authors revised the manuscript adequately to address the points brought by the reviewers. Nevertheless, the revised manuscript still has some unclear statements and many small errors, which should be revised. Reviewer’s and my notes are, I hope, useful but these notes are not comprehensive. Please make careful read to polish the manuscript.

This manuscript is now accepted subject to technical corrections (i.e. subject to neither another review nor editor’s assessment).

Thanks for choosing TC/TCD to present your work.

Kenny Matsuoka, TC/TCD editor

SUGGESTIONS:
P9-10: Is it better to say “We used an inverse approach to retrieve GF from radar-inferred distribution of wet and dry beds”? The current writing sounds like that the authors made a complicated analysis of the radar data in their own work to tie the magnitude of the bed reflectivity and GF.
L12: local distribution “of radar-inferred basal melting”
L15-16: It is said “two main subregions” at L15 but then “a third one” at L16.
L49: “parameter’s”
L68: typo? “are rare in Antarctica…” Delete “East”
L70: Add a reference supporting a typical length scale of 10 km.
L70-75: Melting spots can be found as spots with anomalously high bed return power, only if the study area includes both melting and freezing regions. If the entire study area has melting bed, then the radar data are not necessarily capable to show the melting spots.
L110: add “today” after “melting occurs”
L145: remove the first “and”
L428: what is the basis to argue “probably up to 3 mW/m2” here?
L436-L437: Do you mean “Hence, considering the duration of deglaciation and strong dependence on the ice thickness, the thermal state of the basal ice may ….”?
L445: “positive GF anomaly”
L469-470: Do you mean “highest (with thinnest ice) DRY points and the lowest (with thickest ice) WET points”?
L532: will now be performed?? Do you mean “is being performed” or “will be performed soon”?
L577: “state”
Table 1 caption: GHF -> GF
Table 1: make the column header consistent; Hc should be Hc +/- sigma.
Fig. 1 caption: change the second dry to “(red)” in the first line.
Fig. 2: GHF to GF.
Fig 3: Add “shape parameter” in front of the italic p.
Fig. 5: change to “Geothermal flux”. Also change the legend in the figure accordingly.
Fig. 6: Change the x axis. Add italic “m” after Basal melt rate”. Again, geothermal flux. Add “shape parameter” in front of the italic p.
Fig. 7: “Averaged past” remains not clear enough.
Fig. 8: Geothermal flux.
L12, 35, 46, 52, …, 548 (and at many other places): Geothermal flux -> GF

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AR by Olivier Passalacqua on behalf of the Authors (19 Aug 2017) Author's response Manuscript

Short summary

As the Dome C region is a key area for oldest-ice research, we need to better constrain the geothermal flux (GF) so that past basal melt rates are well constrained. Our inverse heat model significantly reduces the confidence intervals of the GF regional field around Dome C, which ranges from 48 to 60 mW m⁻². Radar echoes need to be interpreted knowing the time lag of the climate signal to reach the bed. Several old-ice targets are confirmed and a new one is suggested, in which the GF is very low.