Temperature and mineral dust variability recorded in two low-accumulation Alpine ice cores over the last millennium

Bohleber, Pascal; Erhardt, Tobias; Spaulding, Nicole; Hoffmann, Helene; Fischer, Hubertus; Mayewski, Paul

doi:https://doi.org/10.5194/cp-14-21-2018

Articles | Volume 14, issue 1

Clim. Past, 14, 21–37, 2018

https://doi.org/10.5194/cp-14-21-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Clim. Past, 14, 21–37, 2018

https://doi.org/10.5194/cp-14-21-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 14, issue 1

Research article 10 Jan 2018

Research article | 10 Jan 2018

Temperature and mineral dust variability recorded in two low-accumulation Alpine ice cores over the last millennium

Pascal Bohleber et al.

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Final revised paper (published on 10 Jan 2018)
Supplement to the final revised paper
Preprint (discussion started on 16 Jun 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review', Anonymous Referee #1, 17 Jul 2017
- AC1: 'Response to anonymous referee #1', Pascal Bohleber, 30 Sep 2017
RC2: 'Review of “Temperature and mineral dust variability recorded in two low accumulation Alpine ice cores over the last millennium” by Bohleber et al., 2017', Anonymous Referee #2, 25 Jul 2017
- AC2: 'Response to anonymous referee #2', Pascal Bohleber, 30 Sep 2017

Peer-review completion

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

ED: Reconsider after major revisions (01 Oct 2017) by Amaelle Landais

AR by Pascal Bohleber on behalf of the Authors (09 Oct 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Oct 2017) by Amaelle Landais

RR by Anonymous Referee #2 (25 Oct 2017)

RR by Anonymous Referee #1 (08 Nov 2017)

Suggestions for revision or reasons for rejection

I find this version of the paper considerably improved and I believe the authors clarified my most important points. However, the authors may consider these additional comments.

Main points:
I think the supplementary figures A1 and A2 provide important additional information/value to the paper.

Figure A1: This figure provides a good idea of 1) how the seasonal cycles of delta 18O and Ca2+ can be preserved at Colle Gnifetti and 2) the partitioning of summer and winter accumulation. While I see how the large amplitude seasonal signal can be conserved and transferred to greater depths over time, I do not see how the same can happen for the minor Ca2+ peaks, as indicated by the arrows. To me this figure does not support the concept of “group of peaks” observed at greater depths and referred as annual cycle. Counting these groups as annual layers is still equivocal and, while this could still be correct, (another unknown post-depositional glaciological mechanism may concur to form this presumed annual feature) the dating of this core remain well constrained only in its upper and bottom parts. Identifying absolute time horizons in the time interval of 100-300 years before present, seems however a frequent problem of Alpine cores whose dating might typically suffer of a lower relative accuracy at that time.

Figure A2: This figure strongly supports the idea that the occurrence of dust in snow layers facilitates their consolidation and thus preservation on site. I was wondering whether it would be possible to also display and comment delta 18O in this figure, as it might be telling about the role of atmospheric temperature and the timing of occurrence of this consolidation process. In any event I strongly recommend this figure to be incorporated within the main text as this seems the most convincing evidence supporting the arguments proposed by the authors.

The indication of the potential source area of dust remains elusive to me. However, regardless whether the Sahara is constantly the source of these large inputs of dust to Colle Gnifetti, this does not influence the main message of the paper. I would only recommend the authors to provide some significant references for isotopic and elemental tools/methods (e.g. Sr and Nd isotopes, REE etc.) that could possibly be employed in the future to better constrain potential source areas of dust that reached Colle Gnifetti.

A graphical comparison with the Thevenon record might be also helpful.

I would also recommend a final polishing of the English as it does not always sound correct to me.

Specific points:
Pag 1, Line 12: I would suggest to replace “advection” with “convection”.

Pag 3, Line 17-18 “A changing amount of winter precipitation contributing to annual mean values may introduce a coupling on the inter-annual scale among seasonal varying signals, including δ18O and most impurities”. This sentence is not clear.

Pag. 4, Line 27 I would remove “specific”.

Pag. 18 Line 11 (and elsewhere within the text, e.g. in caption of figure A2). You may replace “snow preservation” with “snow consolidation”. This latter is more focused on the process.

Pag 18 Line 18 “This revealed that the resulting bias from incomplete snow preservation on the average Ca2+ level is already in the same order of magnitude as the long-term Ca2+ trends found in previous studies”. This sentence is not clear.

Pag 20 Line 8 “depend on”

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ED: Publish subject to technical corrections (20 Nov 2017) by Amaelle Landais

AR by Pascal Bohleber on behalf of the Authors (23 Nov 2017) Author's response Manuscript

Short summary

The Colle Gnifetti (CG) glacier is the only drilling site in the European Alps offering ice core records back to some 1000 years. We aim to fully exploit these unique long-term records by establishing a reliable long-term age scale and an improved ice core proxy interpretation for reconstructing temperature. Our findings reveal a site-specific temperature-related signal in the trends of the mineral dust proxy Ca²⁺ that may supplement other proxy evidence over the last millennium.