the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Jan 2024
Brief communication: Identification of 140,000-year-old blue ice in Grove Mountains, East Antarctica, by krypton-81 dating
Abstract. The presence of exceptionally old ice and the relative ease of access make Antarctic blue ice areas (BIAs) attractive paleoclimate archives. However, only a handful of BIAs, mostly situated in West Antarctica and along the Trans-Antarctic Mountains, have been investigated for this purpose. Here, we present the age of surface ice from the Grove Mountains BIA in Elizabeth Princess Land, East Antarctica, determined by measuring 81Kr in the trapped air. Two samples yield an average age of 143+33-29 kyr. Together with the reported terrestrial age of a chondrite, we conclude that Grove Mountains BIA holds considerable potentials for paleoclimate studies.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-2754', Anonymous Referee #1, 19 Jan 2024
General comments
In the manuscript “Brief communication: Identification of 140,000-year-old blue ice in Grove Mountains, East Antarctica, by krypton-81 dating” by Z. Hu et al., the authors present the results of the determination of the age of air bubbles in blue ice from the Grove Mountains BIA in Elizabeth Princess Land, East Antarctica, using the 81Kr technique. Two samples showed an average age of ~143 ka. Together with the reported terrestrial age of a chondrite, the authors concluded that Grove Mountains BIA holds considerable potential for paleoclimate studies.
The manuscript introduces the identification of a novel area of BIA in Antarctica that could be suitable for paleoclimate studies. The authors highlight that the region of Grove Mountains can be included in the record of BIAs in Antarctica such as Mount Moulton and Patriot Hills in West Antarctica, and Allan Hills, Taylor Glacier, and Larsen Glacier in East Antarctica, holding old ice which could help to investigate past climate changes.
The text is generally clear and the enclosed results are worthy of publication, however, I do suggest some improvements, especially regarding the identification of Grove Mountains as a potential ice coring/paleoclimate studies site. The discussion should be expanded on this topic, including some comments on radar profiles and ice stratigraphy. The dating technique is properly described and I do not have specific comments on that. The use of the English language is appropriate and the concepts are clearly presented.
Here I enclose some comments that I hope would improve the quality of the manuscript. I am looking forward to reading the new version of the text.
Specific comments:
- Materials and methods section: the authors highlight since the introduction section that the BIA of Grove Mountains (GM) could hold ice hold enough for paleoclimate studies, especially for ice core drilling. I believe that this strong affirmation should be followed by a more expanded discussion in the “site and sample” subsection. In Figure 1c the authors show a radar profile of the transect, the discussion may start from this picture such as: how is the ice layering there? Where potential drilling sites could be identified? Is it an area where short cores or long cores could be drilled? If the whole point of this manuscript is to identify a new area for ice coring and paleoclimate studies, this additional discussion would improve the impact of this study.
- Materials and methods section: around line 80 the authors describe how the samples were collected. Could you please provide some additional information? What was the size of the samples? Depth, length, etc.. Did you perform a preliminary visual inspection of the ice? Any cracks, or melted layers? Do you have pictures of the sampling in Antarctica and of the samples? A picture of the sampling in the field would be very interesting to see.
- Discussion and conclusion section: In line 175 the authors stress that the GM BIA could provide large ice samples to study past climate changes. To improve the discussion and support the conclusions Hu et al. here can include some lines about stratigraphy and potential ice core drilling discussed in the “material and methods section” (see comment above).
Technical corrections
- Line 35: would be worth mentioning the Beyond Epica Oldest Ice project and include a more recent reference since the drilling has already started.
See https://tc.copernicus.org/articles/12/2167/2018/ and the official website https://www.beyondepica.eu/en/about/
- Line 40: please change “being exhumed” to “brought to the surface”
- Lines 41-42: the affirmation “The presence of meteorites that have terrestrial ages up to 2 Myr in the BIAs hints at the existence of ice that is older than 800 kyr (Scherer et al., 1997)” is a bit strong especially because Scherer at al. dated the ice close the meteorite to be 325 ka old. The sentence could be rephrased with “300 ka old ice”.
- Lines 45: please substitute “Nevertheless, to date debris-free ice samples have been recovered from only five blue ice areas for the purpose of paleoclimate studies” with “To date debris-free ice, ice samples were recovered from only five blue ice areas” and remove “for the purpose of paleoclimate studies”
- Line 49: please substitute the sentence with “In this study, we focus on the Grove Mountains, which consist of a series…”
- Figure 1b: please enlarge the red triangle size to be easier to spot.
- Line 172: Please start the sentence with “Our study shows that ice surface at Grove Mountains dates back to the Last Interglacial, holding important ..”
- Lines 177-180: this is a very “heavy” sentence and I suggest that this might be too much in this manuscript. Then Allan Hills is located in West Antarctica, which may be too far to make a comparison. I suggest avoiding this sentence and focusing only on the obtained results for GMs and suggesting the presence of older ice.
- Lines 185-190: I suggest moving those lines after line 173 to make this section more easy to read. It is easier for the reader to be reminded of the results at the beginning of the results section.
- Lines 173 onwards should be then adjusted consequently.
- Line 191: please substitute “past warm intervals” with “past Interglacials”
Citation: https://doi.org/10.5194/egusphere-2023-2754-RC1 -
AC1: 'Reply on RC1', Guitao Shi, 31 Jan 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2754/egusphere-2023-2754-AC1-supplement.pdf
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AC3: 'Reply on RC1', Guitao Shi, 15 Feb 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2754/egusphere-2023-2754-AC3-supplement.pdf
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RC2: 'Comment on egusphere-2023-2754', Anonymous Referee #2, 22 Jan 2024
This is an extremely simple brief communication whose purpose is to show that the grove mountains blue ice area would be a good place to do ice coring for palaeoclimate. The novelty in the paper consists of two (similar) dates obtained using 81Kr dating, which show that ice 140000 years old is present at the surface. The authors comment that the isotopic and chemical data suggest that the ice originated somewhere relatively local and not high on the East Antarctic plateau.
There is not really much to comment on. The date is hard-won, as this is a dating method that requires a lot of effort and a lot of ice. The finding is novel if a bit limited - it would of course have been much more interesting if the authors had been able to say anything about ice at depth, or to demonstrate that the greenhouse gas content of the ice was compatible with the ages they found. However, it is what it is. This seems like a result and proposal that is worth publicising, and the science in the paper is correct. I therefore recommend publication with very limited revision.
Minor comments:
Line 25: Princess Elizabeth rather than Elizabeth princess (it’s right elsewhere in the paper)
Line 53 “potential” rather than “potentials”
Table 1. For Allan Hills it might be nice to add a more recent paper such as Yan 2023 (Yan, Y., Kurbatov, A. V., Mayewski, P. A., Shackleton, S., and Higgins, J. A.: Early Pleistocene East Antarctic temperature in phase with local insolation, Nature Geoscience, 16, 50-55, doi: 10.1038/s41561-022-01095-x, 2023)
On page 5 (around line 108), the reader would appreciate more information about why 85Kr indicates contamination. I suppose giving its short half life would explain this.
Line 161. If possible it would be nice to see a small table with the water isotope data for Grove Mts, for nearby sites from the paper by Ma et al, and for inland sites (Dome A, Vostok, Dome Fuji), along with their elevations. This would help to make the point that the ice must have a local rather than plateau origin.
Citation: https://doi.org/10.5194/egusphere-2023-2754-RC2 -
AC2: 'Reply on RC2', Guitao Shi, 31 Jan 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2754/egusphere-2023-2754-AC2-supplement.pdf
-
AC2: 'Reply on RC2', Guitao Shi, 31 Jan 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-2754', Anonymous Referee #1, 19 Jan 2024
General comments
In the manuscript “Brief communication: Identification of 140,000-year-old blue ice in Grove Mountains, East Antarctica, by krypton-81 dating” by Z. Hu et al., the authors present the results of the determination of the age of air bubbles in blue ice from the Grove Mountains BIA in Elizabeth Princess Land, East Antarctica, using the 81Kr technique. Two samples showed an average age of ~143 ka. Together with the reported terrestrial age of a chondrite, the authors concluded that Grove Mountains BIA holds considerable potential for paleoclimate studies.
The manuscript introduces the identification of a novel area of BIA in Antarctica that could be suitable for paleoclimate studies. The authors highlight that the region of Grove Mountains can be included in the record of BIAs in Antarctica such as Mount Moulton and Patriot Hills in West Antarctica, and Allan Hills, Taylor Glacier, and Larsen Glacier in East Antarctica, holding old ice which could help to investigate past climate changes.
The text is generally clear and the enclosed results are worthy of publication, however, I do suggest some improvements, especially regarding the identification of Grove Mountains as a potential ice coring/paleoclimate studies site. The discussion should be expanded on this topic, including some comments on radar profiles and ice stratigraphy. The dating technique is properly described and I do not have specific comments on that. The use of the English language is appropriate and the concepts are clearly presented.
Here I enclose some comments that I hope would improve the quality of the manuscript. I am looking forward to reading the new version of the text.
Specific comments:
- Materials and methods section: the authors highlight since the introduction section that the BIA of Grove Mountains (GM) could hold ice hold enough for paleoclimate studies, especially for ice core drilling. I believe that this strong affirmation should be followed by a more expanded discussion in the “site and sample” subsection. In Figure 1c the authors show a radar profile of the transect, the discussion may start from this picture such as: how is the ice layering there? Where potential drilling sites could be identified? Is it an area where short cores or long cores could be drilled? If the whole point of this manuscript is to identify a new area for ice coring and paleoclimate studies, this additional discussion would improve the impact of this study.
- Materials and methods section: around line 80 the authors describe how the samples were collected. Could you please provide some additional information? What was the size of the samples? Depth, length, etc.. Did you perform a preliminary visual inspection of the ice? Any cracks, or melted layers? Do you have pictures of the sampling in Antarctica and of the samples? A picture of the sampling in the field would be very interesting to see.
- Discussion and conclusion section: In line 175 the authors stress that the GM BIA could provide large ice samples to study past climate changes. To improve the discussion and support the conclusions Hu et al. here can include some lines about stratigraphy and potential ice core drilling discussed in the “material and methods section” (see comment above).
Technical corrections
- Line 35: would be worth mentioning the Beyond Epica Oldest Ice project and include a more recent reference since the drilling has already started.
See https://tc.copernicus.org/articles/12/2167/2018/ and the official website https://www.beyondepica.eu/en/about/
- Line 40: please change “being exhumed” to “brought to the surface”
- Lines 41-42: the affirmation “The presence of meteorites that have terrestrial ages up to 2 Myr in the BIAs hints at the existence of ice that is older than 800 kyr (Scherer et al., 1997)” is a bit strong especially because Scherer at al. dated the ice close the meteorite to be 325 ka old. The sentence could be rephrased with “300 ka old ice”.
- Lines 45: please substitute “Nevertheless, to date debris-free ice samples have been recovered from only five blue ice areas for the purpose of paleoclimate studies” with “To date debris-free ice, ice samples were recovered from only five blue ice areas” and remove “for the purpose of paleoclimate studies”
- Line 49: please substitute the sentence with “In this study, we focus on the Grove Mountains, which consist of a series…”
- Figure 1b: please enlarge the red triangle size to be easier to spot.
- Line 172: Please start the sentence with “Our study shows that ice surface at Grove Mountains dates back to the Last Interglacial, holding important ..”
- Lines 177-180: this is a very “heavy” sentence and I suggest that this might be too much in this manuscript. Then Allan Hills is located in West Antarctica, which may be too far to make a comparison. I suggest avoiding this sentence and focusing only on the obtained results for GMs and suggesting the presence of older ice.
- Lines 185-190: I suggest moving those lines after line 173 to make this section more easy to read. It is easier for the reader to be reminded of the results at the beginning of the results section.
- Lines 173 onwards should be then adjusted consequently.
- Line 191: please substitute “past warm intervals” with “past Interglacials”
Citation: https://doi.org/10.5194/egusphere-2023-2754-RC1 -
AC1: 'Reply on RC1', Guitao Shi, 31 Jan 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2754/egusphere-2023-2754-AC1-supplement.pdf
-
AC3: 'Reply on RC1', Guitao Shi, 15 Feb 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2754/egusphere-2023-2754-AC3-supplement.pdf
-
RC2: 'Comment on egusphere-2023-2754', Anonymous Referee #2, 22 Jan 2024
This is an extremely simple brief communication whose purpose is to show that the grove mountains blue ice area would be a good place to do ice coring for palaeoclimate. The novelty in the paper consists of two (similar) dates obtained using 81Kr dating, which show that ice 140000 years old is present at the surface. The authors comment that the isotopic and chemical data suggest that the ice originated somewhere relatively local and not high on the East Antarctic plateau.
There is not really much to comment on. The date is hard-won, as this is a dating method that requires a lot of effort and a lot of ice. The finding is novel if a bit limited - it would of course have been much more interesting if the authors had been able to say anything about ice at depth, or to demonstrate that the greenhouse gas content of the ice was compatible with the ages they found. However, it is what it is. This seems like a result and proposal that is worth publicising, and the science in the paper is correct. I therefore recommend publication with very limited revision.
Minor comments:
Line 25: Princess Elizabeth rather than Elizabeth princess (it’s right elsewhere in the paper)
Line 53 “potential” rather than “potentials”
Table 1. For Allan Hills it might be nice to add a more recent paper such as Yan 2023 (Yan, Y., Kurbatov, A. V., Mayewski, P. A., Shackleton, S., and Higgins, J. A.: Early Pleistocene East Antarctic temperature in phase with local insolation, Nature Geoscience, 16, 50-55, doi: 10.1038/s41561-022-01095-x, 2023)
On page 5 (around line 108), the reader would appreciate more information about why 85Kr indicates contamination. I suppose giving its short half life would explain this.
Line 161. If possible it would be nice to see a small table with the water isotope data for Grove Mts, for nearby sites from the paper by Ma et al, and for inland sites (Dome A, Vostok, Dome Fuji), along with their elevations. This would help to make the point that the ice must have a local rather than plateau origin.
Citation: https://doi.org/10.5194/egusphere-2023-2754-RC2 -
AC2: 'Reply on RC2', Guitao Shi, 31 Jan 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2754/egusphere-2023-2754-AC2-supplement.pdf
-
AC2: 'Reply on RC2', Guitao Shi, 31 Jan 2024
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Yuzhen Yan
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Xueyuan Tang
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Florian Ritterbusch
Guo-Min Yang
Zheng-Tian Lu
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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