the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Chronostratigraphy of blue ice at the Larsen Glacier in Northern Victoria Land, East Antarctica
- 1School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea
- 2Korea Polar Research Institute, Incheon, South Korea
- 3Hefei National Laboratory for Physical Sciences at the Microscale, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, China
- 4National Institute of Polar Research, Tachikawa, Japan
- 5Department of Polar Science, School of Multidisciplinary Sciences, The Graduate University for Advanced Studies, SOKENDAI, Tachikawa, Japan
- 6Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
- 7College of Earth, Ocean and Atmospheric Sciences, Oregon State University (OSU), Corvallis, OR, USA
- 1School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea
- 2Korea Polar Research Institute, Incheon, South Korea
- 3Hefei National Laboratory for Physical Sciences at the Microscale, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, China
- 4National Institute of Polar Research, Tachikawa, Japan
- 5Department of Polar Science, School of Multidisciplinary Sciences, The Graduate University for Advanced Studies, SOKENDAI, Tachikawa, Japan
- 6Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
- 7College of Earth, Ocean and Atmospheric Sciences, Oregon State University (OSU), Corvallis, OR, USA
Abstract. Blue ice areas (BIAs) allow for the collection of large-sized old ice samples in a cost-effective way because deep ice outcrops and make old ice samples available close to the surface. However, most chronostratigraphy studies on blue ice are complicated due to fold and fault structures. Here, we report a simple stratigraphy of ice from the Larsen BIA, Antarctica, making the area valuable for paleoclimate studies. Ice layers defined by dust bands and ground penetration radar (GPR) surveys indicate a monotonic increase in age along the ice flow direction on the downstream side, while the upstream ice exhibits a potential repetition of ages on scales of tens of meters, as shown in the complicated fold structure. Stable water isotopes (δ18Oice and δ2Hice) and components of the occluded air (i.e., CO2, N2O, CH4, δ15N-N2, δ18Oatm (= δ18O-O2), δO2/N2, δAr/N2, 81Kr and 85Kr) were analyzed for surface ice and shallow ice core samples. Correlating δ18Oice, δ18Oatm, and CH4 records of Larsen ice with existing ice core records indicates that the gas age at shallow coring sites ranges between 9.2–23.4 ka BP and ice age for entire surface sampling sites between 5.6–24.7 ka BP. Absolute radiometric 81Kr dating for the two cores confirms the ages within acceptable levels of analytical uncertainty. Our study demonstrates that BIA in northern Victoria Land may help researchers obtain high-quality records for paleoclimate and atmospheric greenhouse gas compositions through the last deglaciation.
-
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.
-
Preprint
(2679 KB)
-
Supplement
(577 KB)
-
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2679 KB) -
Supplement
(577 KB) - BibTeX
- EndNote
Journal article(s) based on this preprint
Giyoon Lee et al.
Interactive discussion
Status: closed
-
RC1: 'Comment on tc-2021-294', Anonymous Referee #1, 09 Oct 2021
Lee et al establishes the chronology of a blue ice field at the Larsen Glacier in north Victoria Land, East Antarctica by cross-correlating properties recorded in the ice (and the enclosed air). Further aided by absolute radiometric 81Kr dating, the authors report the discovery of a horizontally continuous ice section spanning from the early Holocene through the Last Glacial Maximum, with the age gets progressively older downstream. It is therefore concluded that Larsen Glacier could serve as a paleoclimate archive to study the transition from the Last Glacial Maximum to the Holocene. While the study subject of this manuscript (blue ice) is clearly part of the cryosphere, hence making the manuscript within the scope and aim of the journal The Cryosphere, the manuscript would benefit from more in-depth discussion on the glaciological or climatic implications of the discovery of stratigraphically continuous blue ice at the Larsen Glacier: what does it mean for the local ice dynamics, East Antarctic Ice Sheet, or paleoclimate (given the authors argue this blue ice field could be utilized to study climate changes across the Last Deglaciation)?
It must be acknowledged that a continuous blue ice section is exciting and rewarding for all the field and lab work that was done, but LGM (or Termination I) isn’t a particularly understudied interval. A large number of deep ice cores from Greenland and Antarctica have provided a detailed record of atmospheric composition and local to regional climate. A blue ice field in Taylor Glacier in the Dry Valleys, less than 500 km away from the Larsen Glacier, provides a near continuous surface ice record already providing large-volume samples for various novel geochemical analyses. Therefore one has to wonder what new information blue ice field in Larsen Glacier could bring about. A few questions that may be worthy of consideration: Can you trace the original deposition site by GPR and dust bands? Or if you already know where the ice was deposited, could you estimate the velocity of ice motion? In terms of climate, presumably you could infer annual layer thickness from GPR and that should provide information about past accumulation rates and ice thinning function. If so, what does it mean for the local climate and ice dynamics? Since both hydrogen and oxygen isotopes in water have been measured, could you calculate the deuterium excess and what does that tell us about the hydrological changes in north Victoria Land on glacial-interglacial timescales?
This is not to say that these are the only questions that must be answered here. The bottom line is that as a reader of The Cryosphere I am hoping to see what new scientific discovery is being made. It might be an abrupt change in accumulation rates, or a different local precipitation regime. The current manuscript feels to me more like a detailed progress report without firm conclusion on what new is being presented. Of course it could be argued that the discovery of a potentially useful paleoclimate archive itself is an achievement, but back to my earlier points, the Last Glacial Maximum is already an intensively studied interval.
Finally, before proceeding to detailed comments, I feel a bit confused why the manuscript does not present the absolute dating results first. 81Kr is a well-established absolute dating method for glacial ice and underground water. Unless the authors are worried about contamination of modern air (a hypothesis that was later rejected based on undetectable 85Kr), the results of absolute dating (high accuracy, low precision) should come before the cross-dating efforts that have a high level of precision. In doing so you could easily narrow the range of age search to the last glacial cycle and therefore shorten a considerable portion of the current discussion (in particular 3.5) that might be devoted to more glaciological-focused discussion.
--
Specific comments:
Line 18: the claim of a “simple stratigraphy of ice” seems to contradict the description that the ice upstream has age repetitions (i.e. is folded). Perhaps you could rephrase it into something like “Here we report a surface transect of ice that has a simple horizontal stratigraphy.” This would exclusively correspond to the downstream section described in the current manuscript.
Line 32: please add Lüthi et al (2008) Nature and Bereiter et al (2015) GRL to the citation.
Line 49: it is necessary to point out that the current longest continuous ice core record stops at 800,000 years.
Line 60: this sentence is equivocal. Does “globally well-mixed” also apply to glaciological records? Based on the nature of stable water isotopes I don’t the authors imply that the glaciological records are also globally mixed (in fact, they are not). Please (1) consider splitting the gas age and ice age synchronization methods and (2) point out that the age of the gas is different from the age of the ice at the same depth.
Line 61 & 81: please add Yan et al (2021) Clim. Past to the citation.
Line 62: if absolute dating methods are effective, readers without sufficient knowledge on their limits may why bother correlating gas-phase and ice-phase properties? It may be better to introduce absolute dating methods first, then acknowledge their uncertainties, and finally introduce a more precise way of age synchronization.
Line 85: please specify which “area” you are referring to (north Victoria Land?).
Fig 1: Is there a particular reason for the current orientation of the Antarctic continent?
Line 154: could you please evaluate the potential of in situ methane production in ice cores with high dust concentrations (Lee et al 2020 GCA)?
Line 157: please specify what 2nd gas extraction means. Does it imply the refrozen meltwater is melted once again?
Line 169: please specify the temperature of the water trap.
Line 189: what does “unclear ice” mean? It is not a common word to describe ice cores. Please elaborate.
Line 240: could you define the origin to which downstream and upstream are referenced against?
Line 261: the possibility of large variations in temperature and vapor sources is an interesting one. Perhaps you could quickly test them using deuterium excess data.
Line 289: why aren’t d15N-N2 and d18O-O2 expected not to be altered substantially? The intrusion of modern air might not be a problem, but there could be gas loss from the ice and hence fractionation.
Line 300: the depth at which d15N-N2 and d18O-O2 no longer vary appears to be different at different sites. In Allan Hills BIA gas composition is stabilized below 7 to 10 m (Spaulding et al 2013, Quaternary Res). Can you comment on this variability?
Line 303: it seems that this section could be simplified given your 81Kr dating results.
Line 374-375: the origin of ice age-gas age difference should be introduced in the earlier section.
Line 385: the maximum delta-age at 17.5 ka is another interesting observation that could have important paleoclimate implications (Buizert et al 2021, Science).
Line 403 & 414: it would be worthwhile to calculate the temporal resolution of the Larsen BIA samples, especially in the horizontal dimension (easy to do given Fig A7). How does that compare to, for example, the Talos Dome ice core record nearby?
Line 405: the word “chemical” usually refers to ions in ice cores.
Line 406: again please provide a clear reference point against which downstream and upstream are defined.
Line 412: can you provide more proof to back the claim of “high-precision ages”? It would be helpful if errors associated with cross-correlating different properties could be presented, like what Menking et al (2019) Clim. Past did.
References:
Bereiter, B., Eggleston, S., Schmitt, J., NehrbassâAhles, C., Stocker, T.F., Fischer, H., Kipfstuhl, S. and Chappellaz, J., 2015. Revision of the EPICA Dome C CO2 record from 800 to 600 kyr before present. Geophysical Research Letters, 42(2), 542-549.
Buizert, C., Fudge, T.J., Roberts, W.H., Steig, E.J., Sherriff-Tadano, S., Ritz, C., Lefebvre, E., Edwards, J., Kawamura, K., Oyabu, I. and Motoyama, H., 2021. Antarctic surface temperature and elevation during the Last Glacial Maximum. Science, 372(6546), 1097-1101.
Lee, J.E., Edwards, J.S., Schmitt, J., Fischer, H., Bock, M. and Brook, E.J., 2020. Excess methane in Greenland ice cores associated with high dust concentrations. Geochimica et Cosmochimica Acta, 270, 409-430.
Lüthi, D., Le Floch, M., Bereiter, B., Blunier, T., Barnola, J.M., Siegenthaler, U., Raynaud, D., Jouzel, J., Fischer, H., Kawamura, K. and Stocker, T.F., 2008. High-resolution carbon dioxide concentration record 650,000–800,000 years before present. Nature, 453(7193), 379-382.
Menking, J.A., Brook, E.J., Shackleton, S.A., Severinghaus, J.P., Dyonisius, M.N., Petrenko, V., McConnell, J.R., Rhodes, R.H., Bauska, T.K., Baggenstos, D. and Marcott, S., 2019. Spatial pattern of accumulation at Taylor Dome during Marine Isotope Stage 4: stratigraphic constraints from Taylor Glacier. Climate of the Past, 15(4), 1537-1556.
Spaulding, N.E., Higgins, J.A., Kurbatov, A.V., Bender, M.L., Arcone, S.A., Campbell, S., Dunbar, N.W., Chimiak, L.M., Introne, D.S. and Mayewski, P.A., 2013. Climate archives from 90 to 250 ka in horizontal and vertical ice cores from the Allan Hills Blue Ice Area, Antarctica. Quaternary Research, 80(3), 562-574.
Yan, Y., Spaulding, N.E., Bender, M.L., Brook, E.J., Higgins, J.A., Kurbatov, A.V., and Mayewski, P.A., 2021. Enhanced Moisture Delivery into Victoria Land, East Antarctica During the Early Last Interglacial: Implications for West Antarctic Ice Sheet Stability, Climate of the Past, 17(5), 1841–1855.
- AC1: 'Reply on RC1', Jinho Ahn, 03 Jan 2022
-
RC2: 'Comment on tc-2021-294', Anonymous Referee #2, 15 Nov 2021
General comments
The authors present a thorough analysis of ice samples collected in a blue ice area in Northern Victoria Land, East Antarctica. With complementary methods, both in the field, and in the laboratory, the chronostratigraphy of the ice is analyzed. By comparing the results to existing ice core records, a convincing proof of the estimated age of the ice and the gas entrapped in the ice is provided. Together with radar observations, the analyses from a three-dimensional image of age isochrones, which also allows an estimation of the age of ice near the bedrock. Given the importance of Antarctic blue ice areas in the recent developments in the search for the oldest ice, where 2.7-million-year-old ice has been recovered from a blue ice area in the Transantarctic mountains, the manuscript is very relevant for future paleoclimatic studies, and it can help in defining field work practices of sample collection and motivating site selection for shallow ice cores from blue ice areas.
The authors place their manuscript into context through a short literature review, after which the methods are described with clear subheadings. The results and discussion do justify the conclusions that are drawn, after which the paper is shortly wrapped up in a conclusion.
I do think the implications of the analyses are underexposed and need to be further elaborated without reducing the technical details. These technical details are generally clearly described and seem to ensure reproducible research, although the editor must know that I do not have the required laboratory experience/background to criticize this well. I have noted my suggestions below.
Specific comments per section
Abstract: clear and concise
Line 1: I do think the first line provides a circular argument
Line 26: BIAs
1 Introduction: In general, the introduction gives all necessary background for reading the paper. However, I think the structure is a bit confusing, with paragraphs that do not follow each other in a logical order. Moreover, the last paragraph that introduces the study is too concise and does not clearly bring forward the goal of the research. Proposed solution: I would suggest to merge the paragraph starting on line 77 to the other paragraph on blue ice areas, starting on line 47. Moreover, the approaches in the study (now outlined in the last paragraph), could be merged into the paragraphs starting from line 56 and from line 65 and/or the last paragraph can be more elaborate.
Line 42: I think it is important to mention that the flow is redirected. Normally, the ice flows under gravitational forces towards the margins of the continent. Moreover, it is not the bedrock itself that causes the ice to flow upwards, but it is the bedrock geometry (which in some sense is equal to the mentioned basal topographic obstacles). Also, in many cases these obstacles are exposed above the ice (nunataks).
Line 52: instead of blue ice, specify that you mean samples taken from blue ice areas. This remark also applies to the rest of the paper.
Figure 1: Specify that orange dots represent “a selection” or “examples”, as not all BIA where the chronology has been studied seem to be included (e.g., Zekollari et al. 2019)
- Zekollari, S. Goderis, V. Debaille, M. van Ginneken, J. Gattacceca, A. J. Timothy Jull, J. T. M. Lenaerts, A. Yamaguchi, P. Huybrechts, P. Claeys, Unravelling the high-altitude Nansen blue ice field meteorite trap (East Antarctica) and implications for regional palaeo-conditions. Geochim. Cosmochim. Acta. 248, 289–310 (2019).
2 Study area and methods: In general, well-structured and clearly described.
Line 97: (Fig. 2a)
Line 97-99: A low mean annual temperature does not guaranty the absence of melt in a blue ice area. We need to know either the standard deviation of this annual temperature, or a maximum/high percentile of the observations.
Line 104: Using Quantarctica needs to be acknowledged by also citing the entire dataset and the corresponding paper
- Matsuoka, K., Skoglund, A., & Roth, G. (2018). Quantarctica [Data set]. Norwegian Polar Institute. https://doi.org/10.21334/npolar.2018.8516e961
- Matsuoka, A. Skoglund, G. Roth, J. De Pomereu, H. Griffiths, R. Headland, B. Herried, K. Katsumata, A. Le, K. Licht, F. Morgan, P. D. Neff, C. Ritz, M. Scheinert, T. Tamura, A. Van De Putte, M. Van Den Broeke, A. Von Deschwanden, Quantarctica, an integrated mapping environment for Antarctica, the Southern Ocean, and sub-Antarctic islands. Environ. Model. Softw. 140, 105015 (2021).
Line 104-105: it is remarkable that the stratigraphy is disturbed upstream. Why does this not have implications on the stratigraphy downstream? What is the cause of the disturbances? Is there a temporal component to this? These questions should be addressed in the results and discussion section.
Line 110-113: can be more concise and clearer, something like: reprojected perpendicular to a line parallel to the ice flow direction.
Figure 2: mention that dust bands are observed in the field and how they are measured (GPS tracks?)
Line 135: change “interval” to “spacing”?
Line 136: specify that these are vertical intervals (also in line 146).
Line 154: an average offset should be one number, not a range.
Line 182: in this section I miss the description of the δAr/N2 analyses that are mentioned in the abstract and published in the supplementary materials.
Line 228: please briefly specify here why you use the TALDICE ice core in your research.
3 Results and discussion: In general, the emphasis of this section seems to be more on the results than on the discussion. To make the manuscript more accessible for a wide readership and to do justice to the analyses performed by the authors, most paragraphs would need some additional sentences that discuss (the implications) of the data.
Line 243: This line should be at the end of the subsection 3.1, as now first the authors explain the stratigraphic profile, then discuss the basal topography and then return to discussing the stratigraphic profile. Also, in Figure 3b, the ice thickness varies between 200 and 320 meter (not 400). Lastly, it would be nice to have a qualitative statement that the ice thickness decreases along the flow and how this relates to the exposure of glacial ice (as mentioned in the introduction).
Line 245: are these crevasses, cavities, or cracks observed during the measurement campaign?
Figure 3: From Figure S1, it does not appear that the GPR has been performed as a grid of flight lines, are the results presented in panel a obtained by interpolation? Moreover, in the text there is no reference/analysis of the data shown in panel a, so I would suggest to either move the panel to supplementary materials or discuss it in the main text.
Line 277: Reconsider combining section 3.3 and 3.4 and renaming it: “analysis of gas entrapped in the ice”.
Line 252-271: clear and nice balance between results and discussion of results.
Line 259: Please mention the references to the other published ice core records.
Line 265: why do you conduct a linear interpolation? To have measurements at equal horizontal/vertical spacing?
Line 279: What do you mean by altered? In Figure A1 only large fluctuations can be observed. Proof for altering comes only when discussing the comparison of the results from NIPR to SNU. This textual discussion would be greatly supported by plotting them in a (separate?) figure.
Line 295: Refer to Figure 4.
Line 303: Reconsider combining section 3.5 and 3.6 and adding a little introduction that explains your approach of first identifying the glacial termination, then matching the measured isotope and gas concentration profiles with existing (dated) ice cores, and then confirming your findings with the 81Kr dating.
Line 319: … > 1.95 m (Fig. A2); the offset….
Line 319: It is not clear why the offset may also come from age difference.
Line 321: The statement about that it is altered naturally and/or contaminated is rather speculative. It is also in disagreement with section 3.3. In my opinion, this observation is very interesting and deserves further research (could be mentioned as limitation/recommendation).
Figure 7: Consider omitting T3, T5 and T6, and check the color scheme for color blinds.
Line 342: (Fig 8d)
Line 345-355: Did you consider an automated method such as dynamic time wrapping? Also, it would be nice to discuss already in this paragraph the relation between the corrections made to match the horizontal distance to the age and the observed dip angles (as in line 380-384).
Line 371: I do not understand how biases in the δ18Oice record are avoided by interpolating the original record.
Line 374: This statement is not clear and can be elaborated.
Figure 9: Panel d does not show much more detail and could be omitted.
Line: 398-403: This paragraph sounds more like a part of the conclusion.
Line 398: The first sentence undersells the results. It can be a valuable (but obvious) recommendation but needs an explanation of why we would need more precise ages. Moreover, it is not in line with the statement on Line 412.
Line 401: please specify which atmospheric greenhouse gas can be measured at what depth (very relevant for other field work missions).
Line 401-403: nice and clear statement.
4 Conclusion: The conclusion section can be more elaborate. I suggest including the last paragraph of the previous section (line 398-403). Moreover, an estimation of the horizontal relationship between distance and age (i.e., xxx year/horizontal m), would be informative for other studies at blue ice areas.
Line 409-410: would be nice to guide the reader along the blue ice area and explain why the observations reveal a very typical glacial termination (as for instance Line 304-305, and the mention of the Antarctic Cold Reversal). Moreover, the Δage along the flowline (Figure A6) can be included in this explanation.
Line 414: not only on blue ice areas in the Northern Victoria Land. The comprehensiveness makes it a valuable study for BIAs across the Antarctic continent.
Appendices: clear and concise.
Figure A3, A4: Consider omitting T3, T5 and T6.
- AC2: 'Reply on RC2', Jinho Ahn, 03 Jan 2022
Peer review completion
Interactive discussion
Status: closed
-
RC1: 'Comment on tc-2021-294', Anonymous Referee #1, 09 Oct 2021
Lee et al establishes the chronology of a blue ice field at the Larsen Glacier in north Victoria Land, East Antarctica by cross-correlating properties recorded in the ice (and the enclosed air). Further aided by absolute radiometric 81Kr dating, the authors report the discovery of a horizontally continuous ice section spanning from the early Holocene through the Last Glacial Maximum, with the age gets progressively older downstream. It is therefore concluded that Larsen Glacier could serve as a paleoclimate archive to study the transition from the Last Glacial Maximum to the Holocene. While the study subject of this manuscript (blue ice) is clearly part of the cryosphere, hence making the manuscript within the scope and aim of the journal The Cryosphere, the manuscript would benefit from more in-depth discussion on the glaciological or climatic implications of the discovery of stratigraphically continuous blue ice at the Larsen Glacier: what does it mean for the local ice dynamics, East Antarctic Ice Sheet, or paleoclimate (given the authors argue this blue ice field could be utilized to study climate changes across the Last Deglaciation)?
It must be acknowledged that a continuous blue ice section is exciting and rewarding for all the field and lab work that was done, but LGM (or Termination I) isn’t a particularly understudied interval. A large number of deep ice cores from Greenland and Antarctica have provided a detailed record of atmospheric composition and local to regional climate. A blue ice field in Taylor Glacier in the Dry Valleys, less than 500 km away from the Larsen Glacier, provides a near continuous surface ice record already providing large-volume samples for various novel geochemical analyses. Therefore one has to wonder what new information blue ice field in Larsen Glacier could bring about. A few questions that may be worthy of consideration: Can you trace the original deposition site by GPR and dust bands? Or if you already know where the ice was deposited, could you estimate the velocity of ice motion? In terms of climate, presumably you could infer annual layer thickness from GPR and that should provide information about past accumulation rates and ice thinning function. If so, what does it mean for the local climate and ice dynamics? Since both hydrogen and oxygen isotopes in water have been measured, could you calculate the deuterium excess and what does that tell us about the hydrological changes in north Victoria Land on glacial-interglacial timescales?
This is not to say that these are the only questions that must be answered here. The bottom line is that as a reader of The Cryosphere I am hoping to see what new scientific discovery is being made. It might be an abrupt change in accumulation rates, or a different local precipitation regime. The current manuscript feels to me more like a detailed progress report without firm conclusion on what new is being presented. Of course it could be argued that the discovery of a potentially useful paleoclimate archive itself is an achievement, but back to my earlier points, the Last Glacial Maximum is already an intensively studied interval.
Finally, before proceeding to detailed comments, I feel a bit confused why the manuscript does not present the absolute dating results first. 81Kr is a well-established absolute dating method for glacial ice and underground water. Unless the authors are worried about contamination of modern air (a hypothesis that was later rejected based on undetectable 85Kr), the results of absolute dating (high accuracy, low precision) should come before the cross-dating efforts that have a high level of precision. In doing so you could easily narrow the range of age search to the last glacial cycle and therefore shorten a considerable portion of the current discussion (in particular 3.5) that might be devoted to more glaciological-focused discussion.
--
Specific comments:
Line 18: the claim of a “simple stratigraphy of ice” seems to contradict the description that the ice upstream has age repetitions (i.e. is folded). Perhaps you could rephrase it into something like “Here we report a surface transect of ice that has a simple horizontal stratigraphy.” This would exclusively correspond to the downstream section described in the current manuscript.
Line 32: please add Lüthi et al (2008) Nature and Bereiter et al (2015) GRL to the citation.
Line 49: it is necessary to point out that the current longest continuous ice core record stops at 800,000 years.
Line 60: this sentence is equivocal. Does “globally well-mixed” also apply to glaciological records? Based on the nature of stable water isotopes I don’t the authors imply that the glaciological records are also globally mixed (in fact, they are not). Please (1) consider splitting the gas age and ice age synchronization methods and (2) point out that the age of the gas is different from the age of the ice at the same depth.
Line 61 & 81: please add Yan et al (2021) Clim. Past to the citation.
Line 62: if absolute dating methods are effective, readers without sufficient knowledge on their limits may why bother correlating gas-phase and ice-phase properties? It may be better to introduce absolute dating methods first, then acknowledge their uncertainties, and finally introduce a more precise way of age synchronization.
Line 85: please specify which “area” you are referring to (north Victoria Land?).
Fig 1: Is there a particular reason for the current orientation of the Antarctic continent?
Line 154: could you please evaluate the potential of in situ methane production in ice cores with high dust concentrations (Lee et al 2020 GCA)?
Line 157: please specify what 2nd gas extraction means. Does it imply the refrozen meltwater is melted once again?
Line 169: please specify the temperature of the water trap.
Line 189: what does “unclear ice” mean? It is not a common word to describe ice cores. Please elaborate.
Line 240: could you define the origin to which downstream and upstream are referenced against?
Line 261: the possibility of large variations in temperature and vapor sources is an interesting one. Perhaps you could quickly test them using deuterium excess data.
Line 289: why aren’t d15N-N2 and d18O-O2 expected not to be altered substantially? The intrusion of modern air might not be a problem, but there could be gas loss from the ice and hence fractionation.
Line 300: the depth at which d15N-N2 and d18O-O2 no longer vary appears to be different at different sites. In Allan Hills BIA gas composition is stabilized below 7 to 10 m (Spaulding et al 2013, Quaternary Res). Can you comment on this variability?
Line 303: it seems that this section could be simplified given your 81Kr dating results.
Line 374-375: the origin of ice age-gas age difference should be introduced in the earlier section.
Line 385: the maximum delta-age at 17.5 ka is another interesting observation that could have important paleoclimate implications (Buizert et al 2021, Science).
Line 403 & 414: it would be worthwhile to calculate the temporal resolution of the Larsen BIA samples, especially in the horizontal dimension (easy to do given Fig A7). How does that compare to, for example, the Talos Dome ice core record nearby?
Line 405: the word “chemical” usually refers to ions in ice cores.
Line 406: again please provide a clear reference point against which downstream and upstream are defined.
Line 412: can you provide more proof to back the claim of “high-precision ages”? It would be helpful if errors associated with cross-correlating different properties could be presented, like what Menking et al (2019) Clim. Past did.
References:
Bereiter, B., Eggleston, S., Schmitt, J., NehrbassâAhles, C., Stocker, T.F., Fischer, H., Kipfstuhl, S. and Chappellaz, J., 2015. Revision of the EPICA Dome C CO2 record from 800 to 600 kyr before present. Geophysical Research Letters, 42(2), 542-549.
Buizert, C., Fudge, T.J., Roberts, W.H., Steig, E.J., Sherriff-Tadano, S., Ritz, C., Lefebvre, E., Edwards, J., Kawamura, K., Oyabu, I. and Motoyama, H., 2021. Antarctic surface temperature and elevation during the Last Glacial Maximum. Science, 372(6546), 1097-1101.
Lee, J.E., Edwards, J.S., Schmitt, J., Fischer, H., Bock, M. and Brook, E.J., 2020. Excess methane in Greenland ice cores associated with high dust concentrations. Geochimica et Cosmochimica Acta, 270, 409-430.
Lüthi, D., Le Floch, M., Bereiter, B., Blunier, T., Barnola, J.M., Siegenthaler, U., Raynaud, D., Jouzel, J., Fischer, H., Kawamura, K. and Stocker, T.F., 2008. High-resolution carbon dioxide concentration record 650,000–800,000 years before present. Nature, 453(7193), 379-382.
Menking, J.A., Brook, E.J., Shackleton, S.A., Severinghaus, J.P., Dyonisius, M.N., Petrenko, V., McConnell, J.R., Rhodes, R.H., Bauska, T.K., Baggenstos, D. and Marcott, S., 2019. Spatial pattern of accumulation at Taylor Dome during Marine Isotope Stage 4: stratigraphic constraints from Taylor Glacier. Climate of the Past, 15(4), 1537-1556.
Spaulding, N.E., Higgins, J.A., Kurbatov, A.V., Bender, M.L., Arcone, S.A., Campbell, S., Dunbar, N.W., Chimiak, L.M., Introne, D.S. and Mayewski, P.A., 2013. Climate archives from 90 to 250 ka in horizontal and vertical ice cores from the Allan Hills Blue Ice Area, Antarctica. Quaternary Research, 80(3), 562-574.
Yan, Y., Spaulding, N.E., Bender, M.L., Brook, E.J., Higgins, J.A., Kurbatov, A.V., and Mayewski, P.A., 2021. Enhanced Moisture Delivery into Victoria Land, East Antarctica During the Early Last Interglacial: Implications for West Antarctic Ice Sheet Stability, Climate of the Past, 17(5), 1841–1855.
- AC1: 'Reply on RC1', Jinho Ahn, 03 Jan 2022
-
RC2: 'Comment on tc-2021-294', Anonymous Referee #2, 15 Nov 2021
General comments
The authors present a thorough analysis of ice samples collected in a blue ice area in Northern Victoria Land, East Antarctica. With complementary methods, both in the field, and in the laboratory, the chronostratigraphy of the ice is analyzed. By comparing the results to existing ice core records, a convincing proof of the estimated age of the ice and the gas entrapped in the ice is provided. Together with radar observations, the analyses from a three-dimensional image of age isochrones, which also allows an estimation of the age of ice near the bedrock. Given the importance of Antarctic blue ice areas in the recent developments in the search for the oldest ice, where 2.7-million-year-old ice has been recovered from a blue ice area in the Transantarctic mountains, the manuscript is very relevant for future paleoclimatic studies, and it can help in defining field work practices of sample collection and motivating site selection for shallow ice cores from blue ice areas.
The authors place their manuscript into context through a short literature review, after which the methods are described with clear subheadings. The results and discussion do justify the conclusions that are drawn, after which the paper is shortly wrapped up in a conclusion.
I do think the implications of the analyses are underexposed and need to be further elaborated without reducing the technical details. These technical details are generally clearly described and seem to ensure reproducible research, although the editor must know that I do not have the required laboratory experience/background to criticize this well. I have noted my suggestions below.
Specific comments per section
Abstract: clear and concise
Line 1: I do think the first line provides a circular argument
Line 26: BIAs
1 Introduction: In general, the introduction gives all necessary background for reading the paper. However, I think the structure is a bit confusing, with paragraphs that do not follow each other in a logical order. Moreover, the last paragraph that introduces the study is too concise and does not clearly bring forward the goal of the research. Proposed solution: I would suggest to merge the paragraph starting on line 77 to the other paragraph on blue ice areas, starting on line 47. Moreover, the approaches in the study (now outlined in the last paragraph), could be merged into the paragraphs starting from line 56 and from line 65 and/or the last paragraph can be more elaborate.
Line 42: I think it is important to mention that the flow is redirected. Normally, the ice flows under gravitational forces towards the margins of the continent. Moreover, it is not the bedrock itself that causes the ice to flow upwards, but it is the bedrock geometry (which in some sense is equal to the mentioned basal topographic obstacles). Also, in many cases these obstacles are exposed above the ice (nunataks).
Line 52: instead of blue ice, specify that you mean samples taken from blue ice areas. This remark also applies to the rest of the paper.
Figure 1: Specify that orange dots represent “a selection” or “examples”, as not all BIA where the chronology has been studied seem to be included (e.g., Zekollari et al. 2019)
- Zekollari, S. Goderis, V. Debaille, M. van Ginneken, J. Gattacceca, A. J. Timothy Jull, J. T. M. Lenaerts, A. Yamaguchi, P. Huybrechts, P. Claeys, Unravelling the high-altitude Nansen blue ice field meteorite trap (East Antarctica) and implications for regional palaeo-conditions. Geochim. Cosmochim. Acta. 248, 289–310 (2019).
2 Study area and methods: In general, well-structured and clearly described.
Line 97: (Fig. 2a)
Line 97-99: A low mean annual temperature does not guaranty the absence of melt in a blue ice area. We need to know either the standard deviation of this annual temperature, or a maximum/high percentile of the observations.
Line 104: Using Quantarctica needs to be acknowledged by also citing the entire dataset and the corresponding paper
- Matsuoka, K., Skoglund, A., & Roth, G. (2018). Quantarctica [Data set]. Norwegian Polar Institute. https://doi.org/10.21334/npolar.2018.8516e961
- Matsuoka, A. Skoglund, G. Roth, J. De Pomereu, H. Griffiths, R. Headland, B. Herried, K. Katsumata, A. Le, K. Licht, F. Morgan, P. D. Neff, C. Ritz, M. Scheinert, T. Tamura, A. Van De Putte, M. Van Den Broeke, A. Von Deschwanden, Quantarctica, an integrated mapping environment for Antarctica, the Southern Ocean, and sub-Antarctic islands. Environ. Model. Softw. 140, 105015 (2021).
Line 104-105: it is remarkable that the stratigraphy is disturbed upstream. Why does this not have implications on the stratigraphy downstream? What is the cause of the disturbances? Is there a temporal component to this? These questions should be addressed in the results and discussion section.
Line 110-113: can be more concise and clearer, something like: reprojected perpendicular to a line parallel to the ice flow direction.
Figure 2: mention that dust bands are observed in the field and how they are measured (GPS tracks?)
Line 135: change “interval” to “spacing”?
Line 136: specify that these are vertical intervals (also in line 146).
Line 154: an average offset should be one number, not a range.
Line 182: in this section I miss the description of the δAr/N2 analyses that are mentioned in the abstract and published in the supplementary materials.
Line 228: please briefly specify here why you use the TALDICE ice core in your research.
3 Results and discussion: In general, the emphasis of this section seems to be more on the results than on the discussion. To make the manuscript more accessible for a wide readership and to do justice to the analyses performed by the authors, most paragraphs would need some additional sentences that discuss (the implications) of the data.
Line 243: This line should be at the end of the subsection 3.1, as now first the authors explain the stratigraphic profile, then discuss the basal topography and then return to discussing the stratigraphic profile. Also, in Figure 3b, the ice thickness varies between 200 and 320 meter (not 400). Lastly, it would be nice to have a qualitative statement that the ice thickness decreases along the flow and how this relates to the exposure of glacial ice (as mentioned in the introduction).
Line 245: are these crevasses, cavities, or cracks observed during the measurement campaign?
Figure 3: From Figure S1, it does not appear that the GPR has been performed as a grid of flight lines, are the results presented in panel a obtained by interpolation? Moreover, in the text there is no reference/analysis of the data shown in panel a, so I would suggest to either move the panel to supplementary materials or discuss it in the main text.
Line 277: Reconsider combining section 3.3 and 3.4 and renaming it: “analysis of gas entrapped in the ice”.
Line 252-271: clear and nice balance between results and discussion of results.
Line 259: Please mention the references to the other published ice core records.
Line 265: why do you conduct a linear interpolation? To have measurements at equal horizontal/vertical spacing?
Line 279: What do you mean by altered? In Figure A1 only large fluctuations can be observed. Proof for altering comes only when discussing the comparison of the results from NIPR to SNU. This textual discussion would be greatly supported by plotting them in a (separate?) figure.
Line 295: Refer to Figure 4.
Line 303: Reconsider combining section 3.5 and 3.6 and adding a little introduction that explains your approach of first identifying the glacial termination, then matching the measured isotope and gas concentration profiles with existing (dated) ice cores, and then confirming your findings with the 81Kr dating.
Line 319: … > 1.95 m (Fig. A2); the offset….
Line 319: It is not clear why the offset may also come from age difference.
Line 321: The statement about that it is altered naturally and/or contaminated is rather speculative. It is also in disagreement with section 3.3. In my opinion, this observation is very interesting and deserves further research (could be mentioned as limitation/recommendation).
Figure 7: Consider omitting T3, T5 and T6, and check the color scheme for color blinds.
Line 342: (Fig 8d)
Line 345-355: Did you consider an automated method such as dynamic time wrapping? Also, it would be nice to discuss already in this paragraph the relation between the corrections made to match the horizontal distance to the age and the observed dip angles (as in line 380-384).
Line 371: I do not understand how biases in the δ18Oice record are avoided by interpolating the original record.
Line 374: This statement is not clear and can be elaborated.
Figure 9: Panel d does not show much more detail and could be omitted.
Line: 398-403: This paragraph sounds more like a part of the conclusion.
Line 398: The first sentence undersells the results. It can be a valuable (but obvious) recommendation but needs an explanation of why we would need more precise ages. Moreover, it is not in line with the statement on Line 412.
Line 401: please specify which atmospheric greenhouse gas can be measured at what depth (very relevant for other field work missions).
Line 401-403: nice and clear statement.
4 Conclusion: The conclusion section can be more elaborate. I suggest including the last paragraph of the previous section (line 398-403). Moreover, an estimation of the horizontal relationship between distance and age (i.e., xxx year/horizontal m), would be informative for other studies at blue ice areas.
Line 409-410: would be nice to guide the reader along the blue ice area and explain why the observations reveal a very typical glacial termination (as for instance Line 304-305, and the mention of the Antarctic Cold Reversal). Moreover, the Δage along the flowline (Figure A6) can be included in this explanation.
Line 414: not only on blue ice areas in the Northern Victoria Land. The comprehensiveness makes it a valuable study for BIAs across the Antarctic continent.
Appendices: clear and concise.
Figure A3, A4: Consider omitting T3, T5 and T6.
- AC2: 'Reply on RC2', Jinho Ahn, 03 Jan 2022
Peer review completion
Journal article(s) based on this preprint
Giyoon Lee et al.
Giyoon Lee et al.
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 556 | 184 | 19 | 759 | 56 | 15 | 14 |
- HTML: 556
- PDF: 184
- XML: 19
- Total: 759
- Supplement: 56
- BibTeX: 15
- EndNote: 14
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2679 KB) - Metadata XML
-
Supplement
(577 KB) - BibTeX
- EndNote