Review of "A new coastal ice-core site identified in Dronning Maud Land, Antarctica, for high-resolution climate reconstructions to the Last Glacial Maximum" by Goel et al.

This manuscript presents a study of several ice rises in the Dronning Maud Land region, all being accessible from the Indian Maitri station.

While the DJU and LEN ice rises are briefly mentioned, the focus is then made on the more promising KAM and VER ice rises.

For these two rises, a detailed radar survey has been performed.

These radar surveys are used to map the SMB from a shallow horizon and firn cores at the summits.

The deeper horizons show Raymond bumps, characteristic of stable ice rises.

A simple 1D age model is then fitted onto observed isochrones dated by a Lliboutry-type 1D model at the flanks where the flow is better known.

From this 1D model, a 3D mapping of the age can be done and shows that KAM is the most promising site and should hold LGM ice at an acceptable resolution.

I enjoyed reading this manuscript and I think it is an important contribution for glaciology and ice core science.

In my opinion, this manuscript should be accepted after a few minor corrections and improvements.

General comments:

- The age model used is said to be pseudo-steady, but I have the impression that it is just steady. 

The difference between the two just comes from a change of the time variable based on SMB variations (see Parrenin et al., JG, 2006 and Parrenin and Hindmarsh, JG, 2007 for details).

Here, the temporal variations of SMB could be taken into account by using, e.g., the EDML SMB temporal variations.

This would affect the age and resolution of the deepest layer, close to the LGM, where SMB was probably ~2 times smaller.

Numerically, this is really easy to do so I suggest to do it if it has not been done.

- The value of the Lliboutry exponent (p) is taken between 2 and 4. I am not sure where these values come from, so proper references would help.

From the original 1979 Lliboutry article, an estimate of p can be done using the Shallow Ice Approximation and an estimate of the temperature gradient at the base.

If I remember correctly, the p value for Vostok is more around 8.

Not sure what is the temperature gradient at the base here, so the value might be different.

- From the radargrams, it seems Raymond bumps are surrounded by troughs, at least on one side.

Parrenin and Hindmarsh (JG, 2007), showed that horizontal advection of the ice can create these troughs.

Not sure it is the correct explanation here, but at least it could be worth mentioning.

By the way, using a flow tube model like in Parrenin et al. (GMD, in press) and Chung et al. (TC, in press) could be a possible perspective for the modeling exercise to take into account horizontal advection.

Minor comments:

- l. 66: Maybe introduce the "LEN" notation here.

- l. 134: Not sure your model is really pseudo-steady, see comment above.

- l. 142: "isn't" -> "is not"

- l. 144: "p values lie between 2-4" -> see comment above

- section 4.1: I am not sure to understand the comparison of this section. It is said in the beginning that the comparison will be done at 0.2H over the bed. Then the comparison is made at 0.12H for DJU and VER and 0.16H for KAM.

- Figure 2: I would rather use dark colours for troughs and light colours for highs.

- l. 407: Should not is be Fig. 1a and 1b instead of Fig. 1b and 1c?

- Figure 3: The labels of the sub-figures do not seem to correspond to the legend. They are also ordered from top to bottom, which is not consistent with Figure 2.

- Figure 6d: There is a model-obs discrepancy, which could be due to horizontal advection (see comment above) or to non-steady features such as varying accumulation pattern. 

This article explores the merits of potential ice core sites on 2 ice domes in the Dronning Maud Land region of Antarctica, for extracting an ice core with a high resolution climatic record going back to the Last Glacial Maximum (~20 ka). They present shallow and deep radar surveys over both areas. They carried out a detailed assessment of the topographical setting, deeming the Kamelryggen (KAM) ice dome to be more suitable than Kupol Verbljud. They then applied a simple age-depth model would accounted for both dome and flank ice flow. The model determined the likely age and resolution of ice through the thickness of the ice sheet, concluding that 20 ka ice may be around 80m above the bed at KAM making it a suitable ice core drill site.

The study is detailed and thorough, assessing the area through both observations and modelling. The results and arguments are clearly presented, I especially appreciated Table 1 for easy direct comparison of the ice domes. Therefore, I recommend this paper for publication with a few changes.

Specific comments

My first comment relates to the use of the word “reflector”. Here, the term “internal reflection horizon (IRH)” is commonly used as in the AntArchitecture review covering radar stratigraphy in Antarctica (Bingham et al., accepted). Therefore using “IRH” could help the community move to more standardised language when referring to these radar phenomena. 

It would be helpful to explain fairly early on, that there is a single IRH tracked in the shallow radar used for determining SMB. Then there are several other IRHs presumably tracked in the deep radar used for age-depth profiling. I found it quite difficult to disentangle at various points in the manuscript as they are often just referred to as “the reflector(s)”.

The IRHs in Fig 6d are never fully introduced. From their ages I assume they must be from the deep radar system. There should be a paragraph describing how many IRHs were tracked in total, at what depth/fraction of ice thickness, with which radar system and referencing a figure so the reader can see the coverage.

Such descriptions could be added at the end of section 2.1.

It should then be made clearer throughout the manuscript, whether you are referring to the shallow or deep IRHs. Eg. 

L159-171 - mention that it is the deep IRHs used for this purpose 

L273 - make it clear that here you are talking about the deep IRHs. As in the next sentence you talk about the shallow IRH at KAM

L278 - age mismatch with the deep IRHs.

L281 - Mentions “eight reflectors” but there are only 7 in Fig 6a. Would also be good to reference Fig 6a here.

Figure 7 - There are a few things I could not make out in this figure, even while zooming in on the pdf. 

• I could not see a black curve showing the mean estimate. Perhaps it is the thick dark blue curve that does not follow the colour gradient? In which case it would be good to change this to a thinner black line. My other comments are based on this assumption.
• Does the mean age and resolution mean the most probable? Or is it the weighted average age from your 120 results taking into account each profile’s likelihood. This should be further clarified in the text (L287-290). 
• Ignoring the dark blue line which I think may be the mean, it seems as though the gradient (in Fig 7a), and therefore probability, increases towards the upper bound ie. where older ice is shallower. As the probability increases but does not seem to reach a maximum, why were scenarios not tested where the older ice is even shallower?
• It may be useful to include an inset in the top right hand corner to zoom in on the deeper section, as this would make the colour gradient and lines easier to differentiate by eye.

Minor Corrections

L16 - A radar survey reveals…

L24 - ~ 20 ka

L32 - “… often exhibit distinct characteristics from comparable events…”. This sentence is unclear as is sounds as though event characteristics which appear very clearly in the Northern Hemisphere, also appear in the Southern Hemisphere climate records. But I think you mean that these events can have different characteristics in Southern Hemisphere records, so this should be reworded to make it clearer.

L48 - sea ice variability 

L58 - the Antarctic coast

L104 - add a reference for the value of 169 m us-1

L131 - the ice’s age 

L134 - from your description, it seems to be a steady model, not pseudo-steady but reviewer 1 has already mentioned this in more detail

L183 - “…until the extent of …”

L185 - “…VER has a steep slope just at the summit.” From looking at Fig 2d, it is clear what you are referring to but the sentence alone is unclear. It could be changed to something like “… the summit of VER occurs at the edge of a steep slope in the bed.” 

L190 - “30 years prior” - this phrasing sounds like age of the reflector was determined 30 years before the current study was carried out, so maybe change to “ the age of the reflector is 30 a”, if that is the intended meaning or clarify further if not. 

L236 - “mean spatial” instead of “spatially mean”

Also L236 - “The most critical differences … are bed topography …”

L276 - if I understand correctly, this random value of p is then optimised? So it may be helpful to remind the reader by saying “… assigned a distinct initial value of p…”

L299 - Figure 7c does not exist

Reference 

Bingham, R. G. et al. (Accepted). Antarctica’s internal architecture: Towards a radiostratigraphically-informed age-depth model of the Antarctic ice sheets. EGU Preprint Repository, 17, 33. https://doi.org/10.5194/egusphere-2024-2593