the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Sep 2024
Age-depth distribution in western Dronning Maud Land, East Antarctica, from three decades of radar surveys
Abstract. Radio-echo sounding provides the opportunity to study the internal architecture of ice sheets through imaging stratified englacial reflections, known as internal reflection horizons (IRHs). They represent consistent time horizons formed at the former ice-sheet surface and buried over time, thus reflecting the ice sheet's age-depth architecture. Their analysis allows crucial insights into past and present boundary conditions, e.g. accumulation rates or basal melting, as well as physical properties and ice dynamics. This study presents a comprehensive data set and insight into the age-depth distribution in western Dronning Maud Land (DML), East Antarctica, spanning the Holocene to the Last Glacial Period (4.8–91.0 ka). Using data from various radar systems deployed by the Alfred Wegener Institute between 1996 and 2023, we traced and dated nine IRHs over an area of 450000 km2. A precise age could be assigned to the IRHs by two-way travel time to depth conversion and employing radar forward modelling based on conductivity peaks of the EPICA DML ice core. Six IRHs correlate with past volcanic eruptions. Our findings suggest that most IRHs correspond to IRHs of similar age in other regions of East and West Antarctica, thus likely originating from the same physical reflectors at depth, although they could not be physically connected. This work enhances understanding of the englacial architecture and relationships with snow accumulation and ice-dynamic processes of this sector of the Antarctic ice sheet and provides fundamental data for numerical ice flow models and paleoclimatic studies.
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RC1: 'Comment on egusphere-2024-2349', Rebecca Sanderson, 18 Sep 2024
Review of “Age-depth distribution in western Dronning Maud Land, East Antarctica, from three decades of radar surveys”
The research uses radio echo sounding data to explore internal reflection horizons (IRHs) and the age-depth distribution of ice across western Dronning Maud Land, East Antarctica. Using various radar systems, the researchers trace nine IRHs and assign ages from a two-way travel time to depth conversion and by employing radar forward modelling based on conductivity peaks from the DML ice core. The article presents a new, useful cryospheric dataset that has been used here to explore the englacial architecture across DML. The work is very well written, meticulously constructed, clearly elucidates all the methodologies employed, as well as demonstrating the possibilities of tracing the same IRH across multiple radar surveys.
While the article presents a very useful data set, I believe that its application could be expanded in places, e.g. the relationship of the IRH depths/normalised depth with current ice velocity or accumulation rates (may only require a figure and a line or two adding in places). This would allow for a science focus rather than a data driven focus. I believe that this can be achieved through minor corrections, as the data is already telling the story. Therefore, I suggested that the paper be published with only minor revisions to account for this.
Specific comments:
In the first paragraph of 3.2, you need to be explicit that you are talking about traceable IRHs.
In section 4.2 you link IRH to volcanic eruptions, this is really interesting for the broader picture but for most of the IRH ages, the suggested eruption dates are a couple of hundred years out, either before or after the eruption. Could you explain the reason for this, e.g. do you think this just a function of dating uncertainty/ radar system resolution?
I think it would be useful to expand section 4.5 to talk about some of the direct application of your dataset. I think the addition of a more detailed explanation of how the IRH that you have traced in the DML region represent dynamic changes over time would improve the manuscript. This could include links to ice velocity, bed topography, accumulation rates.
Your figures are clear and support the text well, but I found myself jumping around a lot when they are mentioned in the text. For example figure 2 is on page 6 but the first time you refer to it is page 12. Likewise, I am unsure that you refer to figure 3 at all in the text.
Line suggestions:
Line 61 Refer to figure 1 here.
Line 105 “An additional gain function was applied to the radar data (also known internally as AGG products) to enhance reflections at all depths.” Unnecessary repetition of text at the beginning of the paragraph, delete this?
Figure 2 caption. Please add the following to be clear as to why you used the frequencies:
“Comparison between simulated radar data for 150 and 335 MHz (150 MHz for the EMR profile, and 335 MHz for the MCoRDS wideband profile) based on measured conductivity…”
Line 148 explain the acronym: “…Finite-Difference Time-Domain (FDTD) method…”
Line 165: Maybe say “We used a constant dielectric permittivity value of ε′r = 3.145 and EM wave propagation velocity of ∼ 1.69 · 108 m s-1.” to avoid repetition.
Line 231-235: refer to a figure here?
Citation: https://doi.org/10.5194/egusphere-2024-2349-RC1 - AC1: 'Reply on RC1', Steven Franke, 28 Oct 2024
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RC2: 'Comment on egusphere-2024-2349', Marie G. P. Cavitte, 13 Oct 2024
Review of “Age-depth distribution in western Dronning Maud Land, East Antarctica, from three decades of radar surveys” by Steven Franke et al.
In this study, the authors trace nine IRHs over western Dronning Maud Land, with radar transects gathered over three different radar systems. They date them at the EDML ice core, using a combination of forward DEP modeling, as well as twtt-to-depth conversion using wave propagation and firn corrections. They then describe the IRH depths and geometries for the whole survey region and highlight the overlap between the IRHs traced here and other tracing studies in East and West Antarctica, showing very good promise for the AntArchitecture endeavour.
This paper is a very important contribution to making sure the interpreted internal stratigraphy of the Antarctic Ice Sheet is published and accessible to the community. Such efforts to document data sets should be praised and encouraged. However, I would suggest to consider submitting this article to ESSD, not for lack of quality of this manuscript, but because it seems like a better fit for a dataset paper. See minor comments below. I suggest this paper be published, here or in ESSD with technical revisions.
Specific comments:
The first sentence of the introduction is very vague, and therefore not so useful, particularly “observing and modelling” which can encompass everything.
The impact of the firn correction of 13m taken as constant for the whole survey region should be discussed, as the snowfall regimes are quite different across it.
Line comments:
Abstract – The last sentence uses “fundamental data”, I would suggest “boundary conditions” instead.
L16 – Comprehend → Understand
L17 – Maybe specific where the melting is occurring (basal, surface)
L21 – hundreds thousands → Hundreds of thousands
L27 – linked to conductivity contrasts and density
L28 – what does “detected across the ice sheet” mean? Reword
L30 – what is mean by boundary layers? And why use the word layer here? Not defined
L30 – suggest to change”time horizons of the same of snow deposits” to “synchronous snow deposits”
Table 1 – Developper → Developer
L39 – why use the word “layer” and not “IRH” ?
L44 – Suggest to modify to “where reflections have a different radar signatures due to their different vertical wavelengths”
L75 – the ice internal structure
L84 – which serves as a transmit and receive
L88 – Define fk
L109 – what is meant by the final sentence? Clarify
L175 – mention Ey after “electric field envelope”
L235 – abscent → absent
L239 – number of data points does not represent much for the readers...I think it could be left out.
L362- The review paper of AntArchitecture can now be cited here (https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2593/)
Figure 1 – The Dome Fuji survey is missing. Also why aren’t the EMR long-pulse lines drawn on this map, as drawn later on Fig.7. It’s confusing to have different datasets on these two sets of figures. I would suggest to also mention in the figure caption what the background map is and also that ice core sites are highlighted with circles. Finally, the three shades of dark blue are really difficult to tell from each other on printed paper.
Figure 2 – the ice base reflection marker on panel c is not visible
Figure 5 – Could Jutulstraumen be added to this figure too as it is discussed? It is helpful to have all the info on that one figure. Also, the figure caption could mention the different Features highlighted. Same for Figure 6.
Citation: https://doi.org/10.5194/egusphere-2024-2349-RC2 - AC2: 'Reply on RC2', Steven Franke, 28 Oct 2024
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