the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Jan 2026
Bedrock topography and ice thickness distribution of three major Patagonian outlet glaciers unveiled by helicopter-borne ground penetrating radar
Abstract. We present the first helicopter-borne ground-penetrating radar dataset over Glaciar Viedma, Upsala, and Perito Moreno, three of the largest outlet glaciers of the Southern Patagonian Icefield in South America. The dataset comprises 116.021 individual ice-thickness measurements along 232 km of flight tracks. Data were acquired during two campaigns in March and April 2022 as well as in October 2024 using a 25 MHz shielded broadband antenna deployed as a helicopter sling load. For the first time, we reveal the complex subglacial topography of these glaciers in their lower regions and measured bed reflections at Glaciar Upsala in depths of up to 800 m. The newly obtained measurements were incorporated into an ice-thickness reconstruction method to derive glacier-wide ice-thickness distribution maps and the corresponding bedrock topography. The latter exerts primary control on the response of water-terminating glaciers to a changing climate. Our 100-m gridded ice-thickness maps indicate that the three glaciers had a combined ice volume of 831.14 km³ in the year 2000. The dataset and the well-constrained glacier-wide grids provide a valuable basis for future studies aiming to better understand the mechanisms driving glacier retreat and the susceptibility of these large outlet glaciers to climate change. All data are publicly available at Zenodo (https://doi.org/10.5281/zenodo.17464164; Koch et al., 2025a).
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Status: open (until 08 Apr 2026)
- RC1: 'Comment on essd-2025-678', Shin Sugiyama, 06 Mar 2026 reply
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Ground Penetrating Radar Data, Ice thickness fields and bedrock topography maps of Perito Moreno, Viedma and Upsala Glacier Moritz Koch et al. https://doi.org/10.5281/zenodo.17802904
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- 1
Review comment on “Bedrock topography and ice thickness distribution of three major Patagonian outlet glaciers unveiled by helicopter-borne ground penetrating radar” by Moritz Koch et al.
- General comments
This manuscript reports ice thickness and bed elevation data for three lake-terminating glaciers in the Southern Patagonia Icefield. The data sets are based on helicopter-borne ice-radar measurements and numerical modeling of ice thickness distributions. Observational ice thickness data are sparse in Patagonia due to environmental challenges (severe weather conditions, heavily crevassed glaciers, large amounts of meltwater) and logistical constraints (glacier access, helicopter availability, material transport). The authors conducted helicopter observations over three large, rapidly changing glaciers on the eastern side of the Southern Patagonia Icefield. The obtained field data were used to estimate glacier ice thickness distributions using a numerical model. Also presented are error analyses of the ice thickness from the radar measurement and modeling.
The radar-measured ice thickness data are novel and important to the glaciological community. The presented field data cover critical areas of three large glaciers that have been the focus of glacier studies in the region. Our understanding of the rapid changes in these glaciers will be improved by ice-thickness and bed-geometry data. The modeled ice thickness and bed elevation maps are very useful for studies in the future. For example, they create a possibility of reliable ice flow modeling, which will contribute to more accurate projections of glacier mass loss and sea level rise. For these reasons, I congratulate the authors on obtaining the valuable data and strongly support the publication of the manuscript and the data in Earth System Science Data.
I list some suggestions to improve the presentation of text and data, from the perspective of a glaciologist engaged in the region. I hope the authors receive more specific guidance from other reviewers on the technical aspects of radar data processing and ice thickness reconstructions.
- Specific comments
The measured and modeled ice thickness and bed elevation are presented on maps with color scales. They show nice overviews, but I have a problem with the maps when detailed features are discussed in the text. For example, the subglacial ridge near the front of Glaciar Perito Moreno is mentioned several times in the text (Line 292, Line 333), but it is not clear which part of the map is referred to. Additional enlarged maps focused on the regions of interest would be very useful for readers. Please also consider using a discrete color scale and/or contour lines, because continuous color scales are less useful for quantitative discussion (Figures 6 and 9).
The bedrock elevation maps (Figure 7 and Supplementary Figure 1) are very useful. It would be more useful for glacier modeling, if lake bottom elevations near the glacier fronts are included. I am proposing this idea because we have published the lake bathymetry near the glaciers studied in this paper (Sugiyama et al., 2016). The bathymetry data are available online.
Sugiyama, S. et al. (2016), Thermal structure of proglacial lakes in Patagonia, J. Geophys. Res. Earth Surf., 121, 2270–2286, https://doi.org/10.1002/2016JF004084.
Sugiyama, S. et al. Bathymetry data from glacial lakes in Patagonia, Mendeley Data, V2, https://doi.org/10.17632/47rhmznjs6.1
Details of the ice thickness modeling are missing. I assume the modeling requires various input data and parameters, including ice velocity, mass balance and sliding rate. However, nothing is clear from the manuscript. Please consider describing sufficient details, including how the ice thickness from the radar survey was incorporated into the model.
I think the text is not very smooth in some places. Please get help to improve your English.
- Specific comments
Line 13: "three of the largest outlet glaciers" >> According to (DeAngelis, 2014), Glaciar Viedma, Upsala and Perito Moreno are 2nd, 4th and 12th largest glaciers in terms of area. I agree that they are well known and important glaciers, but I think "three of the largest" is misleading.
Line 14: "116.021" >> I understand "." is used as a thousands separator, but it is confusing because it's used as a decimal point elsewhere.
Line 22-23: "the well-constrained glacier-wide grids" >> What do you mean?
Line 32: "(Bojinski et al., 2014)" >> I think you need some other citations to state that glacier changes are clear indicators of "anthropogenic" climate change. Something like these?
Ben Marzeion et al. 2014. Attribution of global glacier mass loss to anthropogenic and natural causes. Science, 345, 919-921. https://doi.org/10.1126/science.1254702
Roe, G. H., Christian, J. E., and Marzeion, B. 2021. On the attribution of industrial-era glacier mass loss to anthropogenic climate change, The Cryosphere, 15, 1889–1905, https://doi.org/10.5194/tc-15-1889-2021
Line 40: " Patagonian Andes" >> Because you have just introduced, you'd better discuss "SPI and NPI".
Line 47-48: "Bathymetric surveys of recently retreated outlets" >> Sounds odd to me because bathymetric surveys are performed in lakes and the ocean, but recently retreated outlets mean outlet glaciers.
Line 49: "Minowa et al., 2023b" >> This appears before Minowa et al., 2023a. Please check the citations of Minowa's papers. It looks 2021a and 2021b, and 2023b and 2023c are duplicated (Line 561-574).
Line 60: "outlets" >> outlet glaciers?
Line 64: GPR is already introduced in Line 61.
Line 65: SPI is already introduced in Line 39.
Line 68: "116.021" >> 116,021 or 116021
Line 79: "expanding" >> extending?
Figure 1, 1st line in the caption: "rotated by 90 degree" >> Isn't it (b) which is rotated from north up?
Line 97: "Three of the largest": I think this is OK because they are 1st, 2nd and 4th largest glaciers on the eastern side of SPI.
Line 101: "approximately 896 km^2 and 779 km^2": Please revise to make it clear that these areas are for entire glaciers but not for accumulation zones. "approximately" sounds odd because 896 and 779 are quite precise numbers. The numbers are not consistent with previous studies (De Angelis, 2014, 974 and 647 km^2) (Lo Vecchio et al., 2024, ~645 km^2 for Upsala). How do you measure the areas?
Line 114: Please consider referencing Minowa et al. (2026), as well.
Minowa, M. et al. 2026. Triggering mechanisms of dynamic mass loss at a freshwater-calving glacier in southern Patagonia, Earth and Planetary Science Letters, 681, 119930. https://doi.org/10.1016/j.epsl.2026.119930
Line 116: "a single borehole" >> Actually, it was a single location, but we drilled two boreholes (Sugiyama et al., 2011).
Line 119: Move (Millan et al., 2019) to Line 119 after "… airborne gravity survey."
Line 123-125: This is already mentioned in Line 66-68.
Line 127-133: What about setting up a table to present the numbers associated with the three glaciers?
Line 143: "6 x 4 x 1 m">>"6 x 4 x 1 m3" or "6 m x 4 m x 1 m".
Line 144: "comparatively" >> What are you comparing with?
Line 159: Define "GNSS".
Line 163: "multi-frequency" >> " dual-frequency"?
Line 164: Please indicate the locations of the base stations in Figure 5.
Line "164-165": "a rover antenna was …" >> Already mentioned in Line 159.
Line 166: Abbreviations (TBC and PPP) are not necessary because they are not used.
Line 167: "rover trajectory were" >> rover trajectories were?
Line 170: "GPST–UTC offset " >> What do you mean by this?
Line 206: " Between kilometer 4 and 5 " >> Sounds odd to me.
Line 215: (2016)
Line 217: Isn't the radical sign too short? Don't you need numbers for the equations?
Line 220: "acquisition velocity" >> What do you mean?
Line 223: Please define the variables, x, y, H, ipsilon.
Line 224: What do you mean by "picks"?
Line 229: "picking uncertainty" >> Do you mean something like "uncertainty in time of measurement"?
Line 228: Please use italic for variables, c and t. You do not need to define "TWTT".
Line 237: "WGMS)" >> WGMS
Line 246-247: Omit "with the air layer removed prior to calculation".
Line 257: I suggest "thickness and bed elevation maps for entire glacial basins (for the year 2000)".
Line 266: I suggest " Comparing the modelled and observed ice thickness values (Appendix Fig. ...".
Line 267: How do you compute "misfit"? What do you mean by "The triangular model mesh"?
Line 276: " we perturbed the surface mass-balance gradient within plausible bounds" >> Please give values for the "plausible bounds". Anyway, I encourage the authors to describe more details about the modeling procedures.
Line 287: Do you mean that bed elevation was not available for 41% of the survey routes over the glacier?
Line 289: What about setting up a single table to present these numbers associated with each glacier?
Line 290: Please indicate in the plot the location of the measured maximum depth.
Line 292: Please indicate in the plot the location of the ridge. I encourage the authors to provide a larger plot of key areas, including the region near the front of Glaciar Perito Moreno. The following sentences describing ice thicknesses (180, 220, 130, 140 m) are difficult to follow without such an additional plot.
Figure 5, 2nd line in the caption: What do you mean by "densest survey grid was collected"?
Line 304: "The mean ice thickness" >> Is this the mean along the flight route or the mean of available data points?
Line 306: "stepped glacier bed" >> Can you indicate in the plot which region you are referring to? An enlarged plot helps readers.
Line 323: "small-scale" >> How small?
Line 325: Why don't you compare your measurements with existing data? Because such data sets are widely used, it is essential to validate them with observational data. That's one of the values of your measurements, I think. For example, Minowa et al. (2021) used inverted ice thickness for ice flux calculation, and Lannutti et al. (2024) studied the thickness distributions of the three glaciers that you studied. By the way, what do you mean by "REFs"?
Line 327: "2D reconstructions" >> the reconstruction of bed elevation?
Line 333: Please show "subglacial ridge" on the plot.
Line 335: "1.292 m" >> 1292 m Where is the deepest part of the glacier?
Line 337: "well constrained" >> What do you mean by this? Based on which data?
Line 340: "1.400 m" >> 1400 m
Line 346: "in the Supplement" >> Refer to the figure number.
Line 350: "After" >> Above?
Line 347-Line 359: Please consider providing additional maps focused on the regions near the terminus.
Figure 7, 3-4th line in the caption: Omit "areas at or below".
Line 367: ... cross points of survey routes?
Line 388: Please clarify that Figure 9 shows the uncertainty of the ice thickness obtained by modeling.
Figure 9: Please indicate the regions covered by the radar survey because the uncertainty should be directly affected by the existence of field data.
Line 409: Omit "densely gridded".
Reviewed by Shin Sugiyama