the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 May 2025
Seismic data analysis for subglacial lake D2 beneath David Glacier, Antarctica
Abstract. Subglacial lakes beneath Antarctic glaciers are pivotal in advancing our understanding of cryosphere dynamics, basal hydrology, and microbial ecosystems. We investigate the internal structure and physical properties of Subglacial Lake D2 (SLD2), located beneath David Glacier in East Antarctica, using seismic data acquired during the 2021/22 austral summer. The dataset underwent a comprehensive processing workflow, including noise attenuation, velocity analysis, and pre-stack time migration. Migrated seismic sections revealed distinct reverse- and normal-polarity reflections at the glacier–lake and lake–bed interfaces, respectively. We compared the synthetic seismogram generated through wave propagation modelling based on our structural interpretation of the migrated sections with the field data to validate the subglacial lake structure inferred from the seismic data. This confirmed a water column thickness ranging from around 53 to 82 m and delineated the broader structure of the subglacial lake. Also, discontinuous reflections detected on seismic sections transverse to the ice flow were interpreted as scour surfaces formed by ice movement. Comparison with airborne ice-penetrating radar (IPR) data acquired in 2018 further supported the consistency of the ice thickness estimates. Notably, a steeply dipping bedrock boundary identified along profile 21YY provided a more precise definition of the lateral extent of SLD2 than was possible using IPR data alone. Collectively, these findings enhance our understanding of subglacial lake environments and inform the selection of future drilling sites for in situ sampling.
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RC1: 'Comment on egusphere-2025-2055', Huw Horgan, 16 Jun 2025
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General comments
This manuscript presents a considerable field effort examining an active subglacial lake beneath the upper reaches of David Glacier. The location is significant, and the analysis of the data is appropriate. The data are difficult to acquire, and the authors are correct in their assertion that the methods they employ are the most suitable for characterising subglacial lakes from the surface. The manuscript does require some modifications, particularly in the presentation of the seismic data. (Seismic data are notoriously difficult to present so this is understandable). The study makes good use of synthetic seismograms to aid interpretation, but some aspects of the presentation and interpretation of results need to be checked.
Specific comments
The manuscript would benefit from the following:
1. Some additional justification of the survey location. Figure 3 shows that the survey location falls almost entirely outside of the active lake boundary from Smith et al., 2009. Please explain why this is the case. A useful addition to Figure 3 would be to show contours of equal hydropotential. This would further support the site selection, especially if they showed a hydropotential sink (closed contours of hydropotential.)
2. Please include a more detailed description of the reasons for the unsuitability of the seismic data acquired previously. This would be of benefit to other researchers as it would allow them to avoid similar pitfalls.
3. Seismic data can be very hard to present. I think presentation could be improved here. Reflections from and ice over water interface are high amplitude and negative polarity. The follow issues occur to me:
- Figure 4. The image and zoom sections are too small for me to identify the dominant polarity in the basal returns. I suggest presenting exemplar shot records of ice over water and ice over rock, and including larger insets showing the basal returns.
- Figure 6 images are too small as well. Making these subfigures larger would aid interpretation.
- Figure 9a looks to have an error. L257 states that this location represents ice over water but the dominant polarity of the basal return is +ve with small –ve side lobes. Also is the wiggle convention of +ve to the right being followed? Currently the right hand wiggle corresponds to the blue (-ve) color coding. This is confusing and should be corrected.
Technical corrections
The distance annotations shown in figures 2 and 6 should be shown on one of the basemaps.
The software used for processing the seismic data should be stated as the naming of routines is not always consistent across processing packages.
The distinction between active and inactive lakes should be made in the introduction.
L79—83 This combination of data used to conclude that the region has contributed to SLR needs more rigour. As this is not the focus of the study I would instead suggest relying on an already published estimate. The ICESat2 surface elevation change results of Smith et al (2020) show the region upstream is thickening over the ICESat2 period.
L91 ‘with minimal exchange’ I don’t know if we know this. To my mind stable lakes just mean water is entering at the same rate it is exiting. More generally I would shift this description of active and stable lakes to the introduction.
L109-110 repeat L61-63.
L112 ‘depressed basal elevations’ Really it’s the presence of hydropotential sinks as surface topography can dominate subglacial topography.
L123 ‘deployed’-> acquired
Figure 3. Add hydropotential contours.
Figure 4. Consider displaying fewer shots and making them larger so polarity can be more easily identified.
L158 ‘A geometry setup was performed...’ -> Acquisition geometry was added to the data...
L159 or soon after – state what software was used for processing.
Figure 5. Consider showing shot record and zoom before and after processing.
L181-182. Please state what you are reporting for resolution. (Looks like ¼ wavelength at for ice velocity at the upper end)
Figure 6. These are too small for me to examine polarity. Please increase in size. You shouldn’t need to reproduce the basemap here if it in presented well previously.
L201 ‘These features may be associated with glacial erosion....’
L240 ‘P-wave velocity...is faster...’ Strictly speaking it’s an impedance increase.
Figure 9. There are some issues with polarity discussed above. There looks to be a polarity reversal up the step in Fig 9b, which would be compelling and a nice example of how seismic data can show abrupt changes in water at the bed but again it’s hard to see in the field data.
L309-310 ‘hydrological barrier’ hard to say without knowing surface. Again hydropotential contours would be helpful here.
The conclusion could include statements on the mismatch between the active lake boundary and the area surveyed here and could suggest a location for direct access.
In summary I thank the authors for presenting this interesting and difficult to acquire data set.
Sincerely, Huw Horgan
Citation: https://doi.org/10.5194/egusphere-2025-2055-RC1
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