the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Englacial Architecture of Lambert Glacier, East Antarctica
Rebecca J. Sanderson
Kate Winter
S. Louise Callard
Felipe Napoleoni
Neil Ross
Tom A. Jordan
Robert G. Bingham
Abstract. The analysis of englacial layers using radio-echo sounding data enables the characterisation and reconstruction of current and past ice-sheet flow. Despite the Lambert Glacier catchment being one of the largest in Antarctica, discharging ~16 % of East Antarctica’s ice, its englacial architecture has been little analysed. Here, we present a comprehensive analysis of Lambert Glacier’s englacial architecture using radio-echo sounding data collected by the Antarctica's Gamburtsev Province Project (AGAP) North survey. We used an “internal-layering continuity index” (ILCI) to characterise the internal architecture of the ice and identify four macro-scale ILCI zones with distinct glaciological contexts. Whilst the catchment is dominated by continuous englacial layering, disrupted or discontinuous layering is highlighted by the ILCI at both the onset of enhanced ice flow (defined here as >15 ma−1) and along the shear margin, revealing the transition from internal-deformation-controlled to basal-sliding-dominated ice flow. These zones are characterised by buckled and folded englacial layers which align with the current ice-flow regime, and which we interpret as evidence that the flow direction of the Lambert Glacier trunk has changed little, if at all, during the Holocene. However, disturbed englacial layers along a deep subglacial channel that does not correspond to modern ice-flow routing suggest that ice-flow change has occurred in a former tributary which fed Lambert Glacier from grid north. As large outlet systems such as Lambert Glacier are likely to play a vital role in the future drainage of the East Antarctic Ice Sheet, constraining their englacial architecture to reconstruct their past ice flow and assess basal conditions is important.
Rebecca J. Sanderson et al.
Status: open (until 07 Apr 2023)
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RC1: 'Comment on tc-2023-13', Steven Franke, 10 Mar 2023
reply
Please see supplementary pdf.
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RC2: 'Comment on tc-2023-13', Marie G. P. Cavitte, 27 Mar 2023
reply
Review of Englacial Architecture of Lambert Glacier, East Antarctica, by Rebecca Sanderson et al.
General Comments Sanderson and others present interesting and original work focused on deriving a very detailed picture of the englacial layering within the Lambert Glacier in East Antarctica. We recognize the amount of time and effort required to trace such a huge volume of radar data, and this will be a key asset for the AntArtchitecture SCAR project as well as for large-scale modeling efforts that are learning to invert for englacial layering. There are several novelties in this work, including the mapping of a large-scale englacial buckling feature over 100s of kilometers across many radar transects, and its mapping with surface topography and ice flow velocity, as well as the interesting point that a low ICLI does not necessarily imply unmappable englacial reflectors, which opens up the potential for a subtler use of the ICLI in many other glacier catchments…? The figures are all very impressive with a lot of information and the use of 3D effects for the radargrams and basemap views are very helpful to better understand the flow dynamics. We applaud the authors for this. We recommend this manuscript for publication after some minor revisions outlined here below.
Specific comments
-In the discussion section, I found myself flipping a lot between fig 1 to have the ice thickness, bed topography and general ice flow speed geometries to compare to fig 3 where each zone with discussed in details. Would it be possible to perhaps add some ice thickness contours or ice velocity contours, or have one of the two panels overlying ice thickness/ice flow velocities so we don’t have to flip between the two figures? It would make it easier to really see for ourselves what is discussed.
In particular, it made it hard for me to see the gradual transition discussed in Section 5.2. For me, the transition shown in Fig 3 is quite abrupt but perhaps I am missing where the “onset region” is referring to? Could this be labeled on figure 3, as was the tributary T ? Same point L338-339 where I need the ice velocities to be mapped on Fig 3 so I can see where the ILCI returns map with the ice velocities.
-In Section 4.2, has the fact that the ICLI gives low values yet englacial layering is still laterally continuous (i.e. be traced) been highlighted in previous studies? If not, I think it’s something that should be highlighted more strongly here, for impacts in other (past, future) studies.
-The order in section 5.1 of the Discussion is a little confusing as the three likely causes for the low ILCI values are discussed at the very start and the evidence is only given in the 3rd paragraph starting L305. Could the order be revised a little?
-Will the englacial reflectors be published with this manuscript ? There is no mention of this in the Data availability section.
Technical comments
Abstract
L31 – I would not use inverted commas around internal-layering continuity index.
Introduction
L44 - “...lower in magnitude…”
L46 – I would suggest to cite the latest IPCC AR6 report here too.
L69 – For the accumulation rates reconstructions, suggestion to cite also Cavitte et al, 2018, The Cryosphere?
Methods
L104-105 – I would change “reduce echo signal noise” to “increase signal-to-noise”.
L135 – it is stated that englacial layers “are often absent in RES returns”, however, I think this is specific to how the radar system is set up. You can set up to get shallow layering with a high gain channel. And snow radar can also capture surface layering. I would suggest to be more specific, by adding “in deep RES returns” ?
Discussion
L195 – add “likely” in front of “the cause of low layer…” and maybe replace “layer” here by “reflector” to be consistent with your naming convention? Although I understand here it is referring to the ILCI…
L226 – It might be more interesting to say at what height above the bed you are here, instead of how deep (2.5 km depth)?
L228 – The deflection of the fold axes is not visible or marked on fig 5, is it? It would be nice to highlight it.
L399 – Adding the Gerber et al., 2021 paper here would be great! https://tc.copernicus.org/articles/15/3655/2021/ .
Figure 1 – It’s hard to see the yellow circles on panel a. Also, i printed form, in panel c, we don’t see the underlying raster of maximum horizontal gradient. And what does the “65” in brackets refer to each time? Can you explain somewhere how this raster is derived? It is used in several figures yet it is unclear to me.
Figure 2 – the caption mentions panel (d) but the figure itself has panel (e) marked ? Are the red unsmoothed ILCI results really useful on panels a-c? I feel like they could be removed to declutter a little the radargrams (and they are difficult to see at this scale), up to the authors.
Figure 4 – the radargram is very washed out in printed format. Is it possible to increase the contrast? Also, the red curve and the brown shading of the bedrock should be mentioned in the figure caption. If it corresponds to the velocity, it might be clearer if the velocity magnitude axis were also written in red.
Figure 5 – there is some striping on the radargrams that makes it difficult to see the layering well. Could the radargrams be enhanced somehow? I understand this is always tricky. Panel d is missing the little d on the panel itself, and the underlying raster is not described in the caption.
Figure 7 - Why is Figure 7 so far down in the paper, and not close to figure 4?
Citation: https://doi.org/10.5194/tc-2023-13-RC2
Rebecca J. Sanderson et al.
Rebecca J. Sanderson et al.
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