the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Oct 2024
Glacial erosion and history of Inglefield Land, northwest Greenland
Abstract. We used mapping of bedrock lithology, bedrock fractures, and lake density in Inglefield Land, northwest Greenland, combined with cosmogenic nuclide (10Be and 26Al) measurements in bedrock surfaces, to investigate glacial erosion and the ice-sheet history of the northwestern Greenland Ice Sheet. The pattern of eroded versus weathered bedrock surfaces and other glacial erosion indicators reveal temporally and spatially varying erosion under cold- and warm-based ice. All of the bedrock surfaces that we measured in Inglefield Land contain cosmogenic nuclide inheritance with apparent 10Be ages ranging from 24.9 ± 0.5 to 215.8 ± 7.4 ka. The 26Al/10Be ratios require minimum surface histories of ~150 to 2000 kyr. Because our sample sites span a relatively small area that experienced a similar ice-sheet history, we attribute differences in nuclide concentrations and ratios to varying erosion during the Quaternary. We show that an ice sheet history with ~900 kyr of exposure and ~1800 kyr of ice cover throughout the Quaternary is consistent with the measured nuclide concentrations in most samples when sample-specific subaerial erosion rates are between 0 and 2 x 10-2 mm yr-1 and subglacial erosion rates are between 0 and 2 x 10-3 mm yr-1. These erosion rates help to characterize arctic landscape evolution in crystalline bedrock terrains in areas away from focused ice flow.
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RC1: 'Comment on egusphere-2024-2983', Anonymous Referee #1, 27 Nov 2024
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General comments
This manuscript describes a field and GIS campaign conducted in Northwestern Greenland. Using cosmogenic nuclide dating, landfom/geological mapping, and modelling of possible exposure histories the authors describe exposure/ice-cover history at the margin of a relatively passive section of the Greenland Ice Sheet. The authors find a signal consistent with the onset of ice streams and periods of warm based ice amongst an otherwise predominantly cold-based regime. I found the manuscript to be clearly laid-out, well-written, and enjoyable to read.
Specific comments
Figure 1. Relating to my comment below (Line 100-102), I think adding an annual ice velocity composite (e.g, GrIMP) to the figure would be useful.
Figure 1. Could the approximate location of the images in Figure 3 be labelled here?
Figure 6. Does the size of the transparent arrow scale with the approximate magnitude of erosion?
Figure 7. As with figure 3, the location of these (and indeed all) sampling sites might be of interest and could be included as a supplementary figure.
Line 31-37: This might be a stronger opening paragraph if the formal definition of ice streams is moved elsewhere, and line 33 transitions straight into line 38. As it is here, it is not immediately clear what the relevance of ice streams are to this work.
Line 81: Given discussion of transitions between thermal state earlier in the intro, I’d suggest this reference to a key transition is unnecessarily unclear and the sentence could instead be simplified to something along the lines of: “Cosmogenic nuclide and luminescence analysis of sediment and bedrock samples collected from the glacier bed...”
Line 89--94: I would normally expect to see this text in the conclusions. A summary of the work along these lines is already given in the abstract and these may not be necessary.
Line 100-102: As far as I can see, this is the only comment on the current behaviour of ice bordering the study area. I wonder if there is a missed opportunity to further contextualise this study by commenting further on the current variability (or lack thereof) of the ice sheet along this margin. Annual ice velocity, though broadly fairly low (<~50 m yr-1) is variable and Hiawatha glacier in particular is relatively fast compared to surrounding ice.
Line 112: Is the Fig 1. On this line in reference to that of England 1999? Otherwise, the Figure 1 here does not show the LGM ice sheet configuration of the study area and I would suggest the removal of the reference here.
Line 117: “maintaining to a smaller position” is the to necessary?
Section 3.3.2: Could an approximate scale range for “landscape scale” be given here. Even a mapping scale (if fixed) or a minimum mapping scale (if variable) would be useful.
Line 187: Given this is a paper on variable erosion rates within a small area of an ice sheet, “erosive ice sheets” here feels a bit reductionist and could be more precise if it was "areas of high erosion rates beneath ice sheets" for example.
Line 200: What is meant by lakes “dammed by sediments”?
Line 274: Could you specify the threshold value here please?
Line 281: Is there precedent for this scaling? If not, could you include a brief comment on why you expect this to not affect your conclusions? It seems there might potentially be some uncertainty introduced if there was any lateral variation in retreat or any changes in the speed of retreat.
Line 355: could an example of glacial erosional features be given? I understand they are absent but it might be useful for a reader to know exactly what is absent that might otherwise be expected.
Line 381: I am missing the link here between the presence of ice-sculpting and the duration of any “wet-based ice”. As a sidenote, could a consistent terminology be used throughout (see also 573-575)? In the introduction it is warm and cold based, but here it is wet-based.
Line 438: Could a reference to recent advance and retreat patterns be added here?
Line 443: I am not sure how relevant the Petermann Glacier is to this exact setting. Although relatively close to the study site, the ice dynamic contexts are very different, with Petermann draining a large portion of the ice sheet relative to this peripheral area of the ice sheet.
Line 476: I am not suggesting this is carried out here, but bathymetric investigation in the Kane Basin may be a fruitful avenue for future work to look for geomorphic investigation of ice stream signatures.
Line 525: suggest adding “while our results suggest that Inglefield Land was covered…”
Lines 537-541: multiple uses of “these” make the subject of these sentences unclear.
Lines 540-541: It might also be worth adding the role of increased meltwater delivery to the bed in a warming climate
Technical comments
Line 44 (and elsewhere): glaciated is understood to mean “formerly occupied by glaciers”. The use of previously here and subsequent use of formerly are therefore redundant throughout.
Line 171: misspelling of terrains?
Line 162: these should be EM dashes.
Line 186: …generally topographically smooth on the landscape-scale…
Line 440: is there a missing the? E.g., …collapse over the Nares Strait
Citation: https://doi.org/10.5194/egusphere-2024-2983-RC1
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