the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 May 2024
Spatiotemporal variations in the East Antarctic Ice Sheet during the Holocene
Abstract. The past changes in East Antarctic Ice Sheet (EAIS) are crucial for understanding the ice sheet dynamics and its response to the Earth’s climate system. Field-based geological data and various model simulations, such as ice sheet and glacial isostatic adjustment (GIA) modellings, provide significant insights into the behaviour of EAIS during the interglacial–glacial cycle. Recent in-situ cosmogenic nuclide surface exposure studies have revealed a large-scale thinning occurred in the Dronning Maud Land and Enderby Land of East Antarctica during 9–6 ka. However, the timing of this EAIS thinning event necessitates a revision of the ICE-6G model, which is a widely used GIA-based ice sheet history. To account for this temporal discrepancy, it is necessary to compare the sea levels calculated by GIA modelling with sea-level reconstructions to evaluate the validity of this refinement. The computed sea levels by GIA modelling are consistent with the relative sea-level reconstructions and indicate the spatial difference in the Holocene sea-level peaks, which is primarily due to the differences in the timings of ice-mass losses in the east and west of the Indian Ocean sector of East Antarctica. This finding challenges the prevailing assumption of synchronized ice-sheet growth and decay across this region, suggesting that the ice mass changes in the EAIS exhibit significant spatial differences.
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Status: closed (peer review stopped)
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RC1: 'Comment on egusphere-2024-275', Anonymous Referee #1, 16 Aug 2024
This paper presents new GIA modelling that uses two different ice loading histories (ICE6G and Nice6g...), alongside two values for mantle viscosity (weak and strong) to simulate spatiotemporal changes in RSL in the Indian Ocean facing sector of East Antarctica (Enderby Land and Mac Robertson Land). These modelled RSL histories are then compared to (mostly) previously published RSL reconstructions to assess which ice loading history and mantle viscosity are most consistent with the data. My understanding is that the Nice6g refinement was motivated by new cosmogenic data that shows a difference in deglaciation age from that applied in the ICE6G model. So to test if the refinement is appropriate this study uses it to model RSL.
In these terms this is a solid study but I find the main body of text quite difficult to follow if my understanding of the broader motivation is correct. The introduction would benefit from an expanded and explicit paragraph on the aims and objectives of this specific study. the last sentence (lines 75-76) doesn't fully articulate this.
I also think the paper slightly overstates its"sea level" reconstruction aspect. I appreciate the work that goes into recalibrating datasets so they are internally consistent and how this is done needs to be documented. But as far as I can tell the paper uses previously published RSL reconstructions supplemented by some new ages which, while i agree should be included, don't really change the RSL story. I think the paper would benefit from trimming down the RSL data side of things and being more focussed on, and expanding, the modelling aspect. It is, at heart, a modelling paper and should wear that badge with pride so-to-speak. One way to do this would be to remove "3.1 RSL reconstructions" from results and move it to a new section before the methods that covers "study sites". This could describe both the deglaciation story (and the difference in timing relevant to ice loading histories) and the RSL curves (supplemented with new data).
Similarly, the discussion covers a lot of material (i.e., lines 232-259) that, although relevant, would be better placed before results as it really sets the scene for the study (i.e., shows the different deglaciation timeframes) rather than being a point of discussion for the results of the work done here (i.e. GIA modelling). I then think the discussion needs a restructure, I'm not sure exactly how. Maybe discuss LHB and PB separately first before making comparisons. I think there are some interesting points here but they are quite hard to pull out from a discussion that jumps about so much.
I want to be supportive of this paper and think there is a body of work here that will be a good addition to our understanding of EAIS history and RSL change. However i think to realise its full potential and ensure it is picked up upon it needs some significant restructuring to more clearly state its motivation and focus more on the results of this study rather than re-discussing previous work.
Specific comments
Title: I don't think this title is appropriate. It doesn't really describe what this work did or what its contribution to knowledge is. "Refined ice loading histories improve fit of GIA models to relative sea level data in East Antarctica" is just one that comes to mind (I'm not a modeller so this maybe a poor suggestion). but i think something that better describes the work/conclusion of this paper is needed.
Lines 50 - 55 : Think the overall picture of RSL change needs to be described in the intro (or in a new section as suggested above)
Lines 62 - 67: Not needed, there is no new TCN data being presented so a description of the method in any form is not required.
Line 69: Ok so studies show difference in timing to that used in ICE6G...what did ICE6G use?
Throughout the paper the authors refer to Nice6gSi6g_09-05_PART. This is really awkward to read inline and i wonder if it should be referred to more simply e.g., Suganuma ice history (vis a vis ICE6G).
My understanding is that the high marine limit on Skarvsnes is related to neotectonics but this isnt discussed anywhere. It has implications about the utility of the RSL record at this site for constraining GIA models. cf. discussion on lines 242-242.
Lines 244-259 belong in an introduction or study site section.
Fig 2. Units on colour bars missing. Coastline is really not clear. Label panels A/B with ice loading model.
Fig 3. Is Nice6gSice6g the same as ICE6G, check labels below panel C.
Fig 5. Colour scheme should be divergent around zero surely? really hard to see at a glance where RSL is higher/lower than present. I would label the panels with the ice loading model/viscosity used. Its hard to keep referring back to the caption.
Citation: https://doi.org/10.5194/egusphere-2024-275-RC1 -
RC2: 'Comment on egusphere-2024-275', Anonymous Referee #2, 28 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-275/egusphere-2024-275-RC2-supplement.pdf
Status: closed (peer review stopped)
-
RC1: 'Comment on egusphere-2024-275', Anonymous Referee #1, 16 Aug 2024
This paper presents new GIA modelling that uses two different ice loading histories (ICE6G and Nice6g...), alongside two values for mantle viscosity (weak and strong) to simulate spatiotemporal changes in RSL in the Indian Ocean facing sector of East Antarctica (Enderby Land and Mac Robertson Land). These modelled RSL histories are then compared to (mostly) previously published RSL reconstructions to assess which ice loading history and mantle viscosity are most consistent with the data. My understanding is that the Nice6g refinement was motivated by new cosmogenic data that shows a difference in deglaciation age from that applied in the ICE6G model. So to test if the refinement is appropriate this study uses it to model RSL.
In these terms this is a solid study but I find the main body of text quite difficult to follow if my understanding of the broader motivation is correct. The introduction would benefit from an expanded and explicit paragraph on the aims and objectives of this specific study. the last sentence (lines 75-76) doesn't fully articulate this.
I also think the paper slightly overstates its"sea level" reconstruction aspect. I appreciate the work that goes into recalibrating datasets so they are internally consistent and how this is done needs to be documented. But as far as I can tell the paper uses previously published RSL reconstructions supplemented by some new ages which, while i agree should be included, don't really change the RSL story. I think the paper would benefit from trimming down the RSL data side of things and being more focussed on, and expanding, the modelling aspect. It is, at heart, a modelling paper and should wear that badge with pride so-to-speak. One way to do this would be to remove "3.1 RSL reconstructions" from results and move it to a new section before the methods that covers "study sites". This could describe both the deglaciation story (and the difference in timing relevant to ice loading histories) and the RSL curves (supplemented with new data).
Similarly, the discussion covers a lot of material (i.e., lines 232-259) that, although relevant, would be better placed before results as it really sets the scene for the study (i.e., shows the different deglaciation timeframes) rather than being a point of discussion for the results of the work done here (i.e. GIA modelling). I then think the discussion needs a restructure, I'm not sure exactly how. Maybe discuss LHB and PB separately first before making comparisons. I think there are some interesting points here but they are quite hard to pull out from a discussion that jumps about so much.
I want to be supportive of this paper and think there is a body of work here that will be a good addition to our understanding of EAIS history and RSL change. However i think to realise its full potential and ensure it is picked up upon it needs some significant restructuring to more clearly state its motivation and focus more on the results of this study rather than re-discussing previous work.
Specific comments
Title: I don't think this title is appropriate. It doesn't really describe what this work did or what its contribution to knowledge is. "Refined ice loading histories improve fit of GIA models to relative sea level data in East Antarctica" is just one that comes to mind (I'm not a modeller so this maybe a poor suggestion). but i think something that better describes the work/conclusion of this paper is needed.
Lines 50 - 55 : Think the overall picture of RSL change needs to be described in the intro (or in a new section as suggested above)
Lines 62 - 67: Not needed, there is no new TCN data being presented so a description of the method in any form is not required.
Line 69: Ok so studies show difference in timing to that used in ICE6G...what did ICE6G use?
Throughout the paper the authors refer to Nice6gSi6g_09-05_PART. This is really awkward to read inline and i wonder if it should be referred to more simply e.g., Suganuma ice history (vis a vis ICE6G).
My understanding is that the high marine limit on Skarvsnes is related to neotectonics but this isnt discussed anywhere. It has implications about the utility of the RSL record at this site for constraining GIA models. cf. discussion on lines 242-242.
Lines 244-259 belong in an introduction or study site section.
Fig 2. Units on colour bars missing. Coastline is really not clear. Label panels A/B with ice loading model.
Fig 3. Is Nice6gSice6g the same as ICE6G, check labels below panel C.
Fig 5. Colour scheme should be divergent around zero surely? really hard to see at a glance where RSL is higher/lower than present. I would label the panels with the ice loading model/viscosity used. Its hard to keep referring back to the caption.
Citation: https://doi.org/10.5194/egusphere-2024-275-RC1 -
RC2: 'Comment on egusphere-2024-275', Anonymous Referee #2, 28 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-275/egusphere-2024-275-RC2-supplement.pdf
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