the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Feb 2025
Building multi-satellite DEM time series for insight into mélange inside large rifts in Antarctica
Abstract. Front calving is a primary mechanism through which Antarctic ice shelves discharge ice mass into the Southern Ocean. It is an important process that influences ice shelf stability and thus, impacts the Antarctic Ice sheet’s contribution to global sea level rise. However, there has been a significant gap in large-scale, high-resolution observations of three-dimensional (3D) rift structural changes and mélange dynamics, which hinders our understanding of the role of mélange in ice shelf retreat and mechanisms underlying the weakening of ice shelf stability. We propose an innovative multi-temporal DEM adjustment model (MDAM) that builds a multi-satellite DEM time series from meter-level resolution small DEMs across large Antarctic ice shelves by removing biases, as large as ~6 m in elevation, caused by tides, ice flow dynamics, and observation errors. Using 30 REMA and ZY-3 sub-DEMs, we establish a cross-shelf DEM time series from 2014 to 2021 for the Filchner-Ronne Ice Shelf, the second largest in Antarctica. This unified and integrated DEM series, with an unprecedented submeter elevation accuracy, reveals quantitative 3D structural and mélange features of a ~50 km long rift, including rift lips, flank surface, pre-mélange cavities, and mélange elevations. For the first time, we have observed that while the mélange elevation decreased by 2.1 m from 2014 to 2021, the mélange within the rift experienced a rapid expansion of (7.93±0.03) × 109 km3, or 130 %. This expansion is attributed to newly calved shelf ice from rift walls, associated rift widening, and other factors related to rift-mélange interactions. The developed MDAM system and the 3D mélange dynamics analysis methods can be applied for research on ice shelf instability and the future contribution of the Antarctic Ice Sheet to global sea level rise.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-175', Ann-Sofie Priergaard Zinck, 04 Mar 2025
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RC2: 'Comment on egusphere-2025-175', Mattia Poinelli, 23 Mar 2025
Dear Menglian Xia and co-authors,
The manuscript “Building multi-satellite DEM time series for insight into mélange inside large rifts in Antarctica” by Xia et al. presents a novel approach to monitor rifts’ infill on the Filchner-Ronne ice shelf using observations from different satellites at high resolution Understanding variations in rift infill is crucial for assessing rift dynamics, which ultimately influence calving events. I commend the authors for their creative approach, thorough analysis, and well-designed, highly informative figures. Overall, I strongly believe this paper would be a valuable addition to the literature, and its scope and format make it well-suited for publication in The Cryosphere. Below, I provide a general comment along with more specific, line-by-line suggestions that I hope will further strengthen the manuscript.
GENERAL COMMENT:
I admit that DEM processing is not my direct area of expertise, but the logic of the technical part seems sound and appropriate for a reader, like me, who is not necessarily familiar with technicalities of DEM analysis. However, I believe this manuscript would benefit from a few improvements to enhance readability and impact. In some sections, the text becomes somewhat difficult to follow, partly due to the frequent use of acronyms and the listing of numbers with excessive significant figures. At times, this made it challenging to stay engaged with the flow of the manuscript. I recommend streamlining certain parts, as indicated in my line-by-line comments, to improve clarity and coherence.
More importantly, I find that this manuscript lacks a thorough discussion, a comparison with existing literature, and a clear background motivation. I was surprised to see that it does not include a dedicated discussion section, where I had expected to find these elements. To strengthen the manuscript’s impact, I recommend contextualizing the observational results within the broader framework of rift monitoring and their implications for ice shelf and glacier dynamics, while also drawing comparisons with existing studies.
While rifts and calving are natural processes in the life cycle of ice shelves, the calving of their seaward-most extensions does not necessarily lead to significant upstream glacier acceleration. I have not performed the calculations myself, but rifts T1 and T2 on the Filchner-Ronne Ice Shelf (FRIS) appear to lie beyond the ‘compressive arch’ (Doake, 1998), suggesting they may not directly precondition the ice shelf for collapse—similar to the ‘passive portion’ described by Fürst et al. (2016). This raises a key question: if these rifts are not an immediate destabilizing factor for FRIS, why is their study important?
This is, of course, a provocative question, and I fully agree with the authors that rifts play a critical role. Future calving triggered by T1 and T2 and the resulting ice front retreat may expose the ice shelf to increased warm water intrusion, a process simulated for Larsen C and supported by theoretical work (Poinelli, 2023a,b). In the context of global warming, this is particularly relevant for FRIS, as warm water has recently been observed near Berkner Island (e.g., Davis, 2022). Such changes could ultimately lead to destabilization mechanisms like those proposed for Larsen C. I encourage the authors to incorporate these considerations to provide a stronger and more comprehensive discussion of their findings.
In the introduction, there is a strong focus on technical studies related to altimetric and stereo mapping of rifts, but the broader scientific goal and the significance of this region of Antarctica seem underdeveloped. For a paper in The Cryosphere, I would expect a more robust scientific background that clearly establishes the relevance and utility of this work.
One crucial aspect that appears to be missing is the role of ice mélange variation in modulating rift dynamics. A thick mélange layer can effectively "freeze" a rift, enabling mechanical stress transmission between its flanks and ultimately suppressing rift propagation (Rignot, 1998; Larour, 2021). This process is fundamental to understanding rift evolution and should be better integrated into the manuscript’s scientific framing. I may have overlooked this point, and I apologize if it was addressed, but I encourage the authors to clarify and emphasize its importance.
SPECIFIC COMMENTS
Line 13: The connection between calving and ice mélange is not clearly established in the manuscript. Why is the observed "significant gap" in mélange dynamics particularly relevant to calving processes? Ice mélange, when sufficiently thick, can bond rift flanks together, suppressing rift widening and propagation. Clarifying this link would strengthen the manuscript’s argument and better highlight the importance of studying mélange dynamics in the context of ice shelf stability.
Line 20: Mélange volume expansion is directly correlated with rift widening, but its relevance in the context of ice sheet modeling is unclear. Can we speculate on causality—does mélange volume drive rift widening, or is it simply a byproduct? Since mélange volume necessarily increases as the rift widens due to greater exposure of open ocean to surface heat loss, a more informative parameter to monitor might be mélange thickness relative to ice shelf thickness. This ratio is crucial in determining how stress is transmitted between rift flanks (Larour, 2021).
Line 29: This line is a bit confusing, mass discharge across the GL is the cause of sea level rise, but what does ‘lost ice mass enters’ mean?
Line 39: Like my comment in the abstract, I don’t fully see the link between calving and ice mélange? What does ‘the importance … on studying mélange … are fully recognized’ mean?
Figure 1: Really nice figure.
Line 67: What do you mean with ‘tie point’?
Line 76: This sentence is a bit confusing.
Line 124: This is good example of the scientific motivation of this study. Perhaps this should be included in the introduction and not in methodology.
Line 157,176: Acronyms in the title are hard to follow ad makes the reading experience confusing.
Figure 8-9: Great figures! Congrats!
Line 264: I appreciate the precision in these values but is it necessary? This may be a question of personal preference, but I find it a bit confusing to follow these numbers. These details are also reported in Table A3 no? So why don’t discuss the orders of magnitude of these changes?
Line 282: What is a ‘cavity’ in this context? Please specify.
Line 290: Volumetric change is a good parameter to monitor, but it would also be interesting to see an estimation of mélange thinning, which is relevant to ice sheet modeling. The observed decreased in ice mélange elevation most likely means that this layer has thinned. This is extremely important as the stress propagation between flanks may be compromised (Larour 2004).
Line 300: What do you mean with ‘newly calved’? I may have missed this, but I thought the ice shelf has not calved during this period. Do you perhaps mean that the rift has widened due to partial collapse of its flanks? If so, can you speculate about what may have caused it? Mélange thinning may be the answer itself, and I agree that it is hard to point at a cause. Setting up a discussion on this would be very important.
Line 302: I was surprised to see that the manuscript does not include a discussion section. What are the strengths of this novel approach? How does this compare to previous studies that employed ICESat2? for example Walker 2021, Fricker 2005, …? Why is monitoring of these rifts important? Can you extend this novel processing techniques to other highly fractured areas of Antarctica (Larsen C, Totten, Brunt, Amery?)
Line 307: I may have missed it, but is there a similar analysis applicable to T2? The manuscript presents these rifts as a pair, yet the analysis appears to be restricted to T1, which seems inconsistent. To be clear, I am not suggesting additional analysis, but the rationale for focusing solely on T1 should be explicitly stated, even if it is due to data limitations.
Yours sincerely,
Mattia Poinelli
Mattia.poinelli@uci.edu
University of California, Irvine
Jet Propulsion Laboratory, California Institute of Technology
REFERENCES:
Doake 1998 Breakup and conditions for stability of the northern Larsen Ice Shelf, Antarctica, Nature
Fuerst 2016, The safety band of Antarctic ice shelves, Nature Climate Change
Larour 2021, Physical processes controlling the rifting of Larsen C Ice Shelf, Antarctica, prior to the calving of iceberg A68, PNAS
Davis 2022, Observations of Modified Warm Deep Water Beneath Ronne Ice Shelf, Antarctica, From an Autonomous Underwater Vehicle, JGR: Oceans
Poinelli 2023a: Can rifts alter ocean dynamics beneath ice shelves? The Cryosphere
Poinelli 2023b: Ice-Front Retreat Controls on Ocean Dynamics Under Larsen C Ice Shelf, Antarctica, GRL
Rignot 1998, Ice-shelf dynamics near the front of the Filchner-Ronne Ice Shelf, Antarctica, revealed by SAR interferometry, GRL
Larour 2004, Modelling of rift propagation on Ronne Ice Shelf, Antarctica, and sensitivity to climate change, GRL
Walker 2021, A High Resolution, Three-Dimensional View of the D-28 Calving Event From Amery Ice Shelf With ICESat-2 and Satellite Imagery, GRL
Fricker 2005, ICESat's new perspective on ice shelf rifts: The vertical dimension, GRL
Citation: https://doi.org/10.5194/egusphere-2025-175-RC2
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