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https://doi.org/10.5194/egusphere-2025-6081
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-6081
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
23 Dec 2025
| 23 Dec 2025
Year-round assessment of sea ice pressure ridges by multi-frequency electromagnetic induction sounding
Abstract. The thickness and consolidation state of pressure ridges are variables relevant for sea ice mass balance, melt processes and ecosystem habitat. We show how both variables can be detected by the multi-frequency electromagnetic induction (EMI) sounding, based on data collected during Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) in the central Arctic Ocean between November 2019 and July 2020. We validate the EMI results by collocating them to sea ice topography from the airborne laser scanner, underwater topography from multi-beam sonar, and sea ice thickness and structure from drill holes. Selected channels of low frequency give good estimates of total thickness, while selected channels of high frequency give good estimates of consolidated layer thickness. The MOSAiC EMI dataset was collected over a large number of ridge systems formed between freeze-up and break-up. Nine individual ridge transects can be used to track the seasonal development. The footprint size and sensitivity of the method make the EMI sounding appropriate for the detection of ridges with up to 10 m total thickness. Where available, the ridge structure data from other methods are consistent with our results. The superior temporal and spatial coverage of the MOSAiC EMI data permits further analysis that indicates a slow reduction of the total thickness towards the consolidated layer thickness. Interestingly, the consolidated layer thickness exceeds the level ice thickness by a factor of 1.6 to 2 and also shows, at least for individual ridges, a seasonal decrease. This may be a feature of the thin snow cover at MOSAiC. Multi-frequency EMI is a promising method for non-intrusive pressure ridge surveying with a large potential for pressure ridge dataset extension.
How to cite. Itkin, P., Salganik, E., Divine, D. V., Jutila, A., Katlein, C., Neudert, M., Raphael, I. A., and Ricker, R.: Year-round assessment of sea ice pressure ridges by multi-frequency electromagnetic induction sounding, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-6081, 2025.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
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- RC1: 'Comment on egusphere-2025-6081', Anonymous Referee #1, 21 Feb 2026
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RC2: 'Comment on egusphere-2025-6081', Andrew Mahoney, 13 Apr 2026
Year-round assessment of sea ice pressure ridges by multi-frequency electromagnetic induction soundingby Polona Itkin and othersSubmitted to The CryosphereReview by Andy MahoneyApril 10, 2026SummaryThis manuscript presents an interesting timeseries of multifrequency EM sounding observations of pressure ridges surrounding the MOSAiC expedition. The data presented show great promise for advancing our understanding of both the thermodynamic evolution of ridge keels and the effect of macroporosity on EM sounding of sea ice. I very much look forward to seeing this work published, but I fear the manuscript is currently in a somewhat unpolished state and relies too much on key details and results that are presented in other papers. It is clear that the authors are highly familiar with the adjacent literature, but I feel that more details from these other sources should be provided so that the manuscript can better stand alone as a separate publication. At the same time, the paper presents some results that feel tangential to the key findings presented. Hence, if length becomes an issue, I think the authors could omit some of this material to make room for greater discussion of details that are currently delegated to citations of other literature. I also find that readability of the text is made more difficult by a somewhat unorthodox structure that deviates from the more typical practice of using separate, clearly defined sections for the methods, results, and discussion. I recognize that this may sound like strong criticism, but I do not want to discourage the authors as I believe all my concerns can be addressed quite readily. I have provided more details for my principal concerns below and where possible I have tried to make constructive guidance for addressing them.Major Comments1. Over reliance on material published elsewhereA number of the manuscript’s findings rely on drill-based measurements of macroporosity within the ridge keel and the identification of the consolidated layer (CL). However, the text devotes just 4 lines to explain the underlying methodology and reports the associated results without uncertainty estimates or, in some cases, any clear source (e.g, macroporosities reported on line 308). I understand that the relevant details are provided in recent work by Salganik et al, but I feel the reader should still be given enough information to understand the method and results necessary for this work without having to read another paper.Similarly, I feel the brief description of the thermistor chains would likely only be meaningful to a reader already familiar with the SIMBA instrument and no data from these instruments are presented in the text. Instead, the thermistor results are reported entirely through citation of other work. If the thermistor data are important for supporting the thermodynamic modelling then I feel they should be given more space within the manuscript.Lastly, I would also like to see brief explanations of how the ALS and multibeam data were tied to local sea level to derive freeboard and draft, respectively, and the associated uncertainties. These details may be provided in the paper cited in the text, but I feel they should be included here for completeness.2. Unclear presentation of EM thickness resultsFigure 5 presents some of the most important results in the manuscript, but I find it very difficult to understand. Based on what is written in the text, I had expected that panel (a) would show in-phase EMI thickness results and panel (b) would show results from the quadrature component. The caption suggests these are distinguished by dots and crosses, respectively, but the plots in both panels show both dots and crosses, making it appear that both plots show the same set of EMI thickness measurements. However, the vertical positions of the data points in panel (a) do not match those in panel (b), suggesting they are not showing the same EMI data. I’m therefore at a loss to understand what should be one of the paper’s key figures. Some of this might be fixed with decluttering of unnecessary data points and a clearer legend and caption, but some attention may also be needed to ensure the correct data are being plotted.3. No explicit explanation of EMI-derived CL thicknessI cannot find any place in the text where the method for determining CL thickness from EMI data is explicitly described. The text on line 298 states “the CL thickness aligns mainly with the quadrature values of the highest frequencies (18, 60, and 98 kHz)”, but there are no specific details regarding how this applied to derive CL thickness from EMI data. A dedicated reader might infer from the preceding paragraph that CL thickness is determined from the average EMI thickness values derived from the 18, 60 and 98 kHz quadrature data, but I would like to see a clear statement of this in the text, together with a quantitative discussion of uncertainty.4. Unnecessary presentation of spatial ridge distributionThe locations and spatial distribution of ridges discussed are not crucial information for supporting the manuscript’s key findings. I also feel the figures presenting this information are somewhat cluttered and difficult to interpret. Hence, if space becomes an issue, I suggest that Figures 3, 4, and 8 and associated text could be omitted or moved to an appendix with minimal impact to the findings.5. Recommended restructuring of method, results, and discussionThis may be partly a matter of style, but I encourage the authors to consider reorganization of the text to improve readability, particularly for the benefit of readers who may be encountering this subject matter for the first time. Specifically, I recommend a cleaner separation of content between the Methods, Results, and Discussion section. In its current form, section 2 presents the reader with both methods and results, while section 3 is a combined “Results and Discussion” section. There are even important drill hole results presented in the Introduction section. As a consequence, I found myself having to go back and forth re-reading sections multiple times to follow the chain of reasoning and evidence. Some further use of subheadings to break-up lengthy sections of discussion into discrete topics may also help.Minor commentsLine 194-195: Does this 10 m accuracy refer to absolute position accuracy, or the accuracy with which you are able to co-locate measurements? The latter seems more important to me in this context, but 10 m seems too high to be useful for co-locating the different measurements described here, all of which have footprints much smaller than this.Line 209: As it is stated, I find this assumption of constant “ridge porosity” a little confusing given the attention paid to ridge consolidation in this paper. Would it be more accurate to state “… and we assume the macroporosity of the unconsolidated rubble remains constant …”?Figures 3 & 4: I find these both of these figures quite cluttered and the information they provide on the spatial distribution of ridges does not seem critical to the discussion. Could they simply be omitted, along with much of this section, or moved to an appendix?Lines 250-273: These lines contain most of the relevant information found in this section and could be better placed into a tableLines 290-293: I do not recommend using the same term for two different properties, even with a qualifying statement like that used here. Could the authors instead use a new term to describe CL thickness plus freeboard? Perhaps something as simple as "CL+" ?Lines 308-310: It took me longer than necessary to realize there was a missing cross-reference to Figure 2, in part because Figure 2 is found within the Introduction, rather than the results, where I would have expected it.Lines 319-320: I’m afraid I don't find this argument to be well supported by the results shown. This may be helped by redrawing Figure 5 to better show the relationships described. I think it would also be helpful to present the frequency sensitivity more clearly so that the reader can better understand how the difference between low- and high-frequency responses related to thickness of unconsolidated ice in the keel.Figure 8: I don't find this figure very useful. It is difficult determine changes in consolidation over time because the regions useful comparison are too small. Figure 9 is much more suitable for this purpose. Since Figure 8 is only referenced once in the text and the spatial distribution of the ridge keels is not critical to any key finding, I suggest this figure could be omitted.Citation: https://doi.org/
10.5194/egusphere-2025-6081-RC2
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Latest update: 01 May 2026
Norwegian Polar Institute, Tromsø, Norway
Evgenii Salganik
Norwegian Polar Institute, Tromsø, Norway
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
Dmitry V. Divine
Norwegian Polar Institute, Tromsø, Norway
Arttu Jutila
Finnish Meteorological Institute, Helsinki, Finland
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
Christian Katlein
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
Mara Neudert
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
Ian A. Raphael
Dartmouth College, Thayer School of Engineering, Hanover, New Hampshire, USA
Robert Ricker
NORCE Norwegian Research Centre, Tromsø, Norway
Short summary
We studied how Arctic ice ridges grow and change through winter and spring using a sensor that measures ice thickness without drilling. By comparing these measurements with data from aircraft, underwater surveys, and field work, we show that the sensor can detect both the full ridge thickness and its solid inner core. Our results reveal slow winter strengthening of ridges and highlight this method's value for understanding ice conditions and ecosystems.
We studied how Arctic ice ridges grow and change through winter and spring using a sensor that...
This manuscript presents a valuable and timely study by utilizing multi-frequency Electromagnetic Induction (EMI) data from the MOSAiC expedition to assess pressure ridge properties. A particular strength is comprehensive validation against drill-hole, airborne laser scanner (ALS), and multibeam (MB) sonar data. The work usefully explores the potential of EMI to estimate both total ridge thickness and consolidated-layer (CL) thickness. The manuscript requires some revisions for clarity. Below are my specific comments.
Abstract:
Please highlight the core innovation of multi-frequency EMI method in the abstract.
The conclusion section could be more concise, focusing on the advantages and limitations of the EMI method. The EMI method performs well in detecting ridges with a thickness of ≤ 10 m, but systematic biases occur in areas with high porosity or steep topography.”
Main text:
The entire paragraph in Line 62 regarding “ridge melting rate” has weak relevance to the main theme of the study and is suggested to be removed.
For the paragraph in Line 73, a smoother transition from “commonly used ridge detection methods” to the “EMI method” is advised. It is recommended to add little sentences explaining the limitations of conventional techniques. This will naturally lead to highlighting the advantages of the EMI method.
- Line 110: The choice of the five specific frequencies (1.5, 5.3, 18, 63, 93 kHz) needs clearer physical justification. Has a sensitivity analysis been conducted to clarify the response characteristics of each frequency to ridges with different porosities and thicknesses? This is particularly important because, the figures in the appendix, the thicknesses inverted by different frequencies vary.
The EMI method detects overall electrical conductivity, which the manuscript correlates with "macro-porosity". For the same porosity, will concentrate large porosity or scattered small porosity lead to different EMI responses? Moreover, based on drilling data from six ridges, the manuscript suggests that the porosity threshold of the consolidated layer detected by the quadrature of high-frequency EMI is approximately 20–30%. Is this threshold universal? In reality, the porosity of ridges will be lower than 20% after reconsolidation.
Section 3.1 :The matching methods between EMI data and drilling, sonar, and etc. should be clearly stated at the beginning of Section 3.1. This will prevent readers from having to wait until the results section to understand how the data fusion was performed. Additionally, while the manuscript compares EMI data with positioned drilling, ALS, and MB sonar data, there are differences in spatial resolution among these data. How were these differences evaluated? What causes the local discrepancies between EMI, the thermodynamic model, and the thermistor chain data?
After defining CL in Line 38, the definition is repeated in Line 46.
The terms “macro-porosity” and “rubble macro-porosity” are used interchangeably throughout the manuscript. What is the difference between these two terms?
Fig. 3 & Fig. 8:The continuous color bar for snow freeboard uses similar hues to the discrete colors overlain for ridge age groups.
A sentence regarding suggestions for the future application of the EMI method could be added at the end of the conclusion section. This will extend the implications of the study and provide guidance for subsequent research in this field.