The new kids on the block of Arctic coasts &ndash; Formation and Morphodynamics of Paraglacial Moraine Lagoons in Svalbard

Owczarek, Zofia Alicja; Kostrzewa, Oskar; Piskorski, Wojciech; Strzelecki, Mateusz C.

doi:10.5194/egusphere-2026-1226

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https://doi.org/10.5194/egusphere-2026-1226

Preprints

18 Mar 2026

| 18 Mar 2026

The new kids on the block of Arctic coasts – Formation and Morphodynamics of Paraglacial Moraine Lagoons in Svalbard

Zofia Alicja Owczarek, Oskar Kostrzewa, Wojciech Piskorski, and Mateusz C. Strzelecki

Abstract. As Arctic amplification accelerates glacier retreat, new dynamic landscapes are emerging at the interface of terrestrial and marine systems. This study identifies and analyses a distinct coastal landform: the Paraglacial Moraine Lagoon (PML). Formed by coastal barriers composed of terminal or lateral moraines deposited during the Little Ice Age, PMLs represent a critical yet understudied component of the glacier–climate change feedback system. Using a multi-decadal record (1936–2024) comprising aerial photography, satellite imagery, and the Digital Shoreline Analysis System (DSAS), we quantified the evolution of fourteen PML systems across the Svalbard Archipelago. Our results show that PMLs now occupy over 56 % of Svalbard's total lagoon area (ca. 83 km²), nearly triple the area they occupied in the 1930s. We identify two divergent evolutionary trajectories: (1) an erosional–fragmenting pathway (e.g., Tjuvfjordlaguna), where marine forcing leads to barrier narrowing and inlet expansion, and (2) a stabilizing–isolating pathway (e.g., Femtelaguna), where land-terminating glaciers drive rapid terrestrial sediment infilling and barrier progradation. We argue that PMLs function as essential "paraglacial sinks" trapping glaciogenic sediments and organic matter, thereby creating sheltered biodiversity hubs in otherwise harsh coastal environments. As transient features, the formation and eventual destruction of PMLs serve as a high-resolution proxy for the rapid paraglacial adjustment of polar coastlines.

Received: 04 Mar 2026 – Discussion started: 18 Mar 2026

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Zofia Alicja Owczarek, Oskar Kostrzewa, Wojciech Piskorski, and Mateusz C. Strzelecki

Status: final response (author comments only)

RC1:
'Comment on egusphere-2026-1226', Anonymous Referee #1, 21 Apr 2026
General comments

This is a well-written paper that highlights the emergence of Paraglacial Moraine Lagoons (PMLs) and their role within the glacier–fjord/sea system in Svalbard. These features were identified using a multi-method GIS approach, including DSAS, which produced retreat-rate data and a series of quantifiable maps. Although PMLs are rapidly changing features (on geomorphic timescales), they represent an interesting component of the Svalbard landscape, and their full impact on ecological and food-web systems remains understudied. The paper presents a model of PML evolution since the Little Ice Age (LIA).
I was, however, somewhat confused by the authors’ definition of what constitutes a PML. The authors state that they analyse a complete set of 14 PMLs across Svalbard, but further clarification is needed regarding how these features are defined. This may seem basic, but are the authors assuming that PMLs form only proximal to the glacier terminus? There is geomorphic evidence of small “lagoons” forming on one side of the proglacial environment but not the other. Based on the authors’ descriptions, these might also be classified as PMLs, since they are associated with moraines. This only became clearer in lines 267–270. I strongly suggest adding an explanatory definition earlier in the paper (around line 65), or moving lines 267–270 to the Introduction.
Section 5.3

I understand the authors’ argument that PMLs may act as refugia for ecological and fjord food-web systems, and this is likely correct. However, this section is currently too vague. If the authors wish to retain it, it requires further development. For example, they could discuss specific components of the food web that have been altered or established as a direct consequence of PML formation (with appropriate citations). Is there evidence of benthic species establishing themselves after PML formation? Alternatively, do the authors consider the transient nature of PMLs too rapid for species establishment? If so, which species? Without clear empirical evidence, this discussion remains speculative.
It may also be worth considering moving this section to the end of the paper and framing it as an area for future research. In its current form, it appears somewhat disconnected and disrupts the overall flow.
There should also be a comparison between the authors’ calculated glacier retreat rates and previously published retreat rates for the same glaciers (where available). How do these values compare, and what might explain any differences? This could be incorporated into Section 4.2.

Specific comments
Figures 2–7:

While I understand the authors’ intention to show detailed landscape and lagoon-size changes, these figures are somewhat repetitive. It may be more effective to combine them into a single multi-panel figure (a, b, c, etc.). This would also benefit the reader by allowing easier comparison across sites.
Figure 8:

Please include the orthophoto date from NPI (presumably 2010?).
Figure 12:

It is not immediately clear from the figure what distinguishes panels E and F. Including the explanation from line 398 in the caption would improve clarity.
Table 4:

Revise the caption to define EPR and NSM. I had to refer back in the text for clarification; including this information in the caption would improve readability.
Table 5:

Consider merging this dataset with another table (e.g., Table 1) to reduce the total number of tables. Additionally, the terms “leaky” and “choked” should be explicitly defined. While their meaning can be inferred, a clear explanation is preferable. Since “leaky” is also used in line 272, a definition is necessary.
Line-specific comments
Lines 32–33: Include a quantitative estimate of Arctic warming, rather than stating “four times” alone.

Line 49: Add a date for the end of the LIA in Svalbard for clarity.

Lines 50–55: This section is unclear—does it refer to one surge event or multiple (e.g., one earlier and another in 2019–2020)? Please clarify.

Line 65: Define GLOF and LGM in full before using abbreviations. (Agreed: PML is a better abbreviation than MCPALS.)

Line 89: See general comment regarding the definition of PMLs.

Line 116: Why were both ArcGIS and QGIS used? Could the workflow have been completed within a single GIS platform?

Line 118: A note: manual vectorization can sometimes yield higher accuracy, as the operator is more aware of precision requirements.

Lines 185–188: The stated average recession rates—can these be compared with values from other studies or empirical datasets for the same sites?

Lines 346–347: The point about the absence of PMLs in models is valid. However, given their transient nature, it would be useful to assess how significant their omission is. This section would benefit from a more rigorous discussion.

Line 371: Why focus specifically on the LIA? The conceptual diagram could represent any time slice during which glacier advance occurs.

Line 367: The framework relies heavily on a single citation (Ballantyne, 2002). Additional relevant references should be incorporated throughout.

Line 400: The authors correctly note that glacier re-advances (e.g., during the LIA) can destroy lagoons. However, glacier surges—common in Svalbard—can have similar effects. This process should be included and considered throughout the paper.
Citation: https://doi.org/10.5194/egusphere-2026-1226-RC1
- AC1: 'Reply on RC1', Zofia Owczarek, 19 May 2026
  
  We would like to thank the Reviewer for the constructive and insightful comments, which have significantly helped us refine the manuscript. We have addressed all suggestions, particularly regarding the formal definition of PMLs, the framing of our ecological hypotheses, and the comparison of glacier retreat data.
  1. Definition and Placement of PML Concept
  We fully agree that an earlier definition is essential. We have moved the structural definition and geomorphological criteria of Paraglacial Moraine Lagoons (PMLs) from the Discussion to the Introduction. We now explicitly define PMLs as coastal water bodies separated from the open sea by barriers primarily composed of former push or terminal moraines, often ice-cored, deposited during recent glacier retreat. This distinguishes them from deltaic or wave-built systems. We have also clarified that while these features originate in proglacial zones, their classification depends on the moraine barrier's presence, regardless of the current proximity of the glacier terminus.
  We appreciate critique in 5.3 on Geoecology. We have removed the speculative biological claims from the Discussion to maintain the manuscript’s geomorphological focus. As suggested, we have created a new section (5.5 Perspectives and Future Research) where we frame the potential of PMLs as ecological refugia as a central hypothesis for future interdisciplinary study. Section “5.3 Potential for Geoecological Shifts” now focuses strictly on the physical shifts in habitat—specifically the transition from high-energy open coasts to sheltered, low-energy basins—that occur as a direct result of barrier formation.
  Updated Section 5.3 Potential for Geoecological Shifts
  The following section has been changed to address the Reviewer’s geoecological suggestion.
  “The formation of PMLs introduces a fundamental shift in the physical energy of the nearshore environment. By establishing a moraine barrier, these systems transform high-energy, wave-dominated open coasts into sheltered, low-energy basins. This transition significantly alters the physical template available for colonization. In Svalbard, such sheltered conditions are typically associated with increased retention of fine-grained sediments and organic matter, which are otherwise flushed into the deeper fjord (Kavan and Strzelecki, 2023). While the temporal window of PMLs is transient, the immediate transition from a glacial terminus to a sheltered lagoon creates a unique brackish-water habitat. These geomorphological changes suggest that PMLs may function as temporary biodiversity centres, though empirical evidence regarding the specific rate of benthic species establishment or the role of these lagoons as stopover sites for migrating fauna remains to be gathered.”
  Updated Section 5.5: Perspectives and Future Research
  The following section has been added to the end of the Discussion to address the Reviewer’s suggestion for a future-oriented framing of the ecological and physical uncertainties:
  “The identification of Paraglacial Moraine Lagoons (PMLs) as a distinct landform category opens several new avenues for Arctic coastal research. Because these features represent a transient state in the paraglacial landscape cycle, their future evolution will likely serve as a high-resolution indicator of the pace of Arctic coastal reorganization. However, fully decoding the role of PMLs in the changing Arctic requires a shift toward integrated, interdisciplinary studies that bridge the gap between geomorphology, cryospheric science, and marine ecology:
  A critical uncertainty remains regarding the internal structure of PML barriers, necessitating collaboration between geomorphologists and geophysicists. Since many terminal moraines in Svalbard are known to be ice-cored, rising Arctic temperatures may trigger internal degradation through thermo-erosion and settlement. This could lead to catastrophic barrier failure and breaching, independent of surface wave action. Future research utilizing Ground Penetrating Radar (GPR) or electrical resistivity tomography is needed to quantify the volume of ground ice within these barriers and predict their vulnerability to sudden structural collapse.
  The function of these basins as low-energy traps suggests a major opportunity for paleoenvironmental reconstruction. PMLs likely contain undisturbed, high-resolution sedimentary records of post-Little Ice Age environmental change that are often erased on high-energy open coasts. Extracting these site-specific insights into past glacier retreat and meltwater fluctuations requires an interdisciplinary approach combining sedimentology with biogeochemical investigations to quantify the potential for these lagoons to sequester terrestrial organic carbon before it reaches the deep ocean.
  The physical transition from high-energy open coasts to sheltered, brackish-water basins create a unique template for colonization, raising a fundamental question for marine biologists regarding the successional window of these systems. It remains unknown if the transient lifespan of a PML—often only decades to a few centuries—is sufficient for the establishment of stable benthic communities and mature food webs. Interdisciplinary efforts are required to investigate whether these lagoons provide critical refugia for species moving northward due to "atlantification," or if their rapid geomorphological evolution makes them too ephemeral for successful biological succession.
  Finally, large-scale climate and oceanographic models must account for the geomorphological "pause" created by PML formation. By trapping coarse glaciogenic material that would otherwise be lost to the shelf or deep sea, PMLs fundamentally alter the sediment budget of glaciated coasts. Integrating these landforms into regional sediment transport models is essential for coastal managers and oceanographers to avoid miscalculating the volume of material delivered from land to sea in a warming Arctic.”
  
  Reviewer Specific comments
  RC1: Figures 2–7:
  
  While I understand the authors’ intention to show detailed landscape and lagoon-size changes, these figures are somewhat repetitive. It may be more effective to combine them into a single multi-panel figure (a, b, c, etc.). This would also benefit the reader by allowing easier comparison across sites.
  Response: Thank you for this comment. The convention we have adopted for this section is to present a fragment of text followed with a corresponding illustration. We would like it to stay that way.
  RC1: Figure 8:
  
  Please include the orthophoto date from NPI (presumably 2010?).
  Response: Thank you for this comment. We added information about the dates. A, B, E – 2010; C, D – 2011; F, G, H - 2009 .
  RC1: Figure 12:
  
  It is not immediately clear from the figure what distinguishes panels E and F. Including the explanation from line 398 in the caption would improve clarity.
  Response: Thank you for your comment. To clarify the differences between the stages, we have added descriptions for each stage directly onto the graph.
  RC1: Table 4:
  
  Revise the caption to define EPR and NSM. I had to refer back in the text for clarification; including this information in the caption would improve readability.
  Response: Thank you for pointing that out. We added the information about EPR (End Point Rate) and NSM (Net Shoreline Movement) in the caption of the figure.
  RC1: Table 5:
  
  Consider merging this dataset with another table (e.g., Table 1) to reduce the total number of tables. Additionally, the terms “leaky” and “choked” should be explicitly defined. While their meaning can be inferred, a clear explanation is preferable. Since “leaky” is also used in line 272, a definition is necessary.
  Response: Thank you for your suggestion. However, we decided that presenting this data in a separate table would be better. Please note that each table presents different data; therefore, combining data on the lagoon’s openness with, for example, its surface area would break with established convention. We have added an explanation regarding the morphological types of lagoons “Temporal changes in lagoon openness. Closed – a closed lagoon, with only a temporary connection to the sea; choked – single-inlet lagoons; restricted – two-inlet lagoons; leaky – lagoon with three and more inlets (Kjervfe, 1994)”.
  
  Line-specific comments
  RC1: Lines 32–33: Include a quantitative estimate of Arctic warming, rather than stating “four times” alone.
  Response: Thank you for your feedback. However, we have determined that this term better captures the nature of Arctic amplification. For more information, readers are referred to the relevant literature.
  RC1: Line 49: Add a date for the end of the LIA in Svalbard for clarity.
  Response: Thank you for noticing this. We have added the information that the end of the Little Ice Age in Svalbard is dated to the early 20th century.
  RC1: Lines 50–55: This section is unclear—does it refer to one surge event or multiple (e.g., one earlier and another in 2019–2020)? Please clarify.
  Response: Thank you for pointing out this ambiguity. We have revised this paragraph to clearly distinguish between two separate historical episodes of glacier advance and their contrasting impacts on the lagoon's morphology. The first event refers to the historical glacier surge (early 20th century) that originally formed the lagoon by creating a natural barrier, as documented by Zagórski et al. (2012). The second event refers to the recent 2019–2020 surge/readvance of Recherchebreen, which led to rapid delta growth and a subsequent reduction in the lagoon's surface area, as documented by Kavan et al. (2024).
  Now, in the text, is states “The initial development of the paraglacial lagoon – Recherchelaguna – was documented by Zagórski et al. (2012) and was associated with a rapid glacier surge that created a natural dam from emerging deltas, enabling the rapid establishment of a water body at the glacier front. Decades later, following a new surge and the readvance of the marine-terminating Recherchebreen between 2019 and 2020, the formation of a massive delta was observed once again in front of the glacier meltwater outlet, this time significantly reducing the lagoon’s surface area (Kavan et al., 2024)“.
  RC1: Line 65: Define GLOF and LGM in full before using abbreviations. (Agreed: PML is a better abbreviation than MCPALS.)
  Response: Thank you for pointing that out. However, we have revised the text, and the abbreviations no longer appear in this section. The new text is as follows: “Although the preliminary concept of these landforms was introduced previously under different terminology (Owczarek, 2025 – MCPALS from moraine-controlled paraglacial lagoon systems), we now advocate adopting PML as the standard geomorphological nomenclature”.
  RC1: Line 89: See general comment regarding the definition of PMLs.
  Response: Thank you for this comment. We have refined the definition of PML. The exact change is described above.
  RC1: Line 116: Why were both ArcGIS and QGIS used? Could the workflow be completed within a single GIS platform?
  Response: The two GIS software programmes were used solely because the team members prefer different programmes. However, all the analyses can be carried out using a single programme.
  RC1: Line 118: A note: manual vectorization can sometimes yield higher accuracy, as the operator is more aware of precision requirements.
  Response: Thank you for this note, we appreciate it. We also believe that manual vectorisation has its advantages, although it is, unfortunately, time-consuming.
  RC1: Lines 185–188: The stated average recession rates—can these be compared with values from other studies or empirical datasets for the same sites?
  Response: Thank you for this valuable suggestion. While a single, unified database tracking long-term coastal glacier recession specifically for all fourteen of our studied lagoon sites does not exist, we have cross-referenced our calculated retreat rates with broader regional glacier inventories (Li et al., 2025) and published site-specific studies to validate our findings.
  Our calculations show good agreement with available literature. For instance, our data for Eidembreen (a calculated total retreat of over 3.1 km since 1936) closely aligns with the independent findings of Šiaulys et al. (2026), who noted a landward retreat of approximately 3 km between 1936 and 2023. On a regional scale, the high retreat rates we quantified for major systems like Deltabreen (75.5 m per year) and Eidembreen (36.1 m per year) are entirely consistent with the accelerated multi-decadal frontal recession rates and mass loss trends documented across the Svalbard archipelago by Geyman et al. (2022) and the historical datasets maintained by the Norwegian Polar Institute (NPI).
  RC1: Lines 346–347: The point about the absence of PMLs in models is valid. However, given their transient nature, it would be useful to assess how significant their omission is. This section would benefit from a more rigorous discussion.
  Response: Thank you for this suggestion. However, we consider the analysis we have presented to be sufficient. In that section, we highlighted the role of the PML in the paraglacial sedimentary cascade as a sedimentary reservoir. We also pointed out that this mechanism disrupts the standard transport of water and sediments from land directly to the sea, which stands in opposition to the generally accepted model of Arctic coast functioning, which assumes direct transport of water and sediments to the sea.
  RC1: Line 371: Why focus specifically on the LIA? The conceptual diagram could represent any time slice during which glacier advance occurs.
  Response: Thank you for this comment. Our framework is based on specific data and forms from the LIA; therefore, the LIA is a natural point of reference for us in creating a conceptual model for PML development.
  RC1: Line 367: The framework relies heavily on a single citation (Ballantyne, 2002). Additional relevant references should be incorporated throughout.
  Response: Thank you for this suggestion. We updated the text with the appropriate references “Their buffering role aligns with paraglacial slope readjustment and sediment redistribution after glacier retreat (Ballantyne, 2002; Zagórski et al., 2012; Strzelecki et al., 2020; Kavan et al., 2024)”.
  RC1: Line 400: The authors correctly note that glacier re-advances (e.g., during the LIA) can destroy lagoons. However, glacier surges—common in Svalbard—can have similar effects. This process should be included and considered throughout the paper.
  Response: Thank you for pointing that out. We consider glacier surge to be just one example of the glacier re-advance, which is shown in the diagram as point G. We have added information about the surge to the text to make it clearer. “However, glacier re-advances (also glacial surge) can destroy lagoons, as likely occurred during LIA glacier expansions (Fig. 12G).”
  
  Citation: https://doi.org/10.5194/egusphere-2026-1226-AC1
RC2:
'Comment on egusphere-2026-1226', Sergej Olenin, 21 Apr 2026
General Evaluation
This manuscript presents a timely and well-executed study of emerging coastal landforms in Svalbard, defined as Paraglacial Moraine Lagoons (PMLs). The use of a multi-decadal dataset (1936–2024) combined with geomorphological and the Digital Shoreline Analysis System (DSAS)-based shoreline analysis provides a strong empirical foundation. The identification of two contrasting evolutionary pathways (erosional vs stabilizing) and the proposed conceptual model are particularly valuable contributions.
Overall, the manuscript is scientifically sound, novel, and relevant, and it has clear potential for publication. However, several aspects require clarification and refinement, particularly regarding the definition and novelty of PMLs, the strength of some interpretations, and the depth of the Discussion.
Recommendation: minor revision
Specific Comments
Conceptual clarity

The introduction of PMLs is a key contribution, but the definition remains somewhat broad. The manuscript would benefit from:
a clearer diagnostic definition (criteria for classification),

a stronger distinction from other lagoon types (e.g. deltaic or moraine-dammed systems),

a more cautious framing of PMLs as a “formalized” rather than entirely “new” landform type.

Interpretation of ecological and sedimentary roles

Statements regarding PMLs as biodiversity hubs and sediment/carbon sinks are interesting but appear somewhat speculative based on the data presented. These claims should be either softened or more clearly framed as hypotheses for future research, and, where possible, supported by relevant recent studies on Svalbard lagoons.
Results

The Results section is strong and represents one of the main strengths of the paper. The quantified expansion of lagoon area and the clear documentation of morphodynamic variability are particularly convincing. Some descriptive parts could be slightly shortened.
Discussion

The Discussion would benefit from:
stronger synthesis (clear hierarchy of controlling processes),

reduced repetition of Results,

broader contextualisation (e.g. relevance to other Arctic regions),

tighter integration of the conceptual model.

Minor points

Simplify long sentences for clarity.

Avoid repetitive phrasing (e.g. “it is worth noting that”).

Ensure consistent terminology throughout.

Conclusion
This is a strong and original contribution to Arctic coastal geomorphology. With clearer conceptual framing and slightly more cautious interpretation, the manuscript will be suitable for publication and likely to have significant impact.
Citation: https://doi.org/10.5194/egusphere-2026-1226-RC2
- AC2:
  'Reply on RC2', Zofia Owczarek, 19 May 2026
  We would like to thank Reviewer 2 for their positive evaluation of the manuscript and for recognizing the value of our multi-decadal dataset and the proposed evolutionary pathways for PMLs. We are particularly encouraged that the reviewer finds the study timely and scientifically sound. In response to the reviewer’s overarching concerns, we have undertaken a comprehensive revision of the manuscript:
  We have revised the Introduction and Discussion to more clearly define the structural and genetic criteria that distinguish Paraglacial Moraine Lagoons (PMLs) from standard Arctic lagoons (e.g., those sheltered by deltaic or wave-built sandy barriers). We have emphasized that the novelty lies in the moraine-core foundation, which dictates a unique set of morphodynamics and a distinct paraglacial lifespan.
  We have refined our analysis in Section 4 to ensure that our interpretations of shoreline change (DSAS) and glacier retreat are more explicitly linked to the underlying data, avoiding over-generalization where local factors (e.g., bathymetry) play a dominant role.
  Following the reviewer’s guidance, we have expanded the Discussion to include a more nuanced look at the role of these lagoons as sedimentary buffers. We have also added a new section (5.5 Perspectives and Future Research) to address the interdisciplinary implications of our findings, which we believe adds the depth and "broader impact" requested.
  We believe these refinements have significantly strengthened the manuscript’s scientific narrative.
  
  Reviewer Specific Comments
  Conceptual clarity. The introduction of PMLs is a key contribution, but the definition remains somewhat broad. The manuscript would benefit from:
  a clearer diagnostic definition (criteria for classification),
  
  a stronger distinction from other lagoon types (e.g. deltaic or moraine-dammed systems),
  
  a more cautious framing of PMLs as a “formalized” rather than entirely “new” landform type.
  
  Response: We appreciate the Reviewer’s guidance on the conceptual framing of the PML term. We agree that "formalizing" the nomenclature of an existing but under-described phenomenon is a more scientifically accurate approach than claiming the discovery of an entirely "new" landform.
  To address these points, we have revised the manuscript as follows:
  We have added a specific set of classification criteria in Section 1 (Introduction) and Section 3 (Methods). To be classified as a PML in this study, a system must meet three criteria: (1) its seaward barrier must be primarily composed of landforms of glacial origin (terminal or lateral moraines); (2) the basin must have been formed as a direct result of post-LIA glacier retreat; and (3) the moraine must remain the dominant control on the lagoon’s hydrodynamics.
  We have strengthened the distinction between PMLs and other common systems. Unlike deltaic lagoons (governed by fluvial sediment flux) or spit-governed lagoons (governed by longshore drift), the stability of a PML is dictated by the mechanical and thermal properties of the moraine itself (e.g., ice-core presence). We also clarify the difference from moraine-dammed proglacial lakes, which lack marine connectivity and tidal exchange.
  Throughout the text, we have shifted the language from a "new" landform to a "formalized landform category." This acknowledges that while these features have long been observed, they have lacked a standardized geomorphological definition and a systematic analysis of their unique evolutionary trajectories.
  
  RC2: Interpretation of ecological and sedimentary roles
  Statements regarding PMLs as biodiversity hubs and sediment/carbon sinks are interesting but appear somewhat speculative based on the data presented. These claims should be either softened or more clearly framed as hypotheses for future research, and, where possible, supported by relevant recent studies on Svalbard lagoons.
  Response: Thank you for the suggestion which was also expressed by the Reviewer 1.
  
  We agree that our discussion of geoecology was speculative in the absence of direct biological sampling. We have followed the suggestion to move the more exploratory and speculative aspects of this discussion to the new "5.5 Perspectives and Future Research" section at the end of the paper. There, we frame the potential of PMLs as ecological refugia as a key hypothesis for future interdisciplinary studies. We have significantly shortened Section 5.3 now entitle “Potential for Geoecological Shifts” in the Discussion, focusing strictly on the physical shifts in habitat—such as the creation of low-energy, brackish environments—that occur as a direct geomorphological consequence of moraine-barrier formation.
  
  RC2: Results
  The Results section is strong and represents one of the main strengths of the paper. The quantified expansion of lagoon area and the clear documentation of morphodynamic variability are particularly convincing. Some descriptive parts could be slightly shortened.
  Response: Thank you for the comment. We have shortened the descriptions in this section in a few places.
  
  RC2: The Discussion would benefit from:
  stronger synthesis (clear hierarchy of controlling processes),
  
  reduced repetition of Results,
  
  broader contextualisation (e.g. relevance to other Arctic regions),
  
  tighter integration of the conceptual model.
  
  Response: Thank you for these constructive suggestions to improve the depth and structure of our Discussion. We have revised the text to ensure a more robust synthesis and broader scientific impact. We appreciate this point and have revised Section 5.1 to clarify the primary geomorphological thresholds. We explicitly state that the overarching control is the structural transition of the "parent" glacier from marine-terminating to land-terminating. This transition triggers a fundamental shift from marine-dominated forcing (scouring, calving waves) to terrestrial-dominated forcing (fluvial sediment delivery via proglacial rivers). While secondary factors—such as local bathymetry, fetch, and storm frequency—introduce localized variability, we have now structured the discussion to clearly reflect this primary glacio-marine vs. terrestrial hierarchy.
  We appreciate the reviewer’s diligence regarding text economy. Our intention in including specific metrics in the Discussion was not to repeat the Results section, but to provide immediate empirical support for the geomorphological mechanisms being discussed. However, to address your concern, we have thoroughly audited the Discussion and removed redundant numerical values, keeping only the essential benchmarks necessary to substantiate our comparative arguments. We believe this has significantly streamlined the narrative flow.
  While systematic, multi-site studies focusing explicitly on moraine-controlled lagoon systems (PMLs) are currently lacking in other Arctic sectors, we agree that the manuscript benefits from a broader circum-Arctic context. We have expanded the text to discuss how these paraglacial mechanisms apply to other rapidly deglaciating, ice-cored coastal landscapes, such as parts of Greenland, the Canadian Arctic Archipelago, and Alaska. We have also expanded our comparisons of shoreline erosion rates to position Svalbard's PML dynamics within the wider spectrum of Arctic coastal change (e.g., contrasting them with thermo-abrasional permafrost coasts).
  To ensure a tighter integration of our conceptual model within the broader narrative, we have restructured the final part of the Discussion. Rather than presenting the model as an isolated component, we have woven its core stages directly into the synthesis of the two divergent evolutionary trajectories (the erosional-fragmenting pathway vs. the stabilizing-isolating pathway). This allows the conceptual figure to serve as a direct visual summary of the processes discussed throughout Section 5.
  
  Minor points
  RC2:
  Simplify long sentences for clarity.
  
  Avoid repetitive phrasing (e.g. “it is worth noting that”).
  
  Ensure consistent terminology throughout.
  
  Response: Thank you for your suggestions. We have made the necessary corrections in this regard.
  
  RC2: Conclusion. This is a strong and original contribution to Arctic coastal geomorphology. With clearer conceptual framing and slightly more cautious interpretation, the manuscript will be suitable for publication and likely to have a significant impact.
  Response: Thank you for this comment.
  
  Citation: https://doi.org/10.5194/egusphere-2026-1226-AC2

Zofia Alicja Owczarek, Oskar Kostrzewa, Wojciech Piskorski, and Mateusz C. Strzelecki

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https://doi.org/10.5194/egusphere-2026-1226-supplement

Zofia Alicja Owczarek, Oskar Kostrzewa, Wojciech Piskorski, and Mateusz C. Strzelecki

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As Arctic warming speeds glacier retreat, new coastal landscapes emerge. Paraglacial Moraine Lagoons (PMLs), formed by Little Ice Age moraines, now cover 56 % of Svalbard's lagoons, triple their 1930s area. We propose a model of their evolution: erosion by marine forces or stabilization by sediment infill, functioning as sediment traps and biodiversity refuges.


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