the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Sep 2025
Evidence and interpretation of non-linear recession behaviour in a periglacial cliff at Port Foster, Deception Island (South Shetlands, Antarctica)
Abstract. Cliff recession in periglacial coastal environments is highly sensitive to climate-driven changes in temperature, sea ice, and permafrost dynamics. While previous studies have predominantly relied on linear models to describe shoreline retreat, these methods often fail to capture the non-linear, episodic, and threshold-driven nature of coastal erosion in cold regions. Moreover, the scarcity of high-resolution, long-term datasets in polar regions, particularly in Antarctica, has limited the development of predictive models tailored to these dynamic systems. This study aims to improve the understanding of long-term cliff recession patterns in periglacial environments by applying advanced non-linear statistical modelling to a multitemporal dataset. Focusing on the coastal bluffs of Port Foster, Deception Island (South Shetlands, Antarctica), we examined geomorphological changes over a 66-year period (1956–2022), using a unique combination of historical aerial photographs and high-resolution satellite imagery. Photogrammetric pre-processing, orthorectification, and manual digitisation of reference lines were integrated into a transect-based statistical analysis framework. The study applied both linear and non-linear least squares regression models – quadratic and sigmoidal – to reconstruct spatial-temporal erosion trends, with uncertainty-weighted parameters incorporated into the estimation. Results reveal a distinct shift from quasi-stable to accelerated recession after 2000, particularly in areas exposed to dominant marine and thermal forcing. Linear models underestimated these trends, while sigmoidal logistic models more accurately identified inflection points in erosion rates. Maximum recession rates reached up to 5 m/year in the central bluff segment. The findings underscore the importance of integrating non-linear modelling into coastal monitoring and management frameworks, especially in vulnerable and data-scarce polar environments. This approach provides a more realistic understanding of periglacial coastal dynamics and highlights the critical need for adaptive strategies to address climate-induced instability near strategic infrastructure such as research stations.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-3269', Anonymous Referee #1, 24 Dec 2025
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AC1: 'Reply on RC1', carlos paredes bartolome, 04 Jan 2026
We would like to sincerely thank the anonymous reviewer for their careful and insightful evaluation of our manuscript. We deeply appreciate the time, effort, and constructive nature of the comments provided. The feedback received is highly valuable for improving the clarity, scope, and scientific strength of the study.
We understand that the review process remains ongoing (until 4 January 2026) and that additional reports may still be received. Therefore, this document presents a provisional and reflective response, outlining how we intend to address the reviewer’s observations in the next revision stage, once all comments have been received.
We respectfully acknowledge the reviewer’s concern regarding the manuscript’s fit within The Cryosphere’s scope. Nonetheless, we would like to emphasise that the journal explicitly welcomes studies addressing permafrost and periglacial processes, cryosphere–climate interactions, and environmental responses to climatic change—themes that are central to our work. The manuscript provides a quantitative and data-oriented characterization an modeling of periglacial cliff retreat in an Antarctic coastal setting, combining multi-temporal photogrammetric analysis (1956–2022) and non-linear statistical approaches. These aspects directly contribute to The Cryosphere’s mission to advance understanding of the physical processes governing cryospheric change, particularly in regions underrepresented in Antarctic permafrost studies. Furthermore, the results have direct implications for infrastructure safety and environmental management near the Spanish and Argentine research stations located at Port Foster, Deception Island—an issue of practical and scientific relevance that aligns with the journal’s interest in cryospheric processes with societal implications.
We accept and fully acknowledge the reviewer’s observation regarding the limited spatial extent (1.5 km) of the analysed coastal segment. However, this scale reflects the spatial range for which high-quality, consistent, and geometrically accurate imagery was available, covering more than six decades. Crucially, the study area is located diametrically opposite the volcanic centres affected by the 1967–1970 eruptions, ensuring that the observed coastal evolution is less affected by volcanic disturbances and instead possibly governed primarily by periglacial, geomorphological, and marine processes. This provides a stable and representative sector for isolating climate-driven erosion mechanisms, according to the available data time scale—a key objective of the research. While modest in size, this high-resolution, data-constrained approach strengthens the reliability of the results and establishes a robust methodological framework that can be extended to larger sectors of Deception Island and other Antarctic coasts in future works.
Improvement and Planned Revisions
We greatly appreciate the reviewer’s detailed and constructive recommendations, which will guide the forthcoming revision of the manuscript once all feedback has been consolidated. The following points summarise our planned improvements:
Broadened Antarctic Context – The Introduction and Study Area sections will be expanded to integrate regional climate analyses, permafrost studies, wave and storm dynamics, and Antarctic Peninsula environmental trends.
Mechanistic Interpretation of Post-2000 Acceleration – The revised Discussion will incorporate some hypotheses linking the observed inflection point in retreat rates to possible regional temperature anomalies, sea-ice decline, and/or changing wave energy regimes.
Quantitative Model Comparison – We plan to re-explain explicit comparative statistics (STDEs, R2, AICc, and include confidence intervals) for linear, quadratic, and sigmoidal regressions to strengthen claims regarding model performance. We will refine our uncertainty quantification to include shoreline position and rate uncertainties, complementing the georeferencing and photogrammetric accuracy assessments.
Improved Figure Integration and Clarity – We will try to reorganise figures in the results section to merge related temporal and spatial patterns, improving readability and scientific coherence.
The Discussion will include a new subsection on implications for coastal stability and risk management concerning nearby research facilities.
We thank the reviewer once again for their thoughtful and valuable comments, which we regard as an essential opportunity to strengthen the manuscript. We believe that, with the forthcoming revisions, the manuscript will offer a scientifically rigorous and well-contextualised contribution to understanding Antarctic periglacial coastal dynamics—a topic of growing importance within the cryospheric sciences. These planned revisions will collectively enhance the manuscript’s scientific depth, its alignment with The Cryosphere’s editorial standards, and its contribution to Antarctic periglacial research.
Sincerely yours.
Citation: https://doi.org/10.5194/egusphere-2025-3269-AC1
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AC1: 'Reply on RC1', carlos paredes bartolome, 04 Jan 2026
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RC2: 'Comment on egusphere-2025-3269', Jan Kavan, 29 Jan 2026
Review of „Evidence and interpretation of non-linear recession behaviour in a periglacial cliff at Port Foster, Deception Island (South Shetlands, Antarctica)“ by Paredes et al.
The paper describes long-term erosion of a 1.5 km long section of cliff between the two research stations on Deception Island. I appreciate the topic itself as coastal processes in Antarctica are only rarely studied and long-term observations are of great value. On one hand, the paper is well-structured and uses well-developed sophisticated methods. On the other hand, I definitely miss explanation and interpretation of the results presented. What are the factors affecting the reported nonlinear behaviour and spatial heterogeneity of the erosion? There are a few ideas in the discussion but these are not based on real data. For example, you stated that the acceleration of erosion after 2000 is related to increasing warming of atmosphere – do you have any data to prove it? How does this goes together with the cooling trend reported around the Antarctic Peninsula (e.g. https://www.sciencedirect.com/science/article/pii/S0048969716327152)
Can you add these background data to support your findings? Also can you explain why the erosion is so spatially variable? Is there any effect of the research stations on both sides of the study area – there might be certain man made structures to prevent the erosion for example...
The paper is in my opinion very much focused on the methods itself and lack context – I dont see any discussion of the reported erosion rates, comparison to other sites around Antarctica or Arctic. Is the erosion rate low or high? I would also add some data on current wind conditions (wind speed/direction) – it looks that the site is well sheltered from the prevailing SW winds, so the effective wave erosion should me minimal. What is then the primary cause of cliff erosion? Is it really a coastal process or just permafrost degradation/thawing? Both spatial and temporal variability of the reported erosion suggest that permafrost degradation itself might be the main driver of the erosion... Also concentration of the erosion to the vicinity of the river mouth suggests more thermal degradation of the permafrost than mechanical erosion.
Perhaps a detailed geological conditions of the cliff might help in interpretation as different types of rocks have obviously different thermal properties and can be differently susceptible to erosion.
Overall, I appreciate the detailed description and sophisticated methods applied, but I lack some more robust intepretation and background data supporting the interpretation.
I hope my suggestions help to improve the paper!
With regards,
Jan
Citation: https://doi.org/10.5194/egusphere-2025-3269-RC2 -
EC1: 'Comment from the editor on egusphere-2025-3269', Heather Reese, 30 Jan 2026
Please carefully consider and address both reviewers comments to make this a more robust article.
Citation: https://doi.org/10.5194/egusphere-2025-3269-EC1
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Major Comments
This manuscript is a technically sound photogrammetric reconstruction of cliff recession at Port Foster over 66 years. The manuscript is well executed and methodologically coherent. However, in my opinion, the work does not fit The Cryosphere standards for several fundamental reasons that extend beyond revision. The manuscript lacks novelty and significance to meet the journal’s standards.
The 1.5 km study segment is too geographically isolated for a journal emphasising cryospheric processes at regional to global scales. While the location adjacent to BAD and BAEGC research stations provides practical relevance for infrastructure risk assessment, this should be better emphasised in the introduction and study area chapters.
The analysis could reasonably span a larger coastal area, such as the whole island, to enable broader insights into the South Shetland Islands’ coastal dynamics, making it more Antarctic coastal science. In this way, it remains rather isolated.
Coastal retreat accelerated post-2000 is a major finding, but the manuscript does not explain why – this is, for me, the main scientific flaw. Why does the inflexion point occur specifically around 2000? What climate threshold or permafrost property change drives this transition?
“Sigmoidal curves fit better than linear models” (L23-24) is pattern recognition, not mechanism understanding. Regional warming is cited (0.54°C/decade, L145; recent average -1.1°C, L148), yet climate forcing is never mechanistically linked to observed retreat trends. Hypotheses missing that could improve the manuscript are: (1) time-series correlations between temperature anomalies and retreat rates; (2) sea ice extent variability affecting wave fetch and storm frequency; (3) differentiation of thermal versus mechanical driver contributions.
L641-644: “This study advances the understanding of Antarctic periglacial coastal recession by: … (ii) validating sigmoidal models as superior alternatives for characterising episodic erosion” – this claim is not justified by any evidence. Missing: correlation values for linear versus quadratic versus sigmoidal models, for example, among other possibilities like confidence intervals or statistical significance tests. For a paper claiming model superiority, the absence of comparative statistics is worrying, and the central claim is not properly justified without this evidence.
Temporal bias: Dense post-2000 sampling could create an artificial acceleration trend.
Absent but could improve: sensitivity testing, refitting the sigmoidal model using only 1956-2000 data to predict 2001-2022, and assessing how inflexion point timing shifts with gap interpolation variations.
The introduction reads like an Arctic coastal manuscript, with several references to Arctic-specific studies, while there is minimal Antarctic-specific content. Missing are Antarctic Peninsula climate studies, wave-forcing dynamics, storminess patterns, and sea-ice loss relevant to the Antarctic Peninsula and South Shetland Islands region.
The discussion, while generally well performed, lacks a marine forcing analysis, such as wave energy, storm surge, and tidal dynamics, which should be substantively addressed, even if data are limited, through reasonable assumptions grounded in regional oceanographic literature.
The 5 m transect spacing (implied in methods) for a 1.5 km study area is coarse. For bluff proxy analysis with low morphodynamic complexity and sinuosity compared to waterline proxies, denser spacing (1-2 m) is necessary to identify adequate spatial variability. Coarse spacing may artificially favour non-linear model performance due to spatial smoothing effects.
Uncertainty assessments address georeferencing errors (Eq. 1, L334-337) but omit shoreline position uncertainty and shoreline change rate uncertainty independent of imagery quality. It is standard and necessary for coastal analysis studies to include shoreline position or shoreline change trends uncertainty. The uncertainty equations also appear overly complex for this study's scope.
Discussion could incorporate and project the risks for the scientific bases, which would give more significance to the manuscript
Section 5.1 (L383-420) is best fit as a Methods subchapter; it is not a result.
Minor Comments
L60, L63: Acronyms not defined at first use.
L68: The term bluff top or bluff edge is more commonly used than bluff crest. Consider using Bluff top or bluff edge
L82: Roland et al. 2024 cited but absent from the reference list.
L156: “wave heights up to 1.165 m“, while other values have two decimal places, keep consistency.
L170: Vieira et al. (2008) cited for permafrost thickness, but broader Antarctic permafrost dynamics literature is underrepresented, and there is a need for better context.
L178: "Transient dejection cones" terminology is questionable. Dejection cones typically refer to alluvial fans. Consider "erosion cones," "washout cones," or "fan-shaped gully complexes."
L184: In general, I do not agree with the term coastal recession applied in the manuscript. Coastal retreat, or more specifically, coastal erosion, should be used.
3.1. Archive aerial imagery subchapter: several details not relevant to the manuscript can be cut from the text (captured altitudes, exposure ranges, DPIs). Table 1 details of scale, camera model, focal length, and number of photos are enough
L273-276: 37 GCPs identified as "immobile rocky outcrops." Given volcanic activity (eruptions in 1967, 1969, and 1970; L134-135), GCP stability over 66 years is merely an assumption.
L279: Satellite optical images downloaded from Google Earth Pro??? Google Earth Pro or Google Earth Engine?
Some figures in the results section could be combined to join related temporal and spatial patterns, improving readability and focusing attention on key findings.
L484-493: Shoreline change rates should have uncertainty values for the periods (example: 0.50 +- 0.16 m/y)