the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Nov 2025
Svalbard glacier calving front retrievals during the 1960s and 1970s from archived Landsat and declassified intelligence satellite photographs
Abstract. We retrieved calving front locations of 171 Svalbard tidewater glaciers from archived satellite imagery. We used early Landsat images from 1976–1978 as well as declassified intelligence satellite photographs from 1962–1963. To support the geophysical analysis of these calving fronts, we also used historical aerial images from 1936–1938. During our study period between 1936 and 1978, we estimate an average glacier retreat rate of 26.3 m yr-1. This corresponds to an approximately 1 km of average retreat of Svalbard tidewater glaciers during this period. By multiplying the retreats by the glaciers' widths, we estimate the cumulative area loss rate to be 16.0 km2 yr-1 (R2=0.94), which is slightly lower than the estimates found in the existing literature for the periods 1985–2023 and 2000–2020. Looking at individual glaciers, we identify and discuss 15 significant advance events. For four of them, our study provides additional information to current knowledge. We have discovered one undocumented surge – we show evidence that Emmabreen has surged between 1936 and 1963. We have also narrowed down the time windows of two previously known surges: the surge of Allfarvegen to between 1976 and 1978 (previously reported to have happened between 1970 and 1980), and the surge of Stonebreen to between 1936 and 1963 (previously reported between 1936 and 1971). We also show that Schweigaardbreen and Fonndalsbreen have advanced 400 and 541 meters, respectively, between 1938 and 1976. We discuss the potential future uses of our dataset, consisting of georeferenced satellite images used in our study as well as digitized calving fronts, which is freely available for future research.
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Status: final response (author comments only)
- CC1: 'Comment on egusphere-2025-5249', Harold Lovell, 27 Nov 2025
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RC1: 'Comment on egusphere-2025-5249', Anonymous Referee #1, 12 Jan 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-5249/egusphere-2025-5249-RC1-supplement.pdf
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RC2: 'Comment on egusphere-2025-5249', Anonymous Referee #2, 17 Jan 2026
This manuscript presents a historical reconstruction of calving front positions for 171 tidewater glaciers in Svalbard over the period 1936–1978, based on a combination of historical aerial photographs, early Landsat MSS imagery, and declassified KH-5 ARGON satellite photographs. The extension of calving-front observations into the pre-1980 satellite, together with the public release of georeferenced imagery and digitized fronts, gives this study clear long-term value as a data resource for Svalbard glacier research.
However, the scientific contribution of the manuscript is currently not articulated as clearly as it could be. The Introduction largely reads as a chronological listing of previous studies rather than a focused synthesis that motivates why this reconstruction is needed, what specific gap it fills relative to existing datasets, and how it advances current understanding. In addition, although 171 glaciers are mapped, the manuscript lacks a clear overview figure demonstrating the spatial coverage of the dataset, which makes it difficult to fully appreciate the scope and representativeness of the work.
I also have several major concerns related to (i) the treatment and interpretation of georeferencing uncertainties, (ii) the robustness of inferred average retreat and area-loss rates given the sparse temporal sampling, and (iii) the framing of some conclusions, which in places extend beyond what the data can securely support. Addressing these issues would substantially strengthen the scientific rigor, clarity, and long-term usability of the dataset. Overall, I recommend major revision.
Major comments
1. The study relies heavily on polynomial georeferencing of KH-5 ARGON images using many ground control points (typically 100–200 per image), while explicitly abandoning a physically based orthorectification approach (Sect. 2.2.2). Although the authors justify this choice by focusing on relative calving-front positions near sea level, the implications of this decision require a more critical and transparent discussion. High-order polynomial transformations can provide a good local fit at GCPs but may introduce non-physical distortions between control points, particularly over very large scenes such as ARGON images (>500 km wide). The manuscript also acknowledges that uncertainties in 1962–1963 are especially large, yet several key interpretations (e.g. identification and timing of advances, surge attribution) rely strongly on these data. Further clarification is needed:
- Provide quantitative diagnostics of georeferencing performance (e.g. RMSE at GCPs and, if possible, spatial patterns of residuals).
- Explicitly discuss how non-uniform geometric distortions could bias centerline-based distance estimates, especially for wide or curved glacier fronts.
- Clarify whether any spatial filtering or systematic exclusion (e.g. image edges or areas affected by severe distortions) was applied, beyond individual case decisions such as Emmabreen.
Without this information, it is difficult to assess whether some detected advances or retreats can be confidently distinguished from residual geometric artefacts.
2. The manuscript reports an average retreat rate of 26.3 m yr⁻¹ between 1936 and 1978 and discusses variations within this period (Sect. 3.1, Fig. 5a). However, the effective temporal resolution is extremely limited, with only three broad observation windows (1936–1938, 1962–1963, and 1976–1978). Given this sparsity: 1) Linear trends and apparent phases such as “plateaus” or accelerations are poorly constrained. 2)The reported R² values may give a misleading impression of robustness. I suggest that the authors:
- Reframe retreat and area-loss rates explicitly as period-averaged net changes, rather than temporally resolved trends.
- Avoid interpretative language implying acceleration or deceleration unless supported by sensitivity tests.
- Emphasize net changes between observation epochs as the primary result, with trends presented only as descriptive summaries.
3. Area change is calculated as the product of frontal displacement and average glacier width (Sect. 2.5, 3.1), following Li et al. (2025). While this approach is reasonable given the data limitations, it differs fundamentally from outline-based methods used in other studies cited for comparison (e.g. Kochtitzky and Copland, 2022). Although these differences are acknowledged, the manuscript still draws relatively strong comparative conclusions (Sect. 4.1, 5). I therefore recommend that the authors more clearly separate methodological differences from physical interpretation when comparing results across studies, explicitly discuss how width variability, fjord geometry, and non-parallel retreat may bias area estimates, and consider presenting cumulative frontal length change alongside area change as a more methodologically neutral metric.
4. The identification of surge events is one of the most interesting aspects of the manuscript. However, the criteria used to distinguish surges from non-surge advances are not always clearly defined. For example, Schweigaardbreen and Fonndalsbreen are treated cautiously as advancing glaciers, whereas Emmabreen is classified as having undergone a previously undocumented surge, largely based on frontal advance magnitude and geometry. Given the long time intervals between observations, this distinction remains ambiguous. I recommend that the authors explicitly state the diagnostic criteria used to classify an event as a surge versus a non-surge advance, clarify the relative roles of frontal advance magnitude, spatial coherence, and ancillary evidence (e.g. crevasse patterns or later velocity observations), and acknowledge that, in some cases, surge classification remains uncertain given the available data. This would improve the conceptual consistency of Sect. 4.2 and help avoid over-interpretation.
Minor comments:
- Consider using the term “delineation” rather than “retrieval” consistently throughout the manuscript.
- The Abstract and Introduction would benefit from clearer separation between background, methods, and the specific contribution of this study. The Introduction (particularly Sect. 1.2) could be substantially condensed; rather than listing previous studies, it should synthesize why DISP and early Landsat data are essential for the present work.
- Use “calving-front position” rather than “locations” for consistency with common terminology.
- An overview map showing all 171 calving fronts is necessary to demonstrate the spatial coverage of the dataset.
- Clarify how many fronts are shown in Fig. 3 and how this relates to the total number of observations.
- Several statements describing “faster” or “slower” retreat (e.g. Lines 184–186) are difficult to support given the sparse time sampling and should be revised.
- Multi-panel figures (e.g. Fig. 7) are information-rich but visually dense; inset maps or simplified color schemes could improve readability.
- 2.5 notes that centerlines were digitized manually; please clarify whether a single operator performed this task and comment briefly on consistency.
- The uncertainty framework is thorough, but a concise summary table of typical positional uncertainties for each data source in the main text would aid readers.
- Please ensure that metadata in the Zenodo archive clearly document coordinate reference systems and georeferencing procedures.
Citation: https://doi.org/10.5194/egusphere-2025-5249-RC2
Data sets
Svalbard glacier calving fronts (1936-1978) Loris Danjou https://doi.org/10.5281/zenodo.16918636
Model code and software
Svalbard_calving_fronts_1936-1978_data_analysis Loris Danjou https://github.com/lorisdanjou/Svalbard_calving_fronts_1936-1978_data_analysis
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Hello authors,
Just a minor comment on one small aspect of this paper that I noticed, being familiar with the cited study:
Section 4.2.2., page 15, line 245 it is stated:
Schweigaardbreen is not documented as a surge-type glacier, but the presence of crevasse-squeeze ridge networks seen in recent aerial images (Lovell and Boston, 2017) indicates a possible misclassification.
We didn't identify crevasse-squeeze ridges at Schweigaardbreen (nor did Farnsworth et al., 2016: https://doi.org/10.1016/j.geomorph.2016.03.025). Instead, we identified a glaciotectonic composite ridge system, formed as the ice margin advances into proglacial sediments. Lovell and Boston (2017) was mainly focused on identifying these glaciotectonic moraines, which in Svalbard have a very good correlation with known surges or glaciers with other evidence of past surging (e.g. crevasse-squeeze ridges).
Cheers,
Harold Lovell