| 18 May 2026
A Decade of Monthly Frontal Ablation at 147 Tidewater Glaciers in Svalbard
Abstract. We present a novel, regional-scale monthly analysis of frontal ablation at 147 tidewater glacier basins in Svalbard from January 2015 through December 2024. A multi-temporal, deep-learning segmentation model was implemented to reduce the manual labor cost inherent to mapping 203,294 terminus positions, yielding 15,647 monthly-averaged calving fronts derived from Sentinel-1 SAR imagery. In addition, a monthly ice discharge time series is developed from the extensive ITS_LIVE velocity database, as well as regionally existing ice thickness products. To account for ice mass loss due to surface processes between the fluxgate and terminus (i.e. the glacier domain), the climatic mass balance is integrated over the domain area using monthly aggregated daily outputs from the MAR regional climate model. The result is a frontal ablation time series at an unprecedented spatio-temporal scale with 15,500 monthly estimates of frontal ablation, allowing new insights and progress towards a process understanding of frontal ablation. The mean annual frontal ablation rate across all glaciers from 2015 to 2024 is 21.57 ± 0.97 Gt a-1. The Austfonna ice cap accounts for ~48% of Svalbard's frontal ablation, due to the dominant Austfonna Basin 3, with a 5.05 ± 0.35 Gt a-1 annually averaged rate. As frontal ablation measurements have historically been limited to annual and decadal temporal resolution, this dataset addresses the intra-annual and seasonal variability knowledge gap, while providing valuable reference data for the modeling community. The frontal ablation, ice discharge, and calving front time series are publicly available at https://doi.org/10.5281/zenodo.19481461 (Pyles et al., 2026).
In this manuscript, Pyles and co-authors present a dataset of frontal ablation at Svalbard's tidewater glaciers. The dataset is comprehensive and highly resolved, and I expect it to be of great value to the science community. The manuscript is well written, detailed, and clearly illustrated with high-quality figures. I commend the authors on an overall enjoyable and insightful read! I have some minor recommendations and questions that I hope will improve the manuscript:
General comment:
The tone of language is at points -- in particular in the abstract and introduction -- a bit informal/florid or leans toward editorializing. Examples of this are: "...the manual labor cost inherent to mapping..." (L14) - manual labor is not strictly speaking inherent to mapping, so I would just simplify this to "...the manual labor cost of mapping..."; "...from the extensive ITS_LIVE velocity database, ..." (L 15), change to "from the ITS_LIVE velocity database, ..."; "unprecedented" (L19, L61) - I would just remove the word or replace with "high"; "is strongly recommended" (L 40) - reword?; I also recommend following the general guideline of avoiding the terms "novel" or "new" (the science should speak for itself, L 12 and 62). I would encourage the authors to go over the full text with this in mind.
Specific comments:
L 44: the statement on "decadal timescales" appears in conflict with the L 48 statement on annual/seasonal resolution by Minowa et al and Fahrner et al - rephrase?
L 64: Could you clarify why you are not using the Li et al (2024) frontal positions for this study?
Fig 2: While this figure is visually striking, I found it a little hard to interpret. I was trying to figure out which elements were schematic illustrations of the quantities used in the dataset, and which were artist's rendering/ aesthestic additions. I would urge the authors to simplify this and only include what is needed to make sense of the dataset/ processing chain.
L 165: Could you clarify in the main text what the OpenStreetMap is used for?
Fig 3: I found the overall layout of this Figure, with the different insets and zoom-ins somewhat confusing and was wondering whether it could be laid out slightly differently, or maybe panel a should be made its own figure?
L 261: Is the smoothing of the polygon boundaries necessary beyond an aesthetic improvement? Would it be worthwhile to also provide the unsmoothed polygons in the dataset?
L 340-375: I struggled a little to follow this argument; would it be worth adding a schematic to illustrate this process, or adjust Fig 7 to help with this?
L 386: It wasn't quite clear to me here whether you are using the Fuerst et al data or method here - could you please clarify?
L 423: How do you handle days without a velocity measurement?
L 460: Could you provide a short justification for using this reduced density of ice?
L 556: Are all the study polygons located in the ablation zone, in which case a negative CMB would be expected? Could you please comment on this?
L 571: The increase in tidewater termini length: might improved data coverage/quality over time contribute to this increase in the termini length? (Part of my question here is because I thought it a surprising finding - I would expect shortening of the termini as they retreat more onto land?)
Wording/Typos/Grammar etc:
L 27: "the ice-water-air interface" - these are actually (3) different interfaces; rephrase?
L 34: "total mass loss" -> "total ice loss" ?
L 80/89: The two sentences on diverse geometries feel repetitive and could be tightened?
L 129/134 and elsewhere: I was a little confused by the use of "inference" vs "prediction"? Are these terms referring to the same thing? If so, I would just use one of them, if not, maybe the difference could be clarified?
L 140: It may be worth spelling out "Randolph Glacier Inventory (RGI)" here, not just in the Fig 1 caption?
L 176: reword: "...the segmentation model, which is pre-trained ..." (?)
L 177: what do you mean by "unseen domain" ?
L 234: "consensus" seems maybe the wrong term?
L 304: "Like the cross-sectional area definition, ..." -> I struggled to make sense of this wording - could be clarified?
L 305: "We assume no uncertainty in the widths ..." -> rephrase: "We assume the uncertainty in the widths is small ..." (?)
Fig 6a: Is the map inset needed here, since you have the same inset in panel b?
L 487: "m^3 W.E. (Fig. 8)" -> the figure legend gives the total mass in Gt rather than the volume in "m^3 W.E." - could this be made consistent or clarified?
L 606: unit of Gt a^-1 (100 km)^-1 - as on L 608
L 655: remove "heavily" ?
L 663: reword: "mass loss due to frontal ablation *has* rapidly *increased* since 2000 ..."
L 696: "both *study* results"
L 701: These values should be negative, to be consistent?
L 734: "...and *its* implications..."