| 19 Dec 2025
Climatology and Interannual Variations in Arctic Winter Sea Ice Leads in the ICESat-2 Era
Abstract. Sea ice leads play a key role in polar air-sea heat, moisture, and gas exchanges, ocean heat and salinity variations, and ecosystem processes. However, their small-scale nature challenges efforts to assess spatiotemporal variability on a pan-Arctic basis. Here, we use six years of high spatial resolution surface type (ATL07) and freeboard (ATL10) products from Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) to characterize Arctic winter sea ice leads. Both products reveal consistent climatological spatial patterns, with lead fractions generally higher near the ice edge and coastal regions, and lower over the central abyssal plains. Lead sizes follow a power-law distribution, with the exponent increasing with size. We identify four distinct features in the temporal evolution of lead fraction over the ICESat-2 era, including a maximum in winter 2020–2021; increases in lead fraction are primarily driven by changes in the number of larger (>100 m) leads. Our findings show that ICESat-2 measurements provide robust regional-scale characterization of spatiotemporal variability in winter ice leads, which will in turn better inform their underlying response to, and influence on, Arctic climate.
General comments
This manuscript presents a valuable pan-Arctic analysis of winter lead fraction and lead-size statistics derived from ICESat-2, using two complementary products (ATL07 and ATL10). The topic is timely and relevant, and the results (spatial patterns, regional interannual variability, and lead-size scaling behaviour) will be of broad interest. I have several comments that would improve clarity and strengthen the ATL07–ATL10 comparison and the interpretation of the power-law results.
Specific comments
1. Sect. 2 (ATL07 vs ATL10 comparability; ice concentration filtering):
The manuscript applies different sea-ice concentration filters for ATL07 and ATL10 (and the products have different lead definitions). Perhaps discuss how the differing concentration masks could influence the ATL07–ATL10 comparison (e.g., particularly near the ice edge and in marginal seas)/
2. Sects. 2.1–2.2 (methods clarity):
The processing description would benefit from a flow chart alongside the text; this would help readers follow the differences between the ATL07 and ATL10 workflows and provide a nice visual summary.
3. Definition of “climatological wintertime lead fraction” (p7):
Formally define what is meant by the “climatological wintertime lead fraction” (e.g., is the climatology computed by pooling all winter observations across years in each grid cell).
4. Sect. 4.1.2 (power-law / scaling context):
The power-law analysis is interesting and could be better contextualised within the broader literature on geometric scaling in sea ice (while being clear about differences between lead-size and floe-size statistics). The discussion could reference, for example:
o Stern, H. L. (2018). On reconciling disparate studies of the sea-ice floe size distribution. Elementa: Science of the Anthropocene, 6, 49. https://doi.org/10.1525/elementa.304
o Stern, H. L., et al. (2018). Seasonal evolution of the sea-ice floe size distribution in the Beaufort and Chukchi seas. Elementa: Science of the Anthropocene, 6, 48. https://doi.org/10.1525/elementa.305
(These are floe-size focused, but may help frame interpretation of scaling regimes and physical processes.)
5. Figure 3a (readability):
Figure 3a is difficult to read at its current size. Consider splitting into two panels/figures (one for lead-size distribution, one for segment-number distribution) or enlarging/adjusting layout so axes and legends are legible.
6. Figure 6 (visual consistency):
The mix of lines (ATL10) and bars (ATL07) is visually confusing. I recommend using a consistent representation (e.g., lines for both products, or separate panels). Also please adjust titles/labels to avoid overlapping plotted data.
7. Sect. 5 (interpretation of apparent scaling changes):
The apparent change in power-law scaling is an important result. It would benefit from a deeper discussion of plausible mechanisms and why they might differ by region and year (e.g., fracture/strain regimes, wind forcing, consolidation/thermodynamic growth, lead refreezing).