the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Nov 2025
Impact of surface melt and brine infiltration on fracture toughness of ice shelves
Abstract. Ice shelves are heterogeneous composites of firn, meteoric ice, refrozen melt and brine-saturated ice. The properties and distribution of these elements control ice shelf response to stress and susceptibility to fracturing. Here, we quantify how surface-melt and brine infiltration modify the Mode I fracture toughness (KIc) of meteoric ice on the Brunt Ice Shelf (BIS), Antarctica. During the 2023/24 austral summer, we recovered a 37 m core sequence from meteoric infill ice near Halley VI, where radar mapping shows continuous brine horizons at ∼ 37 m depth and line scans indicate that the upper 37 m contain ∼ 7 % refrozen melt. We combined density, salinity, temperature and grain size measurements with semi-circular three-point bending tests on samples representing (i) meteoric ice, (ii) melt-modified meteoric ice, and (iii) brine-infiltrated meteoric ice. Our results show melt-modified samples are consistently tougher than melt-free meteoric ice, with KIc increases up to ∼ 40 %. This is despite their larger grain size, indicating densification dominates over grain-size effects. In contrast, brine-saturated meteoric ice exhibits markedly lower KIc, by 14 %–34 % relative to density-matched, brine-free meteoric ice, consistent with chemical weakening and lower freezing temperatures. Our results demonstrate that as KIc varies strongly with density, salinity and depth, a spatially and temporally constant toughness value is unlikely to reproduce calving behaviour accurately. Implementing spatially and vertically variable KIc values, and understanding how ice shelf structure and composition evolves over time, is essential to improve predictions of rift propagation and calving.
- Preprint
(5613 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 09 Jan 2026)
- CC1: 'Amendment to Affiliation and Acknowledgements', Siobhan Johnson, 06 Nov 2025 reply
-
RC1: 'Comment on egusphere-2025-4904', Anonymous Referee #1, 02 Dec 2025
reply
This paper presents results from fracture toughness experiments performed on ice from the Brunt Ice Shelf, which include samples from firn, refrozen meltwater, and brine-saturated layers. The experiments reveal differences in fracture toughness between the layers, which have implications for the growth of rifts and crevasses through different ice shelf materials.
Measurements of fracture toughness in ice and snow are rare, and extending the existing data record to include a wider range of ice shelf materials is an extremely valuable contribution to the literature. The results presented here will be invaluable to inform more physically realistic models of ice shelf fracture and iceberg calving. The paper is well written and clearly presented, with well chosen figures and a thoughtful discussion of the results. I have only a few minor alterations to suggest:
Figure 1: I assume the red square in panel a is the site of Halley station, but this should be mentioned in the caption. If possible, it would also be nice to indicate in panel b the path of the GPR line shown in panel c.
Lines 123-126: I don’t think you mention what the full ice thickness is at site S2, and it would be interesting to know how it compares to the 37m core length.
Section 3: On first read through it took me a minute to understand the terminology you use to label samples from different core sections (e.g. line 143, “core 35”). I’d suggest either using the terminology “core section” rather than core, or adding a sentence in section 3.1 along the lines of “Each core section was numbered sequentially on retrieval, and we use this number to identify core sections in the text (e.g. core XX)”.
Figure 4: It would help readability if you define the variables here (i.e. “T and R are the thickness and radius of the sample, a is the notch length, and S is the distance between the rollers”).
Line 181: “as quickly as possible” is a little vague – it would be useful to give an indication for how quickly this is, and why speed was important.
Figure 6: The text in some of the panels has ended up quite small and hard to read. It might help to move the colorbar, or even to separate some of the panels into a different figure. In panel a, I wasn’t clear whether there was a difference between the points colored deep blue and those colored in grey – are they all cases with no melt?
Line 224 The sentence “brine infiltration reduces KIc by 14% - 34% relative to density-matched, brine-free meteoric ice” might usefully include the qualification “at the same temperature”.
Section 5: I think it would be useful for the discussion to briefly address the effect of ice temperature and rheology on fracture propagation. Both brine infiltration and refreezing of surface meltwater are likely to increase the temperature of the ice column, and the results from Hulbe et al. (2010) suggest that areas of soft ice (such as areas of warmer ice) can reduce stress intensity at a fracture tip and reduce rift growth.
Lastly, this isn’t a suggestion to make any change to the paper, but your results made me think of Julian Scott’s paper where they found that drilling through a melt layer within the firn triggered crevasse formation – indicating that the melt layer had higher fracture toughness and had essentially been holding that area of fir together (reference below).
Hulbe CL, LeDoux C, Cruikshank K. Propagation of long fractures in the Ronne Ice Shelf, Antarctica, investigated using a numerical model of fracture propagation. Journal of Glaciology. 2010; 56(197):459-472. doi:10.3189/002214310792447743
Scott JBT, Smith AM, Bingham RG, Vaughan DG. Crevasses triggered on Pine Island Glacier, West Antarctica, by drilling through an exceptional melt layer. Annals of Glaciology. 2010; 51(55):65-70. doi:10.3189/172756410791392763
Citation: https://doi.org/10.5194/egusphere-2025-4904-RC1
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 198 | 47 | 16 | 261 | 12 | 8 |
- HTML: 198
- PDF: 47
- XML: 16
- Total: 261
- BibTeX: 12
- EndNote: 8
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
SJ's affiliation is to be amended to include affiliation with the Yusuf Hamied Department of Chemistry, University of Cambridge.
Additionally, the acknowledgements are to be amended to include SJ's funding which is a studentship granted by the Yusuf and Farida Hamied Foundation.