| 10 Oct 2025
Dynamic Thinning and Grounding Line Retreat in Porpoise Bay, Wilkes Land, East Antarctica
Abstract. The East Antarctic Ice Sheet (EAIS) is often considered less vulnerable to climate change than the West Antarctic or Greenland ice sheets, but some regions of the EAIS have been losing mass over recent decades. In particular, mass loss in Wilkes Land, which overlies the Aurora Subglacial Basin, is thought to have accelerated over the past two decades. However, whilst several large outlet glaciers drain this region, few have been studied in detail. Here, we present new data on the recent ice dynamics of four outlet glaciers that drain into Porpoise Bay, Wilkes Land, which includes Holmes East, Holmes West, and Frost glaciers. We use optical satellite imagery, differential synthetic aperture radar interferometry, and a range of previously published datasets to describe changes in the ice-shelf front, grounding line position, ice surface velocity and ice surface elevation over the last three decades. Our results reveal evidence of dynamic changes in the region, characterised by thinning of grounded ice and grounding line retreat, albeit with large uncertainties. We find an indication of Circumpolar Deep Water proximal to the continental shelf break that could access the glaciers through deep cross-shelf troughs, which is consistent with previous estimates of high rates of basal melting beneath their floating tongues/ice shelves. Our results also support previous observations of near-synchronous ice-shelf calving across Porpoise Bay's ice shelves, following the break-out of multi-year sea ice, and find an additional recent calving event, further highlighting the vulnerability of this region to ongoing and future changes in ocean and sea-ice conditions.
Review of “Dynamic Thinning and Grounding line Retreat in Porpoise Bay, Wilkes Land, East Antarctica” by Weatherley et al.,
This study focuses on investigating how ice shelf fronts on Porpoise Bay (Holmes East/West, Frost and the creatively named Glacier 1) have evolved since the late 1990s (or the early ‘60s for ice shelf front) by utilizing a mix of satellite imagery, radar interferometry alongside previously published data on the state of the ice shelf front. This shelf evolution was compared to temperature/salinity data taken in Porpoise Bay from MEOP casts and EN4 reanalysis data to provide evidence of any continental deep water intrusions onto the shelf front, which could support heightened basal melt. The authors also find a previously undocumented calving event on the Holmes East glacier and link the breakup of the protected mélange layer to a loss of local sea ice in the months leading up to calving.
Overall, I found this a well written and interesting manuscript on what is both an underrepresented region in literature, and a difficult region to analyze owing to the aforementioned presence of mélange. With a bit of tightening, it should be a very useful paper for anyone looking to undertake research in the region. Also, low-key love the care put into colour schemes throughout.
Minor comments:
Line 20: following the break-out of multi-year sea ice alongside a recent calving event., further…
Lines 30—35: Seeing there have been a few big mass balance papers out recently, I’d be curious to see some comparison to Green et al., 2022 (doi: 10.1038/s41586-022-05037-w) and Davison et al. , 2023 (10.1126/sciadv.adi0186)
Lines 43-45: The start of “However, there is emerging evidence of a longer-term trend in Wilkes land seems at odds with the previous sentence that Wilkes land is the dominant source of mass loss in EAIS.
2.2 Ice surface elevation general comment 1: I found the repeated usage of “the data” or “this dataset” made this section hard to follow.
Ice surface elevation general comment 2: I wonder if it would flow better if the Nilsson et al., part is given its own paragraph, plus a tad more information on the additional data from ICESat-2 and how it meshed with the previous data.
Line 161: I’d like the error range given for each box instead of the range. Especially seeing that is a rather large difference in error.
Line 178: Uncertainty was derived from…
Line 246: Considering the mention of ice-shelf breakup, I’d also mention grounded icebergs if we’re going for potential “errors” in NSIDC sea ice index.
Line 255: Fluctuated from where (especially as you abandon this kind of measure in the next paragraph to go relative from calving)?
General result comment: isn’t slowed down by – number a double negative? I think the results would be improved by sticking to either a sign to indicate change, or text.
Line 286: There is an additional space after 382.3
Line 291 consistently increased by 7-10% over the study period would make it more concise. Same comment on Line 295.
Ice shelf elevation change: I found this section awkward in its layout, and I think it would benefit from figures 5 and 6 being combined (as much as they’re pretty figures). Alternatively, I wouldn’t be opposed to text, figure 5, figure 6 as the layout.
Line 334: The “we observed lower rates…” in a paragraph that continuously reminds the reader that this data is from other sources seems out of place (not that I’m against the we observed, it just came off as jarring).
Line 365: I’m not a fan of “taken at face value”. It’s a given with results.
Figure 8 and 9: Considering how much these figures interplay with each other, could they be combined?
Line 435: This feeds into a comment I have in the discussion, but how does a February-March combination look for concentration anomaly? Seeing they are typically the two lowest months for sea ice extent.
Figure 13: Can you make each tick visible.
Figure 14: Can you align the ticks to their respective bar. Took a few seconds to get my bearings with this one.
Line 449: Holmes West glacier are consistent with dynamic …
Line 456: ice velocity is increasing across …
Line 476: I’m not sure “down a retrograde slope” is necessary.
Line 485: retreat could be less rapid than we record.
Lines 511-515: I think that would benefit being broken over two sentences.
Line 562: glaciers (Fig 8.) alongside the rapid decrease in surface elevation (Fig 6d)., since Holmes …
4.3 Role in sea ice driving ice shelf and glacier flow change general comment: I found the lack of a mention for the Voyeykov an odd decision here, owing to the similar mélange break up and proximity to Wilkes Land.
Line 571: I’d switch Baumhoer et al., 2021 for Teder et al., 2025 (doi: 10.1038/s41561-025-01713-4). Bit of a double whammy where Baumhoer doesn’t go into great detail about fast ice/melange, and Teder et al., does give evidence for a very large calving event being in response to mélange breakup (seeing the perennial fast ice in north Wilkins is a mélange layer).
Line 577: This does feedback to the comment earlier about being curious about the February concentration and combining the sea ice low period. Considering Teder et al., + Arthur et al., showed evidence that there was a persistently anomalous sea ice low in the couple of months leading up to the breakup of mélange, I’d be curious how well this breakup compared to those two regarding timing.
Line 590: With the bulldozing comment, its certainly possible seeing fast ice growth tends to be limited by depth around Antarctica (Fraser et al., 2023, doi: 10.1029/2022RG000770). That said, I’m not sure how feasible it would be to provide bathymetry of where this mélange was pushed too.
Lines 605—610, seeing proximity, how does this compare to what has been observed on the Totten ice shelf (Green et al., 2018, doi: 10.5194/tc-12-2869-2018)
Line 660: we report on a previously unidentified calving..
References: Personally I’m not a fan of the abbreviated journal titles, though if this is the cryosphere template, please disregard.
Admundson et al., becomes justified in its second line (and there are a couple of others in the reference list)
Favier, L. has F. Pattyn instead of Pattyn, F.
Haran et al., 2021 has a duplicate entry