Mistray et al: “Global Climate System Response to SOFIA Antarctic Meltwater”

Review by N R Golledge 6th Aug 2025

This paper reports results from a suite of experiments using the climate model HadCM3-M2.1, in which a freshwater flux is added to the ocean around Antarctica to mimic the effect of ice melt over the current and future centuries. The description of the methodology and results is relatively clear and the figures are adequate to illustrate the key points raised in the paper. In terms of novelty, this is, ultimately, just another hosing experiment, of which there are already quite a few, and the results are very much in line with previous studies. But the fact that the perturbation experiments are run for 1150 years means that it is one of the few studies that explore long-term climate responses to SO hosing, which is useful. Treatment of previous literature is rather superficial, often defaulting to review papers or the same few studies repeatedly. There are also relevant papers that are absent from the reference list, and some of the claims in the paper seem to be rather bold as a consequence.

Overall, my feeling is that the manuscript is probably a useful contribution to the literature, but could be improved with some closer attention to the points detailed below.

line 27: you mention that previous studies used ‘idealised freshwater hosing experiments’, but don’t clarify what you mean by ‘idealised’. This is important, because your study uses a low-resolution highly-parameterised GCM and imposes a constant salinity flux as a proxy for meltwater. This is what I would call ‘idealised’, since the meltwater flux is entirely fictional, it does not derive from any ice sheet model. By contrast, the papers you cite in lines 30-31 do a far more robust job with the meltwater - Sadai et al used a coupled ice sheet - climate model, Golledge et al used an offline-coupled ice sheet - climate model, and Bronselaer used meltwater fluxes from a previous ice sheet simulation (DeConto & Pollard, 2016). In all three cases, the meltwater added to the climate model comes from a dynamically-evolving ice sheet model, and, in the studies of Sadai and Golledge, that ice sheet evolution is in turn coupled to the evolution of the simulated climate. I wouldn’t therefore call them ‘idealised’.

line 32: again, you mention ‘interactive ice sheets and shelves’ as being absent from previous work, but they are also absent from your model, so...?

line 46-7: I assume here you mean future projections? Because there are several studies that consider multi-centennial to multi-millennial hosing under palaeo scenarios (Weaver et al., 2003; Menviel et al., 2010; Bakker et al., 2017; for example).

line 63-4: Noble et al and Bentley et al are both review papers, and PD09 do not mention meltwater pulses, only ice growth and decay, so why were these references chosen specifically? There are ice sheet simulations published that explicitly focus on AIS meltwater pulses (Stuhne & Peltier 2015; Golledge et al., 2014), so perhaps the referencing could be broadened to at least acknowledge where original work on this topic has been done?

line 68-70: “The results produced here will provide novel insight into the global climate implications of rapid AIS melt expected within this century and beyond” - I’m not sure how well the study succeeds in providing novel insights - perhaps a summary could be added here or later that identifies what the study shows that is consistent with existing knowledge, and what has been found that is new?

line 95-102: there is a long list here of the various parameterisations employed, but I didn’t find a discussion of how these approximations might influence the results? Are there studies that could be referenced here that have shown eg that eddy-resolving models show xx greater or lesser mixing / transport / whatever? I feel like some justification / explanation is needed here.

line 105: “excess salt formed by melting” - I’m sorry if I misunderstand what is meant here, but I thought it was the formation of sea ice (ie by freezing) that rejected salt?

line 111 and throughout: why the use of future tense here? The work has been done, so either use past tense or present.

line 119: Regarding the addition of meltwater at the surface, this is fine and a common approach, but maybe mention the limitation of it. For example, Pauling et al 2016 showed that releasing meltwater at the depth of ice shelf bases can have an influence on its impact: “We found that injecting water at the depth of the front of ice shelf around Antarctica caused the ocean mixed layer to deepen, while adding freshwater at the surface caused the mixed layer to shoal.”

line 126: ‘perturb from’ sounds odd, maybe ‘branch from’?

line 128: “The difference between the piControl and FW experiments taken as modelling responses.” - seems like some words are missing from this sentence.

line 132: “at the level 95%” --> “at the 95% confidence level” perhaps?

line 139-140: “To date, this is the first study to investigate the climate response to AIS meltwater using a fully coupled climate model over such long time scales.” - Given the limitations of the model and methodology, I would suggest tempering this statement a little. Other studies as identified above have done similar things, for example Bakker et al used actual ice sheet meltwater fluxes and ran for 5000 years.

line 148-150: “The area immediately surrounding the AIS experiences a decrease in SSS of up to 0.5 psu (Fig. 3h). Freshening around the AIS is relatively uniform, with no particular region experiencing significantly more freshening (Fig. 3f-h).” - This is the area you apply the meltwater, right? And that is applied as a salinity anomaly? So these aren’t really 'results', this is just what you've put into the model.

line 153: ‘weaker rate’ - ‘lower rate’ maybe?

line 154: ‘This freshening’ - always best to avoid using ‘this’ unless you clarify what it refers to, eg ‘The surface freshening of xx psu described above...’

line 166: ‘ran’ --> ‘run’

line 184-5: NB - Golledge et al 2019 also used freshwater fluxes from the Greenland Ice Sheet, which most likely affects N.Atl SSTs etc.

line 189-194: You refer to ‘this unusual trend’ and ‘this trend’ and an increase in global sea ice thickness of c. 0.1m. But I don't see any trend in any of the data in 6a or 6b. There is a lot of variability, but how have you calculated a thickening trend? And how can the global increase be 0.1m when the plot in 6a shows values of only 0.07 to 0.1? I think the step change between picontrol and the forced run is 0.01m? It is 0.1m in the SO experiment.

line 200-1: Is this because the location of meltwater input in Sadai et al is controlled by locations of mass loss in the ice sheet model? Or is there some other reason?

line 233: Maybe also look at Golledge et al 2019 for how fluxes from AIS and GIS affect AMOC differently.

line 234 and line 236: I don’t think you can make the claim at 236 when you just made the statement at 234!

line 285-6: Can you say anything about the effect of icebergs, eg from simulations that explicitly simulated them (eg Schloesser et al)?

line 294-8: Note that this may be different if GIS meltwater was included in the expts.

line 309: rather than ‘dramatic’ I would just say ‘abrupt’ - this rapid change just reflects your methodology of meltwater addition, correct?