General comments:

A review of “Mechanisms and impacts of extreme high-salinity shelf water formation in the Ross Sea” by Wang et al.

Based on a regional coupled ocean-sea ice-ice shelf model, this study presents an investigation of the High Salinity Shelf Water (HSSW) in the Ross Sea. The model employed in this study was validated in previous studies, and this model can capture the formation and variabilities of HSSW over the continental shelf in the Ross Sea. By analyzing the sea ice production (SIP), the authors found that this coupled model reproduced the observed record-high SIP in the western Ross Ice Shelf Polynya (RISP) in 2007. And then, they quantified the influences of cyclones on the SIP. Consistent with the SIP, both the density of cyclones and the wind speed were elevated in the western Ross Sea in 2007. In contrast, the salinity of HSSW tends to be relatively lower in 2007. By further analyzing freshwater flux and ice shelf melting, it is interesting to find that the melting of ice shelves greatly contributed to the lower salinity of HSSW. The authors also discussed the potential changes of HSSW and Antarctic Bottom Water (AABW) in the future. The production of the HSSW and AABW are both expected to be enhanced due to an intensified positive phase of the Southern Annular Mode and the deepening of the Amundsen Sea Low.

It is very topical because the HSSW formation and outflows from the continental shelf to the deep ocean are key processes for the lower limb of the global meridional overturning circulation, which has global implications for climate change. I believe that this manuscript is very interesting to the Antarctic science community, and the manuscript would be further improved with some necessary revisions before publication. My comments are given below, and I recommend the manuscript for publication in The Cryosphere after minor revisions.

Note: In the following, "L" means Line.

Minor comments:

L50: ISW should not be recognized as warm water mass.

L130: if the authors tend to introduce the conception of ‘austral winter’ here, it would be better to clarify the temporal interval of each season now.

L202-206: when the author shows the SIP in Figure 2, they have not clarified the domain where the SIP was integrated. I think the domain can be shown with an enclosed regime in Figure 1b. In addition, the simulated SIP seems to be one order larger than the observed value. Is there some typo on the left y-axis of Figure 2？

L234: the authors pointed out the specific years of 2005, 2017, and 2019. Yet, the SIP in 2015 seems to be also very strong. Please give some discussions about this year too.

L259: it would be nice if the authors could repeat the threshold that is used to quantify the HSSW volume here, the readers may not remember that clearly.

L266-267: how to quantify the HSSW production in the TNBP? If such an analysis can be achieved, the HSSW in the RISP can also be directly quantified rather than calculating the volume changes over the entire continental shelf.

L280-281: ‘between October and July’; Does it mean the temporal duration starts from October in one year and persists to July in the next year?

L288: it is necessary to clarify the threshold that is used to calculate the volume of ISW.

L303: in Figure 7b, the author can use two-color shading to show the ice shelf basal melting in the Amundsen Sea ice shelves and Ross Ice Shelf, respectively. Such a subplot can greatly support L297-230.

L323-325: I understand the authors want to conclude the delayed influences of ISW on the HSSW, yet such a conclusion based on Figure 8 may not be rigorous enough unless the authors conduct a passive tracer experiment. I would suggest the author delete these descriptions.

L336: It would be nice if the authors could quantify the strength of the volume transport of the coastal current. I think the calculation is similar to the freshwater flux across the same selected transect (the red line Figure 1b). Such numbers can be directly added to each subplot in Figure 9.

L399-402: It may be better to delete these descriptions if the authors do not want to conduct a passive trace experiment to show the precise time of the ISW transport.

Review of "Mechanisms and impacts of extreme high-salinity shelf water formation in the Ross Sea" by Xiaoqiao Wang et al..

Summary:

By investigating the interannual variability of high-salinity shelf water (HSSW) production from sea ice freezing in the Ross Sea, the authors identified a particular season, winter 2007, with an unusually high frequency of cyclones near the Ross Ice Shelf, which in turn contributed to an increase in sea ice production. However, the salinity of the Ross Sea was unexpectedly low during this season. Further examination revealed that the fresh ice shelf meltwater inputs from the Amundsen Sea and Ross Seas balanced the salinity induced by sea ice formation.

Recommendation:

This well-organized, logical, and well-documented manuscript is a comfortable read. The individual case analysis of the winter of 2007 can serve as a classic story of complex Antarctic atmosphere-sea ice-ocean interactions. I have only one major concern about the discussion, which would be worth considering before publishing the manuscript.

General comments:

The discussion section is too general. I favor the authors discussing the generalizability and implications of the results of this paper on a larger spatial/time scale. However, they seem to be ignoring the dramatic changes in the Antarctic in recent years, i.e., the Antarctic sea ice extent is shifting to a new state of frequent minima (Wang et al., 2022; Liu et al., 2023; Purich and Doddridge, 2023). This paper is relevant because the Antarctic sea ice extent in the winter of 2023 was 2 standard deviations below the climatological state, increasing ocean heat loss and storms (Josey et al., 2024). Two opposing effects could affect Ross Sea HSSW formation: ocean heat loss leading to subsidence of highly saline cold water promotes HSSW formation, and more storms would facilitate this process; however, ocean warming could also lead to increased ice-shelf meltwater or even ice-shelf disintegration, which would feed large amounts of freshwater into the ocean.

I suppose that linking the author's work to current changes underway in the Antarctic atmosphere-sea ice-ocean system would be interesting and broaden the impact of this manuscript.

Other issues:

Line 34: "salinity" should be preceded by the article "the"; "unexpected" should be "unexpectedly".

Line 77: I would be very careful about making that statement. In another study by the authors (Wang et al., 2021), the effect of 2 strong wind events in 1998 on HSSW production was analyzed, although the region was Prydz Bay. Please consider rephrasing this sentence.

Line 109: "higher" than what?

Line 143: "observed" should be preceded by the article "the"

Line 149: This URL only provides ice production data from 2003 to 2010, which do not match the line in Fig. 2 up to 2013. I recommend the authors use the newly published dataset (Nihashi et al., 2024), which has extended the record to 2021. Otherwise, I do not think "record-high" is the proper word to describe the 2007 sea ice production regarding the too-short time series.

Line 171: There have been some attempts to improve the classic algorithm in recent years (e.g., Zhong et al., 2023). Would that have any effect on the results? Maybe a sentence of explanation here.

Line 217: The red numbers in the lower right corner partially overlap the map and are not clear.

Line 287: Is this conclusion straightforward to draw?

Line 345: I do not see "both", but just the slope current was high in 2007.

Line 363: Why not cite the results of the updated CMIP6?

References:

Josey, S. A., Meijers, A. J. S., Blaker, A. T., Grist, J. P., Mecking, J., & Ayres, H. C. (2024). Record-low Antarctic sea ice in 2023 increased ocean heat loss and storms. Nature, 636(8043), 635–639. https://doi.org/10.1038/s41586-024-08368-y

Liu, J., Zhu, Z., & Chen, D. (2023). Lowest Antarctic Sea Ice Record Broken for the Second Year in a Row. Ocean-Land-Atmosphere Research, 2, 0007. https://doi.org/10.34133/olar.0007

Purich, A., & Doddridge, E. W. (2023). Record low Antarctic sea ice coverage indicates a new sea ice state. Communications Earth & Environment, 4(1), 314. https://doi.org/10.1038/s43247-023-00961-9

Wang, J., Luo, H., Yang, Q., Liu, J., Yu, L., Shi, Q., & Han, B. (2022). An Unprecedented Record Low Antarctic Sea-ice Extent during Austral Summer 2022. Advances in Atmospheric Sciences, 39(10), 1591–1597. https://doi.org/10.1007/s00376-022-2087-1

Wang, X., Zhang, Z., Wang, X., Vihma, T., Zhou, M., Yu, L., et al. (2021). Impacts of strong wind events on sea ice and water mass properties in Antarctic coastal polynyas. Climate Dynamics, 57(11–12), 3505–3528. https://doi.org/10.1007/s00382-021-05878-7

Zhong, R., Yang, Q., Hodges, K., Wu, R., & Chen, D. (2023). Impact of Data Resolution on Tracking Southern Ocean Cyclones. Monthly Weather Review, 151(1), 3–22. https://doi.org/10.1175/MWR-D-22-0121.1

Wang et al. use a new model to understand drivers of "extreme" dense water formation in the Ross Sea. Given the importance of the Ross Sea for Antarctic Bottom Water, this study is timely and relevant to the climate science community. I found the manuscript very interesting and model results well described. I have some major comments below that might require some further analysis. Also minor comments are included.

Major comments

• Section 3.2. Ice Shelf meltwater fluxes. Some parts of this section are not very clear.

1) First, how do you define ISW? It should be water colder than the surface freezing point and therefore coming only from the Ross Sea, not the Amundsen Sea. So, how do you quantify meltwater from the Amundsen Sea?   

2) what is the relative contribution of Ross and Amundsen ice shelves?

3) CDW can affect salinity on the shelf if there is a variability in cross-shelf exchange. It cannot be ruled out.

4) Figure 8 suggest 3000 to 4000 Sv of freshwater transport. Probably a typo, but please clarify.

5) what are the freshwater flux anomalies through the “eastern gate”? are they consistent with salinity changes?

6) By looking at Figure 9, it looks that the largest changes are in the Antarctic Slope Current, not in the coastal current. Is this true? If so, how does this impact the freshwater flux onto the continental shelf?

7) can you show salinity changes at the “eastern gate”?

8) can storm affect this westward flow?

Title: Is this an extreme event? or maybe a different "word" would be more appropriate?

Minor Comments

• Line 132: orange line? Not yellow
• Line 75: I would not call “ISW” the freshwater coming from the Amundsen Sea. Maybe just meltwater?
• Line 102: “ice shelf-seawater interactions”
• Figure 2: how do you define the polynya area to estimate sea ice production?
• Figure 3: can you say few more words on why you chose an area over the Ross Ice Shelf to track the storms? And not a different area?
• Section 3.1. What is the typical structure of a cyclone in the Ross Sea? Is it consistent with southerly winds over the Ross Sea polynya? I would include a figure to highlight this.
• Line 278: “Ross Ice Shelf cavity”
• Line 281: why do you consider a year between October to July?
• Line 384-385: would a deepened ASL strengthen or weaken the Easterlies in this area? A reference might help.
• Observations suggest a slight increase in salinity in 2007 (Castagno et al., 2019). I would add some text to discuss about this.