the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Aug 2025
The role of Antarctic sea ice in the Earth system: Perspectives informed by 130,000 years of sea ice records
Abstract. Antarctic sea-ice cover reached historically low levels in 2023, consistent with the simulated decrease in sea-ice extent in response to anthropogenic warming. Antarctic sea ice is closely linked to multiple components of the Earth system, thus its demise could precipitate widespread, cascading changes across the cryosphere, atmosphere, and ocean. However, the nature and strength of these interconnections are poorly understood, and they are often inadequately represented in models. In this review paper we use modern observations, models and paleoclimate archives covering the last glacial cycle to gain insights into how reductions in sea ice may affect other components of the Earth system. We review how Antarctic sea ice interacts with ocean and atmosphere circulation, ice sheets and ice shelves, marine productivity, and the carbon cycle over the last glacial cycle, for which we have the most robust sea-ice reconstructions. The review finds strong evidence from theory and models for impacts of Antarctic sea ice on the Earth system. Paleo-proxy reconstructions provide examples where changes in sea ice co-occur with changes in the carbon cycle, marine productivity, and ocean circulation. However, challenges remain in isolating the impact of sea ice in a highly interconnected system.
Competing interests: Some authors are members of the editorial board of Climate of the Past.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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RC1: 'Comment on egusphere-2025-3504', Anonymous Referee #1, 01 Sep 2025
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[General comments]
In this manuscript, the authors comprehensively survey numerous papers on the role of sea ice in the Southern Ocean in the climate system, and succeeds in collecting vast amounts of information on the topic. The authors' attempt to provide an excellent overview on the issue surely has a potential to be appreciated by scientists of diverse research fields, and in particular, their effort to discuss how sea ice has interacted with other subsystems during past large-scale climate changes from a paleoclimatological perspective should be a novel and scientifically worthwhile conception. However, I have to raise serious concern that the specific methods used to organize the research findings and the manner to present them to readers are not necessarily optimal. The manuscript tries to cover vast amounts of phenomena and information; of necessity, the authors should pay close attention to methods for organizing and communicating them. I am certain that this manuscript will be dramatically improved and will realize its potential with a proper methodology to convey the authors' arguments in a clear and accessible manner. In addition, I also point out that the manuscript would be further enhanced by including descriptions on interactive feedback between Antarctic sea-ice and other Earth system components and a discussion on the role of paleo studies in the improvement of our knowledge about the Earth system.
[Major issues]1. Each section is poorly structured.
In each of the main sections, descriptions based on varying methodology (e.g. theory, modelling, modern observation, and paleo evidence) appear in a semi-random way, and besides, they have different structures (e.g. some sections have subsections, but others not). Therefore, it would be troublesome for readers to grasp the contents smoothly. To clarify the contributions from different methodologies, I would suggest several ideas for improvement.
- It would be helpful that each section has a table that summarizes the survey corresponding to the section. The potential table would have a similar structure to that of current Table 1; namely, columns for hypotheses based on theory and/or modelling, modern observation, paleo evidence, and so on. Then, rows would be allotted to important processes (rather than sub-components) that are relevant to the section topic.
- All the main sections should have a common subsection structure. The structure might be in line with the section's table that is suggested above.
- I would point out that the current manuscript only has insufficient visualization. I believe it will be certainly beneficial if the manuscript has more schematic illustrations that show not only the name of components but also key mechanisms or processes discussed in the main text. Fig.1 of Lannuzel et al. (2020) might be a good example of such a schematic.
2. Table 1 should be updated accordingly.
I would suggest that the general summary should have more visualized expression that conveys the information in a more intuitive way. For example, direction of changes, correlation strength, uncertainty/reliability, and so forth would be depicted as symbols with different sizes, colors, thickness, etc. An example of such an illustration might be found in Table 1 of Henson et al. (2022; https://doi.org/10.1038/s41561-022-00927-0).Apart from this, Table 1 also raises some conceptual concerns (see item #5).
3. The manuscript contains a huge number of acronyms.
I would suggest that the authors should show a list of the acronyms that are used in the text.
4. "Antarctic sea-ice .... as drivers of substantial Earth system changes." (Lines 113-115)
As represented by this sentence, the authors' only discuss "one-way" influences of Antarctic sea ice on other components of the Earth system. However, the relationship between the sea ice and other components should be interactive: what determines the sea-ice extent? or which controls which? In other words, not only a correlation between them but also their causal relationship should be discussed, which may be based on theoretical inferences and/or fact-based (e.g. timing analyses) discussion.
5. What is the significance of paleo studies?
In some rows of Table.1, especially in the Atmosphere row, (some of) the paleo observations are treated as counter evidence, rather than positive proof. What is the background "philosophy" of this manuscript that gives more weight to other methodologies, although it is defined as "perspectives informed by 130,000 years of sea ice records"? Of course, it is well known that extracting meaningful signals from paleo indicators is not always straightforward, and that non-negligible uncertainty often arises in their interpretation. In a general sense, when reconstructions from paleoenvironmental research conflict with understandings based on other methods, what criteria should be used to judge, and how should we move on? If this manuscript handle and discuss this fundamental issue, it will make a major contribution to research communities.
6. Section 5.2: dimethyl sulphide
It seems to be somewhat peculiar that the authors suddenly start a topic about a particular chemical compound, although they deal with large components or subsystems in the Earth system in other (sub)sections. Is there any particular reasons for that? Otherwise, the section 5.2 would look anomalous.
[A comparatively minor issue]- l.68 regime shift
What exactly does this "regime" indicate? Do we find any evidence or trace of a similar regime shift in the paleo-record? If yes, descriptions about recorded shifts should be added. If not, the reasons why such a shift is not recorded in the history of large-scale climate changes.Citation: https://doi.org/10.5194/egusphere-2025-3504-RC1
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