This manuscript is ambitious and seeks to connect “Physiological and ecological tipping points caused by ocean acidification,” as its title indicates. To my knowledge, this question has never been explored in ocean acidification research field and is of crucial importance for understanding the occurrence of tipping points and their consequences for ecosystem and global earth system functioning. This review addresses research requirements highlighted in the latest International Pannel on Climate Change’s reports and is of major interest for the scientific community. By connecting tipping points in the biosphere to those occurring in the ecosphere, this study is perfectly in the scope of the journal “Earth System Dynamics”.

However, despite the critical interest of its research question, this article requires major revisions before being considered for publication. First, despite its title, the article fails to discuss the link between physiological tipping points and their ecological counterpart. To address this problem, efforts must be made to connect the second part, “direct impact on key physiological processes”, and the third part, “changes at naturally high CO₂ locations”. Key concepts discussed in the article (physiological tipping point, ecological tipping point, reaction norms) are not defined in the introduction, which threatens the understanding of the entire article. There is a lack of a whole body of literature (see references in the supplement file) on physiological tipping points to ocean acidification, particularly for molluscs, echinoderms, and pteropods. Discussion of tipping points is almost absent in parts 2.2 and 2.3, which contrasts with the title of the manuscript. Part 3 on “Ecological Tipping Points” lacks important concepts such as “engineer species” to effectively link with Part 2 on “Physiological Tipping Points”. A figure is missing to help readers understand the ecological concepts described in Part 3. Finally, despite its crucial interest for the study, Table 1 is not really discussed even if it could help to resolve some of the problems mentioned above.

If significant revision work is done, I believe this review could be of great interest to readers of “Earth System Dynamics” and to the scientific community working on climate change in general.

Please find suggestions for improving the manuscript in the supplement file.

This work presents a great depiction of the current state of understanding of the impact of OA on organisms and community structure. The text is generally direct and clearly written. The text generally suggests that identifying tipping points caused by OA is difficult and there are other factors to be considered. My major concern is that the paper reads more as a summary of the impact of OA rather than an assessment of how tipping point can be caused by OA.

The first parts (section 2) have some paragraphs that are a bit clearer about the difficulty of identifying tipping points from a physiological perspective only and translating this to any broader ecological processes.  

From my point of view, the other parts however seem mainly about changes/shifts and do not touch enough on how these changes are likely to occur; gradual (linear) vs abrupt (tipping point/bi-phasic).

Another consideration is whether tipping points are likely to be caused by CO2 alone, or influenced primarily by interactions with other parameters/stressors?

Are there shifts in community structure or simplification of food web occurring through a tipping point or are they more gradual shifts along the spatial/temporal gradient of pCO2? No doubt that a shift in community structure/habitat forming species and so on are likely, and in fact shown in some areas (e.g., CO2 seep having different communities). However, can a proper sudden change in stable state be identified at a given range of pCO2 or are these occurring mostly gradually or randomly at different sites based on the site’s own characteristics? I think it is important here to clearly differentiate between gradual shift vs a sudden tipping point, or maybe the lack of appropriate data/studies to properly infer tipping points.

There is also a lack of more concrete direction on how to look properly into identifying actual sudden change in stable state in natural systems, for example, or thresholds in pCO2, especially in the concluding section.

Nonetheless, in my point of view, this can be a nice addition to the literature and provide some nice insights given it revised carefully and a little restructuring. In its current state, it feels a little as a summary to the impact of OA, to which some inferences about tipping points have been made. I hope that these comments help improve the paper.

Please see attached file for more detailed review comments.