The Milankovitch Theory Revisited to Explain the Mid-Pleistocene and Early Quaternary Transitions

Round 1

Reviewer 1 Report (New Reviewer)

Comments and Suggestions for Authors

This Reviewer thinks that a sufficiently novel approach is reported in this work within the field under the curent investigation; I have not found any essential flaws, errors or methodological issues.  

In this manuscript (“Milankovitch theory revisited to explain the Mid-Pleistocene and Early Quaternary Transitions”, authorships of Jean-Louis Pinault), which was submitted to journal "Atmosphere" (MDPI), author presents his conclusions motivated by recent evidence of 1) a climate transition and of 2) significant variations in the periods of insolation linked to the variations in Earth’s obliquity and eccentricity during the Quaternary (thereby resulting to changes of climate with help of resonantly forced “gyral” Rossby waves (GRWs)). Also, author has concluded that the concept of resonant forcing of aforementioned oceanic and atmospheric Rossby waves has shed new light on major phenomena described by him in the context of presented research.

General ansatz seems to be professionally presented, all the simple logic and kinematic manipulations are under responsibility of the author. Minor remarks:

1) It is not clear why sub-paragraph "2.3.3 Ubiquity of quasi-stationary Rossby waves resonantly forced into (sub)harmonic modes" has not been completed by author;

2) Line 520: Please, explain to the common readears of the journal what does it mean "which is deduced from δ^18^O ..." (or rewrite expression "... from δ^18^O" in a more clearly manner);

3) I suggest to remove Appendix A at all (or, ar least, essentialy shorten it) since theoretical derivation given there and results do not mainly relate to the main body of manuscript (except lines 305-325, 469, 553, 692). To justify explanations given there, it is sufficient to cite theoretic sources with results reported previously (so, please, refer to such required sources in literature). Indeed, Appendix should not be used for a long theoretical derivation justifying conclusions given in the main text.

My only recommendation is to update the level of scientific consideration (I mean overall conception and methodology) of this study by mentioning recent research regarding influencing of Milankovitch cycles on orbital dynamics of Earth in Solar system as well as regarding their influencing on dynamics of Earth’s angular rotation via solar activity and climatic changes:

1. Ershkov S., Leshchenko D., Prosviryakov E.Yu. (2023). A novel type of ER3BP introducing Milankovitch cycles or seasonal irradiation processes influencing onto orbit of planet. Archive of Applied Mechanics, 93, pp. 813-822,
2. Ershkov, S.; Leshchenko, D.; Prosviryakov, E. Revisiting Long-Time Dynamics of Earth’s Angular Rotation Depending on Quasiperiodic Solar Activity. Mathematics 2023, 11, 2117. https://doi.org/10.3390/math11092117;
3. Ganopolski, A.: Toward generalized Milankovitch theory (GMT), Clim. Past, 20, 151–185, https://doi.org/10.5194/cp-20-151-2024, 2024.

Nevertheless, I should especially note that the presented manuscript is the self-consistent development in such area of researches in Earth geophysical science. My recommendation: major revision (mainly, in updating the level of scientific novelty and removing the unnecessary Appendix since it looks like unclear manipulation with reporting the main theoretical basis in Appendix). I wish to review this article after revision again.

Author Response

Please, see the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

The Milankovitch theory describes a possible link between surface albedo and the advance-retreat processes of ice sheets. However, this theory still faces an important unresolved problem: the Mid-Pleistocene Transition (MPT) in climate change. This article questions several hypotheses related to the second transition – the Early Quaternary Transition (EQT) – triggered by the million-year cycle orbital eccentricity parameter. It proposes supplementing the orbital forcing theory by introducing Western Boundary Currents (WBCs) and their role in altering low-to-high latitude heat transport to explain both the MPT and EQT. Its main conclusion is that long-period Rossby waves circulating around the subtropical gyre can be resonantly excited through subharmonic modes of solar radiation variation. This resonance can generate albedo changes caused by ice sheet growth/retreat and modulate the flow velocities of the subtropical gyre's western boundary currents. While this paper does not resolve the issues associated with the MPT, it offers a new perspective for discussing the problem. Indeed, its analysis can be viewed as a novel hypothesis explaining the MPT. The expression of the paper is very clear, and it reads smoothly. I believe it is worthy of publication。

Author Response

According to the second reviewer the manuscript can be published as is.

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

In the paper, long-term climatological cycles are analyzed. The main idea is concerned with the oceanic Rossby waves capable to be an intermediate agent between the Milankovitch astrophysical variability and terrestrial climate processes. The author attempts to explain glacial cycles in the last hundred thousand years, including the Mid-Pleistocene and Early Quaternary Transitions in the troposphere conditions. The topic is actual in order to understand the role of natural processes in climate changes, firstly in the global temperature increase or decrease. I assume that this paper can be useful for researchers studying the Milankovitch cycles and long-term natural climate variability.

In my opinion, the paper is professionally written and considers potentially important ideas. Of course, some conceptions seem very hypothetical (for example, a shift of the gyre centroid by the values lesser 1° latitude, L. 554, 622), but the analyzed topic is far from its complete understanding, which makes similar approaches possible. Besides, the Section 2 in its current form includes much literature information and cannot be considered as only methodological despite of its title. Some other remarks are indicated in the attached file. At the same time, I suggest that these comments are not critical, and the analyzed manuscript can be published in Atmosphere after minor revision.

Comments for author File: Comments.pdf

Author Response

Please, see the attached document.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report (New Reviewer)

Comments and Suggestions for Authors

This Reviewer is quite satisfied by the quality of review. I wish to author every success in his future scientific research. My recommendation is to accept as is.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The work by Pinault proposes a new hypothesis that aims to explain the Mid-Pleistocene Transition (MPT) and the Early Quaternary Transition (EQT). Most of the previous ones either require indirect interaction between certain components (e.g. continental ice sheets) of the Earth system and the 100-kyr eccentricity forcing, or has nothing to do with the eccentricity forcing (e.g. invoking the multiples of obliquity), while the new hypothesis tries to establish a direct relation between the climate system and eccentricity. This relation is established through the resonance between gyral Rossby waves circling the subtropical ocean gyre and the orbital forcings, the waves then modulate the strength of the western boundary currents and the poleward heat transport, which affects the high-latitude glaciations. Although interesting, I do not feel that the hypothesis is supported by the materials provided.

First of all, I do not accept the mathematical derivation in Appendix A. The author expands f to f0+βδ, where δ is the radial coordinate of a circle. This is clearly unrealistic because it will allow the propagation of Rossby waves meridionally along the circle, which does not happen on Earth. On Earth, the Rossby waves, once they arrive at the eastern coast of the ocean, due to the advection of by the gyre as claimed by the author, the energy they contain will be radiated either poleward as Kelvin waves or westwards as Rossby waves when they travel with the gyre along the coast. Therefore, I do not think there should be such gyral Rossby waves in the subtropical oceans. The ones that he uses as evidence of such waves in his 2018 paper (e.g. Fig. 2 of doi:10.3390/jmse6030107), as far as I can see, are neither proved to be Rossby waves nor proved to be physically induced by sunspot related solar activities. The seasonal mode water does circulate around the subtropical gyre, but it does not reveal itself as surface temperature anomalies during most part of the gyre and it does not really collide with the east coast. Moreover, it is still debated whether the mode water should be considered as a wave or not. Therefore, I have doubt on the basis of his hypothesis.

Second of all, even if the gyral Rossby waves exist, they will have to circle the subtropical gyre by hundreds to thousands of times in order for they to resonate with various orbital forcings. This longevity of oceanic perturbations within the upper ocean may be possible but hard to believe. The author will have to prove this. For now, all the subharmonic modes assumed by the author are just imagination to me.

Third of all, the definition of SI in the equation T = SI × Sensitivity is unclear and questionable. Is it averaged over the globe or only the northern mid to high latitudes? Does it stand for only the summer or annual mean insolation? These are very different between the forcings of eccentricity and obliquity.

Therefore, I feel the hypothesis is too subjective to be treated as a logical one and have to recommend a rejection.

 

Minor problems:

The citation of figures does not show up properly in most places.

In later part of the manuscript, by ice sheet, it seems the author meant for sea ice.

Fig. 2a and 4a, should the y-axis label be solar irradiance?

Reviewer 2 Report

Comments and Suggestions for Authors

First of all, I have to admit that maybe it is my fault and that I have not understood the manuscript because I do not have enough backgroud. However, this is my (subjective) opinion:

The topic of this manuscript is very complex, as it deals with the resonance associated with Rossby waves in the Western Boundary Currents of the subtropical gyres. The manuscript should clearly explain the mechanisms (mathematically) that generate this phenomenon, as well as the resonance process. However, instead of this, the only explanations in the main text consist of general statements.

For any mathematical explanations of these phenomena, the reader is referred to Appendices A and B. However, at least in my case, I am unable to understand the process. In my opinion, all the statements are presented in a very vague and imprecise manner.

In summary, I have made a huge effort, but I have not been able to understand the calculations that support the manuscript’s hypothesis: that resonance in the subtropical gyres is responsible for changes in the main periodicities of the glacial-interglacial cycles. I need detailed mathematical explanations instead of just the two appendices.