Modelling the Present Global Terrestrial Climatic Response Due to a Chicxulub-Type Asteroid Impact
Round 1
Reviewer 1 Report
The authors have improved the manuscript compared to the previous version by adding more proper references and also by discussing their results better in the light of previous work. It is still not entirely clear what is novel in their work compared to other published work on the topic.
I still disagree with their statement that "The impact of Chicxulub-like asteroid events occurs on average between ~27 to 200 Myr" - there is no such precision, and they just quote one (of many) models. The proper way to say this is that impacts of that magnitude occur on average every few tens to few hundreds of millions of years". Not much more can be said.
Where the authors have failed miserably, however, is that they did not improve the language quality of the manuscript. They claim, in their reply, that "A native English speaking colleague found the paper quit understandable.". Even this sentence contains an error - the word should be "quite" not "quit". And it's a difference to understand something, versus being written in grammatically proper English, and without so many typographic errors.
A few (or many) examples:
line 34: "...water vapour plums..." - a plum is a fruit!!!!
line 40: This object, known as Chicxulub, of ~11 of diameter [15] - two errors in these few words: the object had no name, the CRATER it created is now called Chicxulub, and after 11 the units (km) are missing (aside from the fact that nobody says it was exactly 11 km in diameter - the usual value given is "about 10 km in diameter", with a large uncertainty.
line 140: "...a partially submerged plataform constituted by a tick sequence (3 Km) of.." - three (!!) errors in these few words: it should be platform, not plataform, a tick is an insect (the word should be "thick"), and it should be km not Km (K means Kelvin...).
Line 280: the exact same wrong sentence (partially submerged plataform constituted by a tick sequence (3 Km)) appears here -- showing that they just cut and paste their sentences - not very honest work.
line 286: "...Northamerica, Africa or North of Asia..." - It is "North America", and what means "North of Asia"? That's where the Arctic is...or maybe it should be "northern Asia"? Who knows....
line 288: what is "oceanic cortex" supposed to mean? A cortex is part of the brain. No such word is used in the international geological language.
line 295: "...one such objet struck..." - should be object, not objet....
It is frustrating to see such a badly written manuscript. If the writing is already so sloppy, and they cannot bother to even properly check their spelling, what does this mean for their calculations? Are they equally sloppy?
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Second review of Mendoza et al
I appreciated the efforts made by the authors to respond to my (and presumably other reviewers) suggestions for improvement. It appears many suggestions were accommodated. However there are a few outstanding issues that should be corrected before publication. These include a need to proofread the text thoroughly as it was especially noted the text in highlighted yellow (presumably the new text) has numerous typos and grammatical errors that need fixing. In consultation with the editor, I have not listed these and their corrections as the journal has a copyeditor that can work with the authors to fix these issues should the paper be accepted. Instead I am keeping this review to the key content issues or tonal issues that need correction. These include: 1) a need to continue to make it clear that the specific effects of Chicxulub were dependent on the target geology; the authors have partially done this but I highlight a few additional locations where its needs to be clear. 2) some clarity on assumptions in several locations so that the results can be better understood. 3) a bit more updating on referencing. Lastly I was uncertain how robust the sulfur content of the average asteroid was…the authors seem to hang a lot on this but did not spend the requisite time explaining why this is a good assumption within the discussion. With these relatively minor edits plus a significant round with the journal correcting typos etc., then this paper should be ready for publication. However, a major caveat is that the 100Gt of S issue really must be clarified that this is a real number since it is uncited. I have seen this number as a very conservative estimate for release at Chicxulub but not a # inherent to the asteroid? In lines 137-141 it makes it sound like there is 100 Gt in the asteroid and then perhaps the same in the target??? In Artemieva et al the calculation is 325 Gt in the target…not the asteroid. Later in the paper there does seem to be an implicit assumption of significant amounts of S from an asteroid itself. This needs citing and explaining especially based on different kinds of asteroids for the reader to know if this is a good assumption. So overall, this issue needs checking, citing and clarifying, but if that is all okay or edits happen around that then the rest of the issues are minor. One final point see comments on lines 285-286 which make no sense geologically…have a geologist colleague assist here to give a more reasonable explanation of other possible targets and their potential climatic consequences.
Line by line
12-13: need to state assuming the same target geology of carbonates and evaporites. The rest of the abstract basically are effects that would only happen if that was the target.
33: tsunami is actually the singular and plural in Japanese
34: plums! Also deposition is not the right meaning…injection perhaps?
40: The asteroid was not called Chicxulub. The impact crater is called Chicxulub. Also the latest papers both Artemieva et al., 2017 and Collins et al. 2020 (Nature Communications published today) suggest 12 km asteroid. Recommend fixing this and adding the new citation.
40-41: Here and throughout might as well use the right spelling for Yucatán and México, no?
49: Combine with previous paragraph
137: I have no idea where this assumption comes from! The 100 Gt # I have seen from Brugger et al was a conservative estimate for release from the Yucatán target rocks not the asteroid…
140: tick!
219:Note Brugger et al used 100 Gt for the target without knowing the actual number. We now know the best estimate is 325 Gt. However you are doing this for a modern Earth so using 325 is not required, but this language in the star tof the discussion needs to explain this. The real value at the K-Pg was at least 325 Gt. A paper that just used 100 Gt from the target showed major effects however and you use this more conservative number for a modern scenario where a Chicxulub impact sized asteroid hits a sulfur rich target today.
251-252: Explain and cite this idea of significant S straight from the asteroid?
285-286: Needs help…what is an oceanic granite craton???? Granitic cratons are the center of continents. Oceanic plates are the polar opposite and are basaltic…the rest of this sentence is also confused as there are a lot of sedimentary basins out there and there are a lot of elements in addition to S. Should discuss what is a sandstone (silica rich) province, what if a carbonate province (Ca CO3 so releases CaO but not S)? This discussion is weak and need improving.
288: Cortex??? Drop the whole parenthetical sentence.
289-290: Again no idea where this amount of S from the asteroid comes from…if you are going to hang your hat on it then needs citing and explaining in terms of % of asteroids with quanity of sulfur etc.
294-297: Again MUST say all of this paper is based on a Chicxulub sized even into a similar sulfur rich target…
312-314: Need to explain this assumption that S is also in the asteroids of sufficient quantity and then explain earlier how you came to this assumption.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
This manuscript may be acceptable for publication and has addressed many of the points raised in the first round of reviews.
However, there are significant enough edits to the English that this reviewer must recommend that the article undergo a thorough proofreading by a writer with a high-level of fluency in scientific English writing.
Finally, on lines 312-314, the authors indicate that smaller asteroids also produce semi-permanent climatic shifts on Earth. Presumably there is a small enough asteroid that no shift in the Earth's climate occurs. For example, a meteorite that does not impact the surface would not be large enough to permanently alter the Earth's climate. Tunguska also did not alter the Earth's climate and that meteorite had a size of 50-160 meters. At what size asteroid, according to the author's model, does the Earth return to its pre-impact climate over the time-span that the model is run? It appears that the authors have done some or many of these calculations and should be able to answer this easily. This information needs to be provided to the readers.
Author Response
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Round 2
Reviewer 1 Report
Thank you for finally providing a well-edited and readable manuscript, besides correcting the last few scientific issues. I have now no more objections regarding publication of this study.
Author Response
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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
I have to point out at the onset that I am not qualified to check the climate model itself; I am a geochemistry specializing in impacts, but not in climate models.
However, reading the parts that I do know something about I noticed some errors and problems. The authors need to do a better job with reviewing the literature on Chicxulub and on impact cratering.
A recent paper that deals with large-scale impact/climate effects might be of interest to the authors:
Meteoritics & Planetary Science 54, Nr 10, 2273–2285 (2019)
doi: 10.1111/maps.13294
Also, some of the literature is not cited correctly or not up to date. Furthermore, the language needs quite some editing/improvement.
Some main problems are:
First line ob abstract (line 12) and further down, the authors claim some "periodicity". In fact the current understanding is that there is NO periodicity involved at all. Maybe what the authors try to say is that events of such magnitude happen on average between ca. 30 and 200 million years - but this is totally different from "periodicity". Maybe it's just bad English...
Line 34, tsunamis and effects of fireball - there are many more recent publications on these topics that are not cited; it appears only outdated papers are cited here. I recommend the authors lo9ok at, for example:
Morgan et al., doi:10.1002/2013JG002428
Gulick et al., www.pnas.org/cgi/doi/10.1073/pnas.1909479116
Robertson DS, et al. (2013) K-Pg extinction patterns in marine and freshwater environments: The impact winter model. J Geophys Res Biogeosci 118:1006–1014.
Robertson DS, et al. (2004) Survival in the first hours of the Cenozoic. Geol Soc Am Bull 116:760–768.
and a few others.
Line 41, the authors state: ...Chicxulub (impacted) in the Yucatan Peninsula in Mexico ~65.5 million years ago [10].
But reading Renne et al. (their reference 10) states an age of 66.04 Ma. How can one misquote such an age (more than once in the current manuscript!).
I would also wish that there was more of a discussion, comparing the current results with those of earlier work by Pierazzo et al., or Brugger et al.
The results themselves appear to be plausible, but the manuscript needs to be improved to reflect the problems cited above.
Best regards,
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Review of Mendoza et al
This paper represents an interesting thought and modeling exercise that basically asks what if the Chicxulub impact happened today. The modeling itself appears quite good however the fundamental underlying assumptions of this paper need to be better stated. The entire paper is based on modeling exactly a Chicxulub event, which is where an 11-12 km asteroid strikes a 2/3 carbonate, 1/3 4 km thick sedimentary basin at 60 degree angle. These are the assumptions that produce the sulfate aerosol numbers in the Artemieva and Morgan 2017 paper which are then modeled for a modern day Earth here. In addition to being totally clear about the assumptions, the authors really need to significantly expanded discussion section which includes: other studies that have modeled the atmospheric effects of Chicxulub in particular Brugger et al 2017 that did exactly the same kind of model as here but for the Cretaceous atmosphere, other possible target locations for the hypothetical impact since the evaporite/carbonate basin might possible be the worst case scenario, and other implications of different parameters such as varying the size, varying the angle of impact etc. Lastly this paper would be really even better if they modeled other impact sites for instance either Antarctica or an ocean would be largely water vapor release…what then? Or what if a river valley and thus silica dust and water release? Or what is a granite craton in the middle of a continent? This would make the paper even more interesting and likely more widely read. See line by line notes below and pay attention to reference issues and mistakes like the age of the impact. Pleasure reading your paper and I hope my comments help.
Line-by-line Comments
32: fireball is not strictly correct. Suggest “…from the thermal radiation..” instead.
38: Should mention the current observations of near Earth objects here and the current lack of any large untracked asteroids … so while statistically this is correct, it might be not be strictly true right “now”.
39: Awkwardly written. Perhaps “One such object, a ~11km diameter asteroid, struck what is now the Yucatán Peninsula in México 66 million years ago (Cretaceous-Paleogene, K-Pg).” Note your age is off, the timescale was changed in 2012 from 65.5 to 66.0 Ma to match the best dates for Chicxulub and these have been subsequently verified. The reference you use here actually does have the right age (66.038 ± 0.025/0.049 Ma).
41: Awkward. “…part of the species..” makes no sense. Perhaps “…extinction of 75% of life”.
41-42: I would drop this sentence or change it. Latest work puts Deccan not a the right time (flows before and after but not during and the extinction is very rapid so not multiple causes). Suggest: “Studies of the affect of CO2 release from the largest Deccan flow show no correlation with the K-Pg extinctions (Hull et al., 2020).” Paper is in Science builds on a large array of papers recently showing how rapid the extinction was and how rapid the impact effects were (see Gulick et al., 2019 in PNAS for instance) and thus how Deccan does not match timing or observations.
44: Suggest “…impact a sulphur-rich…”, also need a reference here. Recommend Artemieva and Morgan, 2017 which is in your citations already plus Artemieva and Morgan, 2020, GRL (on the dust), and Gulick et al., 2019, PNAS (on the Sulphur).
47: Ref 16 could be dropped as it is about soot not Sulphur
48: extra space, also impact where? This would totally depend on if the asteroid struck a similar evaporite rich province right? Not just anywhere. For instance if it hits the oceans then the volatile release would be largely water vapor right?
110: Is this also true if you look at Artemieva and Morgan, 2020 #s? Note Chicxulub made carbonate dust and sulfate aerosols due to a mixed limestone and carbonate target…must explain target choice in this paper.
141: asteroidal is not needed. Just use asteroid
204: This Discussion is really insufficient in my mind. It should have paragraphs on modeling done for Chicxulub in terms of effects of the same processes on the Cretaceous atmosphere (e.g., Brugger et al., 2017, GRL). It should also have paragraphs discussing different effects of where such a hypothetical impact might occur. You are making the assumption that this impact hits in exactly the same type of target at exactly the same angle as Chicxulub did (following the Artemieva and Morgan, 2017 paper)…what if it hit a granite craton in the center of a continent, what if it hit a sediment laden (silts and sands not carbonates and evaporites) river valley, what if it hit an ocean (shallow vs deep), what if it hit Antarctica? All of these would have vastly different effects and you should at least discuss even though you did not model these possibilities specifically. However even better would be a large suite of models wherein you test the effects of hitting different locations on Earth today. That would be really interesting!
218-220: Reword similar to what I recommended for the intro. Also age is wrong, its 66 Ma, and extinction rates can be quantified to 75% of life.
221: “..such an event…”
222: “…assuming the same size asteroid struck at the same angle on the same type of geologic target…”
Author Response
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Reviewer 3 Report
The manuscript investigates the temporal evolution of the Earth’s climate following the major asteroid impact of Chicxulub. The work describes the immediate aftermath, in terms of surface temperatures, sea- and land-ice extent, with the model plausibly claiming gross reductions in insolation due to the asteroid, associated and slightly longer-lived reductions in surface temperatures, with low-latitude reductions being the most severe, and, more controversially, planetary ice coverage continuing for decades into the future. The controversy arises because the persistence ice cover is a finding of the model and insufficient information is provided on how that finding can be verified. Overall, the results of this paper are intriguing and it may be acceptable for publication in Atmosphere subject to major revisions.
First, the manuscript’s results are developed from a thermodynamic climate model that they reference, and for which they appear to be primary developers. However, it is not made clear if this model achieves radiative-convective equilibrium, which would be a necessary prerequisite for using it for this type of analysis. Additionally, how are readers supposed to think about the uncertainty in the results presented in this paper? Much more information is needed about the choices as they relate to feedbacks. Is a cloud feedback derived from observations valid with vast increases in cloud condensation nuclei? Won’t that create a much more reflective planet, at least for a few years, which could increase the formation of sea-ice? Already we see from Figure 2 that clouds offset the water vapor feedback. How does the model perform when compared to Tambora or Krakatoa?
Second, the results seem to suggest that a large perturbation in the Earth’s climate system leads to a change in the Earth’s equilibrium climate, indicating that the Earth’s climate, due to ice-albedo feedbacks is actually metastable, and that asteroidal impacts such as Chicxulub are easily large enough to lead to very long-term changes. If that is a fair reading of the authors’ findings, the authors need to make that point explicitly and then run their model with smaller asteroids to see the point where the Earth’s climate responds elastically to a perturbation. That would be a finding of great scientific interest, because it could show how an instantaneous, large perturbation could lead to mass extinction through a semi-permanent shift in the climate system. Tambora and Krakatoa did not lead to such a shift, but Chicxulub may have.
Finally, and this is the most critical part, it is quite unclear how testable the model’s results are. Why should the readers have confidence in the output of this model? Can it produce falsifiable hypotheses?
A few minor points also need to be considered:
- Figure 6 is not quantitative
- There are enough grammatical errors in the paper to warrant a thorough proofreading for the revised submission.
Author Response
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