|The authors investigate a new red-clay serious with special regard to palaeoclimate reconstruction in a critical region of the Tibetan Plateau. The authors find an abrupt change in precipitation character (to wetter and seasonally more varied conditions) after 4.8Ma, which they interpret as an increased westward reach of the East Asian Summer Monsoon (EASM). This work is important as it helps constrain this westward extension of EASM on the Tibetan Plateau during the late Miocene and Pliocene. |
Overall, the manuscript is well structured and well written. However, important methodical details are omitted in the presentation of results. The language is good, although minor mistakes and occasional poor phrasing can be found throughout the manuscript. I recommend proofreading of a proficient English speaker.
My major concern pertains to the lack of use or description of statistics and signal processing. The main example of this is the seemingly arbitrary subdivision of the record into Interval I and Interval II. I suggest either finding a more robust way for change point detection, or refraining from this subdivision altogether. The broad implications of this study remain the same even without the somewhat unnecessary subdivision. Furthermore, the term significant is used several times, but it is unclear how significance was determined. Furthermore, it is unclear how the statistical dependence between several variables was established. I urge the authors to take advantage of the existing tools in statistics to substantiate such claims. There needs to be a section (in “3. Materials and Methods”) describing these methods.
Lastly, while the inclusion of discussion of possible climate change drivers is important, I urge the authors to highlight the uncertainties of these more, since only limited evidence is presented here.
Note that I cannot comment on details about sample preparation and methods pertaining to proxy reconstructions as those lie outside my fields of expertise. I strongly recommend that other reviewers with complementary expertise comments on these to compensate.
While I do believe this work to be valuable to several geoscientific communities, I can recommend publication only after the points above have been adequately addressed and a reviewer with a stronger geochemical background has commented on the manuscript.
Additional Specific Comments:
In the introduction, the authors correctly point out many problems of using the Pliocene as an analogue for future climate. An additional factor compromising the Pliocene as an analogue are the differences in palaeotopography.
L 50 “in” instead of “on”
L63 It should say “contrast” (not plural) to be consistent with the rest of the sentence, and maybe using “gradient” would be less confusing. What zonal gradients are you referring to? Do you simply mean zonal differences (differences along the same latitudes)? In this case, the term gradient may be a tad misleading, as it is used to describe the slope or one directional change as you have in case of meridional gradients.
L74 “latter” instead of “later”
L75-76 By “structural changes”, I assume you are referring to spatial structure and mean that the regional expressions of global climate change were highly varied?
L76 change to “… the regional climate is like ...”
L84 “was enhanced” instead of “enhanced”
L96 needs some rephrasing
L112 What are these distinct geomorphological and climatic characteristics? Do you mean the above described geographical and climatic setting?
L187 Does the coefficient of variation change significantly for ALL of the records? How was this established? By looking at it purely qualitatively, I would subdivide the section above the division up again into a higher variability lower part and lower variability upper part (that is similar to what is below the currently drawn line). In other words, the subdivision into interval I and interval II seems rather arbitrary. It looks to me like there is only a brief period of higher variability from 15-10m, interrupting the period of relatively low variability.
L264 What correlation analysis is this based on and how was significance determined?
L342 How was the significance of this change determined (see above)?
L393 Again, how was this relationship and significance determined?
Fig. 1c: Please use standard units like km and hPa, not miles and mb.