Late Miocene–Pliocene climate evolution recorded by the red clay cover on the Xiaoshuizi planation surface, NE Tibetan Plateau

Li, Xiaomiao; Peng, Tingjiang; Ma, Zhenhua; Li, Meng; Feng, Zhantao; Guo, Benhong; Yu, Hao; Ye, Xiyan; Hui, Zhengchuang; Song, Chunhui; Li, Jijun

doi:https://doi.org/10.5194/cp-15-405-2019

Articles | Volume 15, issue 2

https://doi.org/10.5194/cp-15-405-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/cp-15-405-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 15, issue 2

Research article

| Highlight paper

|

11 Mar 2019

Research article | Highlight paper |

| 11 Mar 2019

Late Miocene–Pliocene climate evolution recorded by the red clay cover on the Xiaoshuizi planation surface, NE Tibetan Plateau

Xiaomiao Li, Tingjiang Peng, Zhenhua Ma, Meng Li, Zhantao Feng, Benhong Guo, Hao Yu, Xiyan Ye, Zhengchuang Hui, Chunhui Song, and Jijun Li

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Final revised paper (published on 11 Mar 2019)
Preprint (discussion started on 04 Jul 2018)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of Li et al.', Anonymous Referee #1, 06 Aug 2018
- AC1: 'Reply to 'Review of Li et al.'', Xiaomiao Li, 02 Sep 2018
- AC2: 'Reply to 'Review of Li et al.' in detail', Xiaomiao Li, 12 Sep 2018
RC2: 'cp-2018-73 review', Anonymous Referee #2, 06 Aug 2018
- AC3: 'Reply to 'cp-2018-73 review'', Xiaomiao Li, 12 Sep 2018
RC3: 'Review of Cp-2018-73 by Li et al.', Anonymous Referee #3, 26 Aug 2018
- AC4: 'Reply to 'Review of Cp-2018-73 by Li et al'', Xiaomiao Li, 12 Sep 2018

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (03 Oct 2018) by Ran Feng

AR by Xiaomiao Li on behalf of the Authors (20 Oct 2018)

ED: Referee Nomination & Report Request started (27 Oct 2018) by Ran Feng

RR by Anonymous Referee #3 (17 Nov 2018)

Suggestions for revision or reasons for rejection

This is my second round of review of this manuscript. Compared with the last version, the revised manuscript is significantly improved. I have no major concerns but some minor questions and suggestions as listed below.

P82-84: Red clay indicates aridification? And why this indicates uplift of TP? The logics here are not clear. In the next sentence, the authors state that red clay could reflect either arid or humid climate.

P103: what are the climate trends in the northern TP? There is no description. Maybe “central Asia” or “NW China” is more accurate?

P112: “climatic characteristics”? what does this mean?

P124: better to show “Maxianshan” and “Longzhong Basin” in Fig. 1c.

P147: From Fig. 1b, carbonate nodule horizons are more abundant in the upper part, e.g., < 4.8 Ma. So does appearance of carbonate horizons also reflect climate changes?

P192: I can understand that larger CV indicates more variable climate, but how could you infer more humid from CV?

P193: The depositional rate is not a good evidence here. As there are also other abrupt drops or increase. Why do you pick the 4.8 Ma out? I suggest to delete this evidence.

L331: which part of Fig.5? There are many sub-parts in Fig.5, better to denote each clearly.

L345-346: From Table 3, comparing the two intervals, the Rb/Sr difference is only 0.02 and the K2O/Na2O difference is 0.14, no more than 3.5% of the exhibited value range (e.g., 0.3-0.9 for Rb/Sr; and 1-5 for K2O/Na2O). Does this small difference truly reflect climatic difference? What are the analytical errors of these parameters? Could this small difference be interpreted as analytical errors, or the small difference actually indicate no difference between interval I and interval II.

L348-350: Here, the authors indicate that the <2um/>40um ratio is characterized by low values. However, this contradicts with values presented in Table 3! This is apparently a false claim.

L435: apparently, from Table 3, the <2um/>40um ratio is low during interval II!

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RR by Anonymous Referee #4 (04 Dec 2018)

Suggestions for revision or reasons for rejection

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.

General Comments:

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.

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ED: Reconsider after major revisions (19 Dec 2018) by Ran Feng

AR by Xiaomiao Li on behalf of the Authors (16 Jan 2019) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (22 Jan 2019) by Ran Feng

Dear Xiaomiao,

Judging by previous reviews, I lean towards trusting your geochemical and sedimentary analyses. However, I do have concerns about your discussion. I am worried that the discussion of mechanisms accounting for EASM expansion during early Pliocene was built upon misunderstanding of early Pliocene tropical SST records. The records cited in your discussion did not cover late Miocene, and hence should not be used to argue for expansion of monsoon starting from early Pliocene. The long records from western tropical Pacific actually suggest similar and warmer than present-day SSTs for both early Pliocene and late Miocene.

I recommend rewrite and shorten the discussion. Please stick with interpretations from sedimentary and geochemical features to monsoonal climate. The discussion of mechanisms reads very weak, and as shown above, erroneous at various places.

See details in the below:
Line 566 to 572, Brierley et al., 2009; Fedorov et al., 2013 did not suggest that equatorial SSTs remain stable or cooled. Instead, Brierley et al. suggests that warm pool was expanded during the early to mid-Pliocene. Zhang et al., (2014, science) actually suggests that western tropical Pacific was significantly warmer during the late Miocene and early Pliocene. The argument from line 566 and 575 is based on misunderstanding of published literatures.

Line 572 to line 575, the cited studies provide no theoretical basis on how the northern high latitude warming would affect ITCZ position. This argument again has no support.

Line 582 to 584, again, misinterpretation of Brierley et al and Fedorov et al. Notice that the tropical Pacific records discussed in these papers DO NOT cover late Miocene for the most part. You CANNOT cite them to highlight the uniqueness of early Pliocene. In fact, based on Zhang et al., 2012, the western tropical Pacific during late Miocene is not that different from early Pliocene.

Thanks for taking time to revise the manuscript! I am looking forward to your submission!
Ran

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AR by Xiaomiao Li on behalf of the Authors (26 Jan 2019) Author's response Manuscript

ED: Publish as is (17 Feb 2019) by Ran Feng

AR by Xiaomiao Li on behalf of the Authors (22 Feb 2019) Manuscript

Short summary

Multiple proxies for the XSZ planation surface reveal that the climate was dry and stable during the late Miocene but became intermittently humid with more seasonality at 4.7–3.9 Ma. Regional climatic differences between the central and western CLP reveal that expansion of the paleo-EASM occurred during the early Pliocene. The warming of the high northern latitudes in response to the closure of the Panama Seaway may have been responsible for the thermodynamical enhancement of the paleo–EASM.