Review Reports

Round 1

Reviewer 1 Report

Review of Clay minerals and Sr-Nd isotope compositions of core CG 1601 2 in the Northwest Pacific: Implications for material source and 3 rare earth elements enrichments from Qiu et al.

 Overview

This paper from Qiu et al. presents mineralogical and geochemical data on clay samples extracted from core sediments from the northwestern Pacific Ocean. The authors are presenting evidence for an eolian terrestrial source material for those clays sampled in an oceanic basin.

This paper is relatively well-written. The hypothesis is clearly set up in the introduction and the authors provide good evidence that support their ideas.

This paper seems to present scientific novelty – although it could be slightly improve.. I welcome publication in Minerals after considering the comments I list below. I have decided for moderate revisions.

General comments

1. Major revisions needed for the method section. This major concern is why I cannot simply allow a minor revision.

Some results (bulk major and trace element compositions of sediments) are presented in section 3 Method. It should be moved to the appropriate section. However, it appears that this study did not produce new bulk geochemical data. Therefore, the whole paragraph (line 103-114) should be removed.

The isotope method section must be improved. The sample preparation description is sufficient. However, the value presented at line 169 corresponds to the ⁸⁸Sr/⁸⁶Sr (the equivalent for Neodymium is ¹⁴⁶Nd/¹⁴⁴Nd; the value is not given: these values are quite common, but either both should be written or none). These ratios (and associated values) are important for the mass fractionation correction. In short, this sentence at line 169 does not make any sense. Furthermore, I miss many important information and data: which elemental Sr and Nd solution/reference material were used (I assume NBS987 for Sr and JNdi for Nd). What are the short-term or the long-term average for these ratios? How do they compare to the literature data? 2SD (two fold of the standard deviation) of each average should give an idea of how good the standard data are (including the number of measurements, n = 10, 20 , 100?). I appreciate that some rock materials were processed and measured along the samples, but I would welcome a short sentence giving the results and just not citing a paper (you can do both obviously). What about the possible blanks? It would be good to say how much Sr and Nd are present in the samples.

All of these are very important information that must be included. I am sure the authors have produce good quality data and providing that information should not be a problem.

1. Seawater implication for Nd and Sr isotope ratios.

I see here a however a major issue. The authors completely ignore the (possible) influence of seawater on the Sr isotope ratios. In this study, the clay minerals have relatively constant ratios. Seawater has generally a ⁸⁷Sr/⁸⁶Sr ratio of 0.710, which is lower than the samples in this study. Sr is believed to be very fluid-mobile, whereas Nd is believed to be relatively fluid-immobile. Therefore, I find strange than the samples are getting in equilibrium with the Nd seawater composition but not with Sr. The authors must discuss this in their paper. A Sr profile must be shown and some explanations must be given. Perhaps this is a question of mass-balance, and Sr is not affected as much as Nd but it must be discussed in the paper.

Detailed comments:

I have made a number of comments directly in the PDF. Except for the method section, I see no major problems with this manuscript.

Figure:

Figure 1. what is the arrow showing? I believe the arrow should be pointed in the other direction.

Figure 4: what are the arrows showing? I assume you want to show the labels, but in this case, I suggest point to the other direction (from label to the field.

Line 269-272: does it belong to the text or to the figure?

Figure 5. Same comment for lines 305-307. It would be good to extend the MORB field. This is only 4 points. I am sure there is more data to show from databases such as PetDB. At least, it should be mentioned why the MORB field is limited to those 4 data points. It does not change the rest of the story.

Figure 7. Just to be picky, I am not sure at all that Nd correlates with depth. This correlation totally ignores the depth at 75-150 cm.

References cited:

Bouvet et al. (2008), EPSL 273. The Lu–Hf and Sm–Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you so much for your comments, your comments are very helpful for revising and improving our paper, and please see the word profile for our response. Besides all the revisions (including the comments we responded directly in the PDF) we made had been marked up using the “Track Change” in revised manuscript.

Reviewer 2 Report

The studied area is considered to be mainly from the input of Aeolian materials, therefore it is difficult for the study area to form high-grade REY-rich muds. So what is the origin of sediments of a large number of rare earth elements and yttrium (REY)-rich sedimentsin nearby areas? Please discuss the relationship between them, Aeolian material deposition also needs to analyze the morphology of mineral particles through scanning electron microscope. For example, quartz and zircon are rounded in aeolian deposition. In addition, aeolian deposits usually contain pine pollen, because these pollen have air bags and can be transported far away. Try to supplement multiple evidences other than element geochemistry, which can be supplemented by the study of scanning electron microscope.

Author Response

 Dear reviewer,

Thank you so much for your comments, your comments are very helpful for revising and improving our paper. The following is our reply：

The larger number of rare earth elements and yttrium should be directly drive from seawater. At presents, lots of studies have reported the high-grade REY-rich muds in nearby areas (Southern Sea area of Minamitorishima Island). Fossil debris bio-apatites are proposed to be the primary hosts of REY in deep sea sediments (Kon et al., 2014 RG; Yasukawa et al., 2018 OGR; Mimura et al., 2019 Journal of Asian Earth Sciences; Takaya et al., 2018 SR) and followed by micronodules (eg., Yasukawa et al., 2021 Minerals; Bi et al., 2021 OGR; Yu et al., 2021 OGR; Zhou et al., 2021 OGR;). The REY in these sediments is mainly captured directly from overlying seawater by bioapatite and micronodules at the water-sediment interface that make these two kinds of phases enrich in amount of REY.

 The sediments compositions and types of the REY-rich sediments in nearby areas are basically similar with the study sample, for example, core KR13-02 PC06 and core KR14-02 PC01(as also showed in figure 9), they are both clay or clay with zeolite, which are nearly the same with our study. But the core KR13-02 PC06 enriched in relative high grade of REY while our study core-GC01 KR14-02 PC01 did not. It is because of different deposition rate caused by LCDW (which I have also mentioned in second paragraph Section 5.3-from line) resulting in the different grade of REY. So, the origin of sediments of a large number of rare earth elements and yttrium (REY)-rich sediments in nearby areas should also be east Asian dust. And for more clear, in line 375-378, we change the sentence “then the sediments in the South Sea area of Minamitorishima Island, which are very close to each other” as “then the sediments with nearly the same types in the South Sea area of Minamitorishima Island, which are very close to each other in relation to tectonic environments”

      We are sorry that we did not analyze the morphology of mineral particles of aeolian materials by scanning electron microscope, because we focus on clay minerals compositions and element geochemistry (including isotope and bulk geochemistry) our sediments core, and to discuss the material source of our samples. And we discussed reasons for REY depletion of study aera, our study is regional. But we still very thank for such a conductive advice.

Author Response File: Author Response.pdf