Fish Teeth Sr Isotope Stratigraphy and Nd Isotope Variations: New Insights on REY Enrichments in Deep-Sea Sediments in the Pacific
Round 1
Reviewer 1 Report
Dear Authors,
Please find in the attached file my suggestions in order to improve your manuscript. The manuscript is very interesting, but some data needs to be corrected as indicated in the attached document.
Best regards
Comments for author File: 
Comments.pdf
Author Response
We have made sufficient amendments according to the comments of the Reviewer, and the specific amendments are as follows.
- We revised all typos and grammatical errors marked by the reviewer.
2. Line 79-80: Is there any specific reason why you chose P10 among all the other cores? If yes, add this information.
Reply: agree and revised. The P10 contanins both high REY content and low REY content sediments for comparison. In addition, the P10 adjacent to Deep-sea Drilling Project (DSDP, site 170 in the Middle Pacific which has been known the age of the sediments.
3. Figure 1 says Mid-Pacific Basin. Is it the same thing as Central Pacific Basin? If yes, be coherent with the used terminology.
Reply: agree and revised.
4. In the text, you locate the study area in respect to the Marshal Islands. However, the Marshal Islands are not identified in the map! Locate them..
Reply: We have identified the Marshal Islands in the map (Figure. 1).
5. Indicate in the caption of Figure 2 that P corresponds to piston.
Reply: agree and revised.
6. Figure. 3: Indicate in every photo that this corresponds to cmbsf as it is not clear.
Reply: agree and revised.
- Line 195-196: Is this sentence only referring to P10? If yes, refer to it the sentence.
Reply: agree and revised.
- Figure. 4: The used letter fonts for P2 is different from the other Ps.
Reply: agree and revised.
- Line 267: What is the Deep-Sea Drilling Project? Some of the readers may not be familiar with it. Give some short information about it.
Reply: We have added some short information about the Deep-Sea Drilling Project.
- Line 269-270: Are there any references for this assumption?
Reply: We have added reference here (initial reports (Volume 17, Site 170)).
Reviewer 2 Report
General Comment:
This paper report spatial distribution of rare-earth element and yttrium (REY) content in the surface sediments of 14 piston cores collected from the central and western Pacific with an aim to identify REY-rich sediments. In addition, they have measured Sr and Nd isotopic compositions in the fish teeth detritus (apatite) in a piston core in the Central pacific at various depths. They have attempted to constrain the age of sediments (using Sr ratios) and capture the past sea-water signature (using Nd isotope) to possibly understand factors controlling REY enrichment in the sediment. The manuscript is well written and data are thoroughly discussed. The study provides new information with sound scientific interpretation and I believe, such studies are important to advance our understanding while we explore for the deep ocean metal resources. Thus, I recommend for its publication with minor revision.
Specific comments:
- Line No. 98-100: It is stated that the top portion of core P10 consists of pelagic clays, but in the figure 2b it is marked as zeolite clays. From the caption reader may understand that the surface clay type but the author intends to show the dominant clay type I guess. Please make it clear.
- The length of the core P10 is mentioned as 7.2m in the text and given as 5.2m in the table. 1. The caption of table 1, it is given length of surface sediments (< 2m) but different lengths are reported in the table (mostly more than 2 m). This is unclear ! I suggest to revise table caption.
- Figure 2a: The LREE/HREE is declining towards the central pacific from east and west pacific. Most of the pelagic sediments mainly consists of Aeolian deposits or what may be the major sources for this pelagic sediments? Is the high LREE/HREE ratios in the western pacific is due to the sediments input from the rivers? The low LREE/HREE at the central pacific is due to any hydrothermal activity? A brief explanation/information can be added while discussing these results.
- Details on the sub sampling length of the cores will be more informative and help the readers to understand the resolution of the REY concentrations with depth.
- High REY concentration in the core P10 is mainly in the depth from 2 to 6m and consists of zeolite clays. The main reason for the high REY may be because of the Zeolite clays as they can accommodate wide variety of cations. Probably need further discussion.
- Sr ratios are reported with varying significant numbers. Be consistent!
- Figure 7: The εNd values on the X-axis are missing.
- Line 264-265: Need to rewrite.
- Line 327: The opening of Drake Passage is around ~41Ma which is late Eocene. Please check it!
Author Response
We have made sufficient amendments according to the comments of the Reviewer, and the specific amendments are as follows.
- Line No. 98-100: It is stated that the top portion of core P10 consists of pelagic clays, but in the figure 2b it is marked as zeolite clays. From the caption reader may understand that the surface clay type but the author intends to show the dominant clay type I guess. Please make it clear.
Reply: agree and revised. The author intends to show the dominant clay type and have revised the caption of figure 2.
2. The length of the core P10 is mentioned as 7.2m in the text and given as 5.2m in the table. 1. The caption of table 1, it is given length of surface sediments (< 2m) but different lengths are reported in the table (mostly more than 2 m). This is unclear ! I suggest to revise table caption.
Reply: agree and revised. The table.1 shows the water depth and length of the 14 piston cores, with type and REY content of their surface sediments (<2m) in the study area.
The caption of table. 1 has been revised to be clear and the length of the core P10 has been modified to 7.2m in the table. 1.
3. Figure 2a: The LREE/HREE is declining towards the central pacific from east and west pacific. Most of the pelagic sediments mainly consists of Aeolian deposits or what may be the major sources for this pelagic sediments? Is the high LREE/HREE ratios in the western pacific is due to the sediments input from the rivers? The low LREE/HREE at the central pacific is due to any hydrothermal activity? A brief explanation/information can be added while discussing these results.
Reply: The study area is located in the middle and western Pacific Ocean basin. The sedimentary environment of the study area is similar, and it is less affected by hydrothermal activities. The sediment types are mainly pelagic sediments, and their material composition is mainly aeolian clay, followed by zeolite, micro-nodules and biological residues, and a small amount of quartz and feldspar. The North American shale composite (NASC)-normalized REE patterns of the sediments in this area (Fig. 5) shows that the REY distribution pattern is consistent and there is no fractionation. Therefore, the author believes that LREE/HREE declining towards the central pacific from east and west pacific(Fig .2a), mainly because of the overall REY content in the sediments also show the same declining trend, rather than being affected by provenance.
4. Details on the sub sampling length of the cores will be more informative and help the readers to understand the resolution of the REY concentrations with depth.
Reply: agree and revised. Detials on the sub sampling length of the cores have been added in the part of 2.1(Study area and samples): “Samples of were taken for REY analysis at a sampling interval of 15 cm continuously from the top to the bottom of the cores.”
- High REY concentration in the core P10 is mainly in the depth from 2 to 6m and consists of zeolite clays. The main reason for the high REY may be because of the Zeolite clays as they can accommodate wide variety of cation Probably need further discussion.
Reply: Yes. Zeolite clay usually contains high REY content, and zeolite was once considered to be one of the main carrier phases of rare earth elements (kato et al., 2011). However, recent studies have shown that the REY content of zeolite in the Western Pacific is less than 100 μg/g (Wang et al., 2016) and zeolite is not the main factor leading to REY enrichment in sediments. More and more studies have found that the enrichment of REY in deep sea sediments is related to phosphate (Kon et al., 2014; Kashiwabara et al., 2014; Ren et al., 2015; Wang et al., 2016).
References:
Kato, Y., Fujinaga, K., Nakamura, K., Takaya, Y., Kitamura, K., Ohta, J., Toda, R., Nakashima, T., Iwamori, H., 2011. Deep-sea mud in the Pacific Ocean as a potential resource for rare-earth elements. Nature geoscience 3,535–539.
Wang, F.L.，He, G.W.，Sun, X.M.，Yang, Y., Zhao, T.P., 2016. The host of REE + Y elements in deep-sea sediments from the Pacific Ocean. Acta Petrologica Sinica 32(7), 2057–2068 (in Chinese).
Kon, Y., Hoshino, M., Sanematsu, K., Morita, S., Tsunematsu, M., Okamoto, N., Yano, N., Tanaka, M., Takagi, T., 2014. Geochemical Characteristics of Apatite in Heavy REE-rich Deep-Sea Mud from Minami-Torishima Area, Southeastern Japan. Resource Geology 64(1), 47–57.
Kashiwabara, T., Toda, R., Fujinaga, K., Honma, T., Takahashi, Y., Kato, Y., 2014. Determination of host phase of Lanthanμmin deep-sea REY-rich mud by XAFS and u-XRF using high-energy synchrotron radiation. Chem. Lett. 43,199–200.
Ren, J.B., Yao, H.Q., Zhu, K.C., He, G.W., Deng, X.G., Wang, H.F., Liu, Y.G., Fu, P.E., Yang, S.X.,2015. Enrichment mechanism of rare elements and yttrium in deep-sea mud of Clarion-Clipperton region, Earth Science Frontiers 22(4), 200–211 (in Chinese).
- Sr ratios are reported with varying significant numbers. Be consistent!
Reply: Yes. Sr ratios have been revised to be consistent.
7. Figure 7: The εNd values on the X-axis are missing.
Reply: The εNd values on the X-axis has been added. At the same time, the εNd values of the lower layer was added in Figure 7.
8. Line 264-265: Need to rewrite.
Reply: agree and revised. Based on the comments of another reviewer, the whole paragraph has been rewrited.
9. Line 327: The opening of Drake Passage is around ~41Ma which is late Eocene. Please check it!
Reply: Yes, we have checked the time according to the Vérard et al. (2012). “From 84 Ma, a transpressive collision takes place in the Scotia region, with active margin to the east. As subduction propagates northwards into an old and dense oceanic crust, slab roll-back initiates, giving rise to the western Scotia Sea and the Powell Basin opening. The Drake Passage opens.” The opening of Drake Passage opens was continuous and until Oligocene, the opening of Drake Passage resulted in an established deep circumpolar current and an increase in AABW activity.
Vérard, C., Flores, K., Stampfli, G., 2012. Geodynamic reconstructions of the South America–Antarctica plate system. Journal of Geodynamics, 53, 43-60.
Author Response File: 
Author Response.docx
