Investigating the Element Geochemical Behavior and Provenance of Surface Sediments in the Offshore Area of Sierra Leone, Africa: Insights from Major and Trace Elements

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

The authors present a study that addressed to element geochemical behavior and provenance of surface sediments in the offshore area of Sierra Leone. The study provided creditable data, fully discussed the relationships of elements with grain sizes, and compared the data with Chinese coasts. The study is valuable in promoting the understanding of the coastal environment. However, some suggestions and comments must be made; I recommend a minor revision. 

L4: The country is not familiar to readers, so you’d better add “, Africa” after “Sierra Leone”.

L31: More newly published references concerning the “sediment sources and sinks” should be added, such as:

1). Nonnegligible contribution of terrigenous sediment inputs from local small watersheds to west regions of the Pearl River Estuary, northern South China Sea shelf

2). Magnetic fingerprints of surface sediment in the Bohai Sea, China

3). Provenance and sediment dispersal in Pearl River Estuary, southern China unraveled by magnetic properties

L60: Add descriptions of the geological, climate, and oceanic settings in the studying region.

L69: All a global or African map, marking the studying area, add rivers and coastal currents in Fig. 1a. Add a map of Chinese coasts as shown in Fig. 7.

L80: Organic matter and calcium components were removed by using....

L188: Deep discussions are needed in this section. You have to use a map showing three factors, including three regions of Al-rich region (Factor 1 dominated), Ti-rich region (Factor 2 dominated), and Ca-rich region (Factor 3 dominated). Then, add some arrows to show the sediment dispersal model, that is, Region 1 is controlled by suspension, Region 2 is controlled by coarse-grained mineral deposition, and Region 3 is related to marine life activities.

L239: This section needs deep discussions. You should compare the differences in climate, geological background, sediment flux, and human activities between the coasts of Sierra Leone and China.

L258: grammar errors.

L272: Fig. 7 should be “E South Yellow Sea”.

Comments on the Quality of English Language

None.

Author Response

Dear editors and reviewers:

We appreciate the decision of this manuscript. We agree with your comments and suggestions, and have revised my manuscript. In addition, we highlight modifications in different font colors point by point (red for reviewer 1, blue for reviewer 2, green for them both) in the revised manuscript.

 

Comments of reviewer 1:

The authors present a study that addressed to element geochemical behavior and provenance of surface sediments in the offshore area of Sierra Leone. The study provided creditable data, fully discussed the relationships of elements with grain sizes, and compared the data with Chinese coasts. The study is valuable in promoting the understanding of the coastal environment. However, some suggestions and comments must be made; I recommend a minor revision.

 

We appreciate your affirmation about this manuscript. We have carefully read the comments and replied to you one by one in the next.

 

Comment 1: L4: The country is not familiar to readers, so you’d better add “, Africa” after “Sierra Leone”.

Responses: In the revised version, we add the “, Africa”.

 

Comment 2: L31: More newly published references concerning the “sediment sources and sinks” should be added, such as:

1). Nonnegligible contribution of terrigenous sediment inputs from local small watersheds to west regions of the Pearl River Estuary, northern South China Sea shelf

2). Magnetic fingerprints of surface sediment in the Bohai Sea, China

3). Provenance and sediment dispersal in Pearl River Estuary, southern China unraveled by magnetic properties

Responses: In the revised version, we have added these references.

 

Comment 3: L60: Add descriptions of the geological, climate, and oceanic settings in the studying region.

Responses: In the revised version, we add the descriptions. “Sierra Leone is located on the west coast of Africa, bordering Guinea in the north and northeast, Liberia in the East and Southeast, and the Atlantic Ocean in the West and south. The terrain of Sierra Leone is characterized by high in the East and low in the West. It gradually transits from a plain about 70 kilometers wide along the coast to a plateau on the eastern border. Sierra Leone has a tropical monsoon climate and is one of the countries with the most rainfall in West Africa.”

 

Comment 4: L69: All a global or African map, marking the studying area, add rivers and coastal currents in Fig. 1a. Add a map of Chinese coasts as shown in Fig. 7.

Responses: We agree with the reviewers' suggestions, but we have made the greatest improvement based on the following points. (1) The largest river entering the sea in West Africa is the Niger River, but its estuary is more than 2000 kilometers away from the study area. There are no large rivers entering the sea around the study area, and there is a lack of basic data for small rivers, so we didn’t add river information here. (2) The study area is an offshore area, dominated by land-based material input, and the influence of large-scale circulation characteristics on it is limited, so we did not choose to add circulation information.

In the revised version, the selected offshore areas of China are shown in Figure 7.

 

Comment 5: L80: Organic matter and calcium components were removed by using....

Responses: In the revised version, we changed it into “Organic matter and calcium components were removed by using hydrogen peroxide and hydrochloric acid before measurement.”

 

Comment 6: L188: Deep discussions are needed in this section. You have to use a map showing three factors, including three regions of Al-rich region (Factor 1 dominated), Ti-rich region (Factor 2 dominated), and Ca-rich region (Factor 3 dominated). Then, add some arrows to show the sediment dispersal model, that is, Region 1 is controlled by suspension, Region 2 is controlled by coarse-grained mineral deposition, and Region 3 is related to marine life activities.

Responses: We fully understand the opinions of the reviewers, and adding the analysis of regional control factor distribution and sedimentary dynamic control can make the discussion more in-depth. However, we feel that the current logical route of this paper is not suitable for adding this part. At the stage, we will feel that there are many unfinished things, when there is no basic data of sedimentary dynamics, just adding the discussion content of this part. Therefore, if it is impossible to proceed from the perspective of sedimentary dynamics, we choose not to increase relevant discussions.

 

Comment 7: This section needs deep discussions. You should compare the differences in climate, geological background, sediment flux, and human activities between the coasts of Sierra Leone and China.

Responses: We agree with the reviewers' opinions very much, but the theme of this article is mainly to discuss the sedimentary geochemical characteristics of the nearshore of Sierra Leone. The purpose of adding comparison is only to provide readers with an intuitive concept. We will continue to promote further research in the follow-up study.

 

Comment 8: L258: grammar errors.

Responses: In the revised version, we have modified it.

 

Comment 9: L272: Fig. 7 should be “E South Yellow Sea”.

Responses: In the revised version, we have modified it.

 

 

Comments of reviewer 2:

The study was conducted in Shelf's offshore on the geochemical behavior of elements. The design of the study, the number of data, and the experiment were faithfully conducted, and above all, the statistical analysis and interpretation of the results were faithfully conducted, so it is seen as a sufficient result for publication in a journal. I suggest that if some of my small comments below are reflected in the revision step, this manuscript could be published immediately.

 

We appreciate your affirmation about this manuscript. We have carefully read the comments and replied to you one by one in the next.

 

1. Introduction

Comment 1: The first paragraph introduced that many studies have been conducted because the offshore area is a very important hub area, and I would like to introduce some examples of case studies or results how geochemical influences are global or regional. Also, in that respect, please introduce in the introduction what kind of originality or characteristics the research area of this study has compared to other previous studies.

Responses: We agree with the reviewers' suggestions. In the introduction, we cite some references (Ref. 7-13) to clarify the importance of offshore sedimentary geochemistry research. However, the specific content of a specific study is not added here, mainly because a specific study is difficult to be representative.

As for the particularity of the study area raised by the reviewers, we explained in the introduction that the cognitive research in the study area is relatively weak. At the same time, we added part of the background description of the study area in the revised version.

 

3. Result

Comment 2: Figures 2, 3, 4, and 5 are all rather small in numbers and letters in the picture, so it's hard to read. I want the font to get bigger. And most of all, the color bar is missing in Figure 3, 4, and 5.

Responses: In the revised version, we Changed picture size

 

4. Discussion

Comment 3: The authors explained that Fe and Al are not correlated well (because the r value is very small), so the terrestrial input is not the main origin of Fe. Of course, even in the results of factor analysis, Fe and Ti belong to Factor 2, which is different from Al. However, in Figure 6 (Al vs. Fe), the r value is shown to be a little low except for some of the splattered values, and it is difficult to say that Fe and Al are not correlated in general. Since correlations cannot simply explain all causations, we suggest that Fe reconsider the explanation that terreginic sources are not important at all.

Responses: We agree with the reviewers. The content of Fe in the source rock is generally recognized, so we do not have the expression of "non terrestrial product of Fe" in this paper. Our statement was “The results show that Fe is not only affected by terrigenous weathering products, but also by other sources, and Ti is even diluted by terrigenous weathering products.” Here, our view is mainly to explain that the study area is greatly affected by the ore source.

Reviewer 2 Report

Comments and Suggestions for Authors

Review comment is attached

Comments for author File: Comments.pdf

Author Response

Dear editors and reviewers:

We appreciate the decision of this manuscript. We agree with your comments and suggestions, and have revised my manuscript. In addition, we highlight modifications in different font colors point by point (red for reviewer 1, blue for reviewer 2, green for them both) in the revised manuscript.

 

Comments of reviewer 1:

The authors present a study that addressed to element geochemical behavior and provenance of surface sediments in the offshore area of Sierra Leone. The study provided creditable data, fully discussed the relationships of elements with grain sizes, and compared the data with Chinese coasts. The study is valuable in promoting the understanding of the coastal environment. However, some suggestions and comments must be made; I recommend a minor revision.

 

We appreciate your affirmation about this manuscript. We have carefully read the comments and replied to you one by one in the next.

 

Comment 1: L4: The country is not familiar to readers, so you’d better add “, Africa” after “Sierra Leone”.

Responses: In the revised version, we add the “, Africa”.

 

Comment 2: L31: More newly published references concerning the “sediment sources and sinks” should be added, such as:

1). Nonnegligible contribution of terrigenous sediment inputs from local small watersheds to west regions of the Pearl River Estuary, northern South China Sea shelf

2). Magnetic fingerprints of surface sediment in the Bohai Sea, China

3). Provenance and sediment dispersal in Pearl River Estuary, southern China unraveled by magnetic properties

Responses: In the revised version, we have added these references.

 

Comment 3: L60: Add descriptions of the geological, climate, and oceanic settings in the studying region.

Responses: In the revised version, we add the descriptions. “Sierra Leone is located on the west coast of Africa, bordering Guinea in the north and northeast, Liberia in the East and Southeast, and the Atlantic Ocean in the West and south. The terrain of Sierra Leone is characterized by high in the East and low in the West. It gradually transits from a plain about 70 kilometers wide along the coast to a plateau on the eastern border. Sierra Leone has a tropical monsoon climate and is one of the countries with the most rainfall in West Africa.”

 

Comment 4: L69: All a global or African map, marking the studying area, add rivers and coastal currents in Fig. 1a. Add a map of Chinese coasts as shown in Fig. 7.

Responses: We agree with the reviewers' suggestions, but we have made the greatest improvement based on the following points. (1) The largest river entering the sea in West Africa is the Niger River, but its estuary is more than 2000 kilometers away from the study area. There are no large rivers entering the sea around the study area, and there is a lack of basic data for small rivers, so we didn’t add river information here. (2) The study area is an offshore area, dominated by land-based material input, and the influence of large-scale circulation characteristics on it is limited, so we did not choose to add circulation information.

In the revised version, the selected offshore areas of China are shown in Figure 7.

 

Comment 5: L80: Organic matter and calcium components were removed by using....

Responses: In the revised version, we changed it into “Organic matter and calcium components were removed by using hydrogen peroxide and hydrochloric acid before measurement.”

 

Comment 6: L188: Deep discussions are needed in this section. You have to use a map showing three factors, including three regions of Al-rich region (Factor 1 dominated), Ti-rich region (Factor 2 dominated), and Ca-rich region (Factor 3 dominated). Then, add some arrows to show the sediment dispersal model, that is, Region 1 is controlled by suspension, Region 2 is controlled by coarse-grained mineral deposition, and Region 3 is related to marine life activities.

Responses: We fully understand the opinions of the reviewers, and adding the analysis of regional control factor distribution and sedimentary dynamic control can make the discussion more in-depth. However, we feel that the current logical route of this paper is not suitable for adding this part. At the stage, we will feel that there are many unfinished things, when there is no basic data of sedimentary dynamics, just adding the discussion content of this part. Therefore, if it is impossible to proceed from the perspective of sedimentary dynamics, we choose not to increase relevant discussions.

 

Comment 7: This section needs deep discussions. You should compare the differences in climate, geological background, sediment flux, and human activities between the coasts of Sierra Leone and China.

Responses: We agree with the reviewers' opinions very much, but the theme of this article is mainly to discuss the sedimentary geochemical characteristics of the nearshore of Sierra Leone. The purpose of adding comparison is only to provide readers with an intuitive concept. We will continue to promote further research in the follow-up study.

 

Comment 8: L258: grammar errors.

Responses: In the revised version, we have modified it.

 

Comment 9: L272: Fig. 7 should be “E South Yellow Sea”.

Responses: In the revised version, we have modified it.

 

 

Comments of reviewer 2:

The study was conducted in Shelf's offshore on the geochemical behavior of elements. The design of the study, the number of data, and the experiment were faithfully conducted, and above all, the statistical analysis and interpretation of the results were faithfully conducted, so it is seen as a sufficient result for publication in a journal. I suggest that if some of my small comments below are reflected in the revision step, this manuscript could be published immediately.

 

We appreciate your affirmation about this manuscript. We have carefully read the comments and replied to you one by one in the next.

 

1. Introduction

Comment 1: The first paragraph introduced that many studies have been conducted because the offshore area is a very important hub area, and I would like to introduce some examples of case studies or results how geochemical influences are global or regional. Also, in that respect, please introduce in the introduction what kind of originality or characteristics the research area of this study has compared to other previous studies.

Responses: We agree with the reviewers' suggestions. In the introduction, we cite some references (Ref. 7-13) to clarify the importance of offshore sedimentary geochemistry research. However, the specific content of a specific study is not added here, mainly because a specific study is difficult to be representative.

As for the particularity of the study area raised by the reviewers, we explained in the introduction that the cognitive research in the study area is relatively weak. At the same time, we added part of the background description of the study area in the revised version.

 

3. Result

Comment 2: Figures 2, 3, 4, and 5 are all rather small in numbers and letters in the picture, so it's hard to read. I want the font to get bigger. And most of all, the color bar is missing in Figure 3, 4, and 5.

Responses: In the revised version, we Changed picture size

 

4. Discussion

Comment 3: The authors explained that Fe and Al are not correlated well (because the r value is very small), so the terrestrial input is not the main origin of Fe. Of course, even in the results of factor analysis, Fe and Ti belong to Factor 2, which is different from Al. However, in Figure 6 (Al vs. Fe), the r value is shown to be a little low except for some of the splattered values, and it is difficult to say that Fe and Al are not correlated in general. Since correlations cannot simply explain all causations, we suggest that Fe reconsider the explanation that terreginic sources are not important at all.

Responses: We agree with the reviewers. The content of Fe in the source rock is generally recognized, so we do not have the expression of "non terrestrial product of Fe" in this paper. Our statement was “The results show that Fe is not only affected by terrigenous weathering products, but also by other sources, and Ti is even diluted by terrigenous weathering products.” Here, our view is mainly to explain that the study area is greatly affected by the ore source.