the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Feb 2024
Making sense of variation in sclerochronological stable isotope profiles of mollusks and fish otoliths from the early Eocene southern North Sea Basin
Abstract. Stable isotope sclerochemistry of mollusks and otoliths is frequently used for the reconstruction of paleotemperature and seasonality. Constraints on the paleoecology and –environment of these organisms, and how these factors influence intra-and inter-taxon isotope variability and variation, are thus highly valuable. We measured seasonal changes in δ18O and δ13C compositions in multiple specimens of two carditid bivalve species, a turritelline gastropod species, and two species of otoliths from demersal fish, from two early Eocene (latest Ypresian, 49.2 Ma) coquinas in the inner neritic Aalter Sand Formation, located in the Belgian part of the southern North Sea Basin (paleolatitude ~41° N). Results demonstrate variability among taxa in average, amplitude and shape of intra-annual δ18O and δ13C values. This intertaxon variability is at least partly caused by growth cessation during winters in turritellines and otoliths, leading to an incomplete representation of the seasonal cycle in their growth increments, compared to carditid bivalves. Other contributing factors to isotopic variability include sedimentary transport, mobility, and the lifespan of the specimens. Specifically, ophidiid fish otolith isotope records appear to reflect environmental conditions over a wider range of habitats and environments, due to sedimentary transport and postmortem transport by free-swimming predatory fish. Our study therefore highlights the variability between different taxa and environments in the shallow marine realm, which has implications for seasonality reconstructions. We show that by studying multiple taxa and specimens in a death assemblage, a more complete spectrum of isotope variation and variability becomes apparent.
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RC1: 'Comment on egusphere-2024-298', Madeleine Vickers, 19 Mar 2024
This is a detailed study of stable isotopic variation across and within different species commonly used to examine paleotemperature and seasonality, from two early Eocene coquinas at a single locality. This demonstrates the high variability between and within these biotic carbonates, and discusses the possible causes for the variability, concluding with how these findings may be used to inform and improve future studies setting out to examine seasonal trends from the fossil record. It is generally well-written and scientifically sound; my only main comment is that there is much speculation about what drives the large variation in d18O, which could be resolved by clumped isotope thermometry. However, this is identified in the manuscript and will be addressed in a future study. Therefore, my detailed comments are generally limited to small suggestions for grammar and clarity, as follows:
Line 4: space missing between “Claeys,” and “Linda”
Line 15 and 56: “paleoecology and –environment” change to "paleo -ecology and -environment" or "paleoecology and environment".
Line 17: “and two species of otoliths from demersal fish” change to “and otoliths from two species of demersal fish”.
Line 94: reference Fig. 2 here. Generally, there is not enough reference to the figures in the text – make sure each figure referenced at least once, and don’t be afraid to reference it multiple times; it will help the reader to follow the presentation of the results and the discussion
Line 118: label/ show Oedelem Member on Fig. 2
Line 144: "The Aalter Sand Formation also shows..."
Lines 216, 217, 218 and 224: All caps for references – make lower case (e.g. SCHUBERT, 1916 change to Schubert, 1916)
Line 265: “Haustator solanderi” should be in italics
Line 274: δ18Ow should be superscript “18” and subscript “w”. This pervasive throughout the MS (δ13C too) – fix throughout (inc. Figs. 4 – 8 captions; lines 413, 417, 426)
Figure 10: “well mixed to temperature stratified” change to "well-mixed temperature-stratified" for clarity.
Line 590: "grow older" replace with - "live longer"
Lines 684 and 688: reference Fig. 11 here.
Line 685: “…the range of the averages of d18O…” (range of d13C averages looks about the same or smaller for Egem Sands Mb).
Line 711: The sentence isn't very clear - perhaps rephrase to something like "Congrids generally capture more than one full seasonal cycle; however, the Paleogene ophidiids from the sNSB, appear to be generally short-lived (c. 1 yr), hampering accurate assessment of seasonality."
Line 712: Replace “At the same time” with "On the other hand" (now that it is removed from the previous sentence).
Citation: https://doi.org/10.5194/egusphere-2024-298-RC1 -
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
Dear editor,
We thank both reviewers for their valuable comments and suggestions on our manuscript. The remarks by Reviewer 1 (Dr. Vickers) were overall positive, and can easily be incorporated in a revised version on the manuscript. Reviewer 2 provided stronger criticism on the manuscript, through arguing that our work is lacking a clear scientific objective and does not provide any new results.
Based on the comments by reviewer 2, we realize that the overall objectives of our research were not sufficiently clear from the manuscript text. While the overarching rationale for studying isotope sclerochemistry of fossil mollusks and otoliths is indeed to reconstruct past climatic conditions, this was not the goal of our research. Instead, given the common use of fossils to reconstruct paleoseasonality, we wanted to investigate isotope variability within one fossil assemblage, i.e. to test whether different fossils from the same assemblage record the same signals or not, and if not, deduce which groups provide the most robust seasonality signal in the Eocene North Sea Basin. Hence, as was correctly assessed by reviewer 2, our study was indeed not designed as a study to reconstruct paleoclimatic conditions during the Eocene.
We now realize that the introduction of our manuscript creates the false impression that our study presents an attempt to understand the environmental, biological, and taphonomical causes for differences in amplitude and mean of intra-annual isotope variability among specimens and species, rather than to assess what these differences are. We agree with the reviewer, that to understand some of the causes of this variability, a modern death assemblage could be used. Yet, at the same time, it must be stressed that such an assemblage likely would not incorporate long term taphonomic processes, such as reworking and transport, that affected fossil assemblages. In a revised version of the manuscript, we will stress that the aims of our study are to test whether or not the different fossils from the same assemblage from the Eocene North Sea Basin record the same signals.
In the supplement file, we provide specific replies to the detail comments by Reviewer 2.
Johan Vellekoop
Signed on behalf of all the authors
-
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
-
RC2: 'Comment on egusphere-2024-298', Anonymous Referee #2, 28 Mar 2024
This study presents and interprets oxygen and carbon stable isotope records measured in fossil mollusc shells and otoliths from the early Eocene Alter sand formation in Belgium. The authors apply a standard technique for shell sampling and isotopic analyses. The geological context is presented in details and the article in general is precise and well written.
My concern is that it seems like a preliminary work to explore the paleoclimatic potential of a fossil assemblage, but that, at this stage, does not provide any really new result. As suggested by the title, fossil were first analysed with no clear scientific objective and then the authors tried to "make sense" of the data.
Fossil mollusks are presented in the introduction as valuable archives of past climate, which is true, but the sampling was not properly designed for a paleoclimate study because the record is affected by uncertainties related to environmental heterogeneity, movement of the species, taphonomy, uncertain ecology…etc. Well-known uncertainty sources that hinder any interpretation but that are discussed as if they were the object of the study.
This results in a discussion in the form of a long list of speculative interpretations about all the possible causes of the isotopic variability. The article ends with a trivial conclusion as a list of recommendations that summarizes what the authors should have done before starting isotopic analyses, along with long known obvious comments about the influence of growth rate, growth cessation, or the fact that species with different ecology have different isotopic values.
In the introduction, the authors present their study as an attempt to "explore environmental, biological, and taphonomical causes for differences in amplitude and mean of intra-annual isotope variability among specimens and species". This could be an interesting objective, but in order to really make progress, a modern dead assemblage should have been studied, along with living specimens from the diverse habitat where conditions can actually be measured. Here, causes that are already known are speculatively invoked with no mean to test or measure these effects. Nothing new about mechanism or cause of variability is obtained from the dataset.
If the objective is to reconstruct past climate (first sentence of the introduction), the authors should focus on Venericor planicosta, a massive, long-lived, subtidal, non mobile species that provided excellent isotopic records. This species provided the only valuable data here, used in an attempt of paleotemperature reconstruction. The carbon isotopic data in this species seemed also very interesting, although the carbon interpretation section has weaknesses (see detailed comments). There is thus encouraging preliminary data that should be used to design an actual paleoclimate study.
I recommend the authors to pursue the study of Venericor planicota, maybe combine d18O and d13C analyses with D47 measurements as suggested in the conclusion, and submit a new manuscript with novel and robust paleoclimate information.
detail comments:
- in the paleoenvironment and paleoceanography sections, no open question is presented that could be interesting to tackle with these archives.
- L260 : how did you estimate the age (13+) of the specimen?
- L261: why were years 6, 7, 8 selected? Why not earlier years that would be less affected by growth cessation?
- L390: if htere are less than 40 datapoints, the 5% highest or lowest value are just 1 datapoint.
- L 630 - 650. continental freshwater input is not mentioned as a possible cause for d13C variations. It is actually one of the main causes in coastal environments.
- given the small amount of respired carbon in mollusk shells, the influence of trophic level is not significant. In general most of the text is focused on the respired carbon, and overlooks the cause of variations of DIC d13C which accounts for 90% of shell d13C variability.
- L688-690: what good is measuring the 'true' complexity of isotopic variations if it cannot be deciphered?
- L709: "long-lived species are more likely to capture the full seasonal cycle". This is incorrect. The full seasonal cycle is captured if the species lives at least 1 full year without growth cessation. It has nothing to do with the record's length. Robustness may be obtained from multiple specimens.
Citation: https://doi.org/10.5194/egusphere-2024-298-RC2 -
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
Dear editor,
We thank both reviewers for their valuable comments and suggestions on our manuscript. The remarks by Reviewer 1 (Dr. Vickers) were overall positive, and can easily be incorporated in a revised version on the manuscript. Reviewer 2 provided stronger criticism on the manuscript, through arguing that our work is lacking a clear scientific objective and does not provide any new results.
Based on the comments by reviewer 2, we realize that the overall objectives of our research were not sufficiently clear from the manuscript text. While the overarching rationale for studying isotope sclerochemistry of fossil mollusks and otoliths is indeed to reconstruct past climatic conditions, this was not the goal of our research. Instead, given the common use of fossils to reconstruct paleoseasonality, we wanted to investigate isotope variability within one fossil assemblage, i.e. to test whether different fossils from the same assemblage record the same signals or not, and if not, deduce which groups provide the most robust seasonality signal in the Eocene North Sea Basin. Hence, as was correctly assessed by reviewer 2, our study was indeed not designed as a study to reconstruct paleoclimatic conditions during the Eocene.
We now realize that the introduction of our manuscript creates the false impression that our study presents an attempt to understand the environmental, biological, and taphonomical causes for differences in amplitude and mean of intra-annual isotope variability among specimens and species, rather than to assess what these differences are. We agree with the reviewer, that to understand some of the causes of this variability, a modern death assemblage could be used. Yet, at the same time, it must be stressed that such an assemblage likely would not incorporate long term taphonomic processes, such as reworking and transport, that affected fossil assemblages. In a revised version of the manuscript, we will stress that the aims of our study are to test whether or not the different fossils from the same assemblage from the Eocene North Sea Basin record the same signals.
In the supplement file, we provide specific replies to the detail comments by Reviewer 2.
Johan Vellekoop
Signed on behalf of all the authors
-
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
-
EC1: 'Comment on egusphere-2024-298', Denis-Didier Rousseau, 10 Apr 2024
Dear authors,
Your manuscript has undergone two reviews and, before submitting a final response, I strongly recommend that you submit a brief response to each review in order to benefit from the discussion phase.
All the very best
denis-didier Rousseau
CP co-editor in chief
Citation: https://doi.org/10.5194/egusphere-2024-298-EC1 -
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
Dear editor,
We thank both reviewers for their valuable comments and suggestions on our manuscript. The remarks by Reviewer 1 (Dr. Vickers) were overall positive, and can easily be incorporated in a revised version on the manuscript. Reviewer 2 provided stronger criticism on the manuscript, through arguing that our work is lacking a clear scientific objective and does not provide any new results.
Based on the comments by reviewer 2, we realize that the overall objectives of our research were not sufficiently clear from the manuscript text. While the overarching rationale for studying isotope sclerochemistry of fossil mollusks and otoliths is indeed to reconstruct past climatic conditions, this was not the goal of our research. Instead, given the common use of fossils to reconstruct paleoseasonality, we wanted to investigate isotope variability within one fossil assemblage, i.e. to test whether different fossils from the same assemblage record the same signals or not, and if not, deduce which groups provide the most robust seasonality signal in the Eocene North Sea Basin. Hence, as was correctly assessed by reviewer 2, our study was indeed not designed as a study to reconstruct paleoclimatic conditions during the Eocene.
We now realize that the introduction of our manuscript creates the false impression that our study presents an attempt to understand the environmental, biological, and taphonomical causes for differences in amplitude and mean of intra-annual isotope variability among specimens and species, rather than to assess what these differences are. We agree with the reviewer, that to understand some of the causes of this variability, a modern death assemblage could be used. Yet, at the same time, it must be stressed that such an assemblage likely would not incorporate long term taphonomic processes, such as reworking and transport, that affected fossil assemblages. In a revised version of the manuscript, we will stress that the aims of our study are to test whether or not the different fossils from the same assemblage from the Eocene North Sea Basin record the same signals.
In the supplement file, we provide specific replies to the detail comments by Reviewer 2.
Johan Vellekoop
Signed on behalf of all the authors
-
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
Status: closed
-
RC1: 'Comment on egusphere-2024-298', Madeleine Vickers, 19 Mar 2024
This is a detailed study of stable isotopic variation across and within different species commonly used to examine paleotemperature and seasonality, from two early Eocene coquinas at a single locality. This demonstrates the high variability between and within these biotic carbonates, and discusses the possible causes for the variability, concluding with how these findings may be used to inform and improve future studies setting out to examine seasonal trends from the fossil record. It is generally well-written and scientifically sound; my only main comment is that there is much speculation about what drives the large variation in d18O, which could be resolved by clumped isotope thermometry. However, this is identified in the manuscript and will be addressed in a future study. Therefore, my detailed comments are generally limited to small suggestions for grammar and clarity, as follows:
Line 4: space missing between “Claeys,” and “Linda”
Line 15 and 56: “paleoecology and –environment” change to "paleo -ecology and -environment" or "paleoecology and environment".
Line 17: “and two species of otoliths from demersal fish” change to “and otoliths from two species of demersal fish”.
Line 94: reference Fig. 2 here. Generally, there is not enough reference to the figures in the text – make sure each figure referenced at least once, and don’t be afraid to reference it multiple times; it will help the reader to follow the presentation of the results and the discussion
Line 118: label/ show Oedelem Member on Fig. 2
Line 144: "The Aalter Sand Formation also shows..."
Lines 216, 217, 218 and 224: All caps for references – make lower case (e.g. SCHUBERT, 1916 change to Schubert, 1916)
Line 265: “Haustator solanderi” should be in italics
Line 274: δ18Ow should be superscript “18” and subscript “w”. This pervasive throughout the MS (δ13C too) – fix throughout (inc. Figs. 4 – 8 captions; lines 413, 417, 426)
Figure 10: “well mixed to temperature stratified” change to "well-mixed temperature-stratified" for clarity.
Line 590: "grow older" replace with - "live longer"
Lines 684 and 688: reference Fig. 11 here.
Line 685: “…the range of the averages of d18O…” (range of d13C averages looks about the same or smaller for Egem Sands Mb).
Line 711: The sentence isn't very clear - perhaps rephrase to something like "Congrids generally capture more than one full seasonal cycle; however, the Paleogene ophidiids from the sNSB, appear to be generally short-lived (c. 1 yr), hampering accurate assessment of seasonality."
Line 712: Replace “At the same time” with "On the other hand" (now that it is removed from the previous sentence).
Citation: https://doi.org/10.5194/egusphere-2024-298-RC1 -
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
Dear editor,
We thank both reviewers for their valuable comments and suggestions on our manuscript. The remarks by Reviewer 1 (Dr. Vickers) were overall positive, and can easily be incorporated in a revised version on the manuscript. Reviewer 2 provided stronger criticism on the manuscript, through arguing that our work is lacking a clear scientific objective and does not provide any new results.
Based on the comments by reviewer 2, we realize that the overall objectives of our research were not sufficiently clear from the manuscript text. While the overarching rationale for studying isotope sclerochemistry of fossil mollusks and otoliths is indeed to reconstruct past climatic conditions, this was not the goal of our research. Instead, given the common use of fossils to reconstruct paleoseasonality, we wanted to investigate isotope variability within one fossil assemblage, i.e. to test whether different fossils from the same assemblage record the same signals or not, and if not, deduce which groups provide the most robust seasonality signal in the Eocene North Sea Basin. Hence, as was correctly assessed by reviewer 2, our study was indeed not designed as a study to reconstruct paleoclimatic conditions during the Eocene.
We now realize that the introduction of our manuscript creates the false impression that our study presents an attempt to understand the environmental, biological, and taphonomical causes for differences in amplitude and mean of intra-annual isotope variability among specimens and species, rather than to assess what these differences are. We agree with the reviewer, that to understand some of the causes of this variability, a modern death assemblage could be used. Yet, at the same time, it must be stressed that such an assemblage likely would not incorporate long term taphonomic processes, such as reworking and transport, that affected fossil assemblages. In a revised version of the manuscript, we will stress that the aims of our study are to test whether or not the different fossils from the same assemblage from the Eocene North Sea Basin record the same signals.
In the supplement file, we provide specific replies to the detail comments by Reviewer 2.
Johan Vellekoop
Signed on behalf of all the authors
-
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
-
RC2: 'Comment on egusphere-2024-298', Anonymous Referee #2, 28 Mar 2024
This study presents and interprets oxygen and carbon stable isotope records measured in fossil mollusc shells and otoliths from the early Eocene Alter sand formation in Belgium. The authors apply a standard technique for shell sampling and isotopic analyses. The geological context is presented in details and the article in general is precise and well written.
My concern is that it seems like a preliminary work to explore the paleoclimatic potential of a fossil assemblage, but that, at this stage, does not provide any really new result. As suggested by the title, fossil were first analysed with no clear scientific objective and then the authors tried to "make sense" of the data.
Fossil mollusks are presented in the introduction as valuable archives of past climate, which is true, but the sampling was not properly designed for a paleoclimate study because the record is affected by uncertainties related to environmental heterogeneity, movement of the species, taphonomy, uncertain ecology…etc. Well-known uncertainty sources that hinder any interpretation but that are discussed as if they were the object of the study.
This results in a discussion in the form of a long list of speculative interpretations about all the possible causes of the isotopic variability. The article ends with a trivial conclusion as a list of recommendations that summarizes what the authors should have done before starting isotopic analyses, along with long known obvious comments about the influence of growth rate, growth cessation, or the fact that species with different ecology have different isotopic values.
In the introduction, the authors present their study as an attempt to "explore environmental, biological, and taphonomical causes for differences in amplitude and mean of intra-annual isotope variability among specimens and species". This could be an interesting objective, but in order to really make progress, a modern dead assemblage should have been studied, along with living specimens from the diverse habitat where conditions can actually be measured. Here, causes that are already known are speculatively invoked with no mean to test or measure these effects. Nothing new about mechanism or cause of variability is obtained from the dataset.
If the objective is to reconstruct past climate (first sentence of the introduction), the authors should focus on Venericor planicosta, a massive, long-lived, subtidal, non mobile species that provided excellent isotopic records. This species provided the only valuable data here, used in an attempt of paleotemperature reconstruction. The carbon isotopic data in this species seemed also very interesting, although the carbon interpretation section has weaknesses (see detailed comments). There is thus encouraging preliminary data that should be used to design an actual paleoclimate study.
I recommend the authors to pursue the study of Venericor planicota, maybe combine d18O and d13C analyses with D47 measurements as suggested in the conclusion, and submit a new manuscript with novel and robust paleoclimate information.
detail comments:
- in the paleoenvironment and paleoceanography sections, no open question is presented that could be interesting to tackle with these archives.
- L260 : how did you estimate the age (13+) of the specimen?
- L261: why were years 6, 7, 8 selected? Why not earlier years that would be less affected by growth cessation?
- L390: if htere are less than 40 datapoints, the 5% highest or lowest value are just 1 datapoint.
- L 630 - 650. continental freshwater input is not mentioned as a possible cause for d13C variations. It is actually one of the main causes in coastal environments.
- given the small amount of respired carbon in mollusk shells, the influence of trophic level is not significant. In general most of the text is focused on the respired carbon, and overlooks the cause of variations of DIC d13C which accounts for 90% of shell d13C variability.
- L688-690: what good is measuring the 'true' complexity of isotopic variations if it cannot be deciphered?
- L709: "long-lived species are more likely to capture the full seasonal cycle". This is incorrect. The full seasonal cycle is captured if the species lives at least 1 full year without growth cessation. It has nothing to do with the record's length. Robustness may be obtained from multiple specimens.
Citation: https://doi.org/10.5194/egusphere-2024-298-RC2 -
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
Dear editor,
We thank both reviewers for their valuable comments and suggestions on our manuscript. The remarks by Reviewer 1 (Dr. Vickers) were overall positive, and can easily be incorporated in a revised version on the manuscript. Reviewer 2 provided stronger criticism on the manuscript, through arguing that our work is lacking a clear scientific objective and does not provide any new results.
Based on the comments by reviewer 2, we realize that the overall objectives of our research were not sufficiently clear from the manuscript text. While the overarching rationale for studying isotope sclerochemistry of fossil mollusks and otoliths is indeed to reconstruct past climatic conditions, this was not the goal of our research. Instead, given the common use of fossils to reconstruct paleoseasonality, we wanted to investigate isotope variability within one fossil assemblage, i.e. to test whether different fossils from the same assemblage record the same signals or not, and if not, deduce which groups provide the most robust seasonality signal in the Eocene North Sea Basin. Hence, as was correctly assessed by reviewer 2, our study was indeed not designed as a study to reconstruct paleoclimatic conditions during the Eocene.
We now realize that the introduction of our manuscript creates the false impression that our study presents an attempt to understand the environmental, biological, and taphonomical causes for differences in amplitude and mean of intra-annual isotope variability among specimens and species, rather than to assess what these differences are. We agree with the reviewer, that to understand some of the causes of this variability, a modern death assemblage could be used. Yet, at the same time, it must be stressed that such an assemblage likely would not incorporate long term taphonomic processes, such as reworking and transport, that affected fossil assemblages. In a revised version of the manuscript, we will stress that the aims of our study are to test whether or not the different fossils from the same assemblage from the Eocene North Sea Basin record the same signals.
In the supplement file, we provide specific replies to the detail comments by Reviewer 2.
Johan Vellekoop
Signed on behalf of all the authors
-
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
-
EC1: 'Comment on egusphere-2024-298', Denis-Didier Rousseau, 10 Apr 2024
Dear authors,
Your manuscript has undergone two reviews and, before submitting a final response, I strongly recommend that you submit a brief response to each review in order to benefit from the discussion phase.
All the very best
denis-didier Rousseau
CP co-editor in chief
Citation: https://doi.org/10.5194/egusphere-2024-298-EC1 -
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
Dear editor,
We thank both reviewers for their valuable comments and suggestions on our manuscript. The remarks by Reviewer 1 (Dr. Vickers) were overall positive, and can easily be incorporated in a revised version on the manuscript. Reviewer 2 provided stronger criticism on the manuscript, through arguing that our work is lacking a clear scientific objective and does not provide any new results.
Based on the comments by reviewer 2, we realize that the overall objectives of our research were not sufficiently clear from the manuscript text. While the overarching rationale for studying isotope sclerochemistry of fossil mollusks and otoliths is indeed to reconstruct past climatic conditions, this was not the goal of our research. Instead, given the common use of fossils to reconstruct paleoseasonality, we wanted to investigate isotope variability within one fossil assemblage, i.e. to test whether different fossils from the same assemblage record the same signals or not, and if not, deduce which groups provide the most robust seasonality signal in the Eocene North Sea Basin. Hence, as was correctly assessed by reviewer 2, our study was indeed not designed as a study to reconstruct paleoclimatic conditions during the Eocene.
We now realize that the introduction of our manuscript creates the false impression that our study presents an attempt to understand the environmental, biological, and taphonomical causes for differences in amplitude and mean of intra-annual isotope variability among specimens and species, rather than to assess what these differences are. We agree with the reviewer, that to understand some of the causes of this variability, a modern death assemblage could be used. Yet, at the same time, it must be stressed that such an assemblage likely would not incorporate long term taphonomic processes, such as reworking and transport, that affected fossil assemblages. In a revised version of the manuscript, we will stress that the aims of our study are to test whether or not the different fossils from the same assemblage from the Eocene North Sea Basin record the same signals.
In the supplement file, we provide specific replies to the detail comments by Reviewer 2.
Johan Vellekoop
Signed on behalf of all the authors
-
AC1: 'Reply on RC1 & RC2', Johan Vellekoop, 22 Apr 2024
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