the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Aug 2024
Spring-neap tidal cycles modulate the strength of the carbon source at the estuary-coast interface
Abstract. Estuaries are dynamic environments with large biogeochemical variability modulated by tides, linking land to the coastal ocean. The carbon cycle at this land-sea interface can be better constrained by increasing the frequency of observations and by identifying the influence of tides with respect to the spring-neap variability. Here we use FerryBox measurements from a Ship-of-Opportunity travelling between two large temperate estuaries in the North Sea and find that the spring-neap tidal cycle drives a large percentage of the biogeochemical variability, in particular in inorganic and organic carbon concentrations at the land-sea interface in the outer estuaries and the adjacent coastal region. Of particular importance to carbon budgeting is the up to 74 % increase (up to 43.0 ± 17.1 mmol C m-2 day-1) in the strength of the estuarine carbon source to the atmosphere estimated during spring tide in a macrotidal estuary. We describe the biogeochemical processes occurring during both spring and neap tidal stages, their net effect on the partial pressure of carbon dioxide in seawater, and the ratios of dissolved inorganic to dissolved organic carbon concentrations. Surprisingly, while the two example outer estuaries in this study differ in the timing of the variability, the metabolic state progression and the observed phytoplankton species distribution, an increase in the strength of the potential carbon source to the atmosphere occurs at both outer estuaries on roughly 14-day cycles, suggesting that this is an underlying characteristic essential for the correct estimation of carbon budgets in tidally-driven estuaries and the nearby coastal regions. Understanding the functioning of estuarine systems and quantifying their effect on coastal seas should improve our current biogeochemical models and therefore future carbon exchange and budget predictability.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1807 KB) - Metadata XML
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(461 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-2643', Anonymous Referee #1, 24 Oct 2024
The manuscript investigates the influence of spring-neap tidal cycles on carbon dynamics in two North Sea estuarine systems (Humber and Elbe), presenting a comparative analysis supported by field observations. While the study benefits from a comprehensive dataset, several fundamental issues need to be addressed before the manuscript can be considered for publication. Below are the major concerns:
Major Comments:
1. Data Visualization
Consider implementing standardized cartographic conventions for improved clarity and scientific rigor.
- The cartographic elements in Figures 1, 3i, and 5i exhibit significant technical deficiencies in their presentation. The water mass trajectory plots lack scientific justification and supporting methodological documentation.
- The box plots require statistical significance indicators for between-group comparisons.
- The tidal range representations (blue lines, Figures 3 & 5) need proper measurement annotations and methodological context.
2. Analytical Depth and Data Integration
The Discussion section currently provides only cursory analysis of parameter relationships. The study relies heavily on literature values rather than leveraging the original dataset, quantitative assessment of individual contributors to carbon flux variations is inadequately addressed. Recommend incorporating detailed statistical analysis of the collected data to derive system-specific carbon flux contributions.
3. Methodological Documentation
- The FerryBox measurement system requires more comprehensive documentation，suggest including:
- Detailed technical diagrams of the FerryBox installation
- Systematic workflow documentation
- Quality control procedures
- Calibration protocols
- The air-water CO2 flux calculation methodology should either be integrated into the results and discussion or removed entirely
4. Conceptual Framework and Literature Context
The Introduction requires structural reorganization. Current emphasis on general estuarine carbon flux heterogeneity should be condensed. Recommend expanding the discussion of spring-neap tidal influences on carbon dynamics. Strengthen the articulation of the study's novel contributions to the field.
I will save minor comments this time because the current type of this manuscript would need a significant improvement.
Citation: https://doi.org/10.5194/egusphere-2024-2643-RC1 -
AC1: 'Reply on RC1', Vlad Macovei, 20 Dec 2024
We thank the reviewer for reading and commenting on our manuscript. We were planning on waiting for comments from a second reviewer before producing a revised manuscript, but since we don’t currently have a second reviewer and the discussion period for the manuscript is soon closing, we briefly outline here how we will address the first reviewer’s comments. A fully-detailed response to all comments and updated tracked changes manuscript will follow.
We will improve the visualization deficits outlined by the reviewer, including the maps, box plots and tidal representations.
We will better use our dataset to derive carbon fluxes, but it must be kept in mind that the dataset is limiting to accurately determine individual contributions. The scope of our manuscript was to highlight that this tidally-driven variability exists and must not lead to false conclusions (e.g. we see a positive correlation between chlorophyll and pCO2).
We will add details on the quality control, methodology and calibrations, but we will likely not include diagrams of the FerryBox installation, since this is outside the scope of this article. Instead, we will direct the reader to publications that describe such installations. Furthermore, FerryBoxes are well established ocean observation instruments, with many peer-reviewed publications making use of data collected by them. We will provide some examples for the readers.
We will reduce the CO2 flux calculation description and move it to another section.
We will streamline the Introduction where indicated and expand the spring-neap influence on carbon part. However, there are not that many studies published specifically on this aspect, which is exactly what makes the contribution of this current manuscript important.
Citation: https://doi.org/10.5194/egusphere-2024-2643-AC1
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RC2: 'Comment on egusphere-2024-2643', Anonymous Referee #2, 22 Dec 2024
Review of the manuscript egusphere-2024-2643 « Spring-neap tidal cycles modulate the strength of the carbon source at the estuary-coast interface» by Macovei et al. submitted for discussion in Biogeosciences
General comment :
This manuscript reports a detailed analysis of FerryBox measurements (on route near surface measurements from ship of opportunity) acquired during 4 years (2015-2018) on a route in the North Sea between Cuxhaven (Germany) and Immingham (England). The FerreyBox allows to measure temperature and salinity, carbonate chemistry (pH and pCO2), oxygen and optical properties of seawater that allows to derive information on dissolved organic matter and phyto-plancton in seawater. This manuscript only focuses on the date acquired in the Elbe Estuary (Germany) and the Humber Estuary (England) which are both large temperate estuaries that are under the influence of tide.
The temporal resolution of the dataset allows mostly to infer conclusion on the influence of the spring-neap tidal cycle. The study shows this variability regime has an effect on the biogeochemical variability, in particular in inorganic and organic carbon concentrations, on both sites and over the gradients encountered from the land-sea interface to the adjacent coastal region. Air-sea fluxes of CO2 are estimated at the scale of the estuaries and the authors argued that an important increase of the estuarine carbon source to the atmosphere is associated with spring tide through changes in the metabolic state. They suggest that their study has strong implications for the correct estimation of carbon budgets in tidally-driven estuaries.
This study is a significant contribution because it shows some original results at the estuary-coast interface based. In my point of view, one strength of this study is to use FerryBox data collected when the ship is leaving or entering the port, whereas this often corresponds to the moment where ferryBox instruments are disconnected in order to protect the instrument from heavily loaded waters. The manuscript is well written and the results are convincing. The figures and tables are of good quality but could be improved. I would be glad to support the publication of this manuscript after some revisions (which I believe to be minor). My major concerns (detailed in the following sections) are related to some methodological points and the structure of the manuscript.Specific comments :
In my opinion, one major point in this manuscript is the question of how adapted the temporal resolution of the sampling is compared to the variability of the studied process. I have the feeling that this needs to be more deeply discussed in the manuscript. I believe that the information from figures S1, S3 and S4 could be synthesized and presented as a figure in the main manuscript to discuss this question of temporal resolution / variability.
The trajectories presented on figure 3 and 5 are not convincing. I would suggest to make a choice between two options : (1) Use the full potential of the trajectories in the manuscript by giving more details on the calculation, presenting them with a detailed figure and using the results to support the discussion or (2) keep their use in the actual form and just present them as supplementary material.
The results section 3.1 and 3.2 are devoted to describe separately the results in both estuaries. I am wondering if a more synthetic description could be given in order to make section 3.1 and 3.2 a little bit shorter.
The method section for inorganic carbonate chemistry measurements is lacking precision : What type of pH is measured pHT or pH-NBS ? Values of the dissociation constant are not conventional (Dickson et al., 2007) for open-sea oceanography and should be justified if adapted to estuaries? Why are the concentrations converted to µmol.L-1 whereas the dissociation constants are usually defined with mass amount ?
The calculation of air-sea CO2 fluxes are also lacking precision : Why the Mac head station for atmospheric CO2 ? Which wind data have been used and why using average values ? Using average values can lead to strong errors, because if periods of strong seawater pCO2 can be specifically associated to stronger (or weaker) winds, this can lead to large differences in the air sea fluxes.Technical corrections
L182-185 : There is something not clear to me in the correction applied to AOA and Wetlab sensors for chlorophyll. This section could be clarified.
L351-352 : This last sentence of this section could be added to the conclusion rather than in the results section.
Figure 1 :The longitudinal clusters used for figure 2 and 4 could be presented by areas on the maps of the estuaries in order to help the reader to visualize this 0.1° clusters.
Figure 1, 3 and 5 : The projection used for the maps conducts to figures that are not horizontal. Maybe another projection could be used?Citation: https://doi.org/10.5194/egusphere-2024-2643-RC2 -
AC2: 'Reply on RC2', Vlad Macovei, 30 Dec 2024
We thank the reviewer for providing comments on our manuscript and supporting its eventual publication. We have now received reviews from two reviewers and will begin the process of addressing the individual comments and constructing an updated manuscript based on them. In the meantime, we reply to this comment outlining the changes we will make, since the interactive discussion period for the manuscript is soon ending. A detailed response and tracked changes manuscript will follow.
We will take steps to ensure the reader is convinced the sampling resolution is enough to resolve the processes we are discussing. This might involve reorganizing the figures included in the main manuscript versus supplementary material, especially taking into consideration the next comment about the trajectory plots.
Sections 3.1 and 3.2 are simply describing the results that are possible to extract based on the multitude of sensors available and showing how the spring-neap variability influences the biogeochemical measurements. It is unlikely combining the sections will lead to a reduced text length, but we will look into the possibility of streamlining the description.
We will add the necessary carbonate system calculation clarifications. As for the CO2 flux calculations, we are aware of the limitations of our method. We have calculated the associated uncertainties and they are indeed large. We used the Mace Head data since they come from a well-established long-term observing station. We will search for alternative sources of data, but atmospheric xCO2 is usually well mixed and regional differences are small. Furthermore, the main driver of changes in CO2 flux is the seawater pCO2 variability and through this manuscript, we are showing that the changes in the seawater term between the spring and neap tide phases are percentually larger than potential atmospheric variability. We are also using average wind speed to calculate the specific effect of the changes in seawater pCO2 due to spring-neap variability. Using instantaneous wind speed for flux calculations would be more useful for a different scope manuscript.
We will address the highlighted technical corrections.
Citation: https://doi.org/10.5194/egusphere-2024-2643-AC2
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AC2: 'Reply on RC2', Vlad Macovei, 30 Dec 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-2643', Anonymous Referee #1, 24 Oct 2024
The manuscript investigates the influence of spring-neap tidal cycles on carbon dynamics in two North Sea estuarine systems (Humber and Elbe), presenting a comparative analysis supported by field observations. While the study benefits from a comprehensive dataset, several fundamental issues need to be addressed before the manuscript can be considered for publication. Below are the major concerns:
Major Comments:
1. Data Visualization
Consider implementing standardized cartographic conventions for improved clarity and scientific rigor.
- The cartographic elements in Figures 1, 3i, and 5i exhibit significant technical deficiencies in their presentation. The water mass trajectory plots lack scientific justification and supporting methodological documentation.
- The box plots require statistical significance indicators for between-group comparisons.
- The tidal range representations (blue lines, Figures 3 & 5) need proper measurement annotations and methodological context.
2. Analytical Depth and Data Integration
The Discussion section currently provides only cursory analysis of parameter relationships. The study relies heavily on literature values rather than leveraging the original dataset, quantitative assessment of individual contributors to carbon flux variations is inadequately addressed. Recommend incorporating detailed statistical analysis of the collected data to derive system-specific carbon flux contributions.
3. Methodological Documentation
- The FerryBox measurement system requires more comprehensive documentation，suggest including:
- Detailed technical diagrams of the FerryBox installation
- Systematic workflow documentation
- Quality control procedures
- Calibration protocols
- The air-water CO2 flux calculation methodology should either be integrated into the results and discussion or removed entirely
4. Conceptual Framework and Literature Context
The Introduction requires structural reorganization. Current emphasis on general estuarine carbon flux heterogeneity should be condensed. Recommend expanding the discussion of spring-neap tidal influences on carbon dynamics. Strengthen the articulation of the study's novel contributions to the field.
I will save minor comments this time because the current type of this manuscript would need a significant improvement.
Citation: https://doi.org/10.5194/egusphere-2024-2643-RC1 -
AC1: 'Reply on RC1', Vlad Macovei, 20 Dec 2024
We thank the reviewer for reading and commenting on our manuscript. We were planning on waiting for comments from a second reviewer before producing a revised manuscript, but since we don’t currently have a second reviewer and the discussion period for the manuscript is soon closing, we briefly outline here how we will address the first reviewer’s comments. A fully-detailed response to all comments and updated tracked changes manuscript will follow.
We will improve the visualization deficits outlined by the reviewer, including the maps, box plots and tidal representations.
We will better use our dataset to derive carbon fluxes, but it must be kept in mind that the dataset is limiting to accurately determine individual contributions. The scope of our manuscript was to highlight that this tidally-driven variability exists and must not lead to false conclusions (e.g. we see a positive correlation between chlorophyll and pCO2).
We will add details on the quality control, methodology and calibrations, but we will likely not include diagrams of the FerryBox installation, since this is outside the scope of this article. Instead, we will direct the reader to publications that describe such installations. Furthermore, FerryBoxes are well established ocean observation instruments, with many peer-reviewed publications making use of data collected by them. We will provide some examples for the readers.
We will reduce the CO2 flux calculation description and move it to another section.
We will streamline the Introduction where indicated and expand the spring-neap influence on carbon part. However, there are not that many studies published specifically on this aspect, which is exactly what makes the contribution of this current manuscript important.
Citation: https://doi.org/10.5194/egusphere-2024-2643-AC1
-
RC2: 'Comment on egusphere-2024-2643', Anonymous Referee #2, 22 Dec 2024
Review of the manuscript egusphere-2024-2643 « Spring-neap tidal cycles modulate the strength of the carbon source at the estuary-coast interface» by Macovei et al. submitted for discussion in Biogeosciences
General comment :
This manuscript reports a detailed analysis of FerryBox measurements (on route near surface measurements from ship of opportunity) acquired during 4 years (2015-2018) on a route in the North Sea between Cuxhaven (Germany) and Immingham (England). The FerreyBox allows to measure temperature and salinity, carbonate chemistry (pH and pCO2), oxygen and optical properties of seawater that allows to derive information on dissolved organic matter and phyto-plancton in seawater. This manuscript only focuses on the date acquired in the Elbe Estuary (Germany) and the Humber Estuary (England) which are both large temperate estuaries that are under the influence of tide.
The temporal resolution of the dataset allows mostly to infer conclusion on the influence of the spring-neap tidal cycle. The study shows this variability regime has an effect on the biogeochemical variability, in particular in inorganic and organic carbon concentrations, on both sites and over the gradients encountered from the land-sea interface to the adjacent coastal region. Air-sea fluxes of CO2 are estimated at the scale of the estuaries and the authors argued that an important increase of the estuarine carbon source to the atmosphere is associated with spring tide through changes in the metabolic state. They suggest that their study has strong implications for the correct estimation of carbon budgets in tidally-driven estuaries.
This study is a significant contribution because it shows some original results at the estuary-coast interface based. In my point of view, one strength of this study is to use FerryBox data collected when the ship is leaving or entering the port, whereas this often corresponds to the moment where ferryBox instruments are disconnected in order to protect the instrument from heavily loaded waters. The manuscript is well written and the results are convincing. The figures and tables are of good quality but could be improved. I would be glad to support the publication of this manuscript after some revisions (which I believe to be minor). My major concerns (detailed in the following sections) are related to some methodological points and the structure of the manuscript.Specific comments :
In my opinion, one major point in this manuscript is the question of how adapted the temporal resolution of the sampling is compared to the variability of the studied process. I have the feeling that this needs to be more deeply discussed in the manuscript. I believe that the information from figures S1, S3 and S4 could be synthesized and presented as a figure in the main manuscript to discuss this question of temporal resolution / variability.
The trajectories presented on figure 3 and 5 are not convincing. I would suggest to make a choice between two options : (1) Use the full potential of the trajectories in the manuscript by giving more details on the calculation, presenting them with a detailed figure and using the results to support the discussion or (2) keep their use in the actual form and just present them as supplementary material.
The results section 3.1 and 3.2 are devoted to describe separately the results in both estuaries. I am wondering if a more synthetic description could be given in order to make section 3.1 and 3.2 a little bit shorter.
The method section for inorganic carbonate chemistry measurements is lacking precision : What type of pH is measured pHT or pH-NBS ? Values of the dissociation constant are not conventional (Dickson et al., 2007) for open-sea oceanography and should be justified if adapted to estuaries? Why are the concentrations converted to µmol.L-1 whereas the dissociation constants are usually defined with mass amount ?
The calculation of air-sea CO2 fluxes are also lacking precision : Why the Mac head station for atmospheric CO2 ? Which wind data have been used and why using average values ? Using average values can lead to strong errors, because if periods of strong seawater pCO2 can be specifically associated to stronger (or weaker) winds, this can lead to large differences in the air sea fluxes.Technical corrections
L182-185 : There is something not clear to me in the correction applied to AOA and Wetlab sensors for chlorophyll. This section could be clarified.
L351-352 : This last sentence of this section could be added to the conclusion rather than in the results section.
Figure 1 :The longitudinal clusters used for figure 2 and 4 could be presented by areas on the maps of the estuaries in order to help the reader to visualize this 0.1° clusters.
Figure 1, 3 and 5 : The projection used for the maps conducts to figures that are not horizontal. Maybe another projection could be used?Citation: https://doi.org/10.5194/egusphere-2024-2643-RC2 -
AC2: 'Reply on RC2', Vlad Macovei, 30 Dec 2024
We thank the reviewer for providing comments on our manuscript and supporting its eventual publication. We have now received reviews from two reviewers and will begin the process of addressing the individual comments and constructing an updated manuscript based on them. In the meantime, we reply to this comment outlining the changes we will make, since the interactive discussion period for the manuscript is soon ending. A detailed response and tracked changes manuscript will follow.
We will take steps to ensure the reader is convinced the sampling resolution is enough to resolve the processes we are discussing. This might involve reorganizing the figures included in the main manuscript versus supplementary material, especially taking into consideration the next comment about the trajectory plots.
Sections 3.1 and 3.2 are simply describing the results that are possible to extract based on the multitude of sensors available and showing how the spring-neap variability influences the biogeochemical measurements. It is unlikely combining the sections will lead to a reduced text length, but we will look into the possibility of streamlining the description.
We will add the necessary carbonate system calculation clarifications. As for the CO2 flux calculations, we are aware of the limitations of our method. We have calculated the associated uncertainties and they are indeed large. We used the Mace Head data since they come from a well-established long-term observing station. We will search for alternative sources of data, but atmospheric xCO2 is usually well mixed and regional differences are small. Furthermore, the main driver of changes in CO2 flux is the seawater pCO2 variability and through this manuscript, we are showing that the changes in the seawater term between the spring and neap tide phases are percentually larger than potential atmospheric variability. We are also using average wind speed to calculate the specific effect of the changes in seawater pCO2 due to spring-neap variability. Using instantaneous wind speed for flux calculations would be more useful for a different scope manuscript.
We will address the highlighted technical corrections.
Citation: https://doi.org/10.5194/egusphere-2024-2643-AC2
-
AC2: 'Reply on RC2', Vlad Macovei, 30 Dec 2024
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Cited
Louise C. V. Rewrie
Rüdiger Röttgers
Yoana G. Voynova
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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