Distribution and source attribution of alkalinity in the Dutch Wadden Sea

Norbisrath, Mona; van Beusekom, Justus E. E.; Thomas, Helmuth

doi:https://doi.org/10.5194/egusphere-2023-2595

Preprints

https://doi.org/10.5194/egusphere-2023-2595

Preprints

09 Nov 2023

| 09 Nov 2023

Distribution and source attribution of alkalinity in the Dutch Wadden Sea

Mona Norbisrath, Justus E. E. van Beusekom, and Helmuth Thomas

Abstract. As the major global CO₂ sink, the oceanic buffering capacity total alkalinity (TA) is of growing scientific interest. TA is mainly generated by weathering, and further by various anaerobic metabolic processes. The Wadden Sea, located in the southern North Sea is thought to be a source of TA for the carbonate system of the North Sea, but quantifications are scarce. Here, we observed TA, dissolved inorganic carbon (DIC), and nutrients in the Dutch Wadden Sea in May 2019. We sampled transect surface waters to detect spatial distributions and compared it with earlier data. A tidal cycle was sampled to further shed light on TA generation and potential TA sources. We identified the Wadden Sea as a source of TA with an average TA generation of 7.6 µmol kg^-1 h^-1 during ebb tide in the Ameland Inlet. TA was generated in the sediments and washed out with off running water. A combination of anaerobic processes and CaCO₃ dissolution were potential sources of TA in the sediments. We assume that seasonality and the associated nitrate availability in particular influence TA generation by denitrification, which we assume is low in spring and summer.

Received: 03 Nov 2023 – Discussion started: 09 Nov 2023

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Journal article(s) based on this preprint

30 Oct 2024

Alkalinity sources in the Dutch Wadden Sea

Mona Norbisrath, Justus E. E. van Beusekom, and Helmuth Thomas

Ocean Sci., 20, 1423–1440, https://doi.org/10.5194/os-20-1423-2024,https://doi.org/10.5194/os-20-1423-2024, 2024

Short summary

Mona Norbisrath, Justus E. E. van Beusekom, and Helmuth Thomas

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-2595', Anonymous Referee #1, 14 Dec 2023

General comment
The manuscript “Distribution and source attribution of alkalinity in the Dutch Wadden Sea” examines spatial and temporal alkalinity dynamics in the Dutch Wadden Sea. The topic is timely and fits the scope of Ocean Science. The study design is appropriate, and the data set sufficient to answer the stated research questions. However, the manuscript is hard to follow and should be streamlined. The entire manuscript should have 3 to 5 well-structured paragraphs per page that address one specific topic. The introduction reads more like a study site description and does not give a broader context or demonstrates the need for this study. It would be helpful to put some of the results (e.g., most subplots of Figure 2 and Table 1) into a supplementary information and decrease the overall word count by focusing only on most relevant findings. The authors should pick up to three key messages on which they focus through the manuscript. The figures need some improvements. I suggest accepting the article after major revision.

Specific comments
Consider a more interesting and specific title.
L12 remove: “and compared it with earlier data”.
L19-22. This sentence is hard to follow and has too many citations. Consider splitting your sentences into two if they span over several lines and only cite most relevant literature for each statement.
L64 – 66 Add dates.
L75 Which kind of carbon measurements?
L137 Remove first sentence of caption.
L201 Remove sentence. Avoid writing “various parameters “through the manuscript and list parameters instead. Try to be more specific.
L204-205 Explain how you get to this conclusion.
L309 Faber studied mangroves. There is probably a study that is more similar to your study site.
It is very hard to follow your discussion. Suggest reducing to the most interesting findings. Condense the information as much as possible.

Figures and tables:
Fig 1: Remove ESRI source code (in all figures).
Fig. 2: This figure is too big. Show only one figure per page. Choose only most important parameters and put rest into the SI. You could plot all parameters against salinity and/or distance to the coast in one graph with subplots and discuss trends.
Fig. 4 and 5: Increase font size and point size. Axes should be aligned. Salinity looks strange in Fig 4d.
Put Table 1 in SI. Could add averages and standard deviations.

Technical corrections
When you reference two or more citations, the single citations are separated by a semicolon without any spaces. This looks strange. Please double check the citation guideline of the journal.
Avoid paragraphs with only one or two sentences.
L81 Remove “.” before citation.
L191 TA was defined before.
L198 Rephrase this sentence, “arrived” does not make sense in this context.
Do not overuse the term “shed light on…”
The reference list needs to be edited. E.g. CO₂ with subscript and uniform styles for titles. Include volume and page numbers for all references.

Citation: https://doi.org/10.5194/egusphere-2023-2595-RC1
- AC1: 'Reply on RC1', Mona Norbisrath, 22 Mar 2024
  
  The final AC responses are attached in the pdf.
  
  Citation: https://doi.org/10.5194/egusphere-2023-2595-AC1
RC2:
'Comment on egusphere-2023-2595', Anonymous Referee #2, 20 Jan 2024

Strengths:
I really appreciate that the authors left the location names on Figure 2 for easy reference when going from reading the text in the results to the figures. The manuscript as it stands is well organized throughout and easy to follow. The discussion of the results and considerations is also quite comprehensive and strong, aside from the one reservation I have that is listed below. I suggest accepting it after major revisions.

Major Concerns:
Results:
Figure 2: Please make points in figure 2 a color gradient from min to max value instead of grouping many values in one color. That way the reader can more specifically see the actual value at each site. The groupings also aren’t consistently spaced which could be misleading when analyzing spatial trends. Also, this is entirely a personal preference but generally I think blue=lower and yellow=higher based on the ocean of things color bars so it was confusing at first and they may be better reversed.
TA generation section: I think the assumption that TA generation for the entirety of the Wadden Sea does not come from freshwater dilution/river water is not properly supported as stands and is to general. I agree though that this is the correct conclusion for the Ameland region based on the data you’ve shown in Table 1, Figure 4, & 5. However, the authors previously show in Figure 3 that the TA vs salinity trend for the Ameland region is non-conservative, while the Ems-Dollard & Vlie regions of the Wadden Sea are conservative. Therefore, TA & salinity trends are clearly not consistent across the entire region. Which may be attributed to varying degrees of freshwater discharge across the region, which they mention briefly in the discussion. So while it may be true for the Ameland region that TA sources do not come from freshwater dilution/river water, the same cannot be said for these other regions. If the authors had stationary data during ebb tide for the regions that do appear to have a conservative relationship and saw the same pattern then yes they could reasonably assume this is true for the entirety of the Wadden Sea on average. However, they do not appear to have stationary data for either of the conservative regions. Therefore, this statement needs to be more specific to the Ameland region of the study and not the entire Wadden Sea region. If there are river gauges in the region to support similar river discharge across the region then this assumption may have stronger support but would still be rather bold without ebb tide data from the other regions. They also say later that freshwater dominates in the EMS-Dollard.

Minor Concerns:
Throughout manuscript: Please remove any we’s, he’s, etc. Instead refer as “this study” “the data” etc.
Methods:
Is there a reason you focus on calcite saturation instead of aragonite? Is it more relevant to local species? Please state.
Please include how you generated the statistics throughout the paper (i.e. the linear regressions). Did you use Excel, Matlab, R, etc? Also, are these Model I or Model II regressions?
Discussion:
Lines 237-239: Could this also be attributed to seasonal differences or changes in watershed usage over those 30 years?

Minor Edits:
Line 10: “North Sea is hypothesized to be a source…”
Line 10-11: “This study measured TA…”
Line 12: “compared is with historical data.”
Line 14: “ washed out with outgoing tide water.”
Line 27: “Most of the Wadden Sea is located...”
Line 28: “which makes it the world’s largest uninterrupted stretch…”
Line 31: what dynamics? Biogeochemical? Chemistry?
Line 30-33: Split into 2 sentences. One for chemical and one for physical sources of variability.
Line 35-36: what water masses? What is a ‘strong’ exchange? Do you mean that the water masses are very different?
Line 37: “The carbon storage capacity of the North Sea is an important atmospheric CO2 sink as it exports and stores the absorbed…”
Line 40-43: TA, primarily consisting of bicarbonate and carbonate, is generated by chemical rock weathering (citations), calcium carbonate dissolution, and anaerobic metabolic process, such as…”
Line 54-56: during what time of year?
Lines 116-118: please include aragonite saturation values as well. They can simply be added next to calcite values in parentheses.
Lines 204-205: Please include the R-values for the relationships to back this up.
Lines 215: “by enhanced water movement” what does this mean? Be more specific.
Line 219-220: “which could be traced back on an effect of the first four samplings as mentioned above” move to discussion
Line 221: connect this back to higher denitrification and ammonium production compared to nitrification because your ammonium relationship supports this as well.
Line 243: A TA increase of >70 is quite a bit. I wouldn’t say it’s only slightly higher.
Line 271: Where is Marsdiep relative to your study sites? Please add to map.
Lines 282-287: I think these sentences probably belong in the discussion.
Lines 285-287: and more spatial data for the varying TA vs salinity relationships of the different tidal regions in addition to the temporal data mentioned
Line 291: this is not necessarily true. Increased agriculture has led to increased rock and soil exposure, resulting in increased rates of silicate weathering. Also, I’m not sure if this applies to this region but digging of quarries also extracts and exposes silicate minerals during the mining process. However, if the region has little influence from either of these then it could be true. Apologies for I don’t know what the land use is like for this region.
Line 290: “insight” not “inside”?
Line 317: what about the ems-dollard region?
Line 403: what necessary data? This is a good place to suggest future work.

Citation: https://doi.org/10.5194/egusphere-2023-2595-RC2
- AC2: 'Reply on RC2', Mona Norbisrath, 22 Mar 2024
  
  The final AC responses are attached in the pdf.
  
  Citation: https://doi.org/10.5194/egusphere-2023-2595-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-2595', Anonymous Referee #1, 14 Dec 2023

General comment
The manuscript “Distribution and source attribution of alkalinity in the Dutch Wadden Sea” examines spatial and temporal alkalinity dynamics in the Dutch Wadden Sea. The topic is timely and fits the scope of Ocean Science. The study design is appropriate, and the data set sufficient to answer the stated research questions. However, the manuscript is hard to follow and should be streamlined. The entire manuscript should have 3 to 5 well-structured paragraphs per page that address one specific topic. The introduction reads more like a study site description and does not give a broader context or demonstrates the need for this study. It would be helpful to put some of the results (e.g., most subplots of Figure 2 and Table 1) into a supplementary information and decrease the overall word count by focusing only on most relevant findings. The authors should pick up to three key messages on which they focus through the manuscript. The figures need some improvements. I suggest accepting the article after major revision.

Specific comments
Consider a more interesting and specific title.
L12 remove: “and compared it with earlier data”.
L19-22. This sentence is hard to follow and has too many citations. Consider splitting your sentences into two if they span over several lines and only cite most relevant literature for each statement.
L64 – 66 Add dates.
L75 Which kind of carbon measurements?
L137 Remove first sentence of caption.
L201 Remove sentence. Avoid writing “various parameters “through the manuscript and list parameters instead. Try to be more specific.
L204-205 Explain how you get to this conclusion.
L309 Faber studied mangroves. There is probably a study that is more similar to your study site.
It is very hard to follow your discussion. Suggest reducing to the most interesting findings. Condense the information as much as possible.

Figures and tables:
Fig 1: Remove ESRI source code (in all figures).
Fig. 2: This figure is too big. Show only one figure per page. Choose only most important parameters and put rest into the SI. You could plot all parameters against salinity and/or distance to the coast in one graph with subplots and discuss trends.
Fig. 4 and 5: Increase font size and point size. Axes should be aligned. Salinity looks strange in Fig 4d.
Put Table 1 in SI. Could add averages and standard deviations.

Technical corrections
When you reference two or more citations, the single citations are separated by a semicolon without any spaces. This looks strange. Please double check the citation guideline of the journal.
Avoid paragraphs with only one or two sentences.
L81 Remove “.” before citation.
L191 TA was defined before.
L198 Rephrase this sentence, “arrived” does not make sense in this context.
Do not overuse the term “shed light on…”
The reference list needs to be edited. E.g. CO₂ with subscript and uniform styles for titles. Include volume and page numbers for all references.

Citation: https://doi.org/10.5194/egusphere-2023-2595-RC1
- AC1: 'Reply on RC1', Mona Norbisrath, 22 Mar 2024
  
  The final AC responses are attached in the pdf.
  
  Citation: https://doi.org/10.5194/egusphere-2023-2595-AC1
RC2:
'Comment on egusphere-2023-2595', Anonymous Referee #2, 20 Jan 2024

Strengths:
I really appreciate that the authors left the location names on Figure 2 for easy reference when going from reading the text in the results to the figures. The manuscript as it stands is well organized throughout and easy to follow. The discussion of the results and considerations is also quite comprehensive and strong, aside from the one reservation I have that is listed below. I suggest accepting it after major revisions.

Major Concerns:
Results:
Figure 2: Please make points in figure 2 a color gradient from min to max value instead of grouping many values in one color. That way the reader can more specifically see the actual value at each site. The groupings also aren’t consistently spaced which could be misleading when analyzing spatial trends. Also, this is entirely a personal preference but generally I think blue=lower and yellow=higher based on the ocean of things color bars so it was confusing at first and they may be better reversed.
TA generation section: I think the assumption that TA generation for the entirety of the Wadden Sea does not come from freshwater dilution/river water is not properly supported as stands and is to general. I agree though that this is the correct conclusion for the Ameland region based on the data you’ve shown in Table 1, Figure 4, & 5. However, the authors previously show in Figure 3 that the TA vs salinity trend for the Ameland region is non-conservative, while the Ems-Dollard & Vlie regions of the Wadden Sea are conservative. Therefore, TA & salinity trends are clearly not consistent across the entire region. Which may be attributed to varying degrees of freshwater discharge across the region, which they mention briefly in the discussion. So while it may be true for the Ameland region that TA sources do not come from freshwater dilution/river water, the same cannot be said for these other regions. If the authors had stationary data during ebb tide for the regions that do appear to have a conservative relationship and saw the same pattern then yes they could reasonably assume this is true for the entirety of the Wadden Sea on average. However, they do not appear to have stationary data for either of the conservative regions. Therefore, this statement needs to be more specific to the Ameland region of the study and not the entire Wadden Sea region. If there are river gauges in the region to support similar river discharge across the region then this assumption may have stronger support but would still be rather bold without ebb tide data from the other regions. They also say later that freshwater dominates in the EMS-Dollard.

Minor Concerns:
Throughout manuscript: Please remove any we’s, he’s, etc. Instead refer as “this study” “the data” etc.
Methods:
Is there a reason you focus on calcite saturation instead of aragonite? Is it more relevant to local species? Please state.
Please include how you generated the statistics throughout the paper (i.e. the linear regressions). Did you use Excel, Matlab, R, etc? Also, are these Model I or Model II regressions?
Discussion:
Lines 237-239: Could this also be attributed to seasonal differences or changes in watershed usage over those 30 years?

Minor Edits:
Line 10: “North Sea is hypothesized to be a source…”
Line 10-11: “This study measured TA…”
Line 12: “compared is with historical data.”
Line 14: “ washed out with outgoing tide water.”
Line 27: “Most of the Wadden Sea is located...”
Line 28: “which makes it the world’s largest uninterrupted stretch…”
Line 31: what dynamics? Biogeochemical? Chemistry?
Line 30-33: Split into 2 sentences. One for chemical and one for physical sources of variability.
Line 35-36: what water masses? What is a ‘strong’ exchange? Do you mean that the water masses are very different?
Line 37: “The carbon storage capacity of the North Sea is an important atmospheric CO2 sink as it exports and stores the absorbed…”
Line 40-43: TA, primarily consisting of bicarbonate and carbonate, is generated by chemical rock weathering (citations), calcium carbonate dissolution, and anaerobic metabolic process, such as…”
Line 54-56: during what time of year?
Lines 116-118: please include aragonite saturation values as well. They can simply be added next to calcite values in parentheses.
Lines 204-205: Please include the R-values for the relationships to back this up.
Lines 215: “by enhanced water movement” what does this mean? Be more specific.
Line 219-220: “which could be traced back on an effect of the first four samplings as mentioned above” move to discussion
Line 221: connect this back to higher denitrification and ammonium production compared to nitrification because your ammonium relationship supports this as well.
Line 243: A TA increase of >70 is quite a bit. I wouldn’t say it’s only slightly higher.
Line 271: Where is Marsdiep relative to your study sites? Please add to map.
Lines 282-287: I think these sentences probably belong in the discussion.
Lines 285-287: and more spatial data for the varying TA vs salinity relationships of the different tidal regions in addition to the temporal data mentioned
Line 291: this is not necessarily true. Increased agriculture has led to increased rock and soil exposure, resulting in increased rates of silicate weathering. Also, I’m not sure if this applies to this region but digging of quarries also extracts and exposes silicate minerals during the mining process. However, if the region has little influence from either of these then it could be true. Apologies for I don’t know what the land use is like for this region.
Line 290: “insight” not “inside”?
Line 317: what about the ems-dollard region?
Line 403: what necessary data? This is a good place to suggest future work.

Citation: https://doi.org/10.5194/egusphere-2023-2595-RC2
- AC2: 'Reply on RC2', Mona Norbisrath, 22 Mar 2024
  
  The final AC responses are attached in the pdf.
  
  Citation: https://doi.org/10.5194/egusphere-2023-2595-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Mona Norbisrath on behalf of the Authors (17 Apr 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (21 Apr 2024) by Xinping Hu

RR by Anonymous Referee #1 (22 Apr 2024)

ED: Reconsider after major revisions (06 Jun 2024) by Mario Hoppema

Dear authors,

There is obviously a big difference between the two subregions around Ameland and the Ems estuary. This should be made more clearly and separated in the manuscript.

The Introduction still needs work and restructuring, even if some changes were already made after previous rounds of reviews.

It is mentioned that two (half) tidal cycles were sampled and measured. However, data of only one of these are shown and discussed. Do the other data show the same features or are they quite different? This is important info which must be provided. Please mention somewhere what the other data look like, how they compare with the presented data and whether the conclusions are supported by the second half tidal cycle.

A previous review objected against the use of contents instead of concentration. However, the use “contents” instead of concentration is allowed. Maybe cite the paper by Jiang et al (2022, Front Mar Sci), to make this clear.

The notation 2400 umol kg-1 TA, i.e., with TA at the end is not common and may be confusing. Please change it throughout the manuscript for all concentrations/contents.

List of minor and technical issues:
L10 “The oceanic buffering capacity total alkalinity (TA), as the major global CO2 sink, is of growing scientific interest”. This is a strange contention and not necessarily true. Please change, for example, by just saying that TA is an important chemical property which plays a role in oceanic buffering capacity.

L11 “… generated by chemical weathering on land …” Add: on land.
L12-13 This study shows observations of TA, … instead of “This study observed TA, …”
L18-19 “We assume that seasonality and the associated nitrate availability in particular influence TA generation by denitrification, which we assume is low in spring and summer.” This is too much of assumptions in an abstract. Please only present the facts.

L24 “The (still unofficial) Anthropocene describes …” Or something similar, as the Anthropocene has not been acknowledged officially.
L25-26 “The climate and the increasing atmospheric CO2 content is mainly regulated by the open ocean.” This is not correct. The biosphere takes up more anthropogenic CO2 than the oceans – see the Global Carbon Budget.

L26 The around 30% is more like 25% (see Global Carbon Budget).
L32 susceptible to what? Please be more precise.
L49 strong tidal currents instead of: high tidal currents

L55-57 “Understanding of TA sources have recently become increasingly important due to increasing anthropogenic CO2 emissions, and the resulting demand for ocean based net-negative CO2 emissions” This needs a short explanation as the connection between the two is unclear.

L74 Please use format like 21 May 2019
L76 delete: continuously
L80 Add solution after chloride

Section 2: When were the samples measured, i.e., how long after sampling? Please add this to the different methods.
L97 I guess you mean: … both with a measurement precision …
L97 It is kind of strange that you cite the precision with a different study. Did not you yourself determine the precision and accuracy?

L98-99 “To ensure a consistent calibration of both measurements, certified reference material (CRM batch # 187) provided by Andrew G. Dickson (Scripps Institution of Oceanography) was used” How was this CRM used? Did you adjust the measured data?

Section 2.3 What is the precision and accuracy of the nutrient measurements? Were any CRMs used?
L117 change to: (in particular Hoppema, 1990)

L117-118 “ … we observed TA and related parameters from the coastal mainland towards the open North Sea as a surface water transect” (delete: “the spatial distribution of” because that was already mentioned earlier in the sentence.

L119-120 „Salinity was relatively stable with only minor differences varying from 28 to 33“ First, I think stable is the wrong term here. Second, this large range does not indicate a homogeneous salinity but rather significant variations. The range of salinity is obviously larger than this, as values in the Ems are smaller. Please rephrase the whole paragraph.

L123 “oceanic” is not the correct term here. The North Sea is not an ocean. Actually, “In contrast to the oceanic side,” may as well be deleted as it has no function here.

L124 “Only in the Ems Estuary, the contents were even higher” Delete: Only. Also close to Harlingen TA is higher.
L126 support
L126 “supporting the assumption of TA being generated in this tidal flat area.” It is too early for this contention. It may as well be the discharge of river water that causes high TA.

L127 “showed a similar pattern” Similar to what? Please phrase more precise.
L127 Use other word for “ocean” Please also change this at other places in the text.
L129 I think the silicate contents are given with one digit too much, as the accuracy is probably not that high (accuracy has to be stated in the Methods section)

L130 not site, rather region
L134 delete: similarly
L135 region instead of transect. There are a few transects shown in this study.

L144 “The strong impact from the inner Ems Estuary is visible in all parameters with higher values in the outer estuary and its adjacent zones” This is an awkward sentence. Please rephrase.

L145 higher values of what?
L148 in the mixing plot between TA and salinity. Add: plot, namely TA and salinity do not mix themselves.
L148 “A relatively linear mixing behavior” Relatively is awkward here. Please rephrase
L150 “identifying the Dutch Wadden Sea as a source of TA” This is not correct. A linear relation in an estuary in this case shows that the TA of the river water is high.

L150-151 “In contrast to the TA content computed for the salinity end-member in the Ems-Dollard Inlet, we detected higher TA contents around Ameland” This sentence is strange; please be more precise.

L154 The values are not increasing. There is just a range of values at constant salinity.
L156 (figure caption) Change to: Mixing plot of total alkalinity (TA) and salinity …

Figure 3 Please indicate whether the correlations shown are statistically significant or not.
L169 “DIC contents were similar to TA” This is of course not correct, as the data show. This is about the development/course of DIC contents.
L172 “Nitrate concentrations approached seawater concentrations” What are seawater concentrations for nitrate? These are highly variable. Please be more precise in what you intend to say.

L173 delete: slightly
L183 Change to: the maximum pH was 8.07 at high tide
L188 (caption) This is only half a tidal cycle. Maybe it is good to mention the local time difference with UTC

Figure 4: Two important variables are missing, namely salinity and temperature. These must be added here for better understanding of the tidal cycle.
L193 “The 192 strong tidal forcing induces a strong benthic-pelagic coupling” This needs a reference.
L194 hypothesis instead of assumption appears to be the better choice here.

L201-202 “Based on the correlation of TA and silicate (R2 = 0.93), and on the nonlinear relation between both, TA and salinity (R2 = 0.32), as well as silicate and salinity (R2 = 0.21),” How can a non-linear relation have a correlation? And is this correlation significant or not? This must be rephrased to something like: Based on the correlation of TA and silicate (R2 = 0.93), and on the insignificant relation between TA and salinity (R2 = 0.32), as well between as silicate and salinity …

L203 “Both TA and silicate increased almost proportionally” What does this mean? Please describe more clearly.
L204 Change to: non-conservative behavior of TA with respect to salinity and silicate to salinity …
L207 “from high tide to low tide” I guess you just mean the half tidal cycle as treated above. As now, this is confusing.

L208 “recommend” here is awkward. And why would you ignore these data? This sounds quite arbitrary. Please give a good reason for that.
L209-210 “First, the correlation between TA and DIC reveals the ratio between anaerobic and aerobic processes, which identifies a strong positive correlation between DIC and TA (R2 = 0.93) with TA contents higher than DIC contents (Fig. 5a).” This is not well phrased. Change to something like: The correlation between TA and DIC is a measure for the ratio between anaerobic and aerobic processes. Our data show a strong positive correlation between DIC and TA (R2 = 0.93) with TA contents higher than DIC contents (Fig. 5a).

L210-212 “However, even with contents of TA higher than DIC, the slope of 1.87 indicated DIC release excess with an increase in DIC (ΔDIC = 101.3 μmol kg-1) almost twice as high as TA (ΔTA = 51.6 μmol kg-1) (Fig. 5a).” This sentence is unclear. Please rephrase so that it becomes clear what is meant here.

L214 delete: almost
L218-219 “suggest a stronger effect of TA generation than nitrate production”. The word “effect” can be omitted here as it is confusing: … suggest a stronger TA generation than nitrate production …

L239 insert possible or probable before TA
L43 add something like: …similar range, but the spatial gradients are opposite.
L244-246 “The conservative mixing in the Vlie Inlet can be explained by the fact that more North Sea water pass through the deeper inlets and transport more seawater towards the coast.” This is not clear to me. How does this explanation work?

L257 The salinities observed were not constant. They varied possibly not that much, but that is not the same as constant. Please rephrase.
L264 hypothesized instead of: assumed? Did they find indications for it?
L266 “from the early 1990s” The study was actually from the late 1980s.

L268-269 “Our present TA data and the historical TA data show no large differences in the range of values observed during a tidal cycle.” This sentence is strange. What about: Comparing our present TA data and the historical TA data, there is not a large difference in the range of values observed during a tidal cycle.

L269-270 “However, an in-depth interpretation and comparison of both data sets would exceed the capacity of these data, leading us to focus on TA generation during our cruise” I do not understand this sentence. What is the capacity of these data?

L275 estimated instead of assumed. It would be good to add that they used a model for this at this place.
L276-277 “However, an inclusion of our TA export into the model used by Schwichtenberg et al. (2020) would be unreliable, since our TA export based only on one tidal observation” Why should that be unreliable? It can be just part of that estimate, as the present data are observed data. However, if you would use the present tidal data for estimating the entire TA export, that indeed would be unreliable.

L283 “In order to gain further insight into potential sources of TA, we included nutrients in our investigation” This sentence is too general. Earlier in the manuscript, nutrients were already shown.

L285 Write: Van der Zee, or van der Zee
L283-285 “The main focus was on silicate that we used as a natural tracer since it is not directly provided anthropogenically and allowed us to determine the silicate source” This sentence is unclear; please be more precise what you want to convey. The authors base this contention on a reference from 2005. Since the early 2000s the situation in the Wadden Sea could have changed a lot, as was also found for the sources of alkalinity. Do you have any indication that nothing has changed?

L288 hypothesis instead of assumption
L290 “salinity consistently being above 32” It is not clear which area is concerned here. The Ems estuary has lower salinities, but also the Vlie has a salinity of about 30 (Fig.3). Please be more precise.

L291-292 “This can be supported by the relation between silicate and salinity in which we observed a 291 non-conservative behavior (Table B1). Since TA behaves also non-conservative relative to salinity (Table B1)” This says actually the same as the previous sentence. In addition, Table B1 does not show a relation at all; it just shows data. You may just refer to Table B1 after the previous sentence.

L297-298 delete: “In May, they observed low salinities indicating freshwater. However, in September they observed constant marine salinities referring them to be exclusively composed of recirculating seawater.”

L298-299 “Since we constantly observed marine salinities,” This is an awkward sentence. Change to something like: Since we observed relatively constant salinities …

L307 “smaller than” instead of: below
L308 delete (twice) clearly
L311-313 One can write this much easier and understandable. Please rephrase.
L313-314 “However, when silicate occurred dissolved in water it does not contribute to TA generation (Meister et al., 2022).” I do not understand this. Please explain .

L314-315 “A TA excess related to silicate was also observed in the correlation between TA and silicate (Fig. 5b).” Of course, you can see this in Fig. 5b. These are the same data.

L318 Use the Greek symbol for omega. Actually, “With the observed omega values,” can be deleted because the same is written later in the sentence.
L321 “because of the Ω supersaturation of the overlying water” This is not the reason for not being able to determine TA generation in the sediments, so please delete.

L326-327 This is an anacoluthon. Please correct the sentence. Which ΔTA and ΔDIC is this? They have not been defined.
L328 increase of DIC. Which increase? Again, ΔDIC was not defined. Please be more precise.
L330 “high CO2 export” Which export, from where to where?
L330 delete: also, as this is not observed in this study. It is only hypothesized.
L335 continues instead of: continuous

L3345 exceeds instead of: exceeded
L353 less instead of: lower
L357 “due to high turnover rates” I would say: due to high photosynthetic activity
L373 It would be a nice service to the reader and make the paper more readable if the chemical reaction scheme of aerobic OM respiration with the associated formation of ammonium would be shown here.

L375 delete: leading to ammonium formation. This was already written at the beginning of the sentence.
L376 increases instead of: would increase
L388-389 “the simultaneous increase of TA and nitrate is noticeable for us, because nitrification consumes TA” It is unclear what the authors try to convey here. Please rephrase and explain.

L391 “Low nitrate concentrations resulting in a reduced availability of bound oxygen, i.e., electron acceptors.” This is not a correct sentence. Please rephrase.

L401 define POC, as it is used for the first time
L413-414 “While observing the spatial TA distribution and TA generation” This manuscript is does not observe TA generation per se. It only deduces it and speculates about it.

L415 delete: clearly
L420 deduced instead of: identified
L420 and further: It should be made clear that this was not observed but rather deduced with some speculation.
L428 Spatial instead of: Latitudinal and longitudinal

L431 Table B1 It is half a tidal cycle. Please mention the position in the table header. An obviously missing variable in this table is: time.
L432 Format 21 May 2019
L437 Which other data were measured during the cruise? At least it was mentioned that there is a second (half)tidal cycle. The data should be published along with the manuscript. Other data, which is probably not that much, could be published as supplementary material.

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AR by Mona Norbisrath on behalf of the Authors (02 Aug 2024) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (08 Aug 2024) by Mario Hoppema

Dear authors,

The manuscript has much improved since the previous submission. However, there are still some issues that must be accounted for. Most of these are of technical nature, but not all. My comments are listed below:

L81 Temperature and salinity what precision/accuracy? Was the ferry box calibrated?
I guess the salinity values are on the practical salinity scale. If yes, please mention this.

L110 „VKI SW4.1B (NOx, NO2 and NH4) and VKI SW4.2B (Si and PO4)“ Any more info on these standards? Manufacturer?
L111 What is a maximum standard deviation?

L128 “with salinities showing only minor differences varying from 28 to 33” I think differences is the wrong word here, it should be variation. And values between 28 and 33 is not minor.

L185 Use symbol for omega

Fig. 4b The scale for salinity is too large. It prohibits to see any variation, as can be seen in all other sub-panels of this figure. The labels with 3 digits are not correct considering the salinity data given in the tables.
Again Fig. 4: The distribution of data points of pH, calcite and aragonite looks strange. It is necessary to provide the uncertainty of these variables, preferentially in the methods section.

L310 TA generation is not observed in a strict sense, but rather deduced.
L310 “The observed TA generation of 7.6 μmol TA kg-1 h-1 and the silicate increase of 1.4 μmol Si L-1 h-1 indicated an excess of TA” It is not clear what this sentence wants to convey. What is the excess, excess of what?

L311 “A given TA:Si ratio of 2:1” This needs some explanation, i.e., what ratio, why can you use it? Is the mentioned ratio well constrained? Generally this is not the case; there is quite some variability in such ratios.

L317 “in the water column”, instead of: “in the overlying water”
L317 delete: clearly
L325 delete: both
L326 The figure says 1.89, not 1.87

L325-327 “The correlation of DIC and TA reveals an excess of released DIC compared to TA (Fig. 5a), as indicated by the slope of 1.87, while we observed an increase in DIC (ΔDIC) almost twice as high as in TA (ΔTA).” This sentence can be much shorter. The first part essentially says the same as the second part. I think here the use of excess is confusing.

L327-326 “The high ΔDIC points to high aerobic OM degradation and remineralization, resulting in high CO2 production.” I think this is not correct here. A slope of about 2 is just the normal case when CaCO3 is involved.

L339 It is more correct to write a ΔDIC:ΔTA ratio.
L341 delete: potential
L341 … of the observed ΔDIC during the tidal cycle … (add explanation that ΔDIC is from this source)

L342 “ … the expected Redfield ratio of C:N (6.6) …” I do not assume that this ratio is expected. This ratio is quite variable. Please provide a reference that this ratio is valid in this region.

L361 “in the water column”, instead of: “in the overlying water”
L365 “We support their findings of lowered TA generation by denitrification in late spring and early summer.” You did not prove lowered TA generation, you actually only deduced it based on results from other scientists in their papers. The sentence cannot be included as is.

L387 “the northern and the western parts of the Wadden Sea” Please be more specific, which parts do you mean?

L414 Table B1 What exactly are rounded up values? How were they rounded up and why? Why not just give the data as they were measured. For oceanographic purposes it is strange to give salinity by only one digit. Even a ferry box must be able to measure it with greater precision. For the other parameters the number of digits seems to be ok.
Same for Table B2

L424 The data policy of Ocean Science and of almost all other serious journals states that the data should be available as FAIR data. The policy (https://www.ocean-science.net/policies/data_policy.html) says: “If the data are not publicly accessible at the time of final publication, the data statement should describe where and when they will appear, and provide information on how readers can obtain the data until then.” Where and when will the data be published?

Thank you and best regards
Mario

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AR by Mona Norbisrath on behalf of the Authors (27 Aug 2024) Author's response Author's tracked changes Manuscript

ED: Publish as is (30 Aug 2024) by Mario Hoppema

AR by Mona Norbisrath on behalf of the Authors (30 Aug 2024) Manuscript

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30 Oct 2024

Alkalinity sources in the Dutch Wadden Sea

Mona Norbisrath, Justus E. E. van Beusekom, and Helmuth Thomas

Ocean Sci., 20, 1423–1440, https://doi.org/10.5194/os-20-1423-2024,https://doi.org/10.5194/os-20-1423-2024, 2024

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Mona Norbisrath, Justus E. E. van Beusekom, and Helmuth Thomas

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Observational study that investigated total alkalinity (TA) in the Dutch Wadden Sea. We collected discrete water samples to identify spatial TA distribution patterns and to locate and shed light on potential TA sources. By observing a tidal cycle in the Ameland Inlet, we identified the sediments as a local TA source and assumed aerobic metabolic processes eg CaCO₃ dissolution as a TA source in the upper oxic sediments, and anaerobic metabolic processes as a TA source in the deeper anoxic ones.


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Distribution and source attribution of alkalinity in the Dutch Wadden Sea

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