the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Nov 2023
Distribution and source attribution of alkalinity in the Dutch Wadden Sea
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.
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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
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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
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