the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Oct 2024
Intertidal Regions Regulate Seasonal Coastal Carbonate System Dynamics in the East Frisian Wadden Sea
Abstract. Seasonal and regional changes in carbon dynamics in the Wadden Sea, the world's largest intertidal sand and mud flats system, were analyzed to quantify the influence of biogeochemical processes (CaCO3 dissolution and formation, photosynthesis, respiration) on the carbonate system at the land-sea interface. With a focus on the East Frisian Wadden Sea and the highly turbid Ems River estuary, we successfully implemented the proxy of the difference between total alkalinity (TA) and dissolved inorganic carbon (DIC) ([TA-DIC]), as well as the calculated ΔTAexcess, ΔDICexcess and ΔTAP to identify how ongoing biogeochemical processes regulate the carbonate system dynamics and the land-sea interface.
In spring, a phytoplankton bloom with high biological activity was indicated by (a) supersaturated oxygen (up to 180 in % saturation), (b) elevated chlorophyll a (up to 151.7 µg L-1) and (c) low pCO2 (as low as 141.3 µatm). As a result, nitrate (NO3-, 19.29 ± 18.11 µmol kg-1) and DIC (159.4 ± 125.4 µmol kg- 1) decreased, whereas TA slightly increased (9.1 ± 29.2 µmol kg-1) in the intertidal regions from March 2022 to May, most likely through nitrate assimilation. The regression analysis of the differences in NO3− concentrations (ΔNO3−) against the differences in DIC (ΔDIC) between March and May 2022 yielded a slope of 6.90 which is close to the Redfield ratio of 6.625 for the C:N ratio of freshly produced phytoplankton biomass.
In summer, high seasonal TA values (up to 2400 µmol kg-1) in the Western part of the East Frisian Wadden Sea, along with positive ΔTAexcess at 73.3 % of all stations, indicated production of TA during this season in the intertidal regions, complemented the DIC dynamics. The increase of TA enhances the coastal ocean’s ability to absorb and store CO2 through buffering, chemical equilibrium, biological calcification and the carbonate pump, and suggests that the intertidal regions can be a source of total alkalinity to the coastal regions during the warm productive seasons. The study highlights the complex relationships of these factors, emphasizing the need for a comprehensive understanding of regional and seasonal variations to better assess the role of coastal systems in carbon cycling, storage and climate regulation.
- Preprint
(3261 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 12 Jan 2025)
-
RC1: 'Comment on egusphere-2024-3048', Anonymous Referee #1, 02 Dec 2024
reply
Meyer et al. conducted five seasonal cruises in the German Wadden Sea, relying on FerryBox (presumably) surface surveys and discrete samples from its outflow, to assess the controlling factors on total alkalinity (TA) and total dissolved inorganic carbon (DIC). Their results suggest that primary production and benthic contribution both affect water column inorganic carbon system. This study uses standard mixing line approach (for TA and DIC), temperature normalization (for pCO2), as well as reaction stoichiometry in an attempt to tease apart the various processes and changing physical conditions on the carbonate system.
After reading the manuscript, I did not grasp any new information from this study. Several of the coauthors have published numerous articles in this general area with similar conclusions. To improve the writing, I would highly encourage the authors to take a step back and think about how to emphasize the novelty of this work. The writing itself also can use much help to streamline the content, for example the extensive results on turbidity and chlorophyll as well as several spatial maps (for example Figs. 2, 3,7, 12) may be moved to supplementary materials to improve the flow and reduce redundancy, and perhaps merge Figs 4 and 5. Much of the method section can also be simplified because the vast majority of the analytical methods are standard ones hence there is no need to present the procedures in this great length.
Below are some major comments:
First, while the mixing plots are the primary tool being used to separate processes, I find the presentation to be weak. First, Table 1 showed that river DIC endmember for Eastern Wadden Sea in Mar, May and July 2022 had the same value (2647.2 µmok/kg), although this average value was taken from Wester River in Aug and Oct 2021 and Apr 2022. There is no explanation why this was done since the timing doesn’t even match. Given the large, known, seasonal variations (for example Jul and Oct 2021 the values were ~120 µmol/kg apart), this single endmember choice for all three 2022 cruises can easily produce biased results using the following mixing line examination. Aside from the problematic endmember choice, the mixing plots (Figs. 8 and 9) appear to have used the TA and DIC data at both minimum and maximum salinities to draw the lines, instead of the defined endmember values.
Second, even though both TA-DIC and TA vs. DIC plots have been used previously to address reaction stoichiometry, these methods are more of “oceanic” in which relatively narrow salinity ranges are assumed. However, this study covers fairly wide salinity ranges in the coastal sites (for example see Fig. 8) with non-zero and variable river input, I suspect that these approaches are not appropriate in the data interpretation. Some kind of normalization to rid the estuary-coastal mixing needs to fully address the reaction stoichiometry issue.
Third, in separating temperature vs. biological effect on pCO2 variations (note pCO2 does not have “concentration” as several places show), the Takahashi 1993 coefficient applies to the oceanic water under his study, for lower salinity waters with different buffer capacity, 4.2% cannot be directly used.
Below are some minor points that I noted, but certainly this is far from a complete list:
- L248, did you correct possible river Ca contribution? See:
Beckwith, S.T., Byrne, R.H. and Hallock, P., 2019. Riverine calcium end-members improve coastal saturation state calculations and reveal regionally variable calcification potential. Frontiers in Marine Science, 6, 169.
- L352 paragraph, awkward and unclear sentences. There are many like this in the manuscript. Proper proof reading is perhaps needed.
- L364, please show justification why these are considered outliers, the same applies to L370-374.
- L403, what’s “real” signal?
- L537-539, water with lower Ω has carbonate formation but that with higher Ω has carbonate dissolution? Is this arbitrary for the sake of explaining the data or there is actual proof?
- L582, decreasing temperature leads to CO2 (not pCO2) solubility decrease?
- L594, what’s another “CO2-consuming process”?
- L647 and relevant text in discussion – if carbonate dissolution takes place, how does that help to take up atmospheric CO2?
Citation: https://doi.org/10.5194/egusphere-2024-3048-RC1 -
RC2: 'Comment on egusphere-2024-3048', Anonymous Referee #2, 11 Dec 2024
reply
The article examines the contributions of the Wadden Sea to the North Sea's TA and DIC through data collected from five sampling cruises conducted over a year, providing valuable insights into the carbon budget of this region. While the methods are sound and the interpretations are accurate, the article is challenging to read due to its lack of focus and poor narrative flow.It delves extensively into secondary parameters and marginally relevant epiphenomena, detracting from the central story. Additionally, the discussion section includes a detailed exploration of the use of [TA-DIC] as a proxy for assessing ecosystem metabolic status, which could almost constitute a separate article.The study has significant potential, but the manuscript would benefit greatly from streamlining. It should be organized around a clear central research question, with the text and analyses focused solely on the elements most relevant to addressing this question. To enhance readability and impact, the article should be reduced by approximately 30-50% in length, with large portions of the text and many figures moved to supplementary materials.
Moreover, the extensive focus on the relationships between S-TA, S-DIC, and the influence of salinity on TA and DIC could be simplified by normalizing TA and DIC for salinity, eliminating unnecessary complexity and improving clarity.
Ln 25. It reads that calcification stores CO2, which is incorrect. I m not sure what you call carbonate pump.
- repetition, rewrite.
- and…and…and, use punctuation.
- since the onset/start. I guess we are still in the industrial period
- there is more recent meta-analyses than Kroeker et al. on the matter.
- I m unsure of what you are calling intertidal region. The intertidal zone is the area free of water at low tide and inundated a high tide. Regions are at wider scale. The Wadden sea is not an intertidal region, it does not emerge at low tide. It is a macrotidal region maybe. I think there is a misuse of “intertidal” throughout the MS.
Besides, a word of description of the intertidal would be good for people non familiar with the Frisian area. Is it a rocky shore, a mud flat (yes), with or without vegetation, seagrass saltmarshes.
In general, I think the second paragraph could be reduced, if not removed as it reads more as a conclusion/outlook material, so that we get faster to the point of the study.
65 make 2 sentences
- we already know from previous sentence that we are in the east Wadden sea. rewrite the last sentence more clearly.
- Are the cruise 24h day and night, or only day (from what time to what time), how many days? . What time of the day where the sample taken? I guess from reading that there were no nighttime data/samples.
- intertidal: Do you mean you sailed at high tide in 2-3 meters of water? or you were cruising in the channels and offshore/ deep subtidal area (I guess).
- What scale for the pH? How did you calibrate the sensor? TRIS buffers for SW?
Fig1. Do you have a satellite or bathymetry map instead of a road map? It is difficult to understand the nature of the coastal area.
- pCO2obs is the pCO2 measured with the ferry box, or?
- So, if I understand well, you applied one end member to one part of your sampling points and another to another half. How did you decide the limit? Doesn’t this have the potential to create an artifact at the frontier between your 2 zones?
155-160. you need to better explain why this equation and what it does.
155-184. These methods need to be better explained. Btw, where do you get the DICocean and TAocean from?
- the seasonal highest salinity for Si or Socean, and why the highest, not average or else?
Moreover, if I read well, DICexcess is rather a deficit due to photosynthesis which you attribute to primary production. What if you have a (real) excess, you can’t apply PP stoichiometry as DIC can be emitted by numerous redox reactions from the sediment.
- What pH is it? Is it on total scale from TA+DIC, or from the CTD? On which scale?
- Why highlighting calcite over aragonite?
Paragraph 280.
Why don’t you directly calculate normalized TA and DIC with your riverine end member with e.g. Friis et al 2003 equation and directly discuss those TAn and DICn variations, due to coastal Production, and drop all the text regarding mixing/dilution/conservative impact of salinity on TA and. Figure 8 could only be 2 plots, one for DIC and one for TA.
- the opposite would be quite unusual in a marine system. Unless pCO2 of several thousands. I don’t see what use can be done of the difference between TA and DIC.
415 – 422. The text is full of redundant sentences: March… TA positive… explained by PP etc. June… TA positive… explained by PP. July…
The results section is very long, very (over) descriptive, lack flow/focus/direction and, hence, is tedious to read. Focus on the matter of interest here, the production of TAexcess and DICexcess by the coastal area and move to supplement all description of CHla, turbidity, S-TA and S-DIC relationships, nutrients etc. unless it serves the story you are trying to tell.
- this would rather belong to the Material and methods.
Discussion: The lack of focus and the excessive length of the text make the article tedious to read. The [TA-DIC] proxy gains increasing prominence as the article progresses, but it is not introduced in the Materials and Methods section. Instead, it first appears in the results section, leaving readers unsure of its purpose. Only in the discussion section does its relevance and the authors’ intent become clear. This approach makes the manuscript feel disjointed, with section 4.2 reading like a separate article embedded within the main one
The section 4.3 is dispensable, the 4.4 surely as well.
Citation: https://doi.org/10.5194/egusphere-2024-3048-RC2
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 141 | 35 | 8 | 184 | 4 | 3 |
- HTML: 141
- PDF: 35
- XML: 8
- Total: 184
- BibTeX: 4
- EndNote: 3
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1