the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Validation of the coupled physical-biogeochemical ocean model NEMO-SCOBI for the North Sea-Baltic Sea system
Itzel Ruvalcaba Baroni
Elin Almroth-Rosell
Lars Axell
Sam T. Fredriksson
Jenny Hieronymus
Magnus Hieronymus
Sandra-Esther Brunnabend
Matthias Gröger
Lars Arneborg
Abstract. The North Sea and the Baltic Sea still experience eutrophication and deoxygenation in spite of large international efforts to mitigate such environmental problems. Due to the highly different oceanographic frameworks of the two seas, modelling efforts so far mainly focused either on one or the other Sea making it difficult to study inter-basin exchange of mass and energy. Here, we present an ocean model (NEMO-Nordic) coupled to the Swedish Coastal and Ocean Biogeochemical model (SCOBI), which covers the North Sea, the Skagerrak-Kattegat transition zone and the Baltic Sea. We address its validity to further investigate biogeochemical changes in the North Sea-Baltic Sea system. The model reproduces the long-term temporal trends, the temporal variability, the yearly averages and the general spatial distribution of all assessed biogeochemical parameters. It is particularly suitable to be used in future multi-stressor studies such as to evaluate combined climate and nutrient forcing scenarios. In particular, the model performance is best for oxygen and phosphate concentrations. However, important seasonal and spatial differences for chlorophyll-a and nitrate are seen between model results and observations in coastal areas of the southeastern North Sea, the Skagerrak-Kattegat transition zone, the Gulf of Riga, the Gulf of Finland and the Gulf of Bothnia. These are partially linked to different local processes and biogeochemical forcing that lead to a general overestimation of nitrate. The validation of our model results for individual areas are in agreement with policy management assessment areas, which gives an added value to better contribute to international programs aiming to reduce eutrophication in the Baltic Sea-North Sea system.
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Itzel Ruvalcaba Baroni et al.
Status: final response (author comments only)
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RC1: 'Comment on bg-2023-116', Tom Jilbert, 17 Sep 2023
Interactive comment on “Validation of the coupled physical-biogeochemical ocean model NEMO-SCOBI for the North Sea-Baltic Sea system” by Ruvalcaba -Baroni et al.
The paper of Ruvalcaba-Baroni et al. represents an important step forward in coupled physical-biogeochemical modeling of the North Sea and Baltic Sea regions as a single domain. The combination of NEMO with SCOBI is logical and according to the authors’ knowledge is only the third such effort from the modeling community after the papers of Maar et al. (2011) and Daewel & Schrum (2013), based on DMI-BSHcmod/ERGOM and ECOSMO, respectively. Given the need for model ensembles to improve overall understanding of biogeochemical functioning of marine systems, this study is very relevant, even more so with current efforts to better integrate management of the two seas under study.
The paper is generally of very high quality and builds upon the base of previous work in the same group with respect to both the development of NEMO-Nordic and SCOBI. Therefore I do not see any fundamental problems with the research and support its publication. That said, it is interesting to observe the discrepancies between SCOBI-modeled parameters and observational data in certain regions, which show the current limitations in knowledge and hopefully will guide the authors towards future improved iterations of the model. Some of these discrepancies deserve a bit more elucidation in the text, or at least better structuring of the sections, so as not to leave the most important discussion points to the end of the paper. There are also a small number of technical clarifications I would draw attention to, and some suggestions for alternative phrasing and setting the context of the study. These may all be considered minor revisions so I give them as a Line-by-Line list below.
Kind regards,
Tom Jilbert
University of Helsinki, Finland
Line 45-50: Not clear why primary producer assemblages are mentioned here for NS but no equivalent description for BS. I suggest to introduce the physical aspects first, then biogeochemical and finally the plankton assemblages.
Line 66: Replace "recycling of benthic phosphorus minerals" with "recycling of phosphorus from sediments"
Line 70-71: Please update this setting of the context with a citation of the following publication and potentially references therein: "The Baltic and North Sea Strategic Research and Innovation Agenda BANOS SRIA 2021 The final BANOS SRIA draft of the proposed, new, joint Baltic and North Sea Research and Innovation Programme -BANOS BANOS CSA Deliverable 1.5".
Caption of Fig. 1: Capitalize SHARK
Table 1: Modify “mg CHL m-3" to “mg Chl-a m-3"
Figure 2 legend: Typo in “atmosphere”
Line 183: Typo “100 kton N/yr”
Line 195: Does this mean "reduced to 0.3 x and 0.75 x the original value, respectively"? Please clarify. Also clarify (as implied in Fig. 2) that the resulting nutrient flux to the sea is entirely in the dissolved fractions and comment briefly on simplifications with respect to e.g. fluxes of TP, that in reality are largely particulate.
Line 286: Modify to e.g. "depending on their proximity to one another"
Line 301: Typo "to analyze"
Line 315: Replace “80s” with “1980s”
Line 317: Typo “observations are too low”
Line 326: Replace “don’t” with “do not”
Line 346: Typo “statistically”
Line 347: Remove "not studied here", it confusing to state this
Line 349: Rephrase to e.g. "There is a lack of observational data for bottom water oxygen during the period 1975-1995"
Line 407: Typo “less than”
Line 420: Typo “extent”
Line 421: Modify to “The main inference of...”
Line 424: Modify to “"Despite such specificities of..."
Line 457: Modify to “its” (no apostrophe)
Line 471: Modify to "bias is" or "biases are"
Line 497: Modify to “most models”
Line 572: How could low oxygen theoretically inhibit primary production? Not easy to understand what is meant here.
Line 574: The model vs. data discrepancy in the timing of the late winter/spring bloom in the Kattegat is one of the key question marks raised in the study, and indeed it is highlighted in Fig. 7. I think it deserves more elucidation at this point in the discussion, for example an assessment of the degree to which light or temperature might be inhibiting the early onset of the bloom in the model. The authors return to this in Section 3.6 “Future work and data gaps” but in the current version the reader is left hanging for an explanation after it is established that there is no nutrient limitation at the time in question.
Line 590: Again please check the BANOS SRIA for up-to-date statements about the need for integrated modeling of BS-NS system
Line 595: Citations in brackets
Line 604: Modify to "in Ford et al. (2017)..."
Line 616-623: This is a very important section of the discussion: the model assumes (if I understand correctly) that a certain bioavailable fraction of nutrients enters the sea, directly into the dissolved phase state variables PO4, DSi, NO3, NH4 (Fig. 2). This is of course a large simplification of reality, where there is transfer between bioavailable and non-bioavailable fractions within the coastal filter, as well as heterogeneous removal of nutrients. Different types of coastlines may behave quite differently in this regard, see eg. Asmala et al., L&O 62 (2017). Are there any of the observed model vs. data discrepancies e.g. in near shore nutrient or Chl-a concentrations, that could be affected by this simplification? If so, it would deserve some mention higher up in the discussion for those specific areas.
Line 666: typo “therefore”
Appendix Line 737: Important: should this read "BOPREM-BIP decreases with increasing salinity and decreasing bottom oxygen concentrations..." ? That is the implication of the equations and following text, and the logical relationship.
Appendix Line 771: Typo “from”
Appendix Table A2: Comment on the validity of using a single porosity value for entire NS-BS system.
Citation: https://doi.org/10.5194/bg-2023-116-RC1 -
RC2: 'Comment on bg-2023-116', Anonymous Referee #2, 17 Sep 2023
Review of the manuscript “Validation of the coupled physical-biogeochemical ocean model NEMO-SCOBI for the North Sea-Baltic Sea system” by Baroni et al., (2023)
I have completed the review of the manuscript “Validation of the coupled physical-biogeochemical ocean model NEMO-SCOBI for the North Sea-Baltic Sea system” by Baroni et al., (2023). In this work the Authors describe a run made using the newly ocean-biogeochemical model NEMO-SCOBI that has been specifically developed and tuned for the North Sea-Baltic Sea System. I found the manuscript well written and the validation of the model properly carried out by the Authors. On the other hand, I think that the manuscript needs some major revisions whose reasons are listed below
Comments
- While I was reading the manuscript, although it is clear that having a coupled model for the North Sea-Baltic Sea represents a clear advancement for the scientific community, it was not clear to me if its performances are better or worst that other 3D modeling tools available for the region that are cited by Authors at line 80 for example. Are the performances of NEMO-SCOBI better or worse than other modeling tools? Does NEMO-SCOBI improve the biases of other modeling tools or not? I’m asking that since a potential user should have all this information to decide to use your modeling tool/simulated data than others provided by another modeling tool.
- Strictly correlated with that: please provide more quantitative information about these performances. “Good”, “Comparable”, “Acceptable” and so on are not informative from my point of view. Please quantify in the manuscript the biases and the values of the trends and their statistical significance.
Line 11: What do you mean with “differences”? please explain
Line 26 : “Modelled” or “Observational” studies? Please explain
Line 31-40 : What about the intermediate layers of the basin?
Line 54: What do you mean with “point sources”. Please explain
Line 70-76: Please provide more information about these differences since it is the starting point for showing that this model is a step forward for the scientific community
Fig.1: It would be great to have super imposed here the bathymetry of the domain (eventually using contours)
Line 107: Did you assess the drifts in the tracers to assess whether 14 years are (let’s say) enough for the spin up or not? In many ocean/biogeochemical models even 30 years are not enough to stabilize the numerical solutions.
Line 113: what kind of grid are you using? Regular, structured/unstructured? Please explain
Line 119: Is Iron not important in your domain of study? (since I remember that iron is important in the global ocean).
Section 2.1.2 I would include in the paragraph the treatment of light and PAR (that I see located in the SM). How is primary production parametrized? Did you use Q10 formulation? Please explain here
Line 155-170: How tick is your sponge layer in the ocean domain? Why do not you use ORAS5 that is more recent than ORAS4? Did you use bulk formulas for latent and sensible heat fluxes? What formulation of albedo did you use in your ocean model (since it influences the quantity of shortwave radiation reflected by the surface)
Fig3-4 I would put the runoff as first panel in both figures.
Line 289: What do you mean with “similar”? please explain
Figure 6 and after: please move the small panel “Model Obs ..” outside the first panel since it covers partially the lines beneath.
Line 388 What do you mean with “good period”
Paragraph 3.4. I think that this paragraph should go before the comparison between models and observations at the single stations. This could provide a general overview of the model performances better that the comparison with single point
Line 520-541, Line 551-560: These parts should go in the introduction since they provide an interesting description of the Baltic-North Sea system.
Figure 13-14: Put in first row the observations.
Citation: https://doi.org/10.5194/bg-2023-116-RC2 - RC3: 'Comment on bg-2023-116', Anonymous Referee #3, 18 Sep 2023
Itzel Ruvalcaba Baroni et al.
Itzel Ruvalcaba Baroni et al.
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