Chronic Oil Pollution from Vessels and Its Role in Background Pollution in the Southeastern Baltic Sea
Round 1
Reviewer 1 Report
Dear Authors,
Many thanks for this interesting contribution - I enjoyed reading and evaluating your manuscript which relates to long term satellite-based monitoring of oil (hydrocarbon) discharge in the SEB. I am amazed, and happy to read that in spite of the increasing traffic in the SEB, the incidents of discharge / spills seems to be decreasing. This is excellent news for the Baltic region!
The manuscript is in a good shape, nevertheless, in my opinion, it would be much better. Let me break down my comments, as follows:
Figures:
Figures 1 and 12 are confusing, since the symbology used is similar (circles). Please use a different symbol (e.g. stars) or somehow combine the two figures. Also, it seems that there are different periods 1998-2017 and 2004-2020 - so I am not sure if we are comparing apples with pears !
The Bar charts (4, 5, 7, 8, 9, 10, 11) are interesting and useful - but would it not be better to combine these e.g. to have 4 bar charts as sub figures, because, as far as I can see, the absolute numbers are not of interest, only the trends. Furthermore, I would like to see some error bars or at least some discussion of how good these values (quality, errors etc.). Figure 5 - does not really need a bar chart. You could delete it!
General Text:
Kindly go through the text carefully. There are some minor English grammar mistakes that need to be corrected, e.g. line 329 "No one" should be "No single" or line 377 "Blooming" sounds odd and is incorrect, and should be replaced by "Plankton blooms are .." or "The spring bloom is .." etc.
Overall, I am worried about:
- the method of identification, although described elsewhere, it would warrant at least one satellite image with a spill on it, and does your method work as efficiently for all oil products ? Are there any error estimates? How good is your method ?
- definition of a single spill, does this vary from other methods, are you missing spills?
- the use of the word "chronic" in the title and text. From your work, it is obviously not "chronic", so why use this term (because other works suggest that it has to be chronic, or there is chronic OP)? If you use "chronic" then you need to explain this further.
- The lack of oil discharges from D-6. You categorically state that nothing came from D-6. However, there are clearly spills identified in the vicinity (fig 12). Are you sure that these are not related to D-6 ? Most production and exploratory wells in the North Sea / Norway have some, if not minor, impact.
- where does the "chronic" hydrocarbon pollution come from, assuming that it is chronic ? If this is a significant infux from the rivers, then there must be some record (literature) of this. Do you think that the influx might be greater during the winter months, when you are not able to detect spills? It is likely that vessels know that detection is difficult during winter months.
- I think it might be interesting to closely look at the solubility of OP and biodegradation in your estimates. Temperature is not the only parameter that is critical. Furthermore, understanding the sinks for your OP would be also useful for the understanding of the system.
- I am missing some sort of recommendation at the end. The "so what does this mean for the SEB" - there is no chronic pollution and hence no problem, and the systems in place should continue with the same legislation and monitoring practices ?
- Finally, the manuscripts would profit greatly if you were able to compare the current situation in SEB with some other heavily used (shipping) region. Is it common that vessel-based OP discharges are decreasing. Maybe most of them dump their OP outside the 12-mile zone!
Hence, overall I feel the manuscript is in good shape, but it needs to be wrapped up and the above questions addressed.
with regards and thanks for your contribution!
Author Response
Please see attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Authors,
I would like to take your attention to my major concerns about your manuscript.
- I recommend you change the title of your manuscript. I found it more as a monitoring manuscript.
- You submit your manuscript to the remote sensing journal but unfortunately, you didn't dedicate proper sections to highlight the importance of remote sensing application for such study and how did you use such valuable information in your study. The manuscript lacks a description of SAR data, their importance in oil spill detection, their application in this subject, your novelty regarding the application of SAR, the benefit of using satellite data such as SAR for such study, the competency of SAR with your other data and how it could add values.
- The method section is simply missed. It is nuclear how did you analyze SAR data in general. Which methods did you apply to detect spills? How did you analyze them spatially and temporally? What software did you use for your analysis? If there are any documented open-source software or codes where is the access point? This is a serious concern about your paper. Please provide this information and add them to the manuscript.
- Your results are not backed up appropriately by figures and graphs. Please provide enough evidence in this section. Due to the limitation of the results and method section your discussion is weak and is mainly subjective without giving scientific justification based on facts and analyzed data.
I would recommend you consider the above major comments, revise your manuscript, add proper information and data, and improve the quality of the manuscript.
Please find my detailed comments in the attached pdf file.
Regards
Comments for author File: Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript deals with a very specific issue of chronic oil pollution from vessels in the southeastern part of the Baltic Sea. Because it is mentioned already in the title, I would place this note here – do you consider the Southeastern Baltic Sea as the unique topographic location? Or is it meant as the southeastern part of the Baltic Sea? It is deciding to distinguish the initial capital letter in the word southeastern. The abstract is quite condensed. It contains much information. The Introduction section serves as the literature review too. Figure 1 is mentioned in the second paragraph, but it is placed at the end of the section. It would be better to shift it – also because of the empty space on page 2 now. I appreciate the very latest data investigated in the analysis covering the period until December 2020. Figure 2 is placed at the end of the section, which it is mentioned in. It would be appropriate to shift it to the paragraph that refers to it. On the other hand, there is a possibility to place all the figures in the appendix. The satellites, whose images are investigated, have their usage periods overlaid each other. Do you also combine more images of the same area in their common period? This should be explained in the Data and Methods section. The Results is section is very illustrative – presumably, more illustrative that it is desired. It would be more appropriate to apply less colours in all the diagrams, because now each diagram is visualised by the different colours. The Discussion section offers a comparison of the outcome with the other similar studies. The Conclusions section summarises the obtained findings. The manuscript possesses some formal mistakes and grammar errors. Hence, the text should be proofread.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
No More comments
Reviewer 3 Report
The amendments are done as suggested in the review.
