Deep Water PAH Cycling in the Japan Basin (the Sea of Japan)
, Evgeniya Marina 1 and Rodrigo Mundo 3Round 1
Reviewer 1 Report
Deep water PAH cycling in the Japan Basin (the Sea of Japan)
Koudryashova et al.
PAH are important chemicals in the environment as many of them are known to be toxic, carcinogenic and mutagenic. Thus, monitoring their presence, distribution, and profile in the marine environment is crucial as many of these compounds can be taken by aquatic species. This study examined the vertical pattern of fractionated polycyclic aromatic hydrocarbons (PAH) in the Japan Basin in the Sea of Japan. The article is nicely written and easy to follow. However, I want the authors to address my concerns about the paper below prior to its acceptance.
L42-45: PAHs are sorbed into particles including marine snow.. Marine snow is a naturally occurring phenomenon in the open ocean and is known as one of the important carriers of PAHs. Please refer to this paper https://www.mdpi.com/2077-1312/8/10/781. Thus in the Introduction, the role of marine snow in the sequestration or adsorption of PAHs, particularly LMW and HMW PAHs, should be mentioned.
Another important mechanism that is not mentioned in the Introduction is the photooxidation of PAHs in the water column by natural sunlight. The authors must explicitly mention this as the fate of PAHs as aromatic rings in the water column are strongly affected by photooxidation. Please see this article. https://pubs.acs.org/doi/full/10.1021/es991063o?casa_token=J-iZ59UKtf8AAAAA%3Aw6Fgf50LfWO4mCfkIRCM1sCXACaTnObYBDhmjyC5zoCjq-VM-PVs42msFcP94eBiZhvHhZAgBePnwxAXmA
Bacteria was mentioned in the Results and Discussion but not in the Introduction. The concept of the degradation of PAHs by naturally occurring bacteria must be mentioned somewhere in the Introduction.
In line number 80, it says that, “In general, the vertical structure of the Japan Sea concludes following water masses forming outside or inside the sea: Surface water, Intermediate water, Central water, Deep water and Bottom water.” Please indicate or express how deep each layer by meters to know how these layers vary from each other.
In line 236, which says that “There was observed the surface enrichment..” Please clarify the sentence since it appears to be confusing. Be concise and make sure it is understandably expressed.
In line 253-254, it says that,” it is shown that its formation and subduction can provide transporting anthropogenic carbon dioxide into the deep water”. Can you cite what are the anthropogenic activities associated with carbon dioxide loading in the sea?
In line 268, the sentence says “ As mentioned, area of St. 29 received the influx of the surface shelf waters which are enriched in nutrients provided by continental runoff.” Please provide information about what kinds of continental runoffs that are possibly loaded in the sea?
Based from line 288-291, it says that Apart from DPAH input due to water mass circulation we suppose the higher mesopelagic DPAH can be additionally caused by bacteria-derived transforming of POM into DOM in the Japan Sea Intermediate Waters, which leads to a significant amount of PAHs being converted into a dissolved form. Please do identify or list the names of bacteria present in the sea or Sea of Japan that putatively helps in transforming POM into DOM.
In page 10, lines 324-326, you stated “The highest content of POC and DOC were expected to be found in the top meter of the water column and then concentrations were sharply decreased to the mesopelagic (Figure 4c,d).” Can you have the figure below this section? This is just a suggestion.
Page 13, lines 416-420, there should be a citation about the PAHs that enters the coastal environment via the atmosphere…
Page 14, line 445, the authors should at least specify on why the PC2 do not contain any useful information.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
A very well written and comprehensive study of the fate and behavior of PAHs along the continental shelf. Extensive comparison and contrast with other studies places the observations of the authors within ranges previously reported by other authors.
Line 139: Grammar correction as follows: "Some field blanks were found to be polluted with Ace"
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
In this manuscript, measurement of the concentrations of dissolved and particulate phase PAHs as well as radium isotopes, DOC, POC, temperature, salinity, and chlorophyll were measured in profiles the Sea of Japan. The measurements were interpreted to advance the understanding of PAH deep water cycling in this water body and compared with that of other water bodies around the world. Except for English issues, in my opinion the manuscript will be of interest to JMSE's readership. The comparison of the two sites provides a good contrast between shelf water related phenomena and mid-Basin processes. For the most part, except as noted below, the tables and figures included in the manuscript are necessary and helpful to enhance understanding of the text. English seems to be alright in some places and not very easy to understand in others. For example, below the following specific comments, I included a corrected abstract. The beginning of the abstract is acceptable, but then the English becomes unclear. Other than that and with revision according to the following comments, I would recommend publication.
Line Number(s) - Comment
1. 26-27 - This equality is not discussed in the text, but should be. Is it supported by the results?
2. 37 – Are part of the latter’s what?
3. 45 - Because you believe that your results depend in part on the biological pump, description of this phenomenon is needed here.
4. 69 – micromolar (mm), not micro-kilo-molar (two instances).
5. 74-75 – Refer to Figure 1 here.
6. 93 – insert the word “, respectively” after “horizons”.
7. Figure 1 - I suggest including an indicator of direction and a distance scale in Figure 1.
8. Table 1 footnote – I am not sure what the two instances of the special symbol mean.
9. 102-103 – From the way the sentence is worded, it is unclear which Niskin bottle was used to sample which compound(s).
10. 115 – This is a side note, but use of benzene is highly discouraged because of its high carcinogenicity.
11. 134 – Shouldn’t “internal” be “surrogate”?
12. 141 – Were sample concentrations routinely corrected for surrogate standard recovery? I suggested stating the convention used explicitly.
13. 159 – Omit “individual”.
14. 161 – I suggest adding a sentence: “The final units of the partition coefficient are L/kg OC.”
15. Figure 5 - The format of this figure is not easily deciphered. Instead plot LogKoc vs. Depth, and separate BaA, Chr, and Bbf into individual profiles.
16. Figure 5 caption - the partition coefficient symbols need to be capitalized. Also, the source of the Kow values needs to be given.
17. 435, 457 - This what?
18. Figure 7 caption - This caption needs to explain to what the numbers and the star ones refer.
19. 451 - Change to Section 3.
20. 459, Table 3 - Pouget Sound should be Puget Sound.
21. The Supplementary Materials document margins and equation formatting seem to be messed up.
22. Figures – Other than Figure 2, which I presume shows measurements that are continuous with depth, the figures should contain the discrete measurements in the profiles, not lines only. There could, in theory, be discontinuities in the profiles that are not reflected in showing lines alone.
23. References – a number of references contain author lists abbreviated with et al. I’m not sure of the rules of JMSE, but typically this abbreviation is avoided.
Abstract: A vertical pattern of fractionated polycyclic aromatic hydrocarbons (PAH) was studied in the Japan Basin in the Sea of Japan. The highest PAH concentration was found in the mesopelagic realm possibly resulting from deep convection and/or subduction of intermediate water and its biogeochemical setting in the western Japan Basin. Using 226Ra and 228Ra as tracers allowed to revealed that the PAH load to the open sea by the coastal polluted water. Dissolved PAHs (DPAH, fraction < 0.5μm) was significantly prevailed higher in concentration than particulate PAHs (PPAH, fraction > 0.5μm) at all depths that and was associated with the predominance of dissolved organic carbon (DOC) over particulate organic carbon (POC). Hydrophobicity was a more important determining factor for higher molecular weight PAHs, likely causing them to be distributed between particles and solution, while the high Koc ovalues of lower molecular weight PAHs (compared to the lowest molecular weight compounds) indicated that their partitioning probably waswas probably driven other factors like adsorbing adsorption to soot particles. PPAH and DPAH profiles differed from the POC and DOC profiles, respectively, but nevertheless, a positive moderate correlation was found for between DPAH and DOC for depths below the epipelagic zone, that which suggests the a similarity of the between the mechanisms of input of dissolved organic matter and DPAH into the deep interior of the Sea of Japan. Calculating of Calculated PAH fluxes flux values showed that the biological pump and overturning circulation contribute almost equally to remove PAHs from the bathypelagic of the Japan Basin.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
The content of PAHs in the environment is an important issue due to the negative impact of these compounds on aquatic and terrestrial ecosystems. The paper seems interesting, however, it contains many methodological errors and some issues require clarification and correction. Moreover, the discussion is chaotic and too general. The title needs to be changed because it suggests that only PAHs determinations were carried out, while the Authors additionally measured the concentration of the radium isotope. In this form, the publication cannot be accepted, because it requires too many corrections and reformulations.
l. 56: please explain the abbreviation PPAH
l.74-87: Please add the information about the potential sources of PAHs in the study area
l.98-100: What a key information should the table contain? Please make the table more readable. What do the '+' signs mean? The caption under the table should be in English.
l.101: The description of water sample link should be included in section 2.2, while section 2.3 should contain a description of PAHs determination and identification.
l. 102: Please explain why the different volumes of water samples were collected?
l. 103: What are radium isotopes used for? Please explain that the aim of the study.
l.107: Why Authors defined dissolved phase of organic matter <0.5 while lots of researchers recognized it as a fraction smaller than 0.45um?
l.19: Why were 15 of the 16 PAHs on the US EPA list determined? The resolution problems?
l. 19-29: For clarity, please add a table with listed PAHs compounds, their concentration values and detection limits. Mark undetected compounds as ‘non detected’ (n.d) or below detection limit (<LOD)
l.131-141: Please add information on method parameters, i.e. recovery, uncertainty, accuracy and other validation parameters. Please specify what CRM samples were used and whether the samples were spiked by surrogate and internal standards.
l.142: Please add in the title the determination of Ra isotopes (not only PAHs)
l. 155-161: The calculation of PPAH and DPAH in my opinion is unreasonable and unjustified. The dependence of PAH sorption by individual DOC and POC fractions is not linear! Please change the approach to the description of the results in the further part of the work or separate individual DOC and POC fractions from water samples by filtration and then determine PAHs in them.
l.197: I suggest change the name of section to ’Results and discussion’
l. 198: What it mean ‘termohaline’?
L.210: How salinity and temperature were measured? I know that these are simple markings but please include them in the materials and methods.
l. 212-223: Very poor discussion. Please extend.
l. 234-229: Chapter to be reworded in accordance with the previous comment (l.155-161).
l. 323-361/424-451: Please explain why the results obtained by the authors differ from other literature data. Please perform a PCA analysis of the impact and correlation of all measured parameters including salinity temperature and RA concentration- data description and discussion will be more interesting.
Author Response
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Author Response File: Author Response.pdf
