Modeling Functional Organic Chemistry in Arctic Rivers: An Idealized Siberian System

Round 1

Reviewer 1 Report

The manuscript reports novel and interesting modeling of organic carbon transport in Artic Rivers. It has certain added value for the journal but the presentation requires serious revision and shortening. It is too wordy, and at least 30 % of the text can be removed without loosing the scientific message.

Some important papers in the field are ignored and it means the modeling should be refined ; it can not be based solely on work of Lara et al. Example of recent  important work:

Kutscher et al. 2017. Spatial variation in concentration and sources of organic carbon in the Lena River, Siberia. Journal of Geophysical Research: Biogeosciences 122(8) DOI: 10.1002/2017jg003858

I also recommend to examine the references on DOM in rivers of the in Arctic GRO

https://arcticgreatrivers.org/

The paper presents rather rudimentary analysis of what is done in this field, with very few pertinent references.

Validation of the model is not presented

The terms are not clear in the Abstract (i.e., reduced kinetic modeling)

The wording is sometime snot scientific and not acceptable (example, Russian Lena, less than soluble, L 371, 375, 376, L406, 525, 532, 534

Very often, pertinent references are missing (ex., L 216

L368, is this flow rate comparable with that of the Lena’s main steam and tributaries?

Table 2, references for column 3 are needed

L444: this reference here is not appropriate

L539 the term “cold dark northern waters” seems to be far from reality: The water temperature of Lena can rise to 20°C and above during Arctic summer, when the night is just a few hours long

L501-502: This is totally true; important conclusion which should appear in the Abstract and conclusions

The scale of Figs 3 and 4 is not acceptable, reduced it on the Y axis. The figure does not make sence without presenting actual data on these organics in the Lena River

L709, a reference is needed

L762-763: where the measured indicators?

L931-932. The current predictions are rather about decrease of DOC; see Pokrovsky et al. 2015 Biogeosciences; Chupakov et al., 2020 Chem Geol

Author Response

Please see attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Review for: Modeling Functional Organic Chemistry in Arctic Rivers: An Idealized Siberian System

 Summary:

Overall, this paper is well written and provide insight on evolution of riverine organic chemistry as the molecules in Arctic rivers. The manuscript may be suitable to be published in Atmosphere. However, the paper in its current form cannot be accepted and needs minor revision before publication. Please find the comments below.

The Artic riverine organic matter (e.g., terrestrial dissolved organic matter and primary production in ocean) can be directly emitted from surface seawater into the atmosphere via bubble bursting, possibly affecting Arctic primary organic aerosol production. Therefore, it needs to be discussed the effects of the sea-to-air emission on Arctic primary aerosol production in this paper.

Author Response

Please see attached file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revised manuscript still does not satisfy the criteria of publication in an academic journal.

Fig 2 demonstrates that the model predicts abrupt changes after 1000 km distance but these cannot be evaluated because the actual measurements of the Lena River at < 1000 km are not shown. The peak of actual concentrations is observed at 1300 km and the model fails to reproduce it.

Figs 3 and 4 show modeling output for various organic compounds but for none of them the actual data of the Lena River are shown. There should be some in the literature; otherwise please pick up another larger Arctic river and attempt to develop your model so that it can be calibrated with factual measurements.

Otherwise the whole validity of presented modeling exercise remains in doubt.

In many instances in the text, the phrases are diffiuclt to understand and the necessity of having these phrases is unclear. Please be concise in your narrative.

Just a few examples are listed below:

L 323-324, 325, 371-373, 488-490, 645, 677, 679-680, 683-684, 686-687; 698-700 (comparison with actual data is needed), 710-711, 737, 739, 744, 748, 763-764, 766-770, 869

The organisation of section 9 is unsuitable.

Conclusions (L 851-865) cannot be formulated as questions

Author Response

MDPI Editors and Administrators, re: manuscript 812467 aimed at the Barkley Sive VOC Special Issue of Atmosphere,

Thank you for soliciting a second round of reviews on our paper Jayasinghe et al. “Modeling Functional Organic Chemistry in Arctic Rivers…” The new suggestions from a single referee all seem reasonable and manageable. They have now been fully incorporated or handled, as described below my signature lines here. We are of course hopeful that our work is progressing steadily toward acceptability, specifically for the Sive VOC collection. Please do not hesitate to contact us if we can be of further assistance.

Thank you, Scott Elliott

Los Alamos National Laboratory, [email protected] and 505-988-7190

(Second but corresponding author representing all coauthors)

P.S. a PDF-font issue: I want to make you aware that while Word manuscripts for 812467 are displaying perfectly, I am having trouble with fonts in any attempts to print pdf documents. Please keep an eye on this issue if we move toward publication.

COMMENTS HANDLED IN ORDER FROM THE LATEST REVIEW

(All line numbers refer to the most recent official MPDI version which is atmosphere-812467, while edits appear in atmosphereSE-812467)

Figure 2

The points made regarding Figure 2 are already dealt with directly in the existing text. From the outset, we make it clear that the “Lena” flow simulated by our model is merely a facsimile of the real river, which is in fact only about 2700 kilometers long. The model does not in fact fail to reproduce a 1300 kilometer peak, rather it represents the main channel exclusively. Careful inspection of the foundation reference Lara et al. reveals that the single high measurement pointed out by the referee was taken from an off-stream sample, on a tributary known as the Vilyuy. This point is made at several locations in our manuscript, as for example in lines 471-474 (and we quote):

“Furthermore, the black peak extending upwards along the y axis to over one thousand micromolar was really sampled upstream tens of kilometers relative to a confluence with the large tributary known as the Vilyuy. It should therefore be viewed as a separate incoming source, and does not reflect subsequent mixing.”

These sentences have been present in all versions of our paper. And they demonstrate that the maximum referred to by our referee actually provides strong evidence that the model is working properly. The high concentration ultimately appears in only one tributary-level measurement analysis, while the model clearly performs the requisite smoothing thereafter through its mixing function.

Figure 3

To our knowledge there are no openly published and readily referenced organic functional group data running the length of the main watercourse for the Lena. Total DOC which must necessarily be the primary jumping off point is thus compared with model output in Figure 2. The calibration requested by the reviewer is actually performed at the end point of flow, as documented in Tables 3 and 4. These have the further advantage of underscoring enhancements relative to open water. Arctic rivers differ from one another sufficiently significantly in terms of aquatic chemical composition that we are compelled to disagree that alternate upstream data would necessarily be useful. It is also the case that tributary compositions diverge greatly within any single system. These points are made nicely for example in our crucial review citation Dittmar and Kattner, but also in many other sources. For example, we are now working on total suspended matter simulations based on results from the group Gordeev et al. Furthermore, no regionally resolved dissolved organic functional data have become obvious to us in the (terrestrial) aquatic chemistry literature as we proceed.

Figure 4

With respect to Figure 4, our response could effectively be quite similar to that provided just above, but in fact the relevance of the argument is reduced and so it makes more sense for us to simply explain why. The fourth image is in fact an example of serious disagreement with published data. This is made clear both in the caption and nearby text. The degree of divergence is enormous and meant to be -as a matter of demonstration. The point is precisely that rapid change under our fast (coastal) kinetics must be suboptimal. Detailed validation in this case would constitute an unreasonable investment in time, resources and energy. A quick comparison with Tables 3 or 4 should do the trick here.

Problematic Phrases

The referee has identified several dozen locations in the text where our original wording was nonstandard so that it was hard to understand -323, 325, 371, 488, 645, 677, 679, 683, 686, 698, 710, 737, 739, 744, 748, 763, 766 and 869 with several lines of follow-on in certain cases. In all of these locations, we have either shortened a sentence or else simplified the vocabulary. A parenthetical comment appears here in the review relative to lines 698-700, to the effect that comparison with data is needed. In fact a direct side by side example is quickly provided in Table 4 relative to the previous entries of Table 3. Specific literature references for the analytical chemical determinations appear in the succeeding paragraph -the works of Lobbes et al. and Englebrodt respectively are prominently cited. Averages and standard deviations are quoted as a matter of expediency.

Organization of Section 9

The objection here is to our portrayal of outstanding research questions as conclusions… in retrospect we agree with the reviewer that this is an inappropriate combination of terms. The problem is important but also it is readily handled, by altering wording near the top of the bullet points so that the queries are referred to merely as a list of issues to be raised.

Potential final suggestions from Special Issue Editor

We have been in touch with our individual editor Barkley Sive off line, and he informs us that he may have one final round of requests for us regarding choice of words. These will reflect his personal stylistic preferences, which of course must be respected… We are happy to perform a third pass through the manuscript if this turns out to be necessary. And in general, we wish to sincerely thank both Sive and MDPI administrators for their help overall in moving atmosphere-812467 toward acceptability (now atmosphereSE-812467).

Author Response File: Author Response.docx