Editor review of bg-2014-312 Seasonal variations in concentration and lability of dissolved organic carbon in Tokyo Bay by Kubo, Yamamoto-Kawai, and Kanda
Dear Dr. Kobo,

Thanks for submitting the revised version of ms bg-2014-312. I note that you satisfactorily answered questions and comment from both reviewers. However there are three issues that needs you attention in addition to formal comments.
Major issues:

1. There are a few studies that have determined rate constants or resident times of bioactive/reactive DOC. How do your rates compare? This is very important because there are always issues with long incubation times, bottle effect, selection of specific microbial communities with time, etc.

2. Since most of the ocean is oxygenated, and most likely your bottles went anoxic, way before 25 days, Could you say that RDOC concentrations, or rate constants are valid only for DOC undergoing suboxic and anoxic microbial reactions as opposed to the most frequent aerobic degradation?

3. Error propagation. In your regression analyses, if the coefficient of determination R2 is 0.71 it means that 71% is explained and 29% is error. Will propagation of this error would impact your estimate of % RDOC and therefore your conclusion that “Tokyo Bay exported mostly RDOC to the open ocean”. In other words, Would you be able to distinguish terrestrial and ocean origins when you include error bars?


Minor issues:

4. Line 38 The word “Conversely” does not fit here. Better use something like “In coastal waters, DOC consists of …”
5. Map of Tokyo Bay needs to be improved. Land is not shown here (remember that not everyone is familiar with the area). Show the open ocean and the entire bay as well as rivers and the populated area.
6. It is not clear in the Method section if experiments were carried out on board or in the lab, and how many hours passed after sampling.
7. Lines 78-80. “We assumed that GF/F filters allow the passage of a significant fraction of free-living bacteria into DOC samples (e.g. Bauer and Bianchi, 2011); therefore, we did not add the microbial community.” How good is this assumption considering you are selecting the smaller fraction of the microbial population? Would it affect your results?
8. L 84. Blank for “samples were dispensed into glass vials that had been pre-washed with HCl.”; Were they combusted? Show blank measurements for ambient and experiment analyses.
9. L 86. Add the word “sample” between “the” and “volume”
10. L. 91-96. This paragraph includes results so it should be summarized and moved to the Results + Discussion section
11. L. 96-101. Result as well
12. L 152-154 could be combined in one sentence for easy reading.
13. L 161, 180. Replace good with significant
14. L 160-163. Do you think winter would have DOC concentration in that range as well?
15. L204-210. Check figures. There is no DOC data in Figure 3 but in Figure 5, and Figure 4 is about incubations, etc.
16. L 213-215. Replace
“The results of DOC degradation experiments at Tokyo Bay are shown in Figure 4. Rapid degradation of the labile pool occurred within the first 20 days of incubation, indicating that BDOC were remineralized during the residence time of the bay water.”
With:
“Rapid degradation of the labile pool occurred within the first 20 days of incubation, indicating that BDOC were remineralized during the residence time of the bay water (Figure 4).”
17. L 200, 238, 390. Add units to rate constants (d-1)
18. L 265. Replace “chl a” with “chlorophyll a”
19. L 394-395 “and the quality of DOC has become more recalcitrant owing to an increase in STP effluent.”. It is not clear in the text how this conclusion was drawn. Please explain.
20. L 405-406. Even though I know what you mean “the lability of DOC has become more recalcitrant.” DOC becomes recalcitrant, not its lability. Please re-write. Check line 420 as well.
21. L 422. Either “decreased, especially the BDOC fraction.” or “decreased, especially BDOC.” would be better

Looking forward to hearing from you about this matter
Sincerely your

Dr. Silvio Pantoja
Associate Editor