Dear Author,

Thank you for replying to the referees' comments. I invited you to revise the manuscript accordingly. Note that the revised version will be sent to referee #2 who recommended a major revision and requested to review the revised manuscript.

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Thank you for considering BG to publish these results.

Sincerely,
Jean-Pierre Gattuso
BG Editor

Dear Author,

Referee#2 has further comments.

- Pg. 10 Line 32- Pg 11 Line 4. The assumption of a constant N fixation rate of 4.4 nmol/l/d from Day 23 requires more justification and analysis. "continued elevated A. flos-aquae biomass" does not reflect the data in Fig 5a , as there are only episodic increases in biomass apparent after D23 that exceed D21. A more robust approach to estimate N fixation after D21 would be to relate the biomass on each day, or use the post D21 average, to the biomass on D21. Whereas this has assumptions re the relationship between biomass & N fixation this would seem more robust than applying the highest N fixation rate uniformly.

- Note that the delta 15N signal in the suspended & sinking matter increases after D17 (currently this increase is not mentioned) and then levels off, suggesting that if N fixation is responsible for this trend, then the N fixation rate decreases after D17.

- In addition, the assumption of "50% exudation of fixed N as DON or NH4" requires justification and/or citations.

Please address these comments and prepare a point-by-point reply, highlighting the changes made on the manuscript.

Sincerely,
Jean-Pierre Gattuso
BG Editor

Dear Author,

Thank you for submitting a revised version of your manuscript submitted to Biogeosciences, which I am glad to accept for publication.

I look forward to seeing this paper published and thank you for considering Biogeosciences to publish these very interesting results.

Best regards,
Jean-Pierre Gattuso
BG Editor