Dear Dr Bahlmann,

Many thanks for the revised manuscript and response to referee comments. I am satisfied that you addressed the referee comments appropriately. However, there is some editing yet to be done before the paper is acceptable for publication.

I agree with the referees that the data are worth publishing as data on halocarbon fluxes are rare, even if it is difficult to conclusively compare the two seasons, or scale up from these results. However, given the limitations in the experimental approach, where two campaigns from different seasons are presented, and only limited variation in environmental conditions within campaigns, you have to be careful with direct comparisons between “spring” and “summer”, or with extrapolations for an entire year. I appreciate that you want to get a simple figure to make the point that the fluxes from seagrass beds are not globally significant, and overall the ranges are reasonably conservative.

However, the discussion as a whole is length and there is a lot of speculation about potential sources and sinks, where I think you could be briefer.

The conclusions are also much too long. The purpose of this section is not to repeat all that your have previously discussed. Re-stating a key finding is ok, but you should aim to truly conclude what your study has shown, i.e. what the implications are, and what is needed for future research. This should be in one, max. two short paragraphs.

Overall, there is more to do than just technical corrections, and I am happy to reconsider the manuscript after minor revision. I include below a fairly detailed list of suggestions for phrasing and punctuation, which I would ask you to consider for this revision.

Best regards,
Jens-Arne Subke


Detailed comments:

p. 2, l. 20 – 23: Is it sufficient to cite these papers, rather than refer onwards to “references therein”? I suggest using this only where the paper itself is not sufficient to substantiate your argument.

p. 2, l. 30: comma after “systems”

p. 3, l. 3: comma before “seagrass”

p. 3, l. 11: delete “generally”

p. 3, l. 17: comma after “results”

p. 3, l. 21 – 26: These sentences (starting with “To complement”) are not necessary.

p. 3, l. 30: “an area”

p. 4, l. 5: “a quarter” rather than “one fourth”

p. 4, l. 7: Are pers. Comm. Needed to estimate an area (and given that you already cite a reference)?

p. 4, l. 21: delete “to” after “West”

p. 4, l. 23: Delete “Firstly”

p. 4, l. 25: delete “bottom”

p. 5, l. 5/6: “is described in detail elsewhere”.

p. 5, l. 11: delete “rather”

p. 5, l. 13: Bracket before “Bahlmann”, and not before year.

p. 5, l. 15: insert “of” after “volume”

p. 5, l 17 and p. 6, l. 12: “Supplemental Material”.

p. 6, l. 13: Do you mean “adsorbed”, rather than “enriched”?

p. 6, l. 16: “on site” (or “on-site”)

p. 6, l. 22: This description for CH3I determination is not clear. Unless it is explained in the Supplemental Materials (in which case these should b referenced here), it requires more explanation.

p. 7, l. 6: delete “The principle is as follows.”

p. 7, l. 7: replace “the desired” by “a”.

p. 7, l. 8/9: “The difference of mixing ratios of compounds of inlet and outlet air along with the flushing rate… calculation:” Delete final sentence.

p. 7, l. 13: Should be “pmol mol-1”. Delete “ppt”, as this is sometimes used for “parts per thousand”.

p. 8, l. 9: comma after “lagoon”.

p. 8, l. 21-23: Don’t simply repeat values presented in tables, unless you make a specific point about them.

p. 9, l. 15-19: This is a little confusing, as you have not presented any isotopic data. I suggest including this observation of shifts in isotopic abundance with concentration to later when you present isotopic results (p. 11/12).

p. 10, l. 1: delete “to each other”.

p. 10, l. 1-3: I suggest: “There were no significant correlations between…”

p. 10: l. 3-5: “… solar radiation and halocarbon fluxes were poorly correlated…”

p. 10, l. 6-10: Present statistics to show that these estimates are in fact significantly different from zero!

p. 10, l. 14-17: You don’t present these data, so delete sentences here and reference the source in the discussion when you put results of this study into context.

p. 11, l. 8/9: Sorry, I can’t make sense of this sentence.

p. 11, l. 10: comma after “period”.

p. 12, l. 4: comma after “chamber”.

p. 12, l. 6: better: “… were similar during both campaigns (-51 +/- 2 % and -56 +/- 2 %, respectively), and independent…”

p. 13, l. 7: “the net halocarbon production”

p. 13, l. 11/12: “in, rather than “into”, and “but not” rather than “rather than for”.

p. 13, l. 18: “… interact are complex, and it should be noted…”

p. 14, l. 5: delete “especially”.

p. 14, l. 10: delete “Possibly”.

p. 14, l. 25: I would prefer it if you referred to :the spring campaign”, as your observation don’t actually allow you to make robust statements about seasonality – it should be a comparison of two campaigns, with the seasons they were in as context.

p. 14, l. 26: delete “certain”.

p. 14, l. 30: delete “remarkable”

p. 14, l. 32: “… quite unexpected, as in general…”

p. 15, l. 22: “not” rather than “hardly”.

p. 15, l. 24: “short-term change in…”. However, how can a short-term change response explain a sustained emission – just as for the pressure argument, this would result in a pulsed response. I suggest shortening the paragraph and avoiding excessive speculation.

p. 15, l. 31/32: delete “incoming” (as for the ebb flow it would be “out-going”…). Also delete “actually” and “however”.

p. 15, l. 30 to p. 16, l. 2: I agree that you need more data on radiation at the sediment surface to make this speculation. Do you have sufficient data covering different times of day at high tide to rule our possible correlation between inundation and daytime? Again I suggest keeping speculations quite brief.

p. 16, l. 8/9: “generally”, rather then “general”; delete “even” and “assumedly”.

p. 16 l. 15 to 32: The comparability of sites and conditions you discuss here is very limited – please shorten.

p. 17, l. 3: delete “certain”

p. 17, l. 3/4: Clarify that you refer to 13C when stating isotopic mixing ratios.

p. 17, l. 6/7: “Apart from” rather than “Beside the”, and delete “wide-“ before “abundant”.

p. 17, l. 14: What are incubations you refer to? Chamber closures? This must be clarified.

p. 17, l. 24: “from” rather than “built by”.

p. 18, l. 16/17: “These decomposition mechanisms correlate positively with seawater temperature”. The sentence needs a reference!

p. 19, l. 2/3: delete “certain” and “Actually”.

p. 19, l. 4: comma after CH3I.

p. 19, l. 15: “than” rather than “as”.

p. 19, l. 27: “a” before “per”.

Dear Dr Bahlmann,

Many thanks for the revised manuscript, which I think reads better than the previous version. However, I think that the conclusions are still too long and detailed. As I indicated in the last round, the conclusions are not the place to repeat details of results, but concentrate on key messages and an outlook based on presented findings. In the attachment, I propose an edited version, which I hope you will find appropriate. Please check carefully and include in the manuscript in the way you feel it is appropriate.

There are a couple of minor points (wording), that may as well be included in the corrections (see attachment), but otherwise I think that we will be able to conclude the revisions very quickly now.

The final decision on the companion paper (cited here as Bahlmann et al. 2014) is still pending, and I propose that you cite it as "Biogeoscience Discussion" with the full reference. In case it is accepted by the time of typesetting, this can be changed to the full reference, or, if you agree, we can delay at the typesetting stage until the complete reference is available.

With best regards,
Jens-Arne Subke

Dear Dr Bahlmann,

Many thanks for the revised version of this manuscript, which I am happy to accept for publication in Biogeosciences.

Best regards,
Jens-Arne Subke