Dear Dr Piwoni-Piorewicz and co-authors,

I have read the reviews and your responses. I would like to invite you to submit a new version of your manuscript. Considering the weight of the comments provided by both reviewers, I will ask them to asses the new version of your manuscript.

Sincerely,

Lennart de Nooijer

Dear Ms Piwoni-Piorewicz and co-authors,

I have read your replies to the reviewers' concerns and I will contact them again to see whether you have answered them sufficiently. I fully see the points of the reviewers and would like to know whether you have taken away their concerns fully...

Sincerely,

Lennart de Nooijer

Dear Dr Piwoni-Piorewicz and co-authors,

thank you for your revised version. The reviewers are overall positive with your improvements, however, reviewer #1 provided some additional comments that I would like you to have a look at. I will then myself carefully check your new version before acceptance.

Sincerely,

Lennart de Nooijer

Editor comments bg-2019-367 after revisions

Dear Piwoni-Piorewicz and co-authors,

I have carefully read your (revised) manuscript and although it has improved, I have a few more comments that need to be addressed before your paper can be accepted for publication in Biogeosciences.

Abstract.
Please remove the first two sentences of the second paragraph (this is already apparent from the numerous papers published on biogenic carbonates) and combine the two paragraphs into one.
Introduction.
line 34. Now it sounds as if these organisms actively seek for e.g. Sr and Mg to produce their shells. It may well be that these ions are incorporated ‘by accident’ and that only Ca and DIC are actively collected. Please rephrase.
line 39. That they can be found in the same specimen is only true for some taxa.
line 41-42. This is incorrect. The ‘bulk elemental composition’ (a rather vague term, btw) is determined by the biomineralization mechanism of the organism. The presence of organic compounds may also influence the (trace) element composition, but I am not sure what ‘crystal lattice’ does here. The crystal structure is set by the polymorph precipitated, I guess. And it also determines how much of which element can be incorporated (i.e. aragonite has a much lower maximum Mg content than calcite). I think this whole sentence can be omitted. Otherwise please rephrase.
line 63-65. Since the introduction is rather long, I suggest to delete the first two sentences of this paragraph.
line 84-85. Please delete this sentence.
line 96: “...pathway to the skeleton or shell....”, please delete “of the body”
line 99. Doesn’t have to be completely independent: the environment (e.g. temperature) can affect the transport of e.g. Mg towards the fluid from which the CaCO3 is precipitated.
line 113-119. This whole paragraph is a bit repetitious. Consider removing it altogether.
Methods.
line 136-137. “The north-western part of the gulf is separated by...” “... and in the west and south...”
line 151-153. Remove here: the same is already stated in the first paragraph.
Results.
lines 274 and further. Please turn “316,000 +/- 26,000 µg/g” into “316 +/- 26 mg/g”. Also for other high (> 1 mg) concentrations.
line 296. “...variability in four trace...”
Discussion.
line 325. “The average Ca concentration...”
Discussion.
line 380-396. It may also be that ions are present in microscopic fluid inclusions. This will need to be mentioned here, as well as the effect it may have on the assumed lattice-bound element concentrations.
line 412. “lead”

Looking forward to see the final version of your manuscript.

Lennart de Nooijer

Dear authors,

apologies for the delay. I am looking forward to see your manuscript published in BG!

Sincerely,

Lennart