It has been a matter of great pleasure for me that I reviewed the manuscript entitled “The contributions of various calcifying plankton to the South Atlantic calcium carbonate stock” by Anne L. Kruijt and others for possible publication in Biogeosciences (egusphere-2025-4234).

< General comments >

Kruijt et al. evaluated the production and export of calcifying plankton groups (coccolithophores, foraminifera and planktonic gastropods), then estimated their relative contribution to particulate inorganic carbon (PIC) stocks and export based upon the field studies in the South Atlantic. The paper has substantial information that should be shared with the geochemical research community. Quantifying the standing stocks and fluxes of calcifying marine organisms is essential information for establishing ocean carbon cycle models. The author’s paper is well written, and results are clearly presented. In my opinion, if the below minor points are adequately addressed and improved, this manuscript can make a fine contribution to Biogeosciences.

< Specific comments >

In the paper, authors focused on the “production” and “export” of calcifying plankton within the ocean reservoir. In the global carbon cycle, authors know, carbon fluxes between different reservoirs (sediments, oceans, atmosphere, rocks, etc.) are also critically important. I have a little concern that the role of foraminifera in the global carbon cycle might be undervalued. Therefore, would you also mention the importance of the carbon flux of foraminifera/coccolithophores (~0.2 Gt C per year) from the ocean reservoir to the sediment reservoir?

L189: Please refer “Appendix A” here before citing Appendix B (L190).

L278: Please change “Supporting Information S2.7” to an appropriate quote or delete it.

L334: “Eq. 8” is OK? Maybe “Eq. 7”?

L334-335: “Eq. 7” is OK? “Eq. 5”?

Figure 4: If possible, for the reader's easier understanding, please add the water depths for net1-5 in the graph or caption. For example, add 150 at the boundary between 4 and 5 on the Y-axis, 200 at the boundary between 3 and 4, and 300 at the boundary between 2 and 3, etc.

L484, 488: “Eq. 9” is OK? “Eq. 7”?

L577: “fig. 4b” is “Figure 6b”?

L580-581: I think this part (“or dissolution due to microbial respiration induced undersaturation within sinking aggregates”) seems a bit abrupt. If possible, please provide a more detailed description or additional references.

L668: “a 75 μm mesh” is OK? If so, please add the reason for using “a 75 μm mesh”.

< Technical corrections >

L262: Please change from “…interval Export…” to “…interval. Export…”.

L380: Please change from “(Lauvset, et al., 2024)” to “(Lauvset et al., 2024)”.

L404: Please change from “H. Inflatus” to “H. inflatus”.

L425: Please change from “being being” to “being”.

L426: Please change the fonts for “Emiliania huxleyi” and “Gephyrocapsa huxleyi.” to italic.

L430: Please change from “( Appendix Figure G1)” to “(Appendix Figure G1)”.

L757, 759: Please change from “L. Beaufort” to “Beaufort”.

L791: Please change from “𝑔𝑟𝑜𝑢𝑝,,𝑠𝑡𝑎𝑡𝑖𝑜𝑛,1000𝑚” to “g𝑟𝑜𝑢𝑝,𝑠𝑡𝑎𝑡𝑖𝑜𝑛,1000𝑚”.

If the above minor points are adequately addressed and improved, I think this manuscript can make a fine contribution to Biogeosciences. I hope my comments are helpful in improving their paper.