Dear Dr. Seelmann and co-authors,

Thank you for the resubmission of your manuscript. I am generally satisfied with your response to the referees. Below my own comments are listed after reading the manuscript. Please account for these minor comments and corrections before submitting the final version of your manuscript.

P1, L3 „The work described here focuses on impacts of …” Work cannot focus on something, but you yourself can. Please correct the sentence.

P1, L6 did (instead of does). Appears to fit better in such a sentence. If you need to use “does”, the sentence ending must be changed.

P1, L6 I do not see the use of the word “subsequent” here.
P1, L11 “However, it could not be fully overcome.” What could not be overcome? Please clarify in the text.

P1, L19-20 the purest BCG that is purchasable.
P1, L22-23 “not only the biogeochemical processes but also the uptake, transport and accumulation of anthropogenic CO2 in the ocean” I think these three processes could all be taken as biogeochemical processes. Please modify text.

P1, L23 parameters or variables?
L25 I think “corresponding” is not appropriate here.

L27 pH measurements have been common all the time. I think “prominent” fits better here.

L28 I think you mean “decades” instead of “centuries”. Ocean carbon observations are not that old.

L38 “have revealed”, not reveals
L64 please define LC here

L119 Would it be possible to use a different word than “calibrated”, since you do not mean calibrated here, do you? Or possibly rewrite the sentence completely.

L128 accounted for instead of considered?
L159 delete: There,

L160 delete: However, (there is no contradiction here)
L173 delete: respectively

L194-195 This sentence is hard to read. I suggest to change it to: All AT measurements took into account the relative uncertainty of the analyzer, determined as 0.08 % (Seelmann et al., 2019).

L201 Many sentences here begin with “However”. Maybe change this one?
L203-204 Maybe the authors can indicate what they consider to be acceptable for a drifting and changing value of AT. This would give some guidance to readers/users of the system.

L209 change to: on a monthly basis
L227 The phrase “For better presentation” reads odd. It is not just a matter of presentation that you are performing this. Please rephrase.

L228 delete: At the time of this study, (this is superfluous)
L242 “In contrast, "low-purity" indicators behaved totally different.” “in contrast” and “totally different” say exactly the same. Please rephrase.

L257 Could the authors come up with a different word than “calibration”? I think the reader might get confused by bringing it this way. If it is a real calibration, then the use of quotation marks is not necessary.

Table 4 Both the precision and accuracy are given. In some cases the accuracy is better than the precision. I think this is not according to statistical principles. In the requirements for open-cell titrators according to Dickson et al 2007, one can see how it should work: the accuracy has a clearly higher absolute value (often double as large) than the precision. The reason is that for determining the accuracy, one needs to take into account the precision of the measurement of the reference material (or standard) used to determine the accuracy, and of the measurement itself. Please explain and correct your results.

L272 appropriately, not probably
L294 delete However, (not necessary here, and not at the start of a paragraph)
L320 delete: In this study, (superfluous)

As to the Conclusions section, this is much like a summary. Although this cannot be avoided to some extent, the entire structure of this section in the present manuscript is built around this summary. See for example the last sentence of the section in L341 “Furthermore, no characterization of the purified BCG was carried out.” This may well be deleted. Please restructure the Conclusions section and incorporate more real conclusions, which the manuscript definitely has to offer.

L367 CO2 with subscript

Thank you and best wishes
Mario Hoppema