Dear authors,

Thank you for providing the revised responses to the reviewers’ comments. I found more details have been added to many responses but some of them are still lacking substance.

1. Both reviewers disagreed with your recommendation that open-ocean waters do not need to be filtered for FDOM measurement (Reviewer#2’s comment on this point is in the annotated manuscript copy)). Reviewer#1 even used your own data to support his/her argument. This is an important comment but your response, “We sincerely appreciate your insightful comments and will carefully incorporate them into the revised manuscript. Regarding the filtration process for FDOM measurements, we will tone down the description to account for the potential influence of contamination”, essentially does not contain any useful information with respect to the reviewers’ comments. Please directly address the reviewers’ concern in sufficient detail.

2. Comment by Reviewer#2: “line 30-33. Note, it rather the CDOM part of DOM that affects the light, please be clear about that, FDOM as such, with fluorescence would have a lesser role in affecting the light.. a prerequisite for FDOM is that CDOM absorb light first ...”. Your response, “This part has been revised to be more closely related to FDOM”, again does not provide the information on what specific revision was made to address the reviewer’s comment.

3. Comment by Reivewer#1: The authors report some statistical results in the text, but they do not specify which tests were used”. Your response is “In the revised version, we have added a brief explanation in this section where the p-value is first introduced (line 118), clarifying that p values higher than 0.05 are considered not statistically significant.” Please clearly state what statistical test(s) were conducted. Note that this issue had been raised by me twice during the initial review but was not been appropriately addressed.

4. In addition to the separate comments posted in the reviewer’s report, Reveiwer#2 also thoroughly annotated the manuscript on both the scientific and technical aspects. I requested earlier that you address the comments in the annotated copy as well but it seems that you chose to ignore them. Here, I request again that you provide point-by-point responses to the comments in the annotated manuscript (you can copy and paste the reviewer’s comments to facilitate your response).

I look forward to receiving your revised responses before May 20, 2025.

Kind regards,

Huixiang Xie

Dear authors,

Based on the comments appended below, your manuscript requires minor revisions before it can be accepted for publication. Please provide a point-by-point response, and either change the manuscript appropriately or provide convincing reasons for declining to do so.

Kind regards,

Huixiang Xie

Associate editor’s comment
L44-45. Spencer et al. (2007) did not use formalin in their study. Wurl et al. (2009) did use formalin as a sample preservative but they did not measure FDOM. Instead, they measured CDOM absorption coefficients but did not report if formalin had any artifacts on their measurements. Please fully digest the references before considering citing them.

Referee#2’s comments
This revision is much improved.

I only have some minor edits to be suggested to be done, before the paper can be accepted.

Line numbers refer to the traach change version.

Line 21 I would perhaps explicititly state also that ", room temperature storage is not recommended."

Line 34 . There are earlier papers that use FDOM to traer water masses, and I would suggest the authors explore that, to do justice of earlier work. To my knowledge at least this paper did it in the Arctic: https://www.nature.com/articles/srep33978 (could be added here).

Line 37-48. This now reads like only GFF filters are used. However, different types of menbrane filters are also widely used. I think the authors should acknowledge this, since they also use a membrane filter in their study.

Table 1 - just a suggestion, easier to compare the different filtrations if you always have the different peaks side by side, e.g. first have C peak unfilters, C peak 0.7 filt., C peak 0.2 filt., etc. So sort columns by peak, not by unfiltered/filtration.

Line 142-145 Perhaps note that samples were stored in the dark too in every case?

Line 159-160, with the addition of text, the sentence does not read properly, please chech and rephrase.

Line 164 and 169 - the volumes given are for a certain size of filter that is used here, so you need to give tthis volume rather by volume per filter area to indicate a more universal measure of the volume required.

Wurl et al. (2009) in the reference list is shown in the track-change mode. Clean it up.

Line 66: It’s rare to call a 20-L container as a bottle. Change “bottles” to “carboys” or simply “containers”.

Throughout the manuscript (including figures, tables): the units of fluorescence peaks (R.U.) are not concentration units. Avoid using “concentration or concentrations” to describe the magnitude of fluorescence peaks. Instead, use “fluorescence intensity (signal)” or “fluorescence intensities (signals)”.