The authors took tremendous efforts to collect published and unpublished DOC, DON and DOP concentration measurements from global coastal regions and provided a useful dataset to the marine biogeochemistry and DOM community. The dataset is well-organized, and the manuscript introduced this open-access dataset well. It may require some revisions that could help improve the paper.

Suggestions:

Title: I suggest specifying what “dissolved organic matter (DOM) measurements” refer to in the title to make it clearer. I believe they are “Dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) concentration measurements”.

Lines 262-268: Hansell et al,. 2021 DOM data compilation only contains the TDN and DOC concentration measurements. It may be helpful if adding some discussions here about existing open ocean DOP concentration dataset such as an old DOP concentration database called “GOOD DOP” in a book chapter (Karl & Björkman, 2015) and a recently compiled open-access open ocean DOP concentration database (DOPv2021) (Liang et al., 2022).

Reference:

Karl, D. M. & Björkman, K. M. Chapter 5 - Dynamics of dissolved organic phosphorus. in Biogeochemistry of Marine Dissolved Organic Matter 2nd edn (eds. Hansell, D. A. & Carlson, C. A.) 233–334, https://doi.org/10.1016/B978-0-12-405940-5.00005-4 (Academic Press, 2015).

Liang, Z., McCabe, K., Fawcett, S.E. et al. A global ocean dissolved organic phosphorus concentration database (DOPv2021). Sci Data 9, 772 (2022). https://doi.org/10.1038/s41597-022-01873-7

Lines 290-293: Some articles might use key words such as “Total organic carbon”, “Total dissolved nitrogen”, “Total dissolved phosphorus”, “Total organic nitrogen”, and “Total organic phosphorus”. I am not sure if only using the terms “dissolved organic carbon”, “dissolved organic nitrogen”, and “dissolved organic phosphorus” would miss some published data.

Lines 308-310: After oxidation of DON samples, the resulting total nitrate can also be measured by the nitric oxide chemiluminescence method (Knapp et al., 2005;) not just colorimetric method.

Reference:

Knapp, A. N., Sigman, D. M., & Lipschultz, F. (2005). N isotopic composition of dissolved organic nitrogen and nitrate at the Bermuda Atlantic Time‐series Study site. Global Biogeochemical Cycles, 19(1).

Lines 301-308: I believe it needs references here for the approaches for TOC and TDN concentration measurements. Below are some resources.

For TOC: Sharp, J. H., Benner, R., Bennett, L., Carlson, C. A., Dow, R., & Fitzwater, S. E. (1993). Re‐evaluation of high temperature combustion and chemical oxidation measurements of dissolved organic carbon in seawater. Limnology and Oceanography, 38(8), 1774-1782.

For TDN: in the Chapter 4 of the book “Biogeochemistry of marine dissolved

organic matter”, it summarizes different oxidation approaches for DON and includes their references.

Lines 314-317: For TDP analysis, besides UV and wet chemical oxidation, there is another oxidation approach “ash/hydrolysis”. Details of the “ash/hydrolysis” approach can be found in Solórzano & Sharp 1980. However, perhaps no DOP data in this database employed the "ash/hydrolysis" approach?

Reference:

Solórzano, Lucia, and Jonathan H. Sharp. "Determination of total dissolved phosphorus and particulate phosphorus in natural waters." Limnology and Oceanography 25.4 (1980): 754-758.

Line 407: what is the detection limit here for DOC. DON and DOP concentration measurements?

Lines 496-509: How many data points have all DOC, DON and DOP concentration measurements? The article says that observations of DON and DOP concentrations are much less than DOC concentrations. I would add a recommendation here to acknowledge this feature and encourage more paired measurements of DOC, DON and DOP concentrations.

Figures: Why not add a figure to show number of observations for dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) concentrations in different months? I would also distinguish samples from the northern hemisphere and southern hemisphere.  This figure will help readers check the potential bias due to sampling seasons.

Minor comments:

Lines 205-206: I would add the word “concentrations” to clarify these measurements are DOC, DON and DOP concentrations. Similar for other texts in the article. For example, use “DON concentration observations” instead of “DON observations”.

Line 241: I would use “organic material” here.

Lines 246-248: I find this sentence a bit difficult to follow. Why POM less degraded but more bioavailable?

Figure 1c: x- axis unit should be µmol P L^-1

DOM represents a huge reservoir for biogenic elements and should be playing an important role in marine biogeochemical cycles. Given that most coastal waters are among the most dynamic and productive areas in the global ocean, a better understanding of DOM cycle in such environment is essential.However, there is clearly a huge gap between DOM data availability and its biogeochemical importance in coastal waters globally. To address the concern the authors here firstly present the most comprehensive database of DOM concentration in the global coastal waters to date, covering a wide range spatially and temporally as well. The aims of this work are clear and will be of interest to the wide readership of ESSD. It will also likely be a highly cited work considering the urgent call for such a comprehensive compilation of published+unpublished DOM concentration data. In general, the authors did a good job on data compilation. The manuscript is well written  and well organized and will be a contribution to the aquatic science community.

Major comments

Title. The measurement of DOM can be multifaceted, i.e., concentration, chemical composition, bioavailability, age, isotopic ratios, etc. It’s all about the most important parameter, i.e., concentration, in this effort of compilation. 

L279-281. I full agree with the authors that ‘long-term consistency of the measurements, to enable data intercomparison, and establish a robust baseline for assessing,’ is a fundamental issue. The authors have addressed the issue of comparability for data covering a wide range from multiple sources. The authors can provide more information (or give examples in SI) on this in the ms given its importance.

QC assessment part also deserves to be addressed in more detail. I would recommend a flow chart (step/criteria/priority) of data processing and quality control to be presented.

Are there any reliable time-series DOM concentration data included in this compilation that possibly provides a case to present or evaluate temporal variability/human perturbations, which is not generally lacking in its present form?

 I would recommend to try an addition of stoichiometry (ratios C/N/P) part. It may unveil the tight link for the elements and provide implications for understanding biogeochemical cycle in the highly dynamic and rapidly changing coastal waters.

Minor comments

L407-408: ‘In cases where concentrations were below the detection limit, the zero values were replaced with half the value of the limit-of-detection.’ I am not sure if this is the best practice. What about leaving it blank?

Typo: The unit on x axis should read ‘umol P L-1) in Fig.1c.

The color is too light for DON line in Fig.2a.

Fig 3 is not clear enough, especially for histograms.