The manuscript presents information pertaining to the amount and quality of OM supplied to the Arctic Ocean and focuses on the fate of terrestrially-derived OM from coastal erosion, river runoff and potential permafrost contributions. The authors provide a summary and data from four field expeditions in the Mackenzie River Delta collected over 2019. 

I find little to criticise with this paper. It is well structured and easy to follow with well-annotated figures. The table summary at the end is clear, however the Pangaea-download appears to be locked and under moratorium until November. As such, it is unclear how to test access to the datasets shown here. The table summary and information at the end of the manuscript are clear and helpful. I appreciate the available code to reproduce the figures. Congratulations to the authors for their work, especially given the breadth of the data provided here.

My main question is surrounding authorships. Provided close partnerships with community members noted throughout the manuscript and acknowledgements, wouldn't far more inclusion of community members involved in the work not be suitable? Were none of the community members essential in the work conducted?

 

Other queries/ suggestions below: 

Throughout, little information is provided on the error and uncertainties associated with the instruments and methodologies used. Can this be more clearly highlighted in the text, or state that it is in the associated data files (assuming it is?)

109: I am not sure if privileged s the correct word in this sentence. 

140: So to be clear, these were used to profile the water column at each site and not left in-situ at all? Can you just make this more clear earlier as I wasn't sure on first quick read until later on. 

Figure legends and text could be made clearer and larger in many of the figures. Maybe I'm old. 

221-223 "Concentrations of TPC and TPN on filter subsamples required extrapolation assuming uniformity of particulate matter on the filter". Do you have any estimates for the actual variability in TPC/ TPN across the filter, i.e. multiple subsection punches from the same filter? 

245 Leg 1 certainly shows more scatter at the lower end of the POC, TPC and ap(443). Is this within the instrumental measurement error range? Do we have higher uncertainty in the TPC measurements? Whilst I agree that Leg 1 generally fits within the linear regression shown, a little note of whether this pattern is likely down to instrumental uncertainty, or may suggest something else would be helpful. 

Figure 8. Can you please add a description of the units in the figure legend?  

Nutrients - uncertainty in concentrations using these colourimetric methods? The lowest limit of detection?

Fig 10. data points excluded were from Leg 2 of Fig 10b correct? Please clarify in legend. 

390 To clarify, these supplemental datasets (e.g. radon, gases) are also available in Juhls et al. 2021?

Table 2 - method "spectrofluorometry' is spelt incorrectly. 

General Comments:

The manuscript by Lizotte et al. describes a large and unique data set of physical, biological, and biogeochemical properties/variables acquired in the Mackenzie River Delta region in 2019. The data set is directly relevant to our understanding of the origin and fate of terrestrial organic matter during four sequential legs that covered the pre-freshet, freshet, and post-freshet period of 2019. The data itself have already been published (Juhls et al, 2021) and this manuscript provides a description portion of this data set.

This is a very valuable data set that represents a major effort by multiple investigators working in a remote area. The collection of such a complete data set across different seasons covering the pre-freshet to late summer is unprecedented (as far as I know) and this is excellent that the data is made available to the greater community. Overall, the manuscript does a good job at describing the field campaigns, the sampling, and the data available. The figures are of high quality and generally clear and self-explanatory.

The manuscript is generally well written, although writing style can be improved in some parts where sentences are bit wordy, long and convoluted. I suggest spending a little more time on editing and making sure that shorter, more direct sentences are used. This is especially true at the beginning of the manuscript (examples: sentences on Lines 36-41, and Lines 30-32).

There is also a need for a better balance of details and description between the different sections as this aspect can be uneven in some parts.  The manuscript needs to be more balanced throughout in term of the level of details and referencing used to describe the methods and data. Some parts being very detailed (perhaps too detailed) and other being too succinct and without references. The authors should make sure all sections have methods cited and an appropriate level of details. I point out a few places where this is a problem in the “specific comments”.

It is very evident that different sections were written by different contributors (as expected), but the style could be harmonized a little bit more across the manuscript.

Specific comments:

Line 2: I would recommend changing to “in the Mackenzie River Watershed” as permafrost is present in much of the Mackenzie watershed and C released for other parts of the watershed permafrost could also influence the Delta OC dynamics

Figure 1: I would suggest adding the date ranges for each leg in the captions for rapid comparison to the location of points.

Figure 3: River discharge from the Mackenzie River in 2019 was lower than average I think,…I would recommend adding a statement mentioning it in order to indicate how the 2019 discharge compared to the climatological average (e.g., 2000-2022)…Maybe a plot of the river discharge climatology could be added to Figure 3a.

Figure 4: Mention in caption that there was unconsolidated ice during Leg 2.

Figure 5: Is this showing surface salinity? If not, what was the depth? Please mention in caption. (Because it says profiles in line 139)

Section 4.1.2: Two methods were used (Ultrapath and dual-beam spectrophotometer). First, what was the threshold used to switch from one method to the other? Second, how many samples were measured using the Ultrapath and how many with the dual-beam spectrophotometer. Please add this information in the text.

Also, a pathlength of 200-cm is likely to be too long for UV measurements made at 254 nm in these coastal waters and nearshore waters (and perhaps for some made at 350 nm).

Has there been any assessment about the quality of the CDOM absorption in the 200-300 nm range for the data measured with the Ultrapath? If there is any doubt the data are questionable below 300 nm, then it should be mentioned in the text.

Section 4.1.4:  Some clarification is needed for how SUVA350 was calculated. Was absorbance (unitless) used here or was it absorption coefficient (units of m-1)? The units of SUVA350 suggest it is absorption coefficient. This needs to be clarified. Please specify the pathlength of the optical measurement and adjust units if absorbance was actually used.

Sections 4.1.5 and 4.1.6:  Please add references for the methods used for TCP/TCN and POC/PON. Also, provide more details regarding what standard was used for the elemental analysis, and what procedure was used to account for the blank.

Section 4.1.8 and Figure 8: Some of the blue reflectances from Leg 4 (where Rrs(412) are higher than Rrs(443)) are a little suspect and seem unlikely in this type of coastal waters. Consider acknowledging this issue in the text so the users are aware. 

Section 4.1.9: The title is misleading and this section is quite incomplete. It needs to be completed. The data here are actually backscattering coefficients and particle size distributions, though this is never mentioned in the text. The term Inherent Optical Properties used in the title is a broader term that includes other variables presented earlier in the manuscript (like absorption coefficient). Please adjust title and describe what variables were produced here. Also, there needs to be referencing to the methodology used to process the Hydroscat, BB3, and LISST data, and some brief description of the methods.

Section 4.4.1: I think photo of the setup (tripod + corer), if available, would be welcome here and would help illustrate the approach. More citations for the methodology also need to be provided in the text.

Section 4.4.2.2: Please explain briefly how the EEM data were processed (and add reference).

Line 495: I recommend changing “Fluorescence spectroscopy was successfully used to determine the origin of the DOM pool. Fluorescence…” by “Fluorescence spectroscopy can be indicative of the origin of the DOM pool. In this dataset, fluorescence…”…considering no analysis or comparison to other indicators were provided

Technical Corrections:

Abstract Lines 4-6 and again Lines 30-32: Lots of commas and convoluted sentence. I recommend rewriting for clarity.

Line 24: change land-mass to landmass

Line 33: Unclear what “circulating” means here.

Line 39 change “modifications in the productivity of the primary producers” by “change in primary production”

Line 90: remove “were sampled within this period”, it’s evident

Lines 92-93: remove “sampled”

Line 504: Change to “Water Samples”

Line 521: Change “Processes” to “properties” considering Processes are not “acquired”.

Figure 13: the map with white and gray areas is a little bit unclear. Use blue for water body to make it more obvious