please see attached comments

I found this paper to be extremely well written, very nicely presenting the results of the field work tracking rhodamine tracer as a preliminary step to tracking a future OAE experiment via the dispersal of a NaOH solution. I commend the authors on stepping through every aspect of the experimental design, deployment, interpretation, and implications for the future OAE experiment in a highly readable and comprehensive way.

I have only one somewhat major suggestion, which doesn’t require new analysis but might trigger some careful thinking about reframing the motivation and recommendation of the paper.  I think my suggestion is related to Reviewer #1’s question about “What is your MRV framework?” I see the work presented in the paper as foundational research that can inform an MRV framework, but not itself MRV nor a framework.  The term MRV signals a set of processes used in a voluntary or regulated carbon marketplace, whereby carbon removal is monitored and reported to a third party who verifies that it met a given set of predefined standards.   The language in the paper should make this distinction.

Further, I suggest the authors to reflect on how much of this kind of extraordinary research effort (deep domain expertise, research vessel and state-of-the-art laboratory infrastructure, a valuable equipment pool, and the funding to support the team) they would recommended for future MRV.   At a minimum, the target audience for the work should be made explicit (my guess: researchers trying to design a comprehensive field experiment with relevance for tracking surface anomalies influencing air-sea gas exchange).  It would be slightly more ambitious, but commensurately more valuable, for the authors to reflect on a trajectory for mCDR researchers and practitioners that uses the knowledge gained from this research to ultimately create a more parsimonious MRV framework for operational mCDR (or at least provide recommendations on how to bridge that gap).

Minor comments:

The first line of abstract is deeply misleading:  The solution to a 10^10th ton emissions problem is not meaningfully “supplemented” by processes that now collectively sum to 10^4th tons of removal.  Please remove this sentence. 

Line 30: Wording is a little confusing.  I think you mean that “Over 36 hours, the ensuing anomalous carbon dioxide uptake by the ocean was driven by the enhanced air-sea gradient in fCO2.  The calculated CDR signal was detectable as a 3 uatm surface ocean fCO2 increase, a pH decrease of 0.003 units, and…”. If this is an accurate interpretation of what is written, it would be more understandable to the reader to spell it all out.

51: typo: Researc

Figure 1 schematic is very helpful and well done. 

Line 133 and throughout - specify air-sea gradient in fCO2 (or name a variable ΔfCO₂) for clarity

357 - Why not make the gas exchange coefficient wind- or wind- and wave- dependent, as we know it is sensitive to wind speed and wave height.  It would seem hard to justify using a constant, given the variability in Figure 2.  

Figure 2:  Specify that bathymetry is in m.  Zooming closer to the ship track would be helpful, as would adding a circle of the size of the initial dispersal spiral.

Figure 3: If you had a drone photo of the patch taken at a later time than Figure 3a that showed the stretching and spreading of the dye, I think it would be super helpful for the reader. 

Figure 6: consider adding salinity-normalized TA to panel d, and temperature and salinity-normalized fCO2 to panel e.  The variability in T and S will be reflected in the carbon variables in a way that would be helpful to separate.

569 - DIC should also be sensitive to biology, no?

Figure 9 - I suggest using some colors!  There are several solid black lines, so that it’s hard to track which one the caption refers to.

Figure 10 - I’m confused why there seems to be only 1 dot per hour, when the sampling frequency was 10-minute.

606 - yellow minus blue values — add note here (and/or in the caption) that the points are barely visible because of overlap in Figures 10 f and g

628 - 638 “MRV approaches that can accurately capture the entire patch budget … “ This is related to my “major suggestion" above:  This statement makes it sound like MRV would be done in a way that mimics this experiment (with RT or similar tracer and a research vessel tracking it for days). But doing such hugely expensive field campaigns is a research-level activity that is likely beyond the scope of scalable MRV.  In fact, I’d be shocked if 1 ton of CO2 wasn’t emitted by the MRV activities in their totality (4 days on the R/V Connecticut + chaser boat + all the instruments, supplies, and shipping), cancelling most/all of the mCDR here.  Thus, I see this as a research activity, rather than an MRV approach, and I am very interested in the authors’ thoughts on the difference.

Please see the attached document