Dear Luca Possenti and co-authors,

Thank you for the revised manuscript and response to the referee. The referee and I are generally satisfied with your response and revised manuscript. There are still some issues, which the referee listed in their review, and my, mostly minor, comments appear below.

There is a bit of a more important comment, which was mentioned by the referee and which I encourage you to give attention. This is in regard of the very high PQ value (O2:CO2 ratio) of the NCP. This is much higher than the usual ratio which is close to 1. It is very important to discuss this in much detail and where you show that this is realistic. The short discussion in the revised manuscript is not sufficient for this purpose. Possibly a better explanation for this high ratio is some error in the calculations or assumptions for calculating NCP. I encourage you to check all calculations carefully.

I suggest you use the more common abbreviations which makes reading much easier: NCP Net Community Production; GPP Gross Primary Production; CR Community Respiration

Some data sets, taken or downloaded from other institutes, are mentioned in the manuscript. Please acknowledge its use and check if there is a specific request of the data originators in a fair data use statement for acknowledging.

L15-16 … in the Norwegian Sea from March to October 2014.
L21 … in situ CT measurements. Instead of direct?

L46 “to observe CO2 variability” Not only the variability is important, but generally CO2, its trends and variability.

L67 c(O2) has not been explained before. Please do that here as this is not the usual notation for a concentration.

L85 The sentence is not logical. I suggest something like: … varies during the year and 5 different periods can be discerned.

L102-106 The info given here is exactly the info which appears in Table 1. It should be deleted or strongly shortened.

L115, 117 Caption of Figure 1: What is shown are not the water masses, but the currents. Please change to make consistent.

L116 Define OWSM
L123-124 Mentioned are 4 cruises, but there are 5 dates for those. Please correct the inconsistency.

L144 It is contended here that the uncertainty in the nutrient concentration is negligible to the calculated c(CO2). However, it is not mentioned what the uncertainty in c(CO2) is, which is vital info here.

Section 2.2. Give precision and accuracy of all measurements. Were CRMs used during the CT and AT analyses? How long have the samples been stored before analysis after the cruises?

L148 do you mean: … which is even worse for the …
L149 I think it is more correct to state: It has been suggested that it is necessary to calibrate

L178 16 March (format)
L224 “… was rLOWESS-smoothed to remove … “ Is this correct? It is hard to understand when a reader is not familiar with this. Please rewrite so that the function or routine becomes clearer.

L250 Figure 6 What is not included in this plot are the uncertainties in the calculated Cws(CO2). I think these are not negligible.

L330-333 This sentence is too long and therefore not well understandable. Please rephrase.

L410 “The uncorrected c(O2) continually decreased (Figure 8c).” This is not clear. Decreased from what to what?

L484-486 (Caption Fig 12) I suggest: Air-sea flux of oxygen and CO2 during spring and summer, a) csat(O2) in blue and c(O2) in red, b) csat(CO2) in blue and c(CO2) in red, …

L496 … decreased the variability to 68±75 m.
L498-499 “This method was used in order to have similar time interval between repeat occupations of the same transect position to calculate the inventory changes and entrainment.” This is duplicated info from the methods section and not needed here.

L607-608 The references are not needed here. They appear in Table 3.
L633-637 This info is not relevant for the case of NCP in the surface layer and should thus be deleted.

L639 Do you not mean inter-annual variability between 1955 and 2005?
L638-644 I think this reasoning is not convincing. The explanation mentions the variability, but N(O2) and N(CO2) should, despite this variability, move in similar directions. A reasonable ratio of CO2:O2 should be the result. Is there any literature value of this ration that is that low as in the present study?

L646-667 The Conclusions section: I think this is not how a typical Conclusion section should look like. As it is now, the large first and second paragraphs are just a summary, with no real conclusions in it. Only the final short paragraph complies with the conditions of a Conclusion section.

L670 Does this hold for all authors?
L680 What kind of publication is this? Please add info accordingly.

L690-692 There are many more authors on this paper.
L698-699 There is no journal and volume

L700 Reference is not correct
L708 Chu et al: Info missing
L714 pCO2 (do not use 0)
There are a large number of incorrect or incomplete references. Please go through all of them for correction.

Thank you and best wishes
Mario Hoppema

Dear Dr. Possenti and co-authors,

Thanks for the revision of your manuscript which took away some inconsistencies.
I am generally satisfied with the revisions and this also holds for referee #1, whom I consulted.

The improved agreement with the SOCAT data, more realistic PQ values, and reasonable agreement with similar NCP estimates made by independent studies listed in Table 3 all point to a much improved optode calibration.

One final observation that the authors might consider is that Figure 6 shows regressions between CO2 concentration and partial pressure using the older and newer optode calibrations. The authors fit these data with linear regressions but a quadratic/parabolic fit might be more suitable. The optode calibration improved when temperature was used as a constraint. With these in mind, the authors might consider including salinity in the optode calibration.

Some few technical issue are listed:

2.1. Please show the abbreviations as a table

References:
Friedlingstein et al has more authors.
Hemsley, J. M.: OBSERVATIONS PLATFORMS| Buoys, 2015. It is not clear what kind of reference this is.

Rey, B. F.: 5 . Phytoplankton : the grass of the sea, 2001. It is not clear what kind of reference this is.

Saetre, R. and Ljoen, R.: THE NORWEGIAN COASTAL CURRENT, 1972. It is not clear what kind of reference this is.

Skjelvan, I., Anderson, L. G., Falck, E. and Anders, K.: A Review of the Inorganic Carbon Cycle of the Nordic Seas and Barents Sea and Christoph through the strength area of 15-75, 2005. It is not clear what kind of reference this is.

With best wishes
Mario Hoppema