Dear Dr. Jiménez López and co-authors,

Thank you for the submission of your revised manuscript, which has much improved. However, the two referees still found issues with which they are not completely satisfied. I selected minor revisions for your manuscript, but actually it is even a bit more than that, somewhere between minor and major revisions.
I hope you will resubmit your manuscript, and please take a look at the comments and account for those in a new revised version of your manuscript.

Thanks and best wishes
Mario Hoppema

Dear Dr. Jiménez-López and co-authors,

Thanks for your revised manuscript, which I have read and corrected. My comments and listed below. Your manuscript is almost there. Please prepare another revised version taking into account the below comments:

L28 de Haas (typo)
L29 I suggest: … total carbon sequestration through the mechanism of the biological pump …

L33 … lower than that …
L42 I suggest: At the continental shelf a high spatiotemporal variability of the air-sea CO2 fluxes occurs due to …

L42-43 “upwelling zones” and “input” are not processes. Please change wording.
L58 “more affected” More than what?

L62 shows (instead of: presents)
L63 “in this zone” This formulation is not clear; is this the former or the latter? Please make clear

L64 “The Gulf of Cádiz is a geographical domain of considerable interest due to its location.” This is a strange formulation. I guess it holds for every oceanic region. Please specify and change wording.

L133 Please define CTD here
L148 Please use SI units instead of mile

L196 please add “water depth” to the > 50 m and < 50 m, as this is not clear now
L212 add USA after NY (and write full New York, correct?)

L219 delete: sampling
L221-222 I suggest: During 2014, SST values were found to be higher than those in 2015 and 2016

L222 delete: for both seasons
L224 delete: spatially

L234-236 This sentence is not clear; I suggest: Sampling during our cruises did not detect the highest temperatures occurring in the Gulf of Cádiz during August, which may indicate that the real range of pCO2 variation be greater than that determined in this study.

L237 Change to: The highest mean values … (since in the previous sentence a higher value was given)

L245-246 This sentence is not clear; change to: These mean values are not significantly different and the standard deviations are high, indicating high spatial and inter-annual variability.

L273 variable (instead of: parameter)
L294 … in the CO2 fluxes … (delete: dataset of)

L294 … similar to pCO2 … (not: as in the values of pCO2)
L305-306 The sentence is unclear. I suggest: In our study, all data from all seasons together exhibited a linear relationship between pCO2 and SST (r2 = 0.37, Fig. 5A).

L306 becomes even more significant … (add: even)
L326-327 Is there any additional evidence, or only indications, from research on land that such is happening in this region?

L337 “the shallower areas as a source of CO2 (mean = 0.2 ± 22.7” I wouldn’t call that a source. This is clearly neither source nor sink, i.e., neutral.

L340 biological processes
L342-343 … the changes produced by air-sea CO2 exchange are relatively small.

L344-345 I suggest to change this to: In regions with shallower mixed layers, the effect of air-sea exchange on the pCO2 variation is larger (Olsen et al., 2008).

L351-352 … except for an area influenced by continental runoff where pCO2 decreases.

L353 biological processes
L353-355 … a dependence between the mean values of pCO2 and pH, AOU and the concentration of chlorophyll-a has been observed at the fixed stations (n = 126, Fig. 7)

L355 AOU and pCO2 show a positive relationship …
L358 delete: However, (this relationship is expected, no surprise)

L366-367 I suggest to change to: Something that could affect the distribution of pCO2 (and be considered to be part of mixing and biology sensu Olsen et al., 2008), is vertical and lateral transport.

L380 delete: Additionally,
Or for that reason delete the whole sentence in L380-381: “Additionally, several authors have described the influence of the continental inputs on the distribution of pCO2 in surface waters.” (because the authors are mentioned in L383-384)

L380-384 Why is this, what you describe? It would be interesting to read the reason here.

L385 derive (instead of: take place)
L402-405 It is not clear to me what you mean here. Please modify sentence.

L407-408 “These authors found a mean benthic flux of 27 ± 8 mmol C m-2 d-1 for stations with a mean depth of 23 m. This flux of DIC is equivalent to a CO2 flux of 198 ± 80 μmol C m-2 d-1, considering a well-mixed water column, a pH = 8 …” I do not understand this calculation. A benthic C flux is given, and from this another C flux is calculated with quite a different amount of C involved. Is the derived flux over a different interface? Please explain what you mean and how you did the calculation.

L425 Please add here what high values (of which variable?)
L440-441 delete: that have been cruised for sampling in the study zone (not necessary, the transects have been introduced earlier in the text)

L441 delete: It can be appreciated that
L445 upwelling (no –s)

L447 show (not: present)
L457 the air-sea flux …

L457 shows, or exhibits (not: presents)
L458-459 I suggest to change to: As can be seen in Fig. 10, seasonal and spatial variations were observed in the air-sea fluxes during the period studied.

L463 As discussed above for pCO2, temperature change is …
L466 as a consequence of the biological utilization of the CO2 and the subsequent tendency for CO2 undersaturation … (please note, biological utilization as such does not cause air-sea fluxes)

L467 Such relationships

In §4.4 several times CO2 fluxes are mentioned, where air-sea fluxes are meant. Please insert air-sea in some cases for clarity.

L489 during the sampling period
L489 With the number of -0.18 mmol m2 d-1 including the order of magnitude larger standard deviation it is not very convincing to call the region a CO2 sink. Please change the wording, and consider to use neither source nor sink.

L498-499 My suggestion for this sentence: A high variability in pCO2 in the Gulf of Cádiz was observed which is associated with its location as a transition zone between coastal and shelf areas, superimposed on the usual seasonal variation due to thermal and biological effects.

L499-500 “The mean value of pCO2 found in this study (398.9 ± 15.5 μatm) indicates that the eastern part of the Gulf of Cádiz could be slightly undersaturated in CO2 with respect to …” This is not sound. A mean value for the entire region is given, which you couple to (only) the eastern part of the Gulf that may be undersaturated. Please correct, or explain and modify the text.

L502 littoral (typo)
L502-503 delete: in this work

L503-504 biological activity, represented by chlorophyll-a
L510 The mean T/B ratio (1.15) of the region suggests …

L510 … by temperature changes.
L510-512 I suggest the following: However, the situation is more complicated if the ratio is considered as a function of bottom depth, which is associated with the existence of non-thermal processes.

L515-516 “In contrast, the highest T/B ratio values have been found in the SP transect, where values of up to 1.54 are obtained for depths greater than 100 m.” With those explanations for the lower ratio earlier, what is the reason for this higher ratio? Please add some text on this.

L520-521 “… since the pCO2 has increased from 360.6 ± 18.2 μatm (Ribas-Ribas et al., 2011) to 398.9 ± 520 15.5 μatm in the actuality.” It is important to provide the years for these values and the accompanying increase of pCO2 in the atmosphere to be able to judge the contention. Please add text.

L905 suggest to write here: data from González-García et al. (2018).

title Table 3: mention that this concerns: air-sea CO2 fluxes
title Table 4: idem ditto

L939 caption Figure 2: please add units of variables shown
L989 caption Figure 6: Observed changes in pCO2 (first row) and pCO2 changes broken down due to:

L994 caption Figure 7: Relationships (instead of: Dependence)

With best wishes
Mario Hoppema