In their revised manuscript, Bianchi et al. addressed all of my major concerns. This paper is an excellent contribution to the field and I recommend publication after considering the few minor points below.
Figure 1/Appendix A: Have the authors considered a model scenario in which nitrite oxidation can occur anaerobically? Some studies indicate the importance of NO2– oxidation in apparently anoxic waters in ODZs (Buchwald et al. 2015; Sun et al. 2021).
Line 80 and Appendix 4: How sensitive are the model results to the assumed stoichiometry of organic matter? The C:P of organic matter in the eastern tropical South Pacific has been hypothesized to be closer to 83:1 (Teng et al. 2014) (and if the authors disagree with Teng et al. from a modeling perspective, I’d love to hear why). Changing C:P ratio should also change N:P, since C:N remains fairly consistent (Martiny et al. 2013). I know that the assumed N:P ratio can have a significant impact on N fixation rates (Mills and Arrigo 2010), although this was a very different modeling framework. On a related note, would it affect the model results for denitrification to remineralize organic matter with a different stoichiometry from aerobic respiration? I’m thinking of the Van Mooy paper showing that the stoichiometry of remineralization via denitrification may not involve PO43- because it’s mostly amino acids (Van Mooy et al. 2002).
Line 343: I might be misunderstanding, but should this say “a random error of up to 20%”?
Line 627: Why only two electrons to reduce 2NO2- to N2O?
Buchwald, C., A. E. Santoro, R. H. R. Stanley, and K. L. Casciotti. 2015. Nitrogen cycling in the secondary nitrite maximum of the eastern tropical North Pacific off Costa Rica. Glob. Biogeochem. Cycles 29: 2061–2081. doi:10.1002/2015GB005187
Martiny, A. C., J. A. Vrugt, F. W. Primeau, and M. W. Lomas. 2013. Regional variation in the particulate organic carbon to nitrogen ratio in the surface ocean. Glob. Biogeochem. Cycles 27: 723–731. doi:10.1002/gbc.20061
Mills, M. M., and K. R. Arrigo. 2010. Magnitude of oceanic nitrogen fixation influenced by the nutrient uptake ratio of phytoplankton. Nat. Geosci. 3: 412–416. doi:10.1038/ngeo856
Sun, X., C. Frey, E. Garcia-Robledo, A. Jayakumar, and B. B. Ward. 2021. Microbial niche differentiation explains nitrite oxidation in marine oxygen minimum zones. ISME J. 15: 1317–1329. doi:10.1038/s41396-020-00852-3
Teng, Y.-C., F. W. Primeau, J. K. Moore, M. W. Lomas, and A. C. Martiny. 2014. Global-scale variations of the ratios of carbon to phosphorus in exported marine organic matter. Nat. Geosci. 7: 895–898. doi:10.1038/ngeo2303
Van Mooy, B. A. S., R. G. Keil, and A. H. Devol. 2002. Impact of suboxia on sinking particulate organic carbon: Enhanced carbon flux and preferential degradation of amino acids via denitrification. Geochim. Cosmochim. Acta 66: 457–465. doi:10.1016/S0016-7037(01)00787-6