|This paper is much improved over the previous version that I reviewed more than six months ago. The authors have done a good job of addressing the issues I brought up in that review. Although the paper is long, it could be published in close to its present form. It is a difficult read, though, because of its length. That’s part of why I was slow in producing this review.|
The best part about the paper, in this reviewer’s opinion, is the section on comparisons between the 1-D and 3-D versions of the code, e.g., Fig. 3 in the paper and my comments 7 and 8 below. The authors have missed a new paper by Cooke et al. (2022) (see comment 7) that compares ozone column depths generated by the WACCM 3-D model with column depths calculated by other 1-D and 3-D models. As I say in more detail below, we are trying to figure out the source of this discrepancy by performing a model intercomparison study. The present authors are welcome to participate in that study if they are so interested.
You may reveal my name to the authors.
1. (l. 15) “The microbial fossils dated to 2.6 Gyr ago found in the Campbell formation of Cape Province in South Africa are identifiable as cyanobacteria (Pierrehumbert, 2010) as many other evidences starting 2.8 Gyr ago (Nisbet et al., 2007; Crowe et al., 2013; Lyons et al., 2014; Planavsky et al., 2014; Satkoski et al., 2015; Schirrmeister et al., 2016). Cyanobacteria are known to produce oxygen by photosynthesis.”
--Not everyone is convinced that cyanobacteria were present and producing oxygen prior to the GOE. See the recent paper by S.P. Slotznick et al., Sci. Adv. 8, eabj7190 (2022).
2. (l. 24) “In the Archean anoxic atmosphere, the sulfur photochemistry was responsible for mass-independent fractionation of sulphur isotopes in sedimentary rocks (Kasting et al., 1989; Pavlov and Kasting, 2002).”
--Delete ref. to Kasting et al. (1989). We did not talk about sulfur MIF. Add reference to J. Farquhar et al. (Science, 2000). They were the ones who found the sulfur MIF signal, not Pavlov and Kasting.
3. (l. 43) ‘The appearance of oxygenic photosynthesis, which was much more efficient than previous metabolisms...”
--Oxygenic photosynthesis is not a metabolism. Metabolism is a process that provides energy to an organism. Photosynthesis is a process that enables them to synthesize organic carbon starting from CO2. So, instead of saying ‘previous metabolisms’, this sentence should say ‘previous mechanisms of photosynthesis’, or simply ‘anoxygenic photosynthesis’.
4. (l. 93) ‘develop’ --> ‘developed’
5. (l. 103) ‘photolyses’ --> ‘photolysis’
6. (l. 112) ‘The 1D version of the model uses a surface ocean, a surface mean albedo of 0.28, a mean solar zenith angle of 60o and an eddy diffusion coefficient vertical profile from Zahnle et al. (2006).’
--Consider changing the solar zenith angle to 48.2o, following P. Liu et al. (PNAS 118, 2021) and Cronin (JAS 71, 2994, 2014, referenced therein). This is the insolation-averaged solar zenith angle. In our (Kasting group) experience, this will generate better agreement with the modern ozone column depth of 292 DU. If you do this, the diurnal averaging factor should be changed from 0.5 to 0.375. See Cronin’s paper for the derivation. This does not need to be done for the present paper but could be done for the model intercomparison study mentioned later in this review.
7. (l. 165) “However, the ozone column is always found larger in 1D, up to 5 times the mean column obtained with 3D.”
--Neat! This may be the most interesting result in the paper. To see why, the authors should see the paper by G.J. Cooke et al. (Royal Soc. Open Science, v. 9, 2022). The title of this paper is “A revised lower estimate of ozone columns during Earth's oxygenated history.” They find a similar result using the WACCM 3-D coupled chemistry-dynamics model. However, the 1-D model(s) with which they compare are not from there own group, but rather they are from the Kasting group (e.g., A. Segura et al., Astrobiology, 2003). We are currently engaged in a model intercomparison study between the Kasting group, Cooke et al., and Way et al. (2017, referenced in the Cooke et al. paper). Curiously, Way et al. do not find lower ozone column depths at low pO2 using their ROCKE-3D coupled chemistry-climate model. Once the current paper has been accepted, we encourage you to contact the Kasting group and determine if you wish to participate in this ongoing model intercomparison study.
8. (l. 171) "The 3D vertical transport seems to transport species more efficiently than the 1D transport model which uses an Eddy coefficient from Zahnle et al. (2006) to mimic the 3D transport.”
--This is equally interesting and important. Maybe it’s the vertical transport that accounts for the differences between 1-D and 3-D ozone column depths at low pO2. Your group is ideally set up to study this problem, as your 1-D and 3-D models share common chemistry. That is not true for the models being used by us in the comparison with Cooke et al. and Way et al.
9. (l. 235) ‘troposause’ --> ‘tropopause’
10. (l. 239) “During glaciations, however, environments able to provide both light and liquid water are considerably limited making likely a considerable drop in the photosynthetic production of O2 and the burial of biomass.”
--Methane production should decrease during a global glaciation, as well, as I mentioned in my previous review. Given that production of both O2 and CH4 should decrease during glaciation, it is not clear how this will affect the transition from low to high pO2. To realistically simulate this feedback, one would need to couple the present model to a biogeochemical box model that simulated O2 and CH4 production. I don’t think that would be easy to do, so I’m not recommending it as a task, but it might be worth pointing out that this is what is really needed to study the effect of these feedbacks on the GOE.
11. (l. 328) “Such an over-abundance of methane is not highlighted by previous studies, nor by the geological record.”
--The authors are talking about the immediate post-GOE timeframe, so this statement may be correct as written. But they should perhaps point out that other authors (e.g., A.A. Pavlov et al., Geology 31, 87, 2003) have argued that methane concentrations could have been high during the Boring Billion periods, 1.8-0.8 Ga. The reasons are likely the same as in the present model: lots of organic matter production, combined with lower destruction rates of organic matter through aerobic decay or sulfate reduction. This has led to an ongoing debate about methane levels during the Mid-Proterozoic. The Cooke et al. (2022) paper referenced earlier is the latest salvo in that debate.
12. (l., 365) The Conclusions section is fairly long and contains new references and new material that were not discussed previously in the paper. Some of this discussion might better be moved to a separate section entitled ‘Discussion’. Conclusions should simply summarize the main results of the paper, with perhaps one or two important implications.
13. (l. 366) ‘establish’ --> ‘established’