Dear authors,
one of the referees who commented on the first version of your manuscript has seen it again and given comments. The referee acknowledges that the paper is improved, but there are still a number of issues that should be updated/clarified. Please update the manuscript accordingly and provide a point-by-point reply to the referee comments.
Best regards
Thomas Röckmann

Dear authors,
thanks for submitting a revised version and the replies to the second round of referee comments.
I have looked at your answers and the revised version and there is one point that has not been addressed satisfactorily.
The referee asked why the (negative) deposition flux should INcrease when the SOC increases (table 5 and 7). This question is based on the assumption that higher SOC provides more substrate for CO formation in the soil, which would DEcrease the soil-atmosphere gradient and DEcrease the deposition flux. There must be one process in your model that leads to an increase in the deposition flux.
You argue now with time step arguments, which apparently play a role, but even with a short timestep the sign of the flux change remains the same, even if the magnitude is reduced. I think it is still required that you explain the physical basis of the effect. And then it would also be good if you can argue a bit more quantitatively why the timestep has such a large influence (and that this then does not affect other results of your model).
Best regards
Thomas Röckmann

Dear authors,
the clarifications that you have added to the paper about the effect of the SOC changes are satisfactory and I am glad to inform you that your article is now accepted for publication in ACP, subject to technical corrections.
The technical issues relate to the use of English grammar and sentence structure, which should be improved throughout the article. Your article will undergo copy editing according to the ACP procedures, but to avoid excessive copy editing, which can sometimes compromise the content, I encourage you to thoroughly go through the text, preferably together with a native speaker or a very proficient coauthor or colleague, and adjust the language before submitting the final version to the editorial office. As an example, below I have made a number of small changes in the new paragraph that you added to correct some mistakes and make the text better readable.
Best regards
Thomas Röckmann

Copy edited new text fragment:
Fourth, from the sensitivity test (Table 5) we notice that an increase in SOC by 5% resulted in a net flux increase from the atmosphere to the soil by 2.57%. The SOC increase enhanced CO production (Equation 3), CO concentration (Equation 1), and CO oxidation (Equation 2). When the change of total oxidation is larger than the difference between the change of total production and the change of total soil CO concentration (Equation 1), the estimate of the net flux change is negative (from atmosphere to soil) using a mass balance approach (Section 2.2), which leads to a 2.57% increase in the net flux in our SOC sensitive test. This is due to the fact that CO production (Equation 3) is calculated independently from oxidation (Equation 2). This will not influence our general findings since SOC varies only slightly during our simulation periods with a 3% increase from 1900 to 2013 (Figure 4d) and up to a 4% increase from 2014 to 2100 (Figure 6g). This model artifact that is apparent in the SOC sensitivity test can be alleviated using a very fine time step (e.g., 1 second), because in this case CO concentrations change only slightly within the short time. Therefore, when a short time step is used, the net flux roughly equals the difference between production and oxidation. If the change of production is bigger than the change of oxidation, the change of net flux will be positive, leading to a decrease of deposition to the soil. The downside is that running the model at a time step of one second will require significantly higher computing time.