This is an attractive paper that identifies a gap in the application of 14C to soil CO2, which can be filled up by adopting the approaches used routinely for the 13C analysis of soil CO2. In particular, this will incorporate into the 14C analysis the isotope effects of diffusion and mixing in addition to the biological fractionation in respiration. The paper demonstrates the error in ignoring this and suggest practical ways to apply it in new measurements and even to correct old ones. This is well written method-based paper that is within the scope of BG and should be published.

The paper was reviewed by three expert referees that indicate the need for significant revisions that should address some weak point and improve the paper. In their initial response the authors generally agree with the comments and I therefore recommend the submission of a revised version.

However, I also find the authors response to the referees’ comments mostly insufficient, and would not expect the referees that will be asked to re-evaluate the revised paper to be satisfied with it. I therefore also urge the authors to re-evaluate all the referees’ comments and provide more detail and in-depth responses, in the body of the paper.

Note that to maximize the value of the review process (and the efforts invested) in improving a paper, Ref comments, that not always point out an error, should be used to identify weak points for the reader that require some clarification and discussion and changes in the text, and a rebuttal in a response letter is not very useful in that regard.

Some examples could include comments by both Ref. 1 and 3 raising relevant questions on terminology, and just deleting ‘fractionation’ form the title and discussing it in a rebuttal letter rather than in the text is not useful to the reader (I would also note that in “mixing” it seems that the respired CO2 and atmospheric CO2 mix to produce soil CO2, and not as indicated, sometime leading to Keeling plots analyses). Likewise, the argument that ALL processes affecting soil CO2 should be considered is in-consistent with the refusal to discuss effects such as exchange with carbonates (raised more than once) that could have larger effects than the mixing correction (it might, in fact, be more important than the disconnected discussion of the chamber methodology in first page of section 5.2, which is not clear and out of scope of this paper). Comments by both Ref 1 and 3 on the need to clarify the principles of diffusional fractionation, is addressed by removing it. Repeated requests for more sensitivity analyses are rejected (Table 1, details change in error with depth, not with variations in key controlling parameters, figures do give an idea but are not this). Similarly, repeated request to discuss ‘realistic’ conditions (isotopic values, the constant production with depth, steady state, etc), put precision in context (correct math does not indicate relevance), repeated requests for more info on the limited field part are generally rejected. In fact, Ref 3 provided what I think are 18 thoughtful comments, only one of which (#17) seems to be fully addressed by simply removing the relevant text on O2 effects... The paragraph above is just to note a few examples that come to mind to further make the point that better considering the Refs’ points in the revisions could further help to improve the paper and avoid unnecessary lengthy process.

PS in the proposed revisions the term “situationally” was introduced that had me run for the dictionary, with little help. Please explain what you mean…

This is a revised version with major revisions. I recommend another cycle of major revisions because the core of the paper, introducing a valid correction for interpretations of 14C in soil CO2 justifies publication. This is in spite of one reviewer being sufficiently frustrated with the revisions to indicate that another cycle is not justified (recommending rejection). And it seems the authors run the risk that our 2nd expert reviewer will respond the same way. I do concur with the main criticisms and the paper must sufficiently address it.

Generally, it seems everyone involved agree the paper raises a valid point regarding the need to introduce additional corrections when dealing with 14C in soil CO2. And as I think I pointed out upon submission, it would probably be most effective as an important short Method note (after considering the confusing parts such as noted by Ref 3). But it seems the author opted for more complicated options. This is apparent already in the Abstract, most of which focuses on “…assess the bias from using the conventional method… etc”. And reach what is the real message of the work only at the last sentence: “…we propose a new correction for radiocarbon applications in soil gas that accounts for diffusion and mixing…” As a result, the paper is loaded with data while insisting it is not Experimental paper and just demonstrate the calculation, and so no need for details, and deferring various points to ‘future work’. This does not seem to work well, raises more questions, provides unrealistic picture, and at the end fails to convince reviewers of the importance of the otherwise valid correction. If at all, a more effective demonstration would be to apply the corrections to a published work with soil profiles by others. (And in general, why focus on the ‘size’ of the correction rather than simply rest the case on the underlying ‘correctness’).

There are also some more minor issues that do not help in getting through these revisions. Just for example, the distinction between mass-dependent diffusion and mass-independent mixing is highlighted (correctly), but much effort is invested in insisting that these are more similar than not, using linguistic changes, such as changing ‘mixing’ to ‘diffusive mixing’ as a response, and using an odd definition of fractionation (which traditionally applies to reactant and product that are the same entity rather than a new one composed of the real product and any additional background). Or, the repeated cut and paste of the same response to different reviewers’ comment (unpolite, to say it politely). BTW, comments on the relevance of carbonates is addressed with a single line saying CO2 interactions with carbonate is not mass-dependent, which seems odd.

I suggest to revise the paper with more attention to all comments, but consider changing the balance of the paper to further clarified theoretical part and reduced otherwise.