Dear Drs Wehr and Saleska,

Many thanks for your replies to the two referee reports. Both referees have made an excellent job of appraising your manuscript critically, and together with your response to their individual points raised, I think it has made this publication even stronger. I’m sure that in its final form, it will become an important reference for isotope biogeochemists.

I’d like you to implement the suggested revision points, including a brief discussion of the issue of instrument uncertainty vs. variability caused by spatial/ecosystem heterogeneity, raised by referee 2 (John Miller).

The new figure illustrating a ‘real data’ example of night-time Keeling plots is also very useful. A detailed figure caption outlining the differences in data sets would obviously be necessary alongside it.

I look forward to reading your new manuscript version prior to final approval.

With best regards,
Jens-Arne Subke

Dear Dr Wehr and Dr Saleska,

Many thanks for your response, outlining all changes to the manuscript. These are all much appreciated, and I am happy for the paper to now be published in this form. I find the paper very well written, and am certain that it is a valuable contribution to how we use isotopic mixing models, and that through Biogeosciences you will reach the right audience for this topic.

With best regards,
Jens-Arne Subke