Dear Dr. Griffith

thanks for carefully revising your manuscript according to the reviewer comments. Overall, I am very satisfied with your replies and changes which sufficiently meet the points raised by the referees. There are some very few minor points (see below) and on request from my side. Let's start with the request:

With introducing section 4.3 you have clarified that the overall precision of isotopic ratios derived from the FTIR instruments does not meet the GAW Standards yet. This is, as you show, not due due to systematic errors made by approximations in the calculations or insufficient calibration issues, but reflects the higher analytical noise compared to IRMS instruments. I think this should be stressed some more by repeating the fact (not yet GAW standard) and arguments in the summary and may be also in the abstract (the latter is optional). Please provide me with a short answer how you accommodated this request in your re-revised version. After this small addition, I will then quickly accept the paper in its final version.

Below some minor points:

page 1 line 22: Potential systematic errors
page 1 line 23: these systematic errors
page 8 line 26: contain
page 10, line 17: "realistic errors" do you mean stochastic analytical error here? please specify.

Regards
Hubertus Fischer (CP editor)