Thank you for proposing revisions to this manuscript in response to the two reviewer comments. I recommend you complete the manuscript as you propose and I believe I will be able to evaluate the response without further reviewer input. It is possible that the additional model diagnosis, if extensive, could require more reviewer input (hopefully not).

I have a few small comments to add:
1) I do not share the second reviewer's concern about the novelty of this work, your response on this issue seems appropriate to me.
2) On the question of the interpolar gradient I recommend also examining the paper by Logan Mitchell et al. (Science, 2013) on aspects of the Holocene gradient. I also suggest some caution on interpreting older studies of the gradient during the last ice age because of a small production of methane in the analysis of dusty Greenland ice (James Lee et al., in press in Geochimica et Cosmochmica Acta). I would be glad to provide more input in to whether this matters if you choose to discuss the gradient in the glacial period.