BG-2019-124

Dear Yan Shen,

First of all let me thank the reviewers Dr. Rienk Smittenberg and Dr. Gordon Love for their thorough and helpful reviews and you for your answers. I would like to ask you to address all their comments, more or less as you have indicated, in your rebuttal and revised version. Both reviewers, and myself, have mentioned that this paper seems to be a continuation of already published work with quite some overlap in the author lists as well. I have mentioned before that you have to make it very clear why this manuscript is able to stand on its own and at least one reviewer made a similar remark, so make that absolutely clear in the rebuttal and revised version. Both reviewers commented on the detection limit of your method and how this might relate to your detection of sterols or absence thereof. Make sure you address this issue and how this might affect your results and discussion. I am not really happy with your reply to the comment about HyPy versus your Py results of Dr. Gordon Love, please try to come up with a better answer.
I do have one other remark concerning microbial mats, degradation and time that I think connects to some of the remarks made by both Dr. Rienk Smittenberg and Dr. Gordon Love. Different from a typical sedimentary setting microbial mats do not simply get buried by material falling on top and therefore getting older with depth. As I understand it, you have photoautotrophic organisms at the top generating biomass and heterotrophic organisms “below” (usually the separations are not so definitive, but to keep it simple). The mats typically grow upwards on top of dead and reworked organic matter from the mat itself. Potentially even similar to say year rings in trees, so new mats, consisting of two layers grown on top of the compacted layers of last year/growing season. The carbonate layer could even be the results of microbial activity, separating layers. This would fit with the observation that age does not increase regularly with depth or that concentration does not decrease linearly with depth, but in steps. High in the fresh photoautotroph layer, lower in the heterotroph layer increasing again into the older photoautotroph layer and lowest in the old heterotroph layer, for instance. This also means that community composition changes with depth, even if it doesn’t really change with time ( the top layer will always be photoautotrophic). How do your results relate to mat development, is there any in formation how this mat develops over time?

Best regards,

Marcel

Dear Yan Shen,

It is a pleasure for me to accept your manuscript for publication in Biogeosciences.

Best regards,

Marcel