Interactive comment on “ Biogeochemical and microbiological evidence for methane-related archaeal communities at active submarine mud volcanoes on the Canadian Beaufort Sea slope ”

Lee and coworkers investigated the biogeochemistry Pingo-like structures (associated with gas/ mud emissions) in the Beaufort Sea, in particular the imprints of the anaerobic oxidation of methane. In figure 1 these structures are shown, figure 2 shows representative GC-runs , fig. 3 the complete specific results for archaeal lipids. Figure 4 shows results from GDGT analysis, in particular the ring distribution of numbers and a phylogenetic tree of important community members. The concentrations and isotopic compositions of specific compounds as well as (relative) number of 16S sequences are presented in the supplements, although they are by far more interesting


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Printer-friendly version Discussion paper representative GC-runs, fig. 3 the complete specific results for archaeal lipids.Figure 4 shows results from GDGT analysis, in particular the ring distribution of numbers and a phylogenetic tree of important community members.The concentrations and isotopic compositions of specific compounds as well as (relative) number of 16S sequences are presented in the supplements, although they are by far more interesting than exemplary GC runs.Hence these data should be displayed in the main text.Most results from the supplementary table and Supplementary Figure 1 are essential to the study -they show that sulfate methane transition zones are in the upper 20 to 50 cm.Somehow this is not further discussed in the manuscript -although this is core to the biogeochemistry.
Reply: We appreciate for the generally positive opinion of the reviewer about our manuscript.As the reviewer mentioned, we provided all the figures and tables necessary for the manuscript.As suggested by the reviewer, we will move Fig.S1 and Table S1 into the main text in the revised version, but Fig. 2 into the Supplemenatry information as Fig. S1.Although we already mentioned the steep sulfate depletion related to AOM processes in the shallow depths (line 339-342) in the submitted version, we will extend the discussion on the sulfate methane transition zone in the revised version.
Although certainly quiet active -AOM has relatively little impacton total organic carbon contents of the sediment, yet lipid and microbial composition data shows presence and activity of key organisms.The data is there -but the discussion of it needs to be strongly revised.The biogeochemistry of AOM as suggested in the title / abstract are -so far -not really covered.
Reply: The reviewer is right that AOM had a comparably little impact on the TOC content but this is not unusual for AOM settings.However, we do not agree with the reviewer for the point mentioned above.In our opinion, we discussed the AOM presence based on the bulk/biomarker and microbial composition in the submitted version.However, we will strengthen this part of discussion extending the biogeochem-C2

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Printer-friendly version Discussion paper istry of AOM in the revised version.For example, we will incorporate a new aspect connecting relatively depleted δ13C values of archaeol and biphytanes with the activity of chemoorganoautoprophs.
Below I discussed some findings in more detail "Evidence for AOM:" The best evidence for AOM here is the depletion of sulfate, the presence of highly depleted lipids and larger sequence numbers in respective horizons.The rest is not very meaningful"However, organic carbon contents and δ13CTOC values of the three sediment cores investigated spanned a narrow ranges of 1.2±0.1 wt.% and -26.4±0.6‰respectively (see Table S1 and Fig. S1), without the negative isotopic excursion that has often been associated with methane-derived biomass from AOM in MVs (e.g.Haese et al., 2003;Werne et al., 2004)."AC: It is quite normal that the total organic carbon content and the total carbon isotopic composition are only slightly influences.I wonder why the TOC data are shown in the main text but those of specific lipids Abundance and isotopic compositions of GDGTs are always very abundant in sediments but they derive with very distinct isotopic compositions around â Ĺij-25 permil from the water column.The Dataset by Lee et al., clearly shows that AOM shifts the GDGT isotopic composition from -25 to around -45 permil.Although this is for sure less than the -60 permil of methane, it is a clear imprint on the isotopic composition.Those data should be transferred into the main text.Moreover assuming an origin of the ANME derived GDGTs from head to head condensation of archaeol lipids (i.e.c.f. Kellermann et al., 2016; Org Geochem) one could determine the contribution of archaea to the GDGT pool assuming similar concentrations of both compounds.
Reply: As mentioned above, we will show Table S1 in the main text which includes the concentration and isotopic values of specific lipid biomarkers.As the reviewer notified above, our bulk data showed relatively little impacton of AOM on total organic carbon contents of the sediment and the total carbon isotopic composition.But lipid and microbial data showed the presence of AOM in our study sites.Although diether lipids (e.g.archaeol) are less specific and likely produced by all ANMEs, we will try

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Printer-friendly version Discussion paper understand methane cycles in this system.Hence, we do think that what stated in the conclusions is valid.In future, a follow-up study will be conducted to examine in more detail distinct methane oxidation processes (e.g.AOM and MOx) near surface using ROV push cores.Nevertheless, we agree that the conclusions also contain a wrapup/summary style of data and will thus rename the section to summary and conclusions.Some detailed comments along reading.Abstract: Please find another start: That sounds very technical (Line 31 to 34): AOM related biomass mainly derives from inorganic carbon (i.e.Kellermann et al., 2012, Wegener et al., 2016 Front. Microbiol), hence this discussion point is rather weak and of course most biphytanes do not come from methane Reply: Several studies including the ones stated by the reviewer could show that AOM communities assimilate DIC, however, in AOM systems, this derives from methane.Thus, AOM-derived lipids (and other biomass) is typically 13C-depleted.As mentioned above, we will emphasize the additionally carbon assimilation of AOM-related archaea along the sharply depleted sulfate profiles.
Line 31 A value cannot be enriched, but is either high or low Reply: We will correct it (as high values).Line 49: Why not simpler: The following mapping of the southern Beaufort Sea revealed numerous Reply: As recommended by review, we will correct it (line 51-53) like "The following mapping of the southern Beaufort Sea revealed numerous PLFs which had the various shaped-features may indicate localized unstable seabed conditions."Line 54: Based on their formation processes PLFs can be classified into five categories; please also state how they are formed Reply: In our opinion, it is somewhat out of focus of our manuscript.However, we will C5