Depth profiles of numbers of the entire microbial and archaeal 16S rRNA gene population, mcrA genes, and nifH and group 2-specific nifD genes in the DNA assemblages and the methane, sulfate, and ammonia concentrations in the sediment core(s). (A) The numbers of the entire microbial 16S rRNA gene population and archaeal 16S rRNA genes in the methane-rich sediment core and reference sediment core are shown, as indicated. Open symbols indicate the proportion of archaeal 16S rRNA genes in the microbial 16S rRNA gene population in the both cores. (B) Red filled squares indicate the number of all the groups (universal) of mcrA genes in the methane-rich sediment core. Numbers of mcrA genes by group are as identified on the figure. (C) The numbers of universal nifH genes and group 2-specific nifD genes in the methane seep sediment core are indicated as shown. (D, E, and F) Data from the methane-rich sediment core and the reference core are shown, as indicated on the figure.