Abstract: Methanogenesis and anaerobic oxidation of methane driven by microbial activites are important for the global methane cycle.Marine gas hydrate is a huge methane reservoir on Earth,however,it remains unclear whether archaeal community structure in marine sediments can indicate marine gas hydrate.In this study,distinct archaeal communities thriving in marine sediments of core 973-3 in southwestern Taiwan Basin of the northern South China Sea were characte-rized by 16S rDNA gene analysis.Moreover,we discussed the effect of diagenetic environment factors on archaeal community distributions.Results show that Methanosaeta is the most abundant in 20~450 cm depths,with 32.9% proportion.Methanosarcinales dominates in 542-870cm depths with 28.3% proportion,while Methanomicrobiales is predominant in 1 075-1 162cm depths with 20.7% proportion.The archaeal community structure in core 973-3 is closely related to the methanogenesis and methane oxidation,indicating the presence of gas hydrate.The variations of diagenetic environment parameters are responding to the gas hydrate formation.The pH values increase with depth,contrary to E_h,salinity and grain sizes.It is obviously different of archaeal communities in core 973-3,compared to that in gas hydrate-containing and -free sediments from Japan Sea and the Shenhu area of South China Sea,owing to the significant effects of pH,E_h and grain sizes on the distributions of archaeal community in core 973-3.Hence,it is essential to focus on the main niche for the methanogens and methanotrophs,to improve archaeal communities indicating marine gas hydrate.

Key words: archaeal diversity, diagenetic environment, gas hydrate, southwestern Taiwan Basin, northern South China Sea