Formation of authigenic carbonates contributed by sulfate- and metal-driven anaerobic oxidation of methane in the northern Okinawa Trough, East China Sea

Authigenic carbonates of the northern Okinawa Trough have been shown to be contributed by both sulfate- and Fe-driven anaerobic oxidation methane (SD-AOM Fe-AOM, respectively); however, microorganisms involved remain poorly constrained. To better understand types roles in specific biological processes, authigenic collected from at water depths between ∼540 m 700 were studied using petrographic, mineralogical, elemental, lipid biomarker analyses. The carbonate minerals primarily aragonite, high-magnesium calcite, low-magnesium or dolomite. extremely low δ13C values bulk (−59.2‰), molecular fossils oxidizing archaea (ANME; −131‰), sulfate-reducing bacteria (SRB; −77‰) indicated that formed as products AOM. Biogenic was confirmed main carbon source for all carbonates, whereas bio-degraded oil hydrothermal input complemented sources, revealed occurrence unresolved complex mixture, strongly enriched As Sb, their correlations with Fe/Al. Combined δ18O (as high +5‰), fluids suggested derive dissociation gas hydrates. ANME-2 a mixture ANME-1 identified two calcitic respectively, patterns. relatively higher contents 13C-depeleted isoprenoids SRB−related fatty acids, strong Mo enrichment, debris calcite- aragonite-dominated reflect precipitation driven SD-AOM shallow sulfate-methane transition. For other seep amounts near absence crocetane suggest dominance assemblage. non-13C-depleted iso-/anteiso-C15:0 acids (−27‰) dolomite-containing indicate decoupling ANME SRB. These most likely below bottom transition included contributions content, dolomite siderite, decreased δ56Fe increasing Fe/Al ratios.