Microbial Reefs in the Black Sea Fueled by Anaerobic Oxidation of Methane

TLDR

Massive microbial mats covering up to 4‑meter‑high carbonate buildups thrive at methane seeps in the anoxic waters of the northwestern Black Sea shelf, composed mainly of densely aggregated ANME‑1 archaea and sulfate‑reducing Desulfosarcina/Desulfococcus bacteria. In vitro incubation demonstrates that these mats perform anaerobic oxidation of methane coupled to sulfate reduction. Strong 13C depletions confirm incorporation of methane carbon into carbonates, bulk biomass, and specific lipids, showing that anaerobic consortia can generate carbonate precipitation and substantial biomass, with implications for ancient carbon cycling.

Abstract

Massive microbial mats covering up to 4-meter-high carbonate buildups prosper at methane seeps in anoxic waters of the northwestern Black Sea shelf. Strong 13 C depletions indicate an incorporation of methane carbon into carbonates, bulk biomass, and specific lipids. The mats mainly consist of densely aggregated archaea (phylogenetic ANME-1 cluster) and sulfate-reducing bacteria ( Desulfosarcina/Desulfococcus group). If incubated in vitro, these mats perform anaerobic oxidation of methane coupled to sulfate reduction. Obviously, anaerobic microbial consortia can generate both carbonate precipitation and substantial biomass accumulation, which has implications for our understanding of carbon cycling during earlier periods of Earth's history.