Evidence for anaerobic methane oxidation by archaea in euxinic waters of the Black Sea

13C-depleted archaeal-derived ether-bound cyclic biphytanes occur in particulate organic matter from the euxinic waters of the Black Sea. These strongly 13C-depleted biomarkers (up to −58‰) provide evidence that archaea are consuming methane in euxinic waters. 13C-depleted archaeal compounds were absent from surface sediments, suggesting that the responsible organisms are in low abundance and leave no characteristic fingerprint in the sedimentary record.