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Biosignatures present in a hydrothermal massive sulfide from the Mid‐Atlantic Ridge
Author(s) -
BLUMENBERG M.,
SEIFERT R.,
PETERSEN S.,
MICHAELIS W.
Publication year - 2007
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/j.1472-4669.2007.00126.x
Subject(s) - archaea , hydrothermal vent , hydrothermal circulation , geology , geochemistry , sulfide , isotopes of carbon , chemistry , environmental chemistry , paleontology , total organic carbon , bacteria , organic chemistry
Mid‐ocean spreading and accompanying hydrothermal activities result in huge areas with exposure of minerals rich in reduced chemicals – basaltic and peridotitic rocks as well as metal sulfide precipitates – to the oxygenated seawater. Oxidation of Fe and S present in these rocks provides an extensive long‐term source of energy to lithotrophs. Investigation of lipid biomarkers and their carbon isotope ratios from a massive iron sulfide of an inactive sulfide mound or inactive chimney sampled at the western flank of the Turtle‐Pits hydrothermal field (Mid‐Atlantic Ridge, 5°S) revealed a unique lipid distribution. The bacterial fauna appears to be dominated by chemolithotrophs with a distinct lipid composition mainly comprising of iso ‐branched fatty acids and nonisoprenoidal dialkyl glycerol diethers partially including the very rare macrocyclic cores with 30–35 carbon atoms (including 13,16‐dimethyloctacosane and 5,13,16‐trimethyloctacosane). The Bacteria are accompanied by most likely hydrogen/CO 2 ‐dependent methanogenic Archaea (e.g. Methanococcus ) as well as other Archaea with a different life style (e.g. Ferroplasma ). Alike some of the bacterial lipids the archaeal lipids predominantly consist of macrocyclic diethers including one C 40 and one C 41 isoprenoid. Structural homologues of the latter are so far only reported from a methanogenic archaeum and a Pleistocene sulfur deposit. Compound‐specific analyses of the stable isotope ratios revealed δ 13 C values for the majority of bacterial and archaeal lipid components of about 0‰ (vs. VPDB), indicative for chemolithoautotrophically fixed carbon which is, for distinct pathways, accompanied by only negligible fractionations. However, the presence of methanogenic Archaea is indicated by 13 C‐depleted isoprenoidal lipids (δ 13 C ~ –50‰) characteristic for certain CO 2 ‐reducing methanogens synthesizing lipids via acetyl CoA.