Archaeal and bacterial glycerol dialkyl glycerol tetraethers in sediments from the Eastern Lau Spreading Center, South Pacific Ocean

The compositions of glycerol dialkyl glycerol tetraethers (GDGTs) in surface sediments and sediment cores from the Eastern Lau Spreading Center (ELSC), South Pacific Ocean, were determined. Isoprenoid GDGTs (isoGDGTs) and branched GDGTs (brGDGTs) are present in all the samples, with archaea and bacteria, respectively, as the sources of these membrane lipids. Greater concentrations of isoGDGTs (0.08–38.0 ng/g dry weight (dw)) than brGDGTs (0.05–27.4 ng/g dw) indicate that archaea made larger contributions to the GDGT pool in the ELSC sediments than bacteria. The relative abundance of brGDGTs and BIT index (the branched vs. isoprenoid tetraether) values are higher in samples taken from the seafloor in the vicinity of or close to hydrothermal vents than in samples taken distant from hydrothermal activity, suggesting that brGDGTs are likely produced in the ELSC hydrothermal vents. Temperature estimates based on TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms) appear to reflect local surface water temperatures despite potential in situ hydrothermal input of GDGTs to the ELSC sediments.