Abundance and distribution of fatty acids in hydrothermal vent sediments of the western Pacific Ocean Toshiro Yamanaka a, *, Susumu Sakata b a Department of Evolution of Earth Environments, Graduate School of Social and Cultural Studies, Kyushu University, Ropponmatsu, Fukuoka 810-8560, Japan b National Institute of Advanced Industrial Science and Technology, Site C-7, Higashi 1-1-1, Tsukuba, Ibaraki 305-8567, Japan Received 27 February 2003; accepted 1 January 2004 (returned to author for revision 23 July 2003) Abstract Sediments obtained from three active seafloor hydrothermal areas in the western Pacific Ocean were measured for the abundances and distributions of total fatty acids (TFAs). Approximately 50 fatty acids were identified, with the chain-length ranging from C 9 to C 29 . The total concentrations of TFAs ( P TFA) show a wide range from 13.2 to 184 mg/g dry sediment. The values of P TFA, over 100 mg/g dry sediment, are significantly higher than those reported for non-hydrothermal seafloor sediments. Furthermore, the observed compositions of TFAs are rich in bacterial bio- markers especially monounsaturated fatty acids, which is common to sediments and symbiotic animal tissues from other sites associated with hydrothermal activities. High ratios of P TFA to total organic carbon content (TOC) rela- tive to the non-hydrothermal seafloor sediment may also reflect a large contribution of organic matter produced at the vents. Due to the limited sample availability from these environments, the TFA compositions were not enough to evaluate relatedness between the vent sediment and vent animal community, while the wide diversity of TFAs suggests a large variation in source organisms in these hydrothermal environments. This study confirms the high contribution of bacteria and other vent organisms to organic matter in the sediments. # 2004 Elsevier Ltd. All rights reserved. 1. Introduction Chemosynthetic-based dense animal communities have been frequently observed around active hydro- thermal vents on the deep seafloor. These animals are believed to feed on bacterial primary production. The dense vent animal and bacterial communities can be a dominant source of sedimentary organic matter around the vents. Some of the organic compounds deposited around the vents could be used as biomarkers to understand hydrothermal vent ecology and physiology. Fatty acids are the major constituents of lipids in living organisms. The myriad structures of fatty acids biosynthesized by organisms, i.e. ‘‘biomarkers’’ (e.g., Bobbie and White, 1980; van Vleet and Quinn, 1979), make them useful tracers of their sources and alteration in particulate matter and sediments (Lee and Wakeham, 1988; Wakeham and Lee, 1993). Analysis of fatty acid biomarkers in deep-sea hydro- thermal environments has been carried out to compare endosymbiotic bacteria and their host species (Conway and Capuzzo, 1991; Ben-Mlih et al., 1992; Fullarton et al., 1995a, b; Pranal et al., 1997). In general, the com- position of fatty acids in common marine invertebrates is characterized by the predominance of two poly- unsaturated fatty acids: 20:5n-3 and 22:6n-3 (Farrington et al., 1973; Sargent, 1976; Joseph, 1982). This pattern reflects the fact that these organisms utilize organic material produced by phytoplankton, the primary 0146-6380/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.orggeochem.2004.01.002 Organic Geochemistry 35 (2004) 573–582 www.elsevier.com/locate/orggeochem * Corresponding author. Tel.: +81-92-726-4640; fax: +81- 92-726-4843. E-mail address: tyama@rc.kyushu-u.ac.jp (T. Yamanaka).