Lipid biomarkers for heterotrophic alteration of suspended particulate organic matter in oxygenated and anoxic water columns of the ocean

The fatty acid, sterol and hydrocarbon composition of suspended particles from the central North Pacific VERTEX IV site and from the Black Sea were used to investigate the abundance of biomarkers produced by heterotrophic alteration of particulate organic matter (POM). At the oceanic VERTEX site, bacterial alteration of organic matter did not contribute significant amounts of diagnostic lipids to particles, whereas zooplankton did leave a marked imprint on particulate lipids. In contrast, in the anoxic zone of the Black Sea there were significant lipid indicators of bacterial decomposition of POM. Most of these were derived from anaerobic sulfate-reducing and phototrophic sulfur bacteria. A comparison of the two sites and their lipid distributions indicates that it may be difficult to use lipid biomarkers to assess the importance of bacterial decomposition of organic matter in the open ocean, as lipids from these bacteria are not readily distinguished from the more abundant planktonic lipids.