Grain size effect on bound lipids in sediments off northeastern Taiwan

Two box-core sediments off the northeastern Taiwan coast have been collected and examined for the relationship between bound lipids and grain size in the mud fraction (<63 μm). No grain size effect was found for the concentrations of σn-alkanes, σn-fatty acids and σn-alcohols. The ratios of branched-chain to normal fatty acids increased progressively with decreasing particle size and correlated highly with BOC (bound organic carbon), suggesting an increasing bacterial input. Moreover, we observed an increase in the ratios of monounsaturated to saturated fatty acids with decreasing grain size, pointing to an increasing microbial contribution. Particularly interesting is phytol, which demonstrated a remarkable grain size effect; the phytol to BOC ratio increased sharply with decreasing particle size. Major sterols normalized to BOC increased progressively with a decrease in grain size and correlated highly with BOC. The results indicate that a plankton contribution to phytol and sterols increased as particle size decreased. The grain size effect is stronger for phytol than for sterols and branched-chain fatty acids in the sediments.