Fatty Acid Composition of Sinking Particles in the Western North Pacific

Fatty acids were measured in sinking particles collected using a time-series sediment trap from the continental slope off Hokkaido, Japan from September 1988 to May 1989. The fatty acids were mainly composed of saturated ones. However, remarkable components of fatty acids were obtained in the sinking particles in September 1988 and April-May 1989. The sinking particles in September 1988 showed a high abundance of 9-octadecenoic acid (18:1 n-9), suggesting a contribution of zooplankton derived materials. On the other hand, the sinking particles in April-May 1989 had a large content of 7-hexadecenoic acid (16:1) and eicosapentaenoic acid (20:5), suggesting a sedimentation of diatom cells during a spring bloom. The low contents of long-chain fatty acids at the same periods indicated a relatively small contribution of terrestrial inputs to the mass fluxes, in comparison to other periods. High values of unsaturated fatty acids to saturated fatty acids ratios (UFA/SAFA ratios) were found in the sinking particles in deep water. During a spring bloom, the sinking particles of large mass flux can transport unsaturated fatty acids, which are one of the most labile compound classes, from surface to deep water. It suggested that sedimentation of intact cells of phytoplankton occurred in the coastal ocean during a spring bloom.