Geochemistry of hydroxy acids in sediments—II. Estuarine and coastal marine environments

Abstract

Homologous series of α/β, (ω-1) and ω-hydroxy fatty acids (FAOHs) were analyzed in relation to their geochemical implication in estuarine and coastal marine environments. Mineral digestion with hydrofluoric/hydrochloric acid followed by alkaline saponification was used for determination of both “acid-labile” and saponifiable FAOHs in modern sediments. Sediment samples examined in the present work were collected from the shallow Tokyo Bay and deep Sagami Bay areas in Japan. A short sediment core, major river mouth sediments and suspended particles in the region were also examined. The most remarkable variation observed was the iso/anteiso abundance ratios of branced C 15 and C 17 β(α)-FAOH, which were high in the river mouth sediments, suspended particles and surface layers of the core sediment. The ratios decreased with increasing burial depth and with the distance from the river mouths or from the shore line. This fact suggested that the ratios might indicate the extent of short term early diagenetic alteration of bacteria-derived organic matter. Another point inferred was the abundances of C 22–C 26 α(β)-FAOH and C 16–C 28 ω-FAOH, both of which were elevated considerably in the river mouth sediments. The abundance of these long-chain α(β) and ω-FAOH was thought to indicate eventually the deposition and/or active microbial reworking of the terrigenous higher plant debris at the freshwater/seawater interface.