Org. Geochem. Vol. 18, No. 6, pp. 923-932, 1992 0146-6380/92 $5.00+ 0.00 Printed in Great Britain.All rights reserved Copyright© 1992Pergamon Press Ltd Geochemistry of hydroxy acids in sediments--lI. Estuarine and coastal marine environments KAZUO FUKUSHIMA, 1 MINORU UZAKI 2 and SUSOMUSAKATA 3 t Department of Geology, Faculty of Science, Shinshu University, Asahi 3-1-1, Matsumoto 390, 2Mitsubishi Kasei Institute of Life Sciences, Minamiooya 11, Machida, Tokyo 194 and 3Geological Survey of Japan, Higashi 1-1-3, Tsukuba, Ibaragi 305, Japan (Received 14 May 1991; accepted in revised form 2 June 1992) Abstract--Homologous series of otlfl, (co-l) and o~-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 branched Cts and Ci7 fl(~t)-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 C22-C26 ~(fl)-FAOH and C~6-C2s co-FAOH, both of which were elevated considerably in the river mouth sediments. The abundance of these long-chain ~t(fl)and o~-FAOH was thought to indicate eventually the deposition and/or active microbial reworking of the terrigenous higher plant debris at the fresh- water/seawater interface. Key words--hydroxy acids, coastal marine environment, source indicators, short-term geochronometer INTRODUCTION Hydroxy fatty acids (FAOHs), which contain both carboxyl and hydroxyl groups in a long-chain molecule are disseminated ubiquitously in sediments (Eglinton et al., 1968, 1974; Boon et al., 1977b; Cardoso et al., 1977; Perry et al., 1979; Cardoso and Eglinton, 1983; Goossens et aL, 1986; Cranwell et al., 1987; Kawamura et al., 1987; Fukushima et aL, 1992b). Their sources were tentatively ascribed to bacterial membrane lipids for short-chain (<CIs) fl-FAOH, to higher plant cutin for co and poly- hydroxy FAOHs, and to microbial and/or chemical oxidation for long-chain ( > C20) ct/fl, (co- 1) and some part of co-FAOH (Boon et al., 1977b; Cranwell, 1981). Because of the wide occurrence and pre- sumably the definite origin. FAOHs have a potential to be used generally as source indicators of sedimen- tary organic matter. Nevertheless, only limited descriptions are avail- able on the fates of FAOHs in the environment. Kollatukudy and Purdy (1973) reported that some polyhydroxy acids derived from higher plant cutinous polyesters could endure microbial degradation in the waste water activated sludge treatment procedures. However, Cardoso and Eglinton (1983) argued that they could detect only trace amounts of FAOHs in the lithified sediments (Green River and Messel shales) and concluded that FAOHs should not be conservative over the geological period of diagenesis. Meanwhile, recent studies by using "harsher sa- ponification" at raised temperature (Kawamura and Ishiwatari, 1982) and "acid hydrolysis" (Goossens et al., 1986; Mendoza et al., 1987; Klok et al., 1988; Fukushima et aL, 1992b) revealed that fl-FAOH are more abundant in sediments than had been estimated by conventional alkaline saponification which had been conventionally used for "bound" lipid analyses. These studies indicate that the analytical data, especially on fl-FAOH, reported so far in sediments might be considerably underestimated and should be re-examined. Under these circumstances, this work was con- ducted aiming to present the early diagenesis of FAOHs and the relationships between sedimentary FAOHs and depositional environments of modern sediments, by using mineral digestion with hydro- fluoric acid/hydrochloric acid coupled with sub- sequent alkaline saponification. In our previous study (Fukushima et aL, 1992b) using the same analytical procedure, we reported the data on FAOHs in some lacustrine sediments. Efficiency of the HF/HCI diges- tion was practically the same as the HCl hydrolysis proposed by Goossens et al. (1984, 1986) and Mendoza et aL (1987) for dissolution of the "acid- labile" FAOHs in sediments. The composition of 923