ENRICHMENT IN SATURATED COMPOUNDS OF BLACK-SEA INTERFACIAL SEDIMENT

THE sediment/water interface of the ocean should consist of organic compounds produced both in the overlying water column and during early diagenesis 1-5. We have found that the uppermost approximately 1 mm of sediment samples obtained from the Black Sea are enriched in saturated sterols and fatty acids relative to both suspended particles and underlying sediments. We speculate that either this 'floc' layer contains a microbial community capable of yielding a distribution of compounds that is high in saturated species, or the floc accumulates low-density, fine material enriched in saturated components produced in the water column 6. Saturated components would thus be formed or concentrated very early during sedimentation and diagenesis. This has important implications for hydrogenation rates in geological environments, and may cast light on the way in which biological materials, rich in unsaturated compounds, become converted into sediments, petroleum and source rocks that contain predominantly saturated compounds.