Variations in the content and composition of organic matter in sediments underlying active upwelling regimes: a study from ODP Legs 108, 112, and 117

Abstract

Abstract An overview is presented of organic geochemical studies on sediments underlying the active upwelling cells off Northwest Africa (ODP Leg 108; Site 658), off Peru (Leg 112; Sites 679, 681, 684, 686) and off Oman (Leg 117; Sites 723, 725, 728). The investigated sediments are all characterized by high organic carbon contents (0.5–9% C org ), being the sedimentary expression of an increased primary bioproductivity induced by upwelling currents of deep nutrient-rich waters. The organic matter is predominantly of marine origin with variable admixtures of a terrigenous component; the highest relative contribution is found at Site 658. The extractable lipids are composed of a wide variety of compounds, of which the most characteristic and abundant compounds were quantified. Long-chain unsaturated ketones usually dominate. Steroids, alkanediols and their corresponding keto-ols are also present in high concentrations, although strong variations in their abundances were noted. In addition, organic sulphur compounds are omnipresent and reveal strong variations in their distribution, but do not make a major contribution to the total amount of extractable lipids.