资源环境科技发展态势分析平台

Nearly half of the global seafloor is overlain by sediment oxygenated to the basement. Yet, despite the availability of oxygen to fuel aerobic respiration, organic carbon persists over million-year timescales. Identifying the controls on organic carbon preservation requires an improved understanding of the composition and distribution of organic carbon within deep oligotro-phic marine sediments. Here we show that organic carbon in sediment from the oligotrophic North Atlantic and South Pacific is low (<0.1%), yet stable to depths of 25 m and ages of 24 million years. This organic carbon is not bound in biomass and has a low carbon/nitrogen ratio. X-ray imaging and spectroscopic analyses reveal that the chemical composition of this old, deep organic carbon is dominated (40-60%) by amide and carboxylic carbon with a proteinaceous nature. We posit that organic carbon persists in oxic oligotrophic sediment through a combination of protective processes that involve adsorption to mineral surfaces and physical inaccessibility to the heterotrophic community. We estimate that up to 1.6 x 10(22) g of organic carbon are sequestered on million-year timescales in oxic pelagic sediment, which exceeds current estimates of the total global sediment organic carbon and constitutes an important, previously overlooked carbon reservoir.