Sources, Removal and Transformation of Carbon in Marine Sediments

As the main source and sink of global carbon, marine sediments play an important role in the marine carbon cycle. This paper reviews the progress of recent years research on the marine carbon cycling in marine sediments. The main forms of carbon in marine sediments are organic carbon and inorganic carbon, which come mainly from river transport, marine autogenesis and atmosphere settlement. The ratios of C/N and δ13C could be used to determine the carbon origin. The dissolved carbon in seawater could be converted to particulate carbon through biological process, such as photosynthesis, and reef building process. Ninety percent of particulate carbon participating in the carbon recycling process are released in the settling process; less than 10% are deposited on the bottom sediments, still less are imbedded. Early diagenesis occurs after carbon is transported to sediments from seawater. Organic carbon is oxidized by oxygen, nitrate, oxides of Fe and Mn, sulfate, then finally become CO2 and other products. CO2 could cause change of the pH value in sediments, and then destroy the balance of carbonate, and result in dissolution or precipitation of carbonate. Carbon may be transferred into seawater and take part in the recycling process, wherein biological processes play an important role. The complex biogeochemistry processes in the compound system of sediment and seawater control the carbon cycle in marine sediments.