Studies on diagenetic change of chemical and isotopic compositions of marine organic matters during sedimentation.

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Sedimentary organic matter and suspended organic particles were collected from the East China Sea, Japan Sea and Hidaka trough, and were analyzed for biomarkers such as stable carbon and nitrogen isotopes, lignin phenols and hydrocarbons. The ^<13>C and ^<15>N of suspended matter changed from -20 to -28*, and 4 to 10*, respectively during settling of particles from surface to deep layr, meaning that degradation of partculate organics in the deep layr might follow simultaneous isotopic fractionation due to preferencial decomposition of organic compounds or isotopic discrimination. In spite of such isotopic change along the water depth, it is emphasized that the particulate matter in themixing layr would play an important role to control isotopic composition of settling particles and surface sediment. We found that there is an isotopic shift among suspended matter, settling particle and surface sediment for both carbon and nitrogen. Our results showed that lignin phenol is basically useful proxy to evaluate cotribution of terrestrial organic matter into the marine sedimentary organic matter. However, it was concluded that lignin lambda which has been defined by Hedges and Mann (1979) would be infuluenced by local factors such as marine productivity so that the relationship between lambda and 8^<13>C (TOC) should be defined for each locations.