Study on transport of terrestrial organic matter into marginal sea inferred from biomarker and stable isotope analysis of sedimentary organic matter.

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The purpose of this project is to reveal historical changes of an interrelation between marine biological production and terrestrial organic matter flux in the North Pacific ocean and its adjacent seas.Sediment core samples were collected from various basins such as Shatsky rise in the North Pacific, Lake Abashiri, and the estuary of Changjiang river etc. Geochemical proxies in sedimentary organic matter, such as carbon and nitrogen stable isotopes, n-alkane, alkenone and sterol were analyzed to reconstruct the temporal change of marine biological productivity and atmospheric precipitation of terrestrial biomarkers. We estimated the historical variation of sedimentary flux of marine planktonic components using alkenone as a planktonic molecular markers. The result showed ten times greater accumulation rate of terrestrial organic matter in the last glacial period, suggesting that aeolian dust flux might be increased in the ice age. We studied also a boring core sample from Lake Abashiri that located in east Hokkaido, and found temporal change of sedimentary organic matter in the last 10 k years, indicating that a unique excursion of nitrogen isotope ratio in sedimentary organic matter. The result indicates that δ^<15>N may be useful tool to figure out the climatic change of coastal environment in last 20 k years. The isotopic results of sediment samples from the sourth of Thailand coast indicated that organic carbon and nitrogen isotopic composition have already recorded evidence of recent anthropological activities, urbanization and eutrophication in watershed. A boring core from Changjian river mouth represented that ^<15>N might be enriched in recent soil perhaps due to nitrogen accumulation in the growth of human population. This work successfully indicated that sedimentary organic matters are useful to study temporal change of marine and lacustrine environment since the last glacial period.