COMPOUND-SPECIFIC RADIOCARBON AGES FROM SURFACE SEDIMENTS IN THE WESTERN NORTH PACIFIC

Compound-specific radiocarbon analysis (CSRA) was conducted on fatty acids, hydrocarbon, sterols and long-chain ketones (alkenones) in order to investigate radiocarbon age diversity of individual compounds preserved in the same horizon of sediment core. The three sediment core samples were recovered from southern Okhotsk Sea, a marginal sea of the western North Pacific. We have found a large age variation among individual compounds of assuredly different origins from both autochthonous (marine) and allochthonous (terrestrial) products. This study will aim to realize organic compound-based chronology for marine sediment, particularly in the westeren North Pacific where is difficult to obtain sufficient amount of planktonic foraminifera for AMS analsysis due to dissolution of calcium carbonate in relation to CCD. The dating approach of CSRA had analytical problems in relation to difficulties of recovering target compounds with higher purities and realistic amount from sediment samples, and extremely small amount AMS radiocarbon analysis (20~100ugC). However, to date we have achieved successfully these problems as the result of technical modifications of a preparative capillary gas chromatography (PCGC) system and individual organic carbon graphitization of compounds for AMS analysis.

Our results of CSRA using the marine sediments would provide the possibility as an chronology tool for estimating the real age of sedimentary seaquence using organic matter for paleoceanographic study.