| 研究実績の概要 |
In this research, I studied the organic matter cycling in marine sediments based on carbon isotope ratios of amino acids. In the first year, I developed a new analytical method for the determination of carbon and nitrogen isotopic compositions of amino acids in environmental samples. Using the new method, high-accuracy analysis of amino acids in marine sediment samples can be achieved. Then, I determined carbon isotopic compositions of amino acids in several surface and sub-surface sediment samples taken from the Japan Sea and off-Boso Peninsula. Results show that carbon isotopic composition patterns of amino acids in sediment samples are very similar, regardless of their different deposition histories and environmental conditions. It shows that organic matter in these sediments have similar sources. On the other hand, a baseline shift of carbon isotopic composition patterns of amino acids indicates that syntheses of organic matter using the bottom dissolved inorganic carbon happened. It demonstrates the contribution of organic matter production in the deep sea. Besides the isotope analysis of individual amino acids, I have also developed a new method for the isotope analysis of individual L- and D-amino acids. In the future, this new method can be applied to determine the isotope ratios of D-amino acids in marine sediments, which can be used to study the microbial sources and transformations of organic matter in marine sediments. Overall, this research expanded our understanding of organic matter cycling in the deep ocean.
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