The study of Geochemical Processes in the trench Environment using trace constituent and isotopic techniques.

本研究的目的是了解超深海沟环境下的地球化学过程，如日本海沟和伊豆-小笠原海沟。海沟具有超过7000 m深的V形谷的地形特征，是沉积物质俯冲的重要带。与孤立的盆地类似，海沟内的海洋环境被认为与典型的海底环境不同。然而，迄今为止对海沟环境的海洋学和地球化学进行的系统调查很少，而且大部分仍然“未触及”。我们通过从日本和伊豆-小笠原海沟的最深处收集海水、沉积物和颗粒物样本进行了调查，并进行了各种分析。为了比较，我们还在印度洋包括苏禄海、南海和安达曼海开展了地球化学研究。今年，我们进一步将研究范围扩大到日本海沟、鄂霍次克海和日本海，并发表了最终报告。结果总结如下；(1)首次获得了日本海沟和伊津小笠原海沟水柱中天然和人造放射性核素及部分重金属的垂直分布数据；2)在《地球与行星科学快报》上发表了日本海沟沉积物捕集器收集的颗粒物中稀土元素的研究结果及其意义；3)继续利用ICP质谱法研究溶解稀土元素和in，并在《地球化学与宇宙化学学报》上发表了两篇论文；4)获得了表层海水中Nd同位素的数据，可用于不同来源解释，水循环。调查结果将于近期公布。我们希望这些结果能在不久的将来促进进一步系统和全面的研究。

The purpose of this study is to understand geochemical processes in super-deep trench environment, such as the Japan and Izu-Ogasawara trenches.Trenches exhibit characteristic topographic features of V shaped valley exceeding 7000 m depth, and are important zone for subduction of sedimentary materials. Similarly to isolated basins, the oceanographic environment inside trenches is considered to be different from that of typical ocean floor. However, systematic investigations of oceanography and geochemistry of the trench environment are few to date and largely remains "untouched". We have investigated by collecting samples of seawater, sediments and particulate matter from the deepest parts of the Japan and Izu-Ogasawara trenches for various analysis. For comparison, we have also carried out geochemical study in the Indian Ocean including the Sulu Sea, South China Sea and Andaman Sea. This year, we have further extended our research to the Japan Trench, Sea of Okhotsk and the Japan Sea and published a final report.Summary of the outcomes are ;1) We obtained the data on the vertical distributions of natural and man-made radionuclides and some heavy metals throughout the water column of the Japan and Izu-Ogasawara trenches for the first time, and published a paper in Oceanologica Acta,2) We published the results and their implications of rare earth elements in particulate matter collected by sediment trap in the Japan Trench in Earth and Planetary Science Letters,3) We continued to work on dissolved rare earth elements and In using ICP mass spectrometry and published the results and their implications in two papers in Geochimica et Cosmochimica Acta,4) We have obtained the data on Nd isotopes in surface seawater which can be interpreted by different sources, water circulation. The results will be published shortly.We hope that these results will stimulate further systematic and comprehensive study in near future.