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

日本海沟和伊豆-小笠原海沟是深7000 m以上的V型沟，是沉积物俯冲的重要地带，因此，研究海沟环境中的地球化学过程具有重要意义。与孤立的盆地类似，海沟内的海洋环境被认为不同于典型的洋底。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，而且基本上仍然“未受影响”。我们从日本和伊豆小笠原海沟的最深处收集了海水、沉积物和颗粒物样品，进行了各种分析。为了进行对比，我们还在印度洋包括苏禄海、南海和安达曼海进行了地球化学研究。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。1）首次获得了日本海沟和伊豆-小笠原海沟水体中天然和人造放射性核素及部分重金属的垂直分布数据，并在《海洋学报》上发表论文，2）我们在地球和行星科学快报上发表了日本海沟沉积物收集器收集的颗粒物中稀土元素的结果及其含义，3）我们继续使用ICP质谱法研究溶解的稀土元素，并在Geochimica et Cosmochimica Acta的两篇论文中发表了结果及其含义，（4）获得了表层海水Nd同位素数据，这些数据可以用不同的来源、水循环来解释。研究结果将于短期内公布，我们希望这些结果将在不久的将来激发进一步有系统和全面的研究。

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.