Study for mechanisms of responses of coastal marine ecosystem and biogeochemical cycle to environmental changes

本论文以面向外海的典型近海濑户内海的丰后海峡为研究对象，研究了海洋生态系统和海洋地球化学循环对环境变化的响应机制。初步揭示了生态系统对以下环境突变的响应机制：1.海洋次表层水侵入海岸底层称为“Sokoirishio”。Sokoirishio从外海向沿岸提供了大量的营养盐，并导致生态系统突变为以藻类为主的生产性生态系统。2012年夏季的特大暴雨为海洋提供了大量的淡水，低盐度、低密度的海水广泛覆盖了沿海地区的表层。这些水阻挡了海洋表层水对海岸表层的入侵，被称为“Kyucho”，可以清洁被污染的海岸水。久草的阻塞可能导致大规模的有害藻华。

I studied mechanisms of responses of marine ecosystem and biogeochemical cycle to environmental changes focusing on the Bungo Chanel in the Seto Inland Sea, where is a typical coastal region fronting to the open ocean. I found the mechanisms of the ecosystem responses to the following abrupt environmental changes;1. The intrusion of oceanic subsurface water to coastal bottom layer is called "Sokoirishio". Sokoirishio supplies much amount of nutrient from the open ocean to the coast, and causes the abrupt change of ecosystem to the productive ecosystem dominated by diatom.2. The super heavy rain in the summer of 2012 supplied huge amount of fresh water to the ocean, and the low salinity and low density water broadly covered the surface layer of coastal region. This water blocked the intrusion of oceanic surface water to coastal surface layer, which is called "Kyucho" and can clean the polluted coastal water. The blocking of Kyucho might be lead to the large scale harmful algae bloom.