Hadal trenches are experimental fields for geological and biological systems

Hadal trench shows integration of landscapes of plate tectonics, geological evolutions of trenches, surface and deep-water circulations, biogeochemical cycles and others. On these environmental components, we can understand historical backgrounds of benthic organisms. I have long been worked on the deep sea benthic foraminiferal communities at the Western Pacific. We analyzed localities of the western Pacific deep-sea, from bathyal to abyssal depths, in particular to hadal depths. Hadal foraminiferal community consists of monothalamous soft-shelled forms, agglutinated forms, porcelaneous forms, hyaline forms and large xenophyophores. In contrast to the bathyal to abyssal depths, the hadal depths are much challenging. Because, a lot of accidental events take place naturally, such as collisions, subductions, separations or fusion of trenches. Trenches are fascinating natural laboratories for thinking about evolution of benthic organisms in connection to trenches. Here, I try to discuss what kind of changes should take place when trench fuse respectively. Case studies will be given from the late Cenozoic marine strata of the Central Kwanto regions at the central Japan (Kitazato, 1997).