Off Hatsushima Island observatory in Sagami Bay: Multidisciplinary long term observation at cold seepage site with underwater mateable connectors for future use

摘要

On the seafloor at a depth of 1175m off Hatsushima Island in Sagami Bay, Central Japan, a cable-connected multi-disciplinary observatory was installed in 1993. Since then long term real time observation has been carried out, experiencing replacement for upgrades in 2000, recovery and re-deployment for repair in 2002. This site is known as one of the most significant cold seepage sites with large chemo-synthetic biological communities consisted mainly of Vesicomyid clams (Calyptogena). The upgraded second observatory is equipped with underwater mateable connectors (optical / electrical). The observatory revealed geophysical and biological events occurred on the seafloor, such as the mudflows and sedimentation generated by swarm earthquakes, spawning of clams triggered by water temperature change. However, several kinds of phenomena and technological problems yet to be identified nor solved still remain. As a next step, the observatory is planned to be utilized as a test bed, by using the underwater mateable connectors.