長崎県橘湾における浅海底熱水系

概要

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Distribution of hydrothermal activities and chemical composition of surrounding sediments were investigated for shallow submarine hydrothermal systems in Tachibana Bay, Nagasaki, Japan as a first step to elucidate its possible influences to the coastal ecosystem. Based on the observations of fumarolic gas emissions using quantitative echosounder, existence of hydrothermal activities was confirmed at 33- 34 m depth near the coast of Obama hot springs. These were many small (2-6 mm in diameter) holes on the surface of the bottom sediment, and the area of the fumarolic gas emissions had a horizontal scale of 6-63 m. Hot (78℃) and dark subsurface-sediment at the hydrothermal activity region showed unusual elemental composition characterized by higher contents of Al, S and As, and lower amounts of Ca, Cl and Br compared with that of the typical coastal sediment.