Observation of deep sea current and change of bottom shapes in the Suruga Trough

The Suruga Trough, located 150 km away to the south-east of Tokyo, Japan, is known to have turbidity and strong deep water currents. In 1989 and 1990, the authors measured the current from the bottom layer to the middle layer using moored current meters in order to understand the characteristics of the bottom current. Visual observation has been also done at the bottom using a 8 mm-video camera. The following results were obtained from the observations: i) There are steady changes of current with about 13 days cycle depending on tide. At the spring tide, current of SSW direction with a period of a day was found; maximum velocity is about 60 cm/sec. At the neap tide, the current is below 20 cm/sec with a period of a half day. 2) A turbidity current in the deep sea area caused by a typhoon was observed at the bottom layer in August 1990. The maximum velocity was over 70 m/sec. 3) Sediment transport processes associated with the bottom current was observed by the video images