相模湾初島沖｢深海底総合観測ステーション｣の設置と長期観測

Abstract

1993年9月、相模湾初島南東沖6km,水深1177mのシロウリガイ群集域の海底に、｢深海底総合観測ステーション｣を設置し、リアルタイムの長期観測を開始した。本ステーションには、カラービデオカメラ(2台),3成分速度型地震計、ハイドロフォン、地中温度計(2台)、CTD、電磁流速計などが搭載されている。ステーション水中部と初島の陸上局は、全長約8kmの鉄線2重鎧装光電気複合ケーブルで接続され、観測データと電力の伝送が行われている。これまでの観測の結果、貝の個体数にはかなりの変動があること、シロウリガイ群集域内では、海底下30cmの地中温度が群集域外に比べて約0.6度C,水温よりも約2.5度Cそれぞれ高いこと、海底では、西向きの湧昇流が卓越していることなどが分かった。

In September 1993, a real time deep sea floor observatory was deployed within the Calyptogena clam colony off Hatsushima Island in Sagami Bay at a depth of 1,177 m. The aim of the long term observation off Hatsushima Island is to know the relations among biological, seismic and volcanic activities in the plate boundary between Philippine and North American plates. The observatory is equipped with two color video cameras, a seismometer, a hydrophone, two heat flow sensors, a CTD and an electromagnetic current meter. The data and power to and from the land station at Hatsushima Island are sent in real time through eight km long electro-optical cable. Also, the data including still video images are sent to Japan Marine Science and Technology Center (JAMSTEC) in Yokosuka through the telephone link. Temperature at 30 cm beneath the sea floor within the clam colony is approximately 0.6 C and 2.5 C higher than those outside the colony and the ambient sea water, which is approximately three C, respectively. This means that the clams live selectively in the warmer sediments. The number of the clams which is seen from the observatory varies significantly with time. It is not yet known what would be the controlling factor of this change.