CHARACTERISTICS OF DEEP CURRENTS ALONG TRENCHES IN THE NORTHWEST PACIFIC

In the deep sea area of the Japan Trench, located about 150 km east fr om northern Honshu, one observes southward flow on the landward slope and the northward flow on the oceanward slope. In 1994 and 1995, moori ngs were deployed on the Japan Trench landward slope around 40 degrees N. One mooring was deployed for 275 days at about 5800 m, and another mooring was deployed for 20 days at 4200 m depth. Results showed the following: (1) A deep western boundary current flows south-southwest o n the landward slope of the Japan Trench with mean speed of 3-7 cm/sec and maximum speed of 15-20 cm/s. (2). Current changes depend mainly o n the M2 tide. (3) Previous measurements, as well as inferences from o bserved benthic fauna, imply oppositely directed flow along the oceanw ard slope of the Trench, forming a trench countercurrent.