Observation of the abyssal current in the West Mariana Basin.

概要

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In order to investigate long-term variations of deep sea currents andtemperature in the western North Pacific, a direct current measurement was made at 12.5°N, 137°E from July 1985 to July 1986. The current meter was moored at adepth of about 4, 000m (bottom depth 4, 604 m) in the West Mariana Basin, very closeto the deep water passage to the North Pacific Basin. Throughout the observedperiod, the current flows southward with an average speed of 0.8 cm sec-1. Thereare significant variations of both currents and temperature within the period of 60days. For the shorter time scales, in addition to the tidal oscillations with oneday and half day periods, there is a notable spectral peak of the current with aclockwise rotation at a period of 2.2 days, which is slightly shorter than the localinertial period of 2.3 days.<BR>The observed southward current seems to indicate that the deep sea water inthe West Mariana Basin flows out through the sill which is deeper than 4, 000mand is located about 200 km southeast of the mooring point. A simple analysis ofthe linear plane wave indicates that the medium time-scale variation with a periodof 60 days is associated with the barotropic Rossby wave whose wavelength is 390 km and whose trough direction is 30° clockwise from the north.
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