Subsurface current structures east of the Amami-Oshima Island based on LADCP observation

The current system east of the Ryukyu Islands has been called the Ryukyu Current System (RCS) to express its possibly different origins and features. In this paper, we presented a new feature on the vertical structure of the current system by using lowered acoustic Doppler current profiler (LADCP) data in early October 2005: a southwestward countercurrent was demonstrated to flow near the eastern slope of the Nansei-Shoto (Ryukyu Islands) Ridge in a layer deeper than the northeastward current core of the RCS. This supports the existence of the countercurrent suggested by Nagano et al. (2009).The maximum speed of the countercurrent was measured to be 25 cm s^-1 at a depth of approximately 600 m.