Study on the Subduction of Low Salinity Water into the Intermediate Layer of the Kuroshio in the East China Sea

点击翻译按钮获取中文摘要

Vertical profiles of temperature, salinity and current velocity were obtained along a cross-stream section around the shelf break in the East China Sea in May 1999, October 1999, May 2000 and October 2000. Temporal variations of temperature and velocity were also obtained with mooring arrays.During the observation in May 1999, low salinity water tended to extend offshore and subduct into the intermediate layer of the Kuroshio. However, origin of the subducted low salinity water was not clear. In October 1999, low salinity water in the shelf area appears to be entrained into the eddy around the Kuroshio front, while subduction of low salinity water cannot be seen clearly. In May 2000, two research vessels were deployed simultaneously and temperature and salinity maps were obtained repeatedly along two sections across the Kuroshio. Along the section downstream of the Kuroshio, temperature front was moved onshore accompanied with distinct subduction of low salinity water during the first half of the observation period. On the other hand, significant cross-shelf migration of the front and distinct subduction of low salinity water cannot be seen along the section upstream of the Kuroshio. This fact suggests that the spatial variability of subduction should be very large. In October 2000, observations were carried out over rather wide area in the southern East China Sea, and some signals of low salinity water subduction were found along a few sections.Short time scale internal waves were observed with mooring current meters. Particularly, distinct development of internal waves were found during the observation in May 1999 and it seems to make the stratification change locally. Vertically detailed structure of current velocity was obtained in the observation of May 2000. Cross-shelf current with a small vertical scale was found accompanied with a change of stratification, while offshore current corresponding to low salinity water subduction was not detected.