Water exchange and circulation structure near the Luzon Strait in early summer

Abstract

Using hydrographic data covering large areas of ocean for the period from June 21 to July 5 in 2009, we studied the circulation structure in the Luzon Strait area, examined the routes of water exchange between the South China Sea (SCS) and the Philippine Sea, and estimated the volume transport through Luzon Strait. We found that the Kuroshio axis follows a epsilon-shaped path slightly east of 121 degrees E in the upper layer. With an increase in depth, the Kuroshio axis became gradually farther from the island of Luzon. To study the water exchange between the Philippine Sea and the SCS, identification of inflows and outflows is necessary. We first identified which flows contributed to the water exchange through Luzon Strait, which differs from the approach taken in previous studies. We determined that the obvious water exchange is in the section of 121 degrees E. The westward inflow from the Philippine Sea into the SCS is 6.39 Sv in volume, and mainly in the 100-500 m layer at 19.5 degrees-20 degrees N (accounting for 4.40 Sv), while the outflow from the SCS into the Philippine Sea is concentrated in the upper 100 m at 19 degrees-20 degrees N and upper 400 m at 21 degrees-21.5 degrees N, and below 240 m at 19 degrees-19.5 degrees N accounting for 1.07, 3.02 and 3.43 Sv in volume transport, respectively.