Mesoscale-eddy-induced variability of flow through the Kerama Gap between the East China Sea and the western North Pacific

The Kerama Gap (KG) is the deepest channel (sill depth 1050 m) along the Ryukyu Island chain connecting the East China Sea (ECS) to the western North Pacific. The observed mean flow through the KG from June 2009 to June 2011 is 2.0±0.7 Sv into the ECS. A 7-day-interval 20-year (October 1992 to September 2012) time series of the KG volume transport is obtained based on a good correlation between satellite altimeter-measured sea-level difference across the KG and 2-year-long in situ-measured volume transport. The 20-year mean volume transport is 1.5±0.2 Sv with standard deviation 2.5 Sv. Comparison of the KG volume transport time series with satellite-measured sea-level anomaly maps reveals that KG transport fluctuations at 40–200-day periods are strongly affected by mesoscale eddies near the KG. Consequently, KG transport’s interannual to decadal amplitude changes are associated with interannual to decadal eddy field changes to the east of the Ryukyu Island chain in the western North Pacific. The mesoscale-eddy-induced variability results in time-varying correlations between the KG throughflow and the Ryukyu Current volume transport south of Okinawa. Additionally, relationship of the KG throughflow with the Kuroshio east of Taiwan and the Kuroshio in the ECS is discussed based on the changes in eddy field.