Program

Water exchange between the open ocean and the shelf sea is important for the environment of shelf regions. Combining satellite altimetry and in situ hydrographic measurement, we estimated the cross-shelf transport (CST) and its spatial and temporal variations across 200 m isobath in the East China Sea (ECS) from 1993 to 2014. The temporal and spatial variations of the CST and the associated mechanisms were explored through the use of the sectionally-integrated CST, the vertically-integrated CSTs, and the vertical profile of geostrophic current. The vertically-integrated CST can be dynamically divided into three parts: surface Ekman transport, geostrophic transport, and bottom Ekman transport. The results show that the 22-year-mean, sectionally-integrated CST to be 1.7±2.0 Sv (positive in the on-shelf direction), comprised of bottom and surface Ekman transports of 2.7±1.0 Sv and 0.6±0.6 Sv, respectively, that are partially offset by a geostrophic transport of -1.5±1.7 Sv. The sectionally-integrated CST shows significantly high power at roughly annual period from 1999-2001, with lower power at intra-annual period. The time-averaged, vertically-integrated CST to the northeast of Taiwan is the main source of sectionally-integrated CST. The vertically-integrated CST also shows significant variations in the 6–15 month period band to the northeast of Taiwan as well. The temporal variations of the sectionally-integrated and vertically-integrated CST are both controlled primarily by geostrophic transport and modulated by bottom Ekman transport. In the upper 50 m, the geostrophic current to the northeast of Taiwan exhibits large mean and significant variability. The empirical orthogonal function analysis of vertical structure of geostrophic current shows two significant modes with strong annual signal. The first mode is associated with the migration of Kuroshio axis near Taiwan, while the second mode is associated with the variation of the meander of the Kuroshio to the northeast of Taiwan. Due to a limitation in available data, the inter-annual baroclinic variations on the CST need to be considered in the further. Also the usefulness of altimetry data in the continental shelf area should be considered with care (especially in the shelf area). The paper focuses on abundant observational data, which extends the knowledge of those previous studies by providing a more comprehensive overview regarding the governing processes and the related various temporal and spatial scales. In the future, the CST will likely be used for the material transport in the ECS to provide a broader view for the process of CST and their effect on the environment.