Cross-shelf water exchange in the East China Sea as estimated by satellite altimetry and in situ hydrographic measurement

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 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 1.72.0 Sv (positive in the on-shelf direction), comprised of bottom and surface Ekman transports of 2.71.0 Sv and 0.60.6 Sv, respectively, that are partially offset by a geostrophic transport of -1.51.7 Sv. The sectionally integrated CST shows significantly high power at roughly annual period from 1999 to 2001, with lower power at intra-annual period. The 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.