Effect of typhoon Maemi on the hydrographic regime and sediment resuspension along the cross-shelf transect PN in the East China Sea

The cross-shelf PN transect in the East China Sea (ECS) extends from the Yangtze River estuary southeastward to the eastern shelf edge. The PN transect was surveyed twice (one right after typhoon Maemi which passed ECS and another in none-typhoon condition) in September, 2003. Hydrographic and suspended sediment data collected at 10 stations along the transect were used for this study. The thermocline as well as the pyclocline in the water column remained after Maemi and strengthened on the western transect. The water structure was separated by the pyclocline into upper and lower layers. The upper layer deepened down with the depth. The barrier layer thicknesses increased on the western transect. The temperature and salinity in the lower layer did not change much, except more cooler and saline water of Kuroshio origin intruded into its eastern part. The change of water structure was resulted from the strengthened mixing of waters of different origins during the typhoon process. Suspended sediment concentration (SSC) presented as water turbidity significantly increased in the lower layer after Maemi while the turbidity in the upper layer remained low as it was in none-typhoon condition. The bottom sediment at 50-90 m was resuspended to 20 m up into the lower layer at the all depths with increased turbidities up to ninefold on the bottom area after Maemi. A turbid water layer with SSC～4.7 mg/l covered 20 m water column above the seabed on the most shelf area. Three high turbid water bodies were found in corresponding to the locations of finer surface sediment types. The sediment resuspension intensity was decreasing with water depth. The height of sediment resuspension in the water column was limited by the pycnocline.