Analysis Of Water Masses On The Northern Slope Of The South Chian Sea

The northern slope region of the South China Sea(SCS)is a hot spot where high primary productivity supports spawning and nursing of commercially and ecologically important fish species.To understand the mechanisms supporting the high primary production,the mesopelagic fish distributions and the vertical export of particular organic carbon in this region,two cruises were conducted between October 13 and 27 2014 and between June 10 and July 2 2015,repectively.Hydrographic and shipboard ADCP data were collected during the cruises.The aim of this thesis is to analyze the composition of water masses and the current distribution over the northern slope of the SCS,as well as the physical mechanism underlying the highly productive slope ecosystem.The geostrophic currents were derived from the Acoustic Doppler Current Profiler measurements,satellite altimetry and CTD data for analyzing the water mass distributions and their transport.The results revealed that during the summer surface in the northern slope of the SCS were primarily composed of waters originated from the South China Sea Water(SCSW),the Kuroshio Water(KW)and the shelf water(SHW).A strong cross-slope current carried the SHW into and through the slope area in the upper 25 m;mesoscale eddies were also found in the northern part of the SCS carrying waters originating from the intruding KW into the slope region.In the southwesterly monsoon,the contribution of the KW in the surface layer was found less than that of the subsurface layer,where the contribution of KW can reach ~50%,and high contribution basically occurred accompany by the mesoscale eddies.In the fall,waters on the northern slope of SCS resulted mainly from mixing of the KW and the SCSW under weak offshore transport of the SHW.Water in the upper 300 m is almost equally contributed by the KW and the SCSW.In both seasons,the intermediate water was primarily made up of SCSW,while in the fall the maximum depth of the intermediate water was slightly shallower than that of the summer.