Influence Of Different Water Masses On Composition And Distribution Of Suspended Particulate Matter(SPM) In Upper Water Of The Southern South China Sea In Spring

In April and May,2012, we collected the water samples of the southern SouthChina Sea and measured the volume concentration of the suspended particulatematter(SPM), Chlorophyll Concentration, turbidity, temperature, salinity withLISST-100(C) and SBE9/17plus CTD.4Typical areas,2sections and4stationsunder the influence of different water masses (including the shelf water in the northrim of the Sunda shelf, the mixed water in the west side on the Balabac Strait of thelocal seawater and the water from Sulu sea, the Nansha central surface water and themixed water from the coast of Indochina) have been selected to analyse thecomposition and the distribution characteristics of the SPM in different water mass.The results show that the SPM in the ocean are mainly composed of biogenic particles,the particle size of which are more than100μm. In addition, a small amount of aninorganic mineral debris, most of its particle size is less than10, a small amount oflarger debris have a larger diameter between10~30μm. The volume concentration(VC) in the surveyarea is low (mean2.96μl/l).Our research shows that, the composition and distribution characterastics of theSPM are mainly influenced by the following factors:(1) Material Source. The SPM inthe study area are composed of terrigenous inorganic particles and biogenic particles,the former are mainly of small diameter that less than32μm, while the latter aremainly of big diameter over100μm. Therefor, the material source has a directinfluence on the characteristic of grain size.(2) hydrologic condition. The affects ofhydrologic condition on the concentration, grain size and composition of the SPM arefrom two aspects: the restriction of temperature, salinity, illumination on thebiomass and the accumulation of the particles settling from the upper water near thespring layer.(3) The influence of terrain and upwelling. The current which is forcedby the winter monsoon that is not completely fade away in the spring form theupwelling by the terrain block on the edge of the Sunda Shelf. The nutriment broughtby the upwelling lead to the high biomass on the edge of the Sunda Shelf and causethe resuspension near the seabed.The SPM of the shelf water on the edge of the Sunda Shelf has the highestvolume concentration but the smallest median size which is due to the influence ofterrigenous matter. The concentration of the terrigenous inorganic particles of smalldiameter is the highest in the four water masses, for this reason, the median size of theSPM in the shelf water is the smallest. The upwelling influence the shelf water on theedge of the Sunda Shelf, it causes the high biomass in the water colum andresuspension near the sea bed. In addition, the salinity gradient here is relatively highand makes the flocculation and accumulation near the spring layer. The water on thewest side of111°E is influenced by the mixed water mass of Mekong River and thesea water which is transported by the alongshore current. The mixed water mass isrich in terrigenous inorganic particles. The water on the west side of the Balabac straitis controlled by the mixed water of the water from the Sulu Sea and the local seawater. This mixed water mass has the highest salinity among all the water mass in the study area. The high biomass of diatom is due to the rich nutrients brought by thewater from the Sulu Sea. Hence, the SPM in the euphotic layer of this water mass aremainly composed of the phytoplankton. The mid Spratly Islands are under theinfluence of the Nansha Islands central water, the SPM of this water mass are almostbiogenetic matter, little terrigenous matter in the SPM. But, on account of lacking ofaccumulation of nutrients, biomass in this area is small. Therefor, the concentration ofthe SPM in mid Spratly Island area is the lowest while the median size is the largestamong the water masses in study area.