Composition and Distribution of Suspended Load in Sea Water off Zhujiang River Mouth and Its Vicinal Shelf

The suspended load in sea waters off Zhujiang (pearl) River Mouth and on its vicinal shelf was studied by grain-size analysis and mineralogical and microbiological assays on more then 100 specimens collected in four cruises in 1985 and 1986. The distribution of suspended load appears temporal and spatial trends. Average concentration is high in winters (25-26mg/l), low in summers (13-18mg/l), and decreases significantly seaward. Alongshore, the suspended load is enriched in Hanjiang River Mouth, Zhujiang River Mouth,west Guangdong coast,and off southeastern Hainan Island. High concentration is seen also on outer shelf of 100-200m water depth. Localities of high suspended load shift with seasons. The variation of concentration intensifies from sea surface downward both alongshore and on the outer shelf. The dominant components of the suspended loads are minerals; secondary shapeless organisms and biogenic particles. Clay minerals consist of the major portion of the mineral composition; one third of the specimens contains more than 70% of clay minerals. The content of clay minerals increases with the increase of total suspended load. Clastic minarals are mainly quartz and feldspar;secondarily mica, limonite,pyrite,and basaltic glass; ocassionally rutile, tourmalime, amphibole, corundum, glauconite, andcite fluorite, olivin, etc. Contents of the clastic minerals may be up to 15%. Biogenic particles are mainly diatom and secondarily foraminifera, with minor radiolaria, Crustacea, etc. Organisms are seen in all the specimens and particularly rich, with content of 45% and 30% respectively, in two specimens collected in summer from the seawater of 200 -400m depth off southeastern Hainan Island. The content of organisms is in general 1-5%; that of greater than 1% occurs in one third of total specimens, which are distributed in 1) Hanjiang River Mouth during winter rather than summer, especially in the water near the mouth where the content of organisms may reach 10%, 2) Zhujiang River Mouth, where the content of organisms may be up to 9%, 3) the water of 100-200m depth on the outer shelf. The specimens with suspended load greater than 70mg were subject to light-transmissive grain-size analyser of the 15 specimens analyzed, 12 were named silt; the rest three clayey silt. Under microscope the grains of 10-40μ diameter are dominant with many of about 120μ. This indicates a high -energy hydrodynamic conditions in these areas, where high concentration of suspended load is provided not only by Zhujiang and Hanjiang, but also by a-longshore currents. East Guangdong upwelling current, West Guangdong circular current, Nanhai warm current, and outer circular current.