The chemical distribution characteristics of variant forms phosphorus in the seawater of the South China Sea

According to tw o cruises investigation information in summer and winter during 1998 and 1999,the phosphorous concentration distribution and changes of summer and winter were discussed primarily in the South China Sea.The results show that the phosphate concentration of surface seawater in summer is distinct lower than that in winter,and average 0.04 μmol/dm³ in summer and 0.35 μmol/dm³ in winter.The organic phosphorous concentration of surface seawater in summer is higher than that in winter,and average 0.12 μmol/dm³ in summer and 0.04 μmol/dm³ in winter respectively.The season change of total phosphor us is similar to phosphate,and average 0.22 μmol/dm³ in summer and 0.61 μmol/dm³ in winter respectively.In vertical direction,phosphate, TDP,and TP content is lowest in the upper 50 m water column,and increases linearly rapidly with water depth, increases slowly under 500 m,reaches to maximum about 1 000 m,then decreases slightly with water depth increasing.The vertical distribution is typical in summer,and there is small dispersion for phosphorus concentration for the same depth of different stations.However,in winter there is a large dispersion for phosphate,TDP,and TP,specifically for phosphate at 200 m at which the concentration is maximum.This result indicates that there is large difference in hydrology and biology condition that affect largely on the chemical environment of the South China Sea.The organic phosphorus is the predominant in the surface seawater of the South China Sea,but the inorganic phosphorus is the predominant in layers more than 150 m.The organic phosphorus concentration in deep water usually decreases with water depth increasing.The organic phosphorus in summer is distinct more than that in winter because of the strong biology activities in summer.