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

According to two 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 distinctly lower than that in winter, averaging 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, averaging 0.12 μmol/dm³ in summer and 0.04 μmol/dm³ in winter respectively. The seasonal changes of total phosphorus are similar to phosphate, averaging 0.22 μmol/dm³ in summer and 0.61 μmol/dm³ in winter respectively. In vertical direction, phosphate, TDP and TP content are the lowest in upper 50 m water column, and increase in linearity rapidly with water depth, increasing slowly under 500 m, reach to maximum about 1 000 m, then decrease slightly with water depth increasing. The vertical distribution is typical in summer, and there is small dispersed for phosphorus concentration for thesame depth of different stations. However, in winter there is a large disperse for phosphate, TDP andTP, specifically for phosphate at 200 m at which the concentration is maximum. This result indicatesthat there are large differences in hydrology and biology conditions that affect largely the chemical environment of the South China Sea. The organic phosphorus is the predominant in surface seawater of the South China Sea, but the inorganic phosphorus is the predominant in layers below depth of 150 m. Theorganic phosphorus concentration in deep water usually decreases with water depth increasing. The or-ganic phosphorus in summer is remarkably more than that in winter because of the strong biology activities in summer.