THE DISTRIBUTION OF LOW-LEVEL PHOSPHATE IN THE NORTHERN SOUTH CHINA SEA

The distribution of phosphate in nanomolar level in the northern South China Sea was determined with magnesium-induced coprecipitation(MAGIC) method in an optimized procedure in which precisions reached 1.53% and 6.63% in recovery rate of 95.5%—98.0% for high and low level measurements,respectively.Samples collected in February and July 2004 representing winter and summer were examined.The horizontal distribution of phosphate was found sig-nificantly influenced by the Pearl River discharge,as the concentration decreased with the distance offshore.The results show that in winter,phosphate concentration in the surface water ranged 6.6—95.0 nmol/L in average of 34.6 nmol/L,while it varied 6.3—66.6 nmol/L in average of 17.4 in summer,lower than that of winter.Vertically,the phosphate profile was apparently stratified and the phosphate gradient was smaller in winter than in summer,and thus a nutricline is revealed by this low-level phosphate measurement.