Spatial and Seasonal Variation of Chlorophyll and Primary Productivity in Summer and Winter in the Northern Yellow Sea

Chlorophyll and primary productivity were measured during two expeditions to the Northern Yellow Sea during the summer and winter of 2006/2007 in order to assess their spatial and seasonal variability as well as controlling factors.The average values of surface chlorophyll concentration were(0.779±0.640) mg·m-3 in summer and(0.652±0.508) mg·m-3 in winter.The chlorophyll content in water column in summer was(30.75±19.01) mg·m-2,whereas the value in winter(18.72±11.98) mg·m-2 showed a significant decrease(P0.05).Due to intense water stratification in the summer,the maximum chlorophyll concentration that appears at the subsurface layer differs from the more uniformly mixed water column in winter.The primary productivity in water column in summer was 471.2 mg·m-2·d-1 on average,compared with only one-fourth of this value(125.4 mg·m-2·d-1) in winter.The horizontal distribution of primary productivity shows less variation in winter than in summer.While both nitrate and phosphate are likely to be the controlling factors of phytoplankton growth in winter,only phosphate can be considered as a controlling factor in summer.The sea surface temperature and chlorophyll concentration showed negative correlations both in summer and winter with R2 values of 0.44(P=0.01,n=73) and 0.41(P=0.01,n=71),respectively.