中文摘要：

2009年2月（冬季）和8月（夏季）在南海北部海域（nSCS）采用流式细胞术对聚球藻、原绿球藻、超微型光合真核生物3类超微型光合浮游生物和异养浮游细菌的丰度和碳生物量的时空分布特征进行了研究,并分析了其与环境因子之间的关系。结果表明,夏季聚球藻和原绿球藻的平均丰度高于冬季,超微型光合真核生物和异养浮游细菌的丰度反之,为冬季高于夏季。聚球藻、超微型光合真核生物和异养浮游细菌在富营养的近岸陆架海域丰度较高,而原绿球藻高丰度则出现在陆坡开阔海域。在垂直分布上,聚球藻主要分布在跃层以上,跃层以下丰度迅速降低;原绿球藻高丰度主要出现在真光层底部;超微型光合真核生物在水层中的高值同样出现在真光层底部,且与Pico级份叶绿素a浓度分布一致;异养浮游细菌在水体中的分布与聚球藻类似。这些分布格局的差异,取决于环境条件的变化和4类超微型浮游生物生态生理适应性的差异。在超微型光合浮游生物群落中,各类群碳生物量的贡献因季节和海域类型的不同而发生变化：聚球藻在夏季近岸陆架区占超微型光合浮游生物总碳生物量的41%,原绿球藻在陆坡开阔海成为主要贡献者（50%）,超微型光合真核生物碳生物量以冬季为高（在近岸陆架区占比68%）。冬、夏季异养浮游细菌碳生物量均高于超微型光合浮游生物碳生物量。

英文摘要：

The abundance,carbon biomass and distribution of picoplankton were investigated during the summer（August）and winter（February）of 2009 extending from near-shore coastal waters to oligotrophic open waters in northern South China Sea（nSCS）.The results showed that the average abundances of Synechococcus（Syn）and Prochlorococcus（Pro）were higher in summer than winter,while Picoeukaryotes（PEuk）and heterotrophic bacteria（HBac）were opposite to Syn and Pro.Syn,PEuk and HBac were most abundant in the eutrophic coast region and continental shelf,while Pro was dominant in the slope and open waters.In vertical profile,the high abundance of Syn mainly appeared above the thermocline and decreased sharply below it.The high Pro abundance in the water column mostly appeared at the bottom of euphotic depth,as well as PEuk.The distribution of HBac was similar to Syn.These different distribution patterns depend on environmental variation and the ecological and physiological adaptation of each group of picoplankton.The contribution of each group of photosynthetic picoplankton biomass varied with the season and sea area：in the summer coastal shelf area,Syn accounted for 41%of total photosynthetic picoplankton biomass;Pro was major contributor（50%）in the slope open waters;while PEuk biomass took40% higher in winter（reached 68%in the coastal shelf area）.And HBac biomass was higher than photosynthetic picoplankton biomass both in the winter and summer.