2009年冬季南海北部浮游植物粒度分级生物量和初级生产力

Distributions of size-fractionated chlorophyll a and primary productivity in northern South China Sea during the winter of 2009

2009年2月在南海北部海域现场观测粒度分级叶绿素a质量浓度和初级生产力(PP)的分布。结果表明,调查海域水柱平均叶绿素a质量浓度的变化范围为0.11~8.37 mg/m3,平均为(1.28±2.23)mg/m3,高值区出现在珠江口及近岸海域;初级生产力的范围为344.8~1 222.5 mg C/(m2·d),平均为(784.2±351.4)mg C/(m2·d),高值区位于近岸及陆架海域。浮游植物粒度分级测定结果表明,在生物量较高的近岸海域,叶绿素a的粒级结构以小型浮游植物占优势,其贡献率为40.9%,微型和微微型浮游植物对总叶绿素a的贡献率分别为34.6%和24.5%;而在生物量较低的陆坡和开阔海域,各粒级浮游植物对叶绿素a的贡献率由大到小依次为微微型浮游植物(78.9%),微型浮游植物(17.2%)和小型浮游植物(3.9%)。相关性分析结果表明,调查海域分级叶绿素a的区域化分布特征与洋流运动下营养盐的分布密切相关,同时叶绿素a又高度影响着此区域PP的分布。此外,我们将调查海域实测所得浮游植物最佳光合作用速率与采用垂向归一化初级生产力模型估算的数据进行对比,发现后者明显低于前者,这说明通过水温估算最佳光合作用速率的算法在冬季南海北部可能存在低估。

Size-fractionated chlorophyll a concentration （Chl a） and primary production （PP） of phytoplankton in the northern South China Sea （nSCS） were investigated during the winter of 2009. The results showed that Chl a and PP had obviously spatial variation in the nSCS. The water column integrated average values of Chl a varied from 0. 11 to 8. 37 mg/m3, the average value was （1. 28!2. 23） mg/m3, and decreased from the coastal zone to the open sea. The lowest and highest value of PP were 344.8 mgC/（m2 · d） and 1 222.5 mgC/ （m2· d）, respectively, with the high value appearing in the coastal zone and continental shelf. The result of size-fractionated Chl a showed that microplankton （Net-Chl a） was greater contributor （about 40. 9%） to phytoplankton stocks in the eutrophic coastal zone and the proportions of nanoplankton （Nano-Chl a） and picoplankton （Pico-Chl a） were 34.6% and 24.5%; while in the oligotrophic continental shelf and open sea, the contributions of three size-fractionated Chl a from greatest to least in order were Pico-Chl a （78. 9 %）, Nano-Chl a （17.2%）and Net-Chl a （3.9%）. Relevant analysis results showed that the regional distributions of Chl a were closely related to the nutrient dynamics driven by the ocean currents; meanwhile the distributions o{ Chl a drastically affected the distributions of PP as well. Furthermore, compared PIo^pt in situ with that estimated by the depth-resolved model for carbon fixation （VGPM）, it was found that the later were less than the former obviously, and this indicated that the underestimated value Popt^B through temperature might be exited in nSCS.