南海叶绿素a浓度垂直分布的统计估算

分析整理了1993—2006年近10 a南海北部海域、南沙海域和南海其他海域的叶绿素a浓度历史航次调查资料,基于前人提出的全球叶绿素浓度垂直分布的统计分析模式,根据南海表层叶绿素a浓度大小的不同分级,对南海叶绿素a浓度进行了参数化处理,拟合估算了南海各水层剖面的叶绿素a浓度分布值,并结合不同海区的环境特征,分析了南海叶绿素a浓度垂直分布与其海水物理环境的关系。初步分析结果表明,叶绿素a浓度随深度垂直变化的拟合曲线呈一定倾斜的正态分布特征,当表层叶绿素a浓度较低时,作为南海深水海盆区的代表,拟合值更接近实测平均值的分布,叶绿素a浓度高值集中在次表层剖面上;当表层叶绿素a浓度较高时,作为近岸区和河口区的代表,高值多集中在表层海水,拟合误差偏大。该统计估算模式对于揭示南海叶绿素a浓度垂直分布结构进行了有益的尝试,为发展适合不同海区特点的模式以及校正参数奠定了基础。利用该模式与海洋水色卫星遥感数据有效结合,将对南海叶绿素a浓度时空分布格局的研究具有重要的意义。

The statistical estimation of the vertical distribution of chlorophyll a concentration in the South China Sea

Samplings of chlorophyll a (Chl a) concentration are analyzed based on historical cruises data for about 10 a in the South China Sea (SCS), including the northern SCS, the Nansha Islands and other sea areas in the SCS. The profiles of Chl a concentration are classified by the values within the surface layer, to develop a parameterization shape of Chl a concentration vertical profiles according to a generalized Gaussian model (adding a linear decline with a slope starting from the surface value). The modeled Chl a concentration vertical profiles show a normal distribution with a slightly declining slope, and fit well with the in situ Chl a concentration. The max value appears in subsurface layer, as the surface Chl a concentration is low, which represents deep-sea basin waters(Case I); while the difference between the modeled Chl a value and the in situ Chl a concentration is obvious, and the max value appears near the surface layer, as the surface Chl a concentration is high, which represents coastal and estuary waters(Case II).The results make an exploratory and tentative contribution to the vertical distributions of the Chl a concentration in the SCS, and lead to an empirical model and parameterization applicable to different oceanic waters. By combining this tool with satellite ocean color data, it becomes possible to reveal spatial and temporal distribution of phytoplankton biomass in the SCS.