南海叶绿素浓度的时空变化特征分析

The temporal and spatial evolution of chlorophyll-a concentration in the South China Sea

运用经验正交函数(EOF)分解方法,分析了SeaWiFS传感器获取的近13年的逐月叶绿素浓度资料,得出南海叶绿素浓度的空间分布形态及其随时间的变化特征。结果显示,南海叶绿素浓度在空间上主要表现为4种典型的分布结构,而时间上以季节变化为主:EOF1呈现了南海叶绿素浓度近海高、海盆区低的基本分布特征;EOF2显示出夏季越南沿岸激流形叶绿素浓度高值带的存在,除显著的季节变化外,其时间序列也表现出明显的年际变化特征,并与ENSO事件关系紧密;EOF3体现了南海叶绿素浓度随东北季风加强而升高的现象,其高值区分布于东北-西南向的海盆主轴以北,并在吕宋岛西北海域形成一个极大值中心;另外,EOF4反映了叶绿素浓度较短时间尺度的变化规律,在空间分布上表现为明显的三涡结构,与南海海面高度的三涡结构有极好的对应关系。

Based on nearly 13 years’ SeaWiFS chlorophyll-a（Chl-a） concentration data,the authors analyzed the temporal and spatial variation of Chl-a in the South China Sea（SCS） using the empirical orthogonal function（EOF）.The first four EOF modes captured the major features of Chl-a in the SCS.EOF1 describes the fundamental variation of Chl-a with higher concentration over the shallow water and lower concentration over the deep basin.EOF2 presents a high Chl-a concentration band extending eastward from the South Vietnam coast in summer,which is related to the coastal upwelling.In addition to its distinct seasonal variation,this EOF mode also shows a significant interannual variability associated with El Ni o-Southern Oscillation events（ENSO）.EOF3 discloses the evidence that the Chl-a concentration increases with the enhancement of northeasterly monsoon in winter.The Chl-a concentration is characterized by high values north of the NE-SW axis and reaches its maximum to the northwest of Luzon Island.Unlike the first three EOF modes,EOF4 reveals a semi-annual variability of Chl-a with a tri-pole structure,which corresponds very well with the spatial distribution of sea surface height.