2016年春季季风转换期的珠江冲淡水分布与生态特征分析*

基于2016年4—6月珠江口航次的现场调查资料及卫星数据, 对春季季风转换期的风场分布特征, 冲淡水路径的时空变化情况以及相应的生态响应进行了分析。结果显示珠江口及其临近海域在4—5月表现为过渡性风场, 受冬季风和夏季风的共同作用, 且风向多变。至6月, 冬季风消失, 西南季风控制了整个研究海域, 与此同时珠江径流量逐月增大, 冲淡水的分布特征也随着风场及径流变化发生转变。具体表现为4—5月份冲淡水向粤西沿岸方向扩展, 且在5月流幅更宽, 可达离岸70km处。6月冲淡水向东西两个方向扩展, 向西的冲淡水在河口外受到夏季风场以及背景流场的抑制, 形成以盐度和浊度为特征的锋面; 向东的冲淡水离岸扩展, 在粤东外海形成大面积的羽状流。此外, 珠江口叶绿素和溶解氧的分布主要受冲淡水的影响, 其分布形态与冲淡水路径相似。垂向上, 可观测到珠江口低氧的形成过程, 海水层化, 稳定水柱的形成以及生物分解过程共同导致了珠江口底部的溶解氧较低。浊度的分布主要受径流携带的悬沙影响, 与盐度有很强的负相关性。

Distribution of Pearl-River diluted water and its ecological characteristics during spring monsoon transitional period in 2016*

Based on in situ physical and biological observations and remote sensing data, we analyzed the distribution characteristics of wind, diluted water and its ecological response in the Pearl River Estuary (PRE) during the spring monsoon transitional period (April — June) in 2016. The results showed that non-unidirectional wind prevailed in the PRE and its adjacent area from April to May, and weak southwest monsoon prevailed in June. Meanwhile, the Pearl-River discharge flux increased over time. Influenced by wind and Pearl-River runoff, the diluted water expanded westward alongshore in April and offshore in May, with a maximum distance of more than 70 km away from the coast. The diluted water expanded both eastward and westward in June. The westward diluted water was restricted, and formed an estuarine front with significant salinity and turbidity gradient outside the mouth of the estuary when encountered the southerly monsoon and background currents. The estuarine front extended offshore and formed a large plume in eastward offshore regions. Furthermore, the distribution of fluorescent and oxygen were mainly influenced by diluted water and showed similar patterns. In the vertical direction, the process of hypoxia formation was observed in the PRE. Seawater stratification and the formation of stable water column together with biodegradation process jointly led to low dissolved oxygen at the bottom of the PRE. The distribution of turbidity was mainly influenced by suspended sediments carried by river discharge, and showed strong negative correlation with salinity.