长江口外海域1998年夏季悬沙浓度特征

Characteristics of Suspended Sediment Concentrations over the Areas Adjacent to Changjiang River Estuary, the Summer of 1998

1998年6～8月长江流域经历了一次特大洪水,在洪水期间,以10mgL^(-1)的悬沙浓度为标志,长江悬沙的影响范围可达123°E.在122°15E附近,悬沙浓度显示出成层现象,底层浓度约为表层浓度的3倍,这一现象主要与物质沉降过程有关.在126°E～127°E之间悬沙浓度最低,代表了黑潮水的特征.在调查期间,长江悬沙扩散的范围比冬季枯水季节有相当程度的扩大,但向NE方向扩散的趋势并不明显.在陆架区,形成了若干个次级高悬沙浓度中心,其原因可能是底质再悬浮,也可能是高悬沙浓度水体的运动.为了弄清研究区内长江细粒沉积物的输运和堆积过程及其对化学物质通量的影响,需要结合多学科(流场、温盐度、营养盐等)数据进行分析.本文根据长江口外海域悬沙浓度的调查结果,结合历史观测数据,初步分析了长江口外海域夏季悬沙浓度特征.

A large scale flood event occurred within the drainage basin of the Changjiang River, in June-August, 1998. Survey in the East China Sea adjacent to the Changjiang River estuary shows that during the flood the turbid water (suspended sediment concentration > 10 mg 1-1) reached 123oE. Stratification of the concentration layers is present near 122ol5E, with the concentration in the bottom layer being 3 times of that in the upper layer, in response to sediment settling processes. The concentration is the lowest in the area of 126oE-127oE, representing a characteristic of the Kuroshio water. Although there is expansion of the turbid water compared with the winter situations with low freshwater discharges, the suspended sediment does not appear to disperse towards the northeast from the Changjiang River. Further, several secondary high suspended sediment concentration centers are present on the continental shelf of the East China Sea, which may result from resuspension of the seabed sediment or advection of seawater containing suspended matter. In order to understand the processes of fine-grained sediment transport/ deposition and their impact on the flux of chemical constituents on the shelf, further studies on the hydrodynamics, temperature, salinity and nutrient characteristics are required.