Abstract
In this study we examine offshore transport and dispersal pathways of the freshwater discharge from the Changjiang River in the East China Sea (ECS), using a regional ECS model. Comparison between the results for 1996 and 1998 clearly shows that the summer monsoon winds play a significant role in spreading the freshwater discharge offshore and determining the dispersal of freshwater in the ECS. Analysis of 10-year simulation demonstrates that a northeastward freshwater transport to Jeju Island across the northwestern shelf of the ECS dominates during the summer period due to the surface Ekman flow by the southeasterly along-shore wind. Meanwhile, there is virtually no relationship between the amount of the summer discharge and the freshwater pathway toward Jeju Island. Our analysis also suggests that when the summer wind is relatively weak, another freshwater pathway toward the central ECS appears with the ambient along-shelf current between the Taiwan Strait and the Korea Strait.
Highlights
Freshwater discharged into the East China Sea (ECS) dominates the distribution of surface salinity in summer when the precipitation amounts are large, especially associated with the Changjiang River, which contributes about 90% of the total discharge to the ECS (Beardsley et al 1985; Kim et al 1991)
In 1998 the outer boundary of the Changjiang diluted water (CDW) by 28 psu is detected in the central region of the ECS as a tongue-shaped plume extending from the Changjiang River mouth (Figs. 2b, c)
The plume moving toward the central ECS is sharply turned northeast due to the strong southeasterly wind during late July, which rapidly pushes the plume to the northeastern shelf of the Changjiang Bank by Ekman dynamics, and the plume in the shelf region is transported to the western coast of Jeju Island in early August
Summary
Freshwater discharged into the East China Sea (ECS) dominates the distribution of surface salinity in summer when the precipitation amounts are large, especially associated with the Changjiang River, which contributes about 90% of the total discharge to the ECS (Beardsley et al 1985; Kim et al 1991). Spreading of freshwater is closely associated with the winddriven surface flow and ambient along-shelf current (Bang and Lie 1999; Chang and Isobe 2003; Chen et al 2008; Moon et al 2009a). The freshwater transport and the pathways in the ECS are still unclear because most of the studies described the response of the CDW to idealized or climatological forcings. In 1998 the outer boundary of the CDW by 28 psu is detected in the central region of the ECS (or southwestern offshore area of Jeju Island) as a tongue-shaped plume extending from the Changjiang River mouth In this study we attempt to quantify the transport of the CDW toward Jeju Island and address the freshwater pathway in the ECS. The two cases provide a distinct difference in the freshwater structure and the pathways, as mentioned above
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