Thermohaline and circulation structures in the northwestern East China Sea adjacent to the Changjiang River estuary are mainly determined by the distributions, variations and interactions of the Changjiang River Diluted Water (CDW) and the Taiwan Warm Current Water (TWCW).
In this paper, the distributions of the CDW and TWCW in summer and winter were studied based on data gathered from 2 surveys in July-August 2001 and January 2002, and the correlationship and interannual variations of the CDW and the TWCW were then discussed through the comparative analyses of observations during the two surveys and 5 other surveys from 1987 through 2001 (summers of 1987, 1998 and 2000, winters of 1997 and 2001), and historical data from 1958 to 1982 along 28ZN, 29ZN and 30ZN sections.
Results showed that, in the summer of 2001, the CDW turned to the northeast at about 122.5ZE. The TWCW reached the latitude of the Changjiang River estuary at depth and caused upwelling along the Zhejiang coast and near 122.2-123ZE, 31.5ZN outside the Changjiang River estuary. Especially, the TWC deep water was found to extend to the north of 30ZN. Temperature above the thermocline was about 2-4ZC higher than climatological values.
In January of 2002, the unusual stratification was observed and possibly caused by the abnormal warmer climate and southerly prevailing wind during the survey. The CDW ran southwards along the coast with its eastern edge extending to the east of 123ZE. The TWCW moved northward to the Changjiang River estuary as usual, while the deep water appeared only near 29ZN, distinctly weaker than the averaged year.
Through the comparative analyses of the 7-survey data and the historical data, the correlationship and interannual variability of the CDW and the TWCW were suggested as follows:
In summer, 1) the path of the CDW eastward extension seemed to be more affected by the amount of the river run-off than by the TWCW; 2) the northward extension of the TWC surface water looked to be evidently influenced by the CDW and its own strength; 3) the northward extension of the TWC deep water, as well as the location of the upwelling along Zhejiang Coast and outside the Changjiang River estuary, had little to do with the CDW.
In winter, 1) the TWCW usually reached the north of 31ZN, which was different from the traditional knowledge suggesting the extension be much weaker in winter; 2) the northward extension of the TWC deep water revealed a significant interannual variability mainly determined by its own strength. |
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