The connectivity between the interannual salinity variations in the Tsushima and Cheju Straits has been investigated on the basis of historical hydrographic data. Salinity in the Cheju Strait correlates positively with that in the western channel of the Tsushima Strait, but does not show a significant correlation with that in the eastern channel. Empirical orthogonal function (EOF) and singular value decomposition (SVD) analyses of temperature and salinity in the Cheju Strait revealed that salinity in the strait is associated with the cold bottom water in summer. Drastic freshening in the Cheju Strait occurs in a period when the Cheju Current intensifies. The results allow us to hypothesize that the mechanism of interannual salinity variations in the Cheju Strait and western channel of the Tsushima Strait is as follows. The intrusion of cold bottom water into the Cheju Strait in summer intensifies the Cheju Current by increasing the baroclinicity. Since colder bottom water develops a stronger eastward surface current, the larger volume of the Changjiang diluted water is drawn into the strait, which results in a lower salinity condition in the Cheju Strait. As the water in the Cheju Strait flows into the western channel of the Tsushima Strait, salinity in the western channel varies synchronously. This hypothesis is supported by SVD analysis of temperature in the Cheju Strait and salinity in the Tsushima Strait. The salinity condition in the East China Sea is suggested to be another important influence on salinity in the western channel of the Tsushima Strait.
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