Seasonal variation of heat and freshwater transports by the Kuroshio in the East China Sea

Abstract

The annual and seasonal means of total transport of volume, heat, and fresh water through a fixed section across the Kuroshio in the central East China Sea (ECS) are estimated. The estimation is done by integrating the absolute geostrophic volume transport for four water masses, using the hydrographic and sea surface current data obtained quarterly by the Japan Meteorological Agency during 1981–1992. While the total volume transport is dominated by Kuroshio Thermocline Water, ranging from 12.6 Sv in fall to 18.2 Sv in spring (1 Sv=10 6 m 3 s −1), the winter volume transport of 14.2 Sv is composed entirely of Kuroshio Thermocline Water. Both Kuroshio Surface Water and Kuroshio Intermediate Water contribute to the total transport in spring through fall with a spring transport of 25.9 Sv and a fall transport of 23.5 Sv. In summer, these three water masses plus ECS Shelf Water contribute to the total volume transport, causing a maximum value of 28.5 Sv. The northward heat transport is found to have a large seasonal variation with a maximum of 0.46×10 15 W in summer and a minimum of 0.25×10 15 W in winter, with an annual mean of 0.33×10 15 W. The northward freshwater transport also exhibits a large seasonal variation with a maximum of +1.7×10 6 kg s −1 in summer and a minimum of −2.0×10 6 kg s −1 in winter, about an annual mean of −0.2×10 6 kg s −1. These results are based on the assumptions that the mean temperature and salinity in the southward return flow region have constant values of 15.11°C and 34.6 psu and there is no net meridional mass transport. The heat transport of the Kuroshio estimated for the same section by Bryden et al. [Bryden, H., Roemmich, D., Church, J., 1991. Ocean heat transport across 24 N in the Pacific. Deep-Sea Res. 38, 297–324.] for June 1985 is shown to be 20% larger than the annual mean.