Present and Future of Volume Transport through the Korea Strait

Abstract

Tsushima Warm Current(TWC) through the Korea Strait transports heat, salt, and other physical properties to the East Sea. Thus, the volume transport in Korea Strait must be studied. As the Tsushima Warm Current is a branch of the Kuroshio Current, it is important to find out the relationship with the Kuroshio Current in order to study the volume transport in the Korea Strait. In this study, ADCP observations and high-resolution reanalysis data such as GLORYS, HYCOM, and OPEM were used for analysis. To obtain current data which tidal components were removed from the ADCP mounted on the Camellia ferry, which travels between Hakata, Japan and Busan, Korea, the route of the observation was newly set using the least squares method, and 14 tidal components were calculated through the harmonic analysis. In addition, in order to estimate surface and bottom ocean currents, which are difficult to observe, we tried to find an extrapolation method suitable for the ADCP data of Camellia ferry using ADCP data observed at NRL. The gradient extrapolation was judged to be the best fit, and gradient extrapolation was performed in the bottom layer, and the surface layer was extrapolated using the observed values of the first layer. As a result, from the Camellia ADCP data, the volume transport of the Korea Strait is about 2.69 Sv in average, and the volume transport through the western channel and eastern channel are estimated to be about 1.34 Sv and about 1.45 Sv, respectively. As a result of the analysis, it was found that the volume transport in the Korea Strait has increased over time. In addition, to investigate the relationship between the Korea Strait and the Kuroshio Current, correlation and spectrum analysis between the Korea Strait and the Tokara Strait were performed. The correlation coefficient between volume transport in Korea Strait and Tokara Strait was found to be –0.76. Coherence spectrum analysis using reanalysis data showed that the volume transport through the Tokara Strait leads that through the Korea Strait for about 2 months in a 5-month frequency. In addition, the results of 10 CMIP6 models were analyzed to find out the relationship between the Korea Strait and the Kuroshio Current in the future climate. In scenarios where radiative forcing becomes stronger, the Kuroshio Current moved northward, the Korea Strait transport increased and the Tokara Strait transport decreased from 2090 to 2100. The boundary of circulation is marked by zero-windstress curl and the mean latitude of the Hadley Circulation in mid-latitude is also moving poleward as global warming progresses, as confirmed by ERA5 data over the past 30 years. The poleward of the Hadley circulation affects the poleward of the Kuroshio Current, which can be interpreted as the cause of the poleward movement of the Kuroshio extension. As a result, the volume transport of the Tsushima Warm Current entering the Korea Strait is expected to increase, while the volume transport of Kuroshio Current through the Tokara Strait is expected to decrease. The increasing volume transport of the Tsushima Warm Current has increased the sea surface temperature around the Korean Peninsula, which may change the oceanic circulation and hydrographic condition in the marginal seas around the Korean Peninsula due to global warming.