Interannual variations in material transport through the eastern channel of the Tsushima/Korea Straits

Abstract

We conducted hydrographic observations 23times across the eastern channel of the Tsushima/Korea Straits (ECTKS) to estimate material transports from 2005 to 2008. Freshwater and nutrient transports through the ECTKS became high from summer to autumn, with quite large interannual variations. Freshwater and dissolved inorganic nitrogen (DIN) transport in 2007 was much lower than in other years. The interannual variation in freshwater transport seemed to show almost the same pattern as that of the volume transport of the Tsushima Warm Current and Changjiang discharge. However, we could not explain the interannual variation in freshwater transport quantitatively. The DIN transport in August 2007 was approximately one third of that in 2005 due to the much lower DIN concentration in the bottom layer of the ECTKS in 2007 than in 2005. The difference of DIN concentration between the years was caused by different water mass intrusions into the ECTKS. Water mass analysis and alkalinity data revealed that the water mass in 2005 came from the Yellow Sea or the shelf of the East China Sea, while that in 2007 came from the Kuroshio region. Examination of long-term water temperature data indicated that the origin of ECTKS water masses has changed many times in the past. We suggest that variations of the Changjiang discharge and wind field over the Yellow and East China seas might relate to the change of water mass in the ECTKS.