Effects of mesoscale eddies on the variation of water exchange through the Kerama Gap

Abstract

The Kerama Gap is an important passage for water exchange between the East China Sea (ECS) and the northwestern Pacific (NP). The mean Kerama Gap transport (KGT) is small into the ECS (~ 2.0 Sv) but with a large standard deviation (~ 4.5 Sv), which has a significant influence on the variation of Kuroshio transport. The effects of mesoscale eddies on the variation of KGT are investigated by using a 25-year Pacific Hybrid Coordinate Ocean Model from 1979 to 2003. Model results show that the variation of KGT is mainly determined by the variation of sea level difference between the northeast and southwest of the Kerama Gap, and these differences are dominated by the westward propagating mesoscale eddies. The effects of mesoscale eddies depend on the meridional location of these eddies. When the anticyclonic (cyclonic) eddy is located in the northeast of the Kerama Gap or the cyclonic (anticyclonic) eddy is located in the southwest of the Kerama Gap, the KGT shows a strong positive (negative) anomaly. However, when the eddy is located in the central region of the Kerama Gap, the KGT shows a relatively smaller anomaly. Besides, the variation of Kuroshio, strongly influenced by the eddies east of Taiwan, also plays an important role in influencing the variation of KGT. When the Kuroshio transport crossing the upstream section of the Kerama Gap is high (low) or the Kuroshio central position shifts to (away from) the Kerama Gap there will be more (less) water flow from the ECS to the NP.