Sea level variations at the Izu Islands and typical stable paths of the Kuroshio

Abstract

Differences in daily mean sea level between Kushimoto and Uragami and daily mean sea levels at Miyake-jima and HachijO-jima in the Izu Islands are examined during the 1964–1980 period, and characteristics of the typical paths of the Kuroshio corresponding to the dominant sea level states are described. Sea levels at the islands show three dominant states: high and low sea level states (45 % and 31 %) in the non-large-meander period (October 1963 –7 August 1975) and high sea level state (64 %) in the large-meander period (8 August 1975–15 March 1980). This indicates the existence of three typical paths of the Kuroshio, and the states correspond to the nearshore and offshore non-large-meander paths and the typical large-meander path, respectively. The first path is located near the coast throughout the whole southern area off Japan, the second path leaves the coast around the Izu Ridge and passes south of HachijO-jima, and the third path is located near the coast over the ridge after meandering far to the south of Enshu-nada. The positions of the three typical paths are almost the same in the farthest upstream and downstream regions south of Japan between 131‡E and 142‡E. The nearshore and offshore non-large-meander paths overlap between Kyushu and the Kii Peninsula, being invariably close to the coast, while the typical large-meander path south of Shikoku is located offshore and changes its position meridionally. At the mid-depth of 400 m the nearshore non-large-meander and typical large-meander paths pass the Izu Ridge through the deep channel between Miyake-jima and HachijO-jima, while the offshore non-large-meander path passes through the deep region south of HachijOjima. The path of the Kuroshio at mid-depth is well constrained by the bottom topography of the Izu Ridge.