Tidal Exchange through the Kuril Straits

Abstract

The tidal exchange between the Okhotsk Sea and the North Pacific Ocean is studied numerically with particular emphasis on the predominant K 1 barotropic component. The calculated harmonic constants of the K 1 tide in and around the Okhotsk Sea agree well with those obtained from extensive tide gauge observations. The features of the simulated tidal fields are similar to those reported in the literature. Since the K 1 tide is subinertial in the Okhotsk Sea, topographically trapped waves are effectively generated, contributing to strong tidal currents with a maximum amplitude of over 1.5 m s 1 in the Kuril Straits. The structures of tide-induced mean flows in most passages of the straits are characterized by ''bidirectional currents'' (in which the mean flow exhibits a reversal in direction across the passages). This feature is clearly indicated in NOAA infrared imagery. The mean transport shows significant net exchange of water via several straits in the Kuril Islands. A transport of about 5.0 Sv (1 Sv 10 6 m 3 s 1 ) toward the North Pacific is produced by the K 1 tide, primarily through the Bussol, Kruzenshterna, and Chetverty Straits. Analysis reveals that the bidirectional mean currents at shallow passages are produced through the well-known process of tidal rectification over variable bottom topography, whereas in deep passages such as Bussol Strait, propagating trapped waves along the islands are essential for generating the bidirectional mean currents. Particle tracking clearly demonstrates these features. The tidal current is therefore thought to play a major role in water exchange processes between the Okhotsk Sea and the North Pacific.