Large-amplitude internal waves observed in the Kruzenshtern Strait of the Kuril Island Chain and possible water transport and mixing

Abstract

Vertical sections of temperature and current velocity across the sill in the Kruzenshtern Strait were observed four times in one day in September 1997. The observations captured nonlinear internal waves near the sea surface, which are likely to be tidally generated. Two of these waves had maximum amplitudes near the surface and each contained a trapped core, suggesting that a significant volumetric flux was induced. At mid depths, isotherms moved vertically more than 50 m, which is consistent with the generation of internal lee waves. From water-mass movements, the currents are estimated to flow from the North Pacific to the Sea of Okhotsk in the temperature-minimum layer at a mean speed of 0.2– 0.3 m s - 1 . The mean flow was weaker and the oscillatory component was stronger at mid depths, with the amplitude of the latter around 0.4 m s - 1 , leading to the above lee wave generation. Active temporal variations in potential temperature, particularly those associated with small-scale patches, suggest the occurrence of vigorous water-mass transformation. Vertical and horizontal diffusivities are estimated to be O ( 10 - 2 m 2 s - 1 ) and O ( 10 2 – 10 3 m 2 s - 1 ) , respectively. Because the tidal amplitude was close to the annual minimum at the time of observation, larger-amplitude internal waves and more vigorous water-mass transformation could take place at other times of the year.