Water exchange and tidal currents through the Bussol' Strait revealed by direct current measurements

Abstract

An outflow from the Sea of Okhotsk to the North Pacific was measured at the Bussol' Strait, the largest strait connecting these basins, from 31 August to 11 September 2001. Yo‐yo casts of a lowered acoustic Doppler current profiler were performed at 13 stations across the narrowest part of the strait. Time series covering more than approximately 24 hours were obtained for each station, and the semidiurnal and diurnal tides were separated. The diurnal tide at the spring tide shows a remarkable peak of the amplitude of 1.1 m s −1 at the depth below 1000 m in the western channel of the strait. The upper part of the mean component flows toward the Pacific, and the lower part flows in the opposite direction. The outflow is in excess of the inflow, and net transport through the strait is 8.2 to 8.8 Sv (1 Sv = 10 6 m 3 s −1 ). The outflow is strong in two density ranges. The upper layer peak around 26.8 σ θ corresponds to the density of North Pacific Intermediate Water and the temperature‐salinity characteristics of this outflow were actually observed in this density range across downstream the Oyashio off the southeastern coast of Hokkaido. Net heat and salt exchanges between the Sea of Okhotsk and the North Pacific are estimated; net heat flux of −34 TW and net salt flux of −1.9 × 10 6 kg s −1 are exchanged from the Sea of Okhotsk to the North Pacific.