Seasonal variation in the in- and outflow of the Okhotsk Sea with the North Pacific

This paper examines the seasonal variation in the in- and outflow of the Okhotsk Sea with the Pacific, mainly based on profiling float and satellite altimeter data. The motions of the floats at depths of 500-750 m show that the waters of the Okhotsk tend to flow out to the Pacific through the southern Kuril Straits, mostly Bussol’ Strait, in winter seasons (November-March). Based on data from the floats exiting the Sea, the mean residence time of the intermediate water in the Kuril Basin is estimated as about one year. Isopycnal analysis from the profiling data shows that, in the mid-eastern area of the Okhotsk Sea, potential temperature of the intermediate water with σθ=26.6-27.2 increases by 0.2-0.5 °C in every spring, suggesting the inflow from the Pacific in the preceding season. These suggest that the in- and outflow predominantly occurs during winter, with the inflow at the northern straits and outflow at the southern straits. The surface current field inferred from satellite altimeter data also shows that the inflow to the Sea of Okhotsk through the northern straits is strengthened in winter, linked with strengthening of the East Kamchatka Current (EKC). From yearly anomalies of the altimeter data, the winter inflow to the Okhotsk through the northern straits is significantly correlated with the EKC and Sverdrup transport over the North Pacific. Further, interannual variations in property of Okhotsk Sea Intermediate Water appear to be related with the EKC and wind stress over the North Pacific in winter, possibly through the change in inflowing Pacific water transport. These suggest that the seasonal and interannual variations of the in- and outflow are, to some extent, controlled by the large scale wind stress over the North Pacific, being consistent with Island Rule qualitatively.