An exchange flow between the Okhotsk Sea and the North Pacific driven by the East Kamchatka Current

A new mechanism for driving the water mass exchange between the Okhotsk Sea and the North Pacific is presented. This exchange flow originates from the East Kamchatka Current (EKC), a western boundary current of the subpolar gyre, and occurs through the two deepest straits of the Kuril island chain, the Kruzenshtern and Bussol straits. An inflow toward the Okhotsk Sea occurs at the northern Kruzenshtern strait and an outflow toward the North Pacific occurs at the southern Bussol strait. By using the Kelvin's Circulation theorem around the island between the two straits, we show that the transport of the exchange flow entering the Okhotsk Sea is determined such that the frictional stresses around the island exerted by the bifurcated EKC integrate to zero. This forcing mechanism is different from the dynamical framework of the widely used “Island rule.” Both an analytical analysis and 1.5‐layer model experiments demonstrate that the strait width, lateral viscosity, and island geometry are controlling parameters for the exchange flow transport because they affect the magnitude and length scales of the frictional stresses. Inertia of the EKC decreases the exchange flow by enhancing the frictional stress along the northern coast of the Kuril island. Model experiments with realistic topography further reveal that while the steep continental slopes have minor impact on the exchange flow transport, the subsurface peninsula located east of the Kuril island works to decrease the exchange flow by altering the length scale of the frictional stresses and enabling the EKC to flow past the island.