Abstract
The wind-driven exchange through complex ridges and islands between marginal seas and the open ocean is studied using both numerical and analytical models. The models are forced by a steady, spatially uniform northward wind stress intended to represent the large-scale, low-frequency wind patterns typical of the seasonal monsoons in the western Pacific Ocean. There is an eastward surface Ekman transport out of the marginal sea and westward geostrophic inflows into the marginal sea. The interaction between the Ekman transport and an island chain produces strong baroclinic flows along the island boundaries with a vertical depth that scales with the ratio of the inertial boundary layer thickness to the baroclinic deformation radius. The throughflows in the gaps are characterized by maximum transport in the center gap and decreasing transports toward the southern and northern tips of the island chain. An extended island rule theory demonstrates that throughflows are determined by the collective balance between viscosity on the meridional boundaries and the eastern side boundary of the islands. The outflowing transport is balanced primarily by a shallow current that enters the marginal sea along its equatorward boundary. The islands can block some direct exchange and result in a wind-driven overturning cell within the marginal sea, but this is compensated for by eastward zonal jets around the southern and northern tips of the island chain. Topography in the form of a deep slope, a ridge, or shallow shelves around the islands alters the current pathways but ultimately is unable to limit the total wind-driven exchange between the marginal sea and the open ocean.
Significance Statement
An ocean circulation model and supporting theory are used to understand the wind-driven circulation and exchange through complex ridges and islands between marginal seas and the open ocean. The interaction between the wind-driven flow and island chain produces strong surface-intensified baroclinic boundary currents. The flows between the island are determined by the diffusive balance around the islands, and are characterized by maximum transport in the center of the island chain with decreasing transport toward the southern and northern islands. The topography will alter the current pathways but is ultimately unable to limit the total wind-driven exchange. These results provide a theoretical framework for understanding the circulation around complex islands such as are found in the marginal seas of the western Pacific Ocean.
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