Wind-driven upwelling in Opunohu Bay, Moorea, French Polynesia

Opunohu Bay is a narrow, straight, 3-km long bay on the island of Moorea, French Polynesia. The bay is open to the ocean with a water depth of about 80 m at the mouth. The sea floor slope reaches one-third offshore. Field observations show that a wind blowing to offshore along the axis of the bay generates an outflow at the surface and an inflow below 20 m depth. A localized upwelling results at the mouth of the bay which may also be detected in the phytoplankton population. This situation is modelled numerically and the results suggest that the wind stress must be taken to be not only a function of the wind speed but also of the wind fetch.