Eddy formation behind the tropical island of Aldabra

Oceanic eddy formation behind the tropical island of Aldabra is examined with a one-layer reduced gravity model. Thresholds for flow separation, eddy formation, eddy shedding, and wake instabilities are determined and compared with theory, observations and results of laboratory experiments for both rotating and non-rotating flows. It is shown that non-rotating fluid theory and the Reynolds number are appropriate for describing the occurrence of eddy shedding. For islands at higher latitudes, thresholds move nearer those found in rotating laboratory experiments. Strouhal numbers calculated from the model results agree with those predicted theoretically, confirming that the frequency of eddy shedding does not increase indefinitely with Reynolds number. Both the model results and data from the CZCS archive suggest that eddy shedding and the associated enhanced biological activity (and thus CO2 uptake) are common phenomena for Aldabra and, by implication, other oceanic islands.