Islands as eddy transformation and generation hotspots: Cabo Verde case study
Résumé
The characterisation of incoming background and island-induced mesoscale eddies in the Cape Verde Archipelago is discussed herein. Special attention is given to the interaction of background eddies with the islands topography and orographic winds, along with the interaction and potential impacts on the generation of island-induced eddies. Some examples of the local biological response to background and island-induced eddies are given. This is achieved by combining remote-sensing satellite observations for wind, Sea Surface Height and Chlorophyll a (Chla) surface concentrations. Results show that the interaction between incoming background eddies and the archipelago is a recurrent phenomenon, which results in eddy deflection, splitting, merging, intensification and termination. Local island-induced disturbances are also significant, mainly due to atmospheric effects. Such processes result in the generation of island-induced eddies and in wind-mediated eddy intensification and confinement, more often observed in the leeward group. It is strongly suggested that many of the local island-induced eddies are a direct product or a by-product of the interaction of background eddies with the archipelago. In respect to the biological realm, background eddies are often associated with enhanced Chla. However, nutrient-injection by a (background related) island-induced cyclonic eddy is observed to originate a pronounced phytoplankton bloom in the vicinity of the tallest island. Such observations challenge the idea that local biological productivity in deep oceanic islands are exclusively driven by island-induced mechanisms.
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