Coastal shelf circulation around a deep-sea island in the Canary Basin

In-situ observations around Madeira Island (32.6°N, 16.8°W) reveal that coastal processes are forced by the interaction between the insular shelf, local winds, and tides, often acting independently of far-field circulation. The Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) system was employed to investigate island shelf circulation; four different scenarios were modeled: three single-forcing cases (Case A: tidal forcing; Case B: local wind forcing; Case C: global model (far-field) forcing) and one combined-forcing case (Case D: all forcings). These simulations provide insight into the key coastal patterns and dominant frequencies associated with each scenario.

Case D was validated against in-situ data. Ocean currents were analyzed using Morlet wavelet techniques and rotary spectra. The findings indicate that wind forcing predominantly controls coastal circulation patterns on the western side of the island and on the northeastern coasts. On the eastern side, tides play a critical role in establishing and sustaining coastal currents. Along the northwest coast, basin-scale Atlantic circulation, including the Azores Current and mesoscale eddies, significantly influences coastal dynamics.

The main finding of this study is that coastal dynamics around oceanic islands are highly variable over a few kilometers, driven by both local and far-field factors, contrasting with traditional wake studies, which often overlook these essential dynamics of the insular shelf.