Insular shelf circulation in deep-sea islands

Jesus Reis1, Rui Vieira2, Gustavo Silva3 and Rui Caldeira2, (1)Dom Luiz Institute, Oceanic Observatory of Madeira, Portugal, (2)ARDITI - Agência Regional para o Desenvolvimento da Investigação Tecnologia e Inovação, Oceanic Observatory of Madeira, Funchal, Madeira, Portugal, (3)Ocean Observatory of Madeira, Portugal
Coastal dynamics on small oceanic islands was usually considered to be mostly influenced by offshore processes. A study, focused on Madeira Island (32.6˚N, 16.8˚W), showed that coastal processes, result from the interaction between the winds and tides with the island shelf. In order to study insular shelf circulation, the Regional Ocean Circulation Model was used considering four different configurations: a) global model forcing; b) local wind forcing; c) tidal forcing and d) all together (a-b-c). The results obtained from these simulations were analyzed with empirical orthogonal functions and Morlet wavelets analysis, in order to discern the dominant patterns and frequencies resulting from each scenario. The model results are also compared with in-situ data for validation. As a result, on the western-flank of the island the wind forcing dominates; whereas on the east-side tides act as the major influence on the coastal current. As for the north coast of the island, the major influence comes from the Basin Scale Atlantic Circulation, namely the Azores current and/or incoming mesoscale eddies. We conclude that the coastal dynamics of deep-sea islands are complex and respond to a set of different processes. Therefore, generalized wake studies often miss relevant local dynamics.