Salt-Finger Convection in the Warm Wake of Madeira Island

The interaction between winds with mountainous islands induces the generation of vortex shedding in the atmosphere, which contributes to weaker winds and the clearing of clouds on the leeward side, exposing the sea surface to intense solar radiation. This in turn results in an increase in the Sea Surface Temperature in the lee, forming what is known as a ‘warm wake’. Approximately 700 profiles (CTD; Rosette; UCTD) of temperature and salinity were used for the characterization and quantification of a diffusive layer (25-70 m) and its variation within the Madeira island warm wake. These layers develop when parcels of hot and dense water sink over cold and less dense water, favouring the formation of salt-fingering. This phenomenon was observed on a stretch of ~30 km, on the southwest coast of the island (17.3⁰W; 16.9⁰W) and its regimes were verified with Turner-angle and density ratio (Rp) calculations. In exposed regions, particularly in the southeast and north coast of the island, the process was not so evident, showing that the warm wake effect is a significant contributor to vertical mixing in the open-ocean, leeward of these islands.