:: Geographic Settings
The Azores, Madeira and Canary Archipelagos lies in the eastern North Atlantic where the sub-tropical Azorean anticyclone mainly determine the predominant weather conditions and its consequent trade winds, currents and oceanographic parameters.
The Azores Archipelago is located on the Atlantic Ridge (37º - 40ºN; 25º - 32ºW) at 900 km NW of the Madeira Archipelago (32º - 33ºN; 16º - 17ºW) and at 1400 km NW of the Canary Archipelago (27º - 30ºN; 13º - 18ºW) these last two being in front of the NW African coast.
Despite the geographic distance between these archipelagos, they make part of the particular Macaronesian biogegraphic region, and are therefore conditioned by similar oceanographic and ecological factors.
To better understand the similar environmental factors between the archipelagos we will briefly describe the role of the Azorean anticyclone. The normal position of this anticyclone is SW of the Azores Islands. However, yearly variations do occur and, during the summer, it moves NE increasing the atmosphere pressure in its centre from 1025 to about 1035 mb.
In the winter, the Azorean anticyclone shifts southward of its normal position associated with a high-pressure system between 30º N and 40º N. The surface currents present in these archipelagos follow the general surface circulation of the N Atlantic Gyre, given the predominance of the Azorean anticyclone. The eastern part of the N Atlantic Subtropical Gyre is made up of four ocean current systems: the Azorean Current, The Portuguese Current, the Canary Current and the N Equatorial Current.
The Azorean Current flows eastwards to the S of the Azores Islands and then becomes narrower and shifts S. It passes N of Madeira and splits into a northward flow, which joins the Portuguese Current, and the S flow which forms the Canaries Current. The Canaries Current flows S past Madeira Islands and along the African coast, and when in the S of the Canary Archipelago, meets with a northward flow originating from the S (Fig. 1).
These currents, together with similar geological characteristics (all the islands are of volcanic origin except Fuerteventura and Lanzarote, which originated by splitting off from the African mainland), and similar bottoms topography, having narrow continental shelf’s and step drops to depths of 4000 m, reflect limitations to plankton productivity. These limitations are caused by the shortage of nutrients, and the upwelling seems non-existent.
Therefore the surrounding waters of these archipelagos are considered oligotrophic. This is despite the fact that recent studies described the occurrence of a few localized eddies, fronts and patches of cold water with high chlorophyll concentrations on the flanks of these islands and seamounts, which could justify the presence of migratory whales. The fish fauna of the more coastal waters, not naturally over-abundant, has been further depleted by over fishing during the last half century.
There is, on the other hand, a rich deep-sea fauna living above the continental slope and pelagic fish such as tunny and mackerel abound. This could feed and justify resident populations like the pilot whale.
These archipelagos are on a Sub-tropical to Temperate region, with salinities oscillating between 36 and 37 psu.
As regards surface seawater temperatures, there is no great contrast between the summer and winter, with median amplitude of annual variation of 5º C. In the Azores Archipelago the surface sea water temperatures varies from 15º to 22º C, in Madeira from 17º to 24º C, and in Canary from 19º to 26º C.