Portuguese EEZ - Environment

Most of the water masses in the region are of either North Atlantic origin, or result from interaction between water from the Atlantic, mixed with Mediterranean water. The region is affected by both subpolar and subtropical gyres depending on latitude, but the general circulation in the area mainly follows the subtropical anticyclonic gyre, although relatively weakly (1-2 cm.s-1).
The circulation off the west coast of the Iberian Peninsula is characterized by a complex current system subject to strong seasonality and mesoscale variability, showing reversing patterns between summer and winter in the upper layers of the slope and outer shelf. During spring and summer, northerly winds along the coast are dominant causing coastal upwelling and producing a southward flow at the surface and a northward undercurrent at the slope.
Summer upwelling is important in the Western Iberian Sea, as the occurrence of upwelling pulses during the summer inject nutrients to the surface layer. This fuels primary production. Under conditions of moderate upwelling, the innermost coastal 25 km are about 10 times more productive than offshore waters and the upwelling centres are about 20 times more productive. Upwelling generally develops between April and October. The Portuguese coastal upwelling is part of a more general system that extends southward to 15ºN, the Canary Current Large Marine Ecosystem. Upwelling influences fish growth and recruitment.
In the autumn and winter, the surface circulation is predominantly northward, partially driven by meridional alongshore density gradients, and higher salinity and warmer (subtropical) waters are transported over the slope and shelf break, the Iberian Poleward Current. These waters are nutrient poor and contribute to fronts which determine the distribution of plankton, fish eggs and larvae.
The North Atlantic Oscillation (NAO) is a complex climatic phenomenon in the North Atlantic Ocean associated with fluctuations of climate between Iceland and the Azores. It is characterised by cyclical fluctuations of air pressure and changes in storm tracks across the North Atlantic. It is the principal climate influence at middle and high latitudes of the North Atlantic Ocean. For example, the NAO induces changes in sea surface temperature (SST) and variations in the upwelling patterns of the Eastern North Atlantic. Changes in the NAO appear to have had substantial impacts on marine ecosystem ecology, in particular, on fish productivity. While broad trends are evident, the mechanisms are poorly understood. Studies are being undertaken on the relationship between NAO and fish recruitment and growth.
Temperature in the studied region is influenced by Mediterranean waters in the south, where they are highest. Furthermore, an increase in mean SST has been observed over the past decades. Increasing temperatures can lead to changes in the biological structure of the ecosystem and effect physiological processes.
The sediment covering the continental margin generally originates from the continent. The inner shelf (depth <100 m) is mainly rocky or sandy substrate, whereas the outer shelf is predominantly covered in muddy substrate.