Region V – Wider Atlantic
Region V is dominated by the North Atlantic Current. The northern sections divert into the North Sea and Norwegian Sea, while a more southerly branch forms the easterly Azores Current that coincides with the southern boundary of the OSPAR area.
Region V is subdivided into two biogeographic regions. To the north of 40° N, the deep mixing of the water column during winter and its stratification in summer results in a strong seasonal cycle of primary production. To the south, the upper water column is stratified throughout the year and so the annual productivity is both lower and less variable seasonally. This causes major differences in the pelagic and benthic ecology, with biological activity almost totally dependent on production in the upper layers of the ocean that receive enough sunlight for photosynthesis. The benthic communities are too deep to be directly supported by photosynthesis, except within the coastal fringes of the Azores, and depend on organic matter sinking or being transported downward.
Biodiversity in Region V is less well-quantified than in the other Regions, particularly in the deep waters. Many deep-sea species have an extensive geographical range due to the small environmental variations in their habitat. Top predators such as sharks probably play an important role in maintaining the structure and diversity of fish communities, which include several long-lived and slow-growing species. Large pelagic predators (tuna and marlin) are highly migratory, ranging far beyond the boundaries of Region V. Region V is also important for Europe’s threatened sea turtles and some oceanic seabirds such as Cory’s shearwater. The main benthic habitats are the flat, featureless abyssal plains, but rising out of these the Mid-Atlantic Ridge, the continental slope and seamounts support vulnerable deep-sea habitats, such as cold-water coral reefs and deep-sea sponge aggregations. These have highly diverse biological communities with many endemic species. Hydrothermal vents along the Mid-Atlantic Ridge support particularly specialised and largely endemic communities.