A flooded portion of the northwest continental margin of Europe occupying an area of over 200,000 mi2 (500,000 km2). The North Sea has extensive marine fisheries and important offshore oil and gas reserves. In the south, its depth is less than 150 ft (50 m), but north of 58° it deepens gradually to 600 ft (200 m) at the top of the continental slope. A band of deep water down to 1200 ft (400 m) extends around the south and west coast of Norway and is known as the Norwegian Trench. The nontidal residual current circulation of the southern North Sea is mainly determined by wind velocity, but in the north, well-defined non-wind-driven currents have been identified, especially in the summer. Two of these currents bring in water from outside the North Sea; one flows through the channel between Orkney and Shetland (the Fair Isle current), and the other follows the continental slope north of Shetland and merges with the Fair Isle current southwest of Norway before entering the Skagerrak. The north-flowing Norwegian coastal current provides the exit route for North Sea waters, and is formed from the waters of these two major inflows and from other much smaller inputs such as river runoff, the English Channel, and the Baltic Sea. There is a rich diversity of zooplankton within the North Sea. Copepods are of particular importance in the food web. There are a wide range of fish stocks in the North Sea and adjacent waters and, in terms of species exploited by commercial fisheries, they constitute the richest area in the northeast Atlantic. The commercially important stocks exploited for human consumption include cod, haddock, whiting, pollock, plaice, sole, herring, mackerel, lobster, prawn, and brown shrimp (Crangon crangon). A number of stocks are used for fishmeal and oil; these stocks include sand eel, Norway pout, blue whiting, and sprat. Marine ecology Zooplankton |
