An arm of the Atlantic Ocean between Great Britain and northwest Europe. It is connected with the English Channel by the Strait of Dover. Major reserves of oil and natural gas were discovered beneath its waters in the late 1960s. the North Sea part of the Atlantic Ocean, between Great Britain and northwest Europe. It is economically important because of its fish, and also for oil and gas which were discovered there in the 1970s. ancient Mare Germanicum Arm of the Atlantic Ocean. Extending south from the Norwegian Sea between Norway and the British Isles, it connects the Skagerrak (channel between Norway and Denmark) with the English Channel. It is about 600 mi (970 km) long and 350 mi (560 km) wide, with an average depth of 308 ft (94 m). Parts of the sea feature deep trenches, while others have excellent fishing, renowned fisheries, and extensive oil and natural gas deposits