A two-kilometre-deep sea keeps Norway's coast free of ice all year
Off Norway's northwestern coast, with the North Sea to its south and the Greenland Sea to its north, the Norwegian Sea drops far beyond any continental shelf, averaging about two kilometres deep. Warm Atlantic water keeps it unfrozen through every winter, and oil and gas lie beneath its shallower margins.
The sea began opening about 250 million years ago as the plate carrying Norway pulled away from the one carrying Greenland, and today's continental slope marks roughly where the two landmasses once met. Settling of the shelf afterwards triggered huge landslides, including the Storegga Slide about 8,000 years ago and its tsunami. Offshore, two deep basins are split by a low ridge between the Vøring Plateau and Jan Mayen; the southern one reaches 3,500 to 4,000 metres. The Norwegian shelf, 40 to 200 kilometres wide, was gouged by ice-age glaciers several kilometres thick, which also cut the fjords.
Four water masses meet here. The warm, salty North Atlantic Current flows in at about 10 million cubic metres a second, cooling from roughly 9.5 °C near the Faroes to 5 °C off Svalbard and releasing some 250 terawatts of heat. Researchers now think this vast store of warm water does more for Norway's mild winters than the Gulf Stream itself. Below 2,000 metres lies old, nutrient-rich deep water colder than 0 °C, and because the Greenland–Scotland Ridge averages only 500 metres deep, little of it escapes; what does spill over helps form North Atlantic Deep Water, one of the currents that supplies the deep ocean with oxygen.
Unlike neighbouring Arctic seas it never freezes, and the 10 °C July air isotherm along its northern edge is often treated as the southern limit of the Arctic. Surface water ranges from 2 to 7 °C in February to 8 to 12 °C in August. Cod come in from the Atlantic and the Barents Sea to spawn in its coastal waters, and Arctic and boreal species overlap across its middle. Oil and gas are produced commercially where the water is up to about a kilometre deep.
Source: Norwegian Sea
