The Barents Sea is a marginal sea of the Arctic Ocean, located north of Norway and Russia. Known in the Middle Ages as the Murman Sea, the sea takes its current name from the Dutch navigator Willem Barents. It is a rather deep shelf sea (average depth 760 feet (230 m) and maximum depth 1,480 feet (450 m)), bordered by the shelf edge towards the Norwegian Sea in the west, the islands of Svalbard (Norway) in the northwest, and the islands of Franz Josef Land and Novaya Zemlya (Arkhangelsk Oblast) in the northeast and east. Novaya Zemlya separates the Kara Sea from the Barents Sea. Significant fossil fuel energy resources exist in the Barents Sea region.
The southern half of the Barents Sea, including the ports of Murmansk (Russia) and Vardø (Norway) remain ice-free year round due to the warm North Atlantic drift. In September, the entire Barents Sea is more or less completely ice-free. Until the Winter War (1939–40), Finland's territory also reached to the Barents Sea, with the harbor at Petsamo being Finland's only ice-free winter harbor.
There are three main types of water masses in the Barents Sea: Warm, salty Atlantic water (temperature >3°C, salinity >35) from the North Atlantic drift, cold Arctic water (temperature <0°C, salinity <35) from the north, and warm, but not very salty coastal water (temperature >3°C, salinity <34.7). Between the Atlantic and Polar waters, a front called the Polar Front is formed. In the western parts of the sea (close to Bear Island), this front is determined by the bottom topography and is therefore relatively sharp and stable from year to year, while in the east (towards Novaya Zemlya), it can be quite diffuse and its position can vary a lot between years.
Due to the North Atlantic drift, the Barents Sea has a high biological production compared to other oceans of similar latitude. The spring bloom of phytoplankton can start quite early close to the ice edge, because the fresh water from the melting ice makes up a stable water layer on top of the sea water. The phytoplankton bloom feeds zooplankton such as Calanus finmarchicus, Calanus glacialis, Calanus hyperboreus, Oithona spp., and krill.
The zooplankton feeders include young cod, capelin, polar cod, whales, and Little Auk. The capelin is a key food for top predators such as the North-East Arctic cod, harp seals, and seabirds such as Common Guillemot and Brunnich's Guillemot. The fisheries of the Barents Sea, in particular the cod fisheries, are of great importance for both Norway and Russia.