The Arctic Ocean is the smallest and shallowest of the world’s five major oceans.
It spans an area of approximately 14,060,000 km2 (5,430,000 sq mi) and is also known as the coldest of all the oceans.
It has been described approximately as an estuary of the Atlantic Ocean.
It is also seen as the northernmost part of the all-encompassing World Ocean.
The Arctic Ocean includes the North Pole region in the middle of the Northern Hemisphere and extends south to about 60°N. The Arctic Ocean is surrounded by Eurasia and North America, and the borders follow topographic features: the Bering Strait on the Pacific side and the Greenland Scotland Ridge on the Atlantic side.
It is mostly covered by sea ice throughout the year and almost completely in winter.
The Arctic Ocean’s surface temperature and salinity vary seasonally as the ice cover melts and freezes; its salinity is the lowest on average of the five major oceans, due to low evaporation, heavy fresh water inflow from rivers and streams, and limited connection and outflow to surrounding oceanic waters with higher salinities.
The summer shrinking of the ice has been quoted at 50%.
The US National Snow and Ice Data Center (NSIDC) uses satellite data to provide a daily record of Arctic sea ice cover and the rate of melting compared to an average period and specific past years, showing a continuous decline in sea ice extent.
In September 2012, the Arctic ice extent reached a new record minimum.
Compared to the average extent (1979–2000), the sea ice had diminished by 49%.The crystalline basement rocks of mountains around the Arctic Ocean were recrystallized or formed during the Ellesmerian orogeny, the regional phase of the larger Caledonian orogeny in the Paleozoic Era.
Regional subsidence in the Jurassic and Triassic periods led to significant sediment deposition, creating many of the reservoirs for current day oil and gas deposits.
The rifting apart of the supercontinent Pangea, beginning in the Triassic period, opened the early Atlantic Ocean.
Rifting then extended northward, opening the Arctic Ocean as mafic oceanic crust material erupted out of a branch of Mid-Atlantic Ridge.
The Amerasia Basin may have opened first, with the Chukchi Borderland moved along to the northeast by transform faults.
Additional spreading helped to create the “triple-junction” of the Alpha-Mendeleev Ridge in the Late Cretaceous epoch.
Throughout the Cenozoic Era, the subduction of the Pacific plate, the collision of India with Eurasia, and the continued opening of the North Atlantic created new hydrocarbon traps.
The seafloor began spreading from the Gakkel Ridge in the Paleocene Epoch and the Eocene Epoch, causing the Lomonosov Ridge to move farther from land and subside.
Because of sea ice and remote conditions, the geology of the Arctic Ocean is still poorly explored.
The Arctic Coring Expedition drilling shed some light on the Lomonosov Ridge, which appears to be continental crust separated from the Barents-Kara Shelf in the Paleocene and then starved of sediment.
It may contain up to 10 billion barrels of oil.
The Gakkel Ridge rift is also poorly understand and may extend into the Laptev Sea.
In large parts of the Arctic Ocean, the top layer (about 50 m [160 ft]) is of lower salinity and lower temperature than the rest.
It remains relatively stable because the salinity effect on density is bigger than the temperature effect.
It is fed by the freshwater input of the big Siberian and Canadian rivers (Ob, Yenisei, Lena, Mackenzie), the water of which quasi floats on the saltier, denser, deeper ocean water.
Between this lower salinity layer and the bulk of the ocean lies the so-called halocline, in which both salinity and temperature rise with increasing depth.