TheArctic Ocean is the smallest and shallowest of the world's fiveoceanic divisions.[1] It spans an area of approximately 14,060,000 km2 (5,430,000 sq mi) and is the coldest of the world's oceans. TheInternational Hydrographic Organization (IHO) recognizes it as an ocean, although someoceanographers call it theArctic Mediterranean Sea[2] orNorth Polar Sea.[3] It has also been described as anestuary of theAtlantic Ocean.[4][5] It is also seen as the northernmost part of the all-encompassingworld ocean.
The Arctic Ocean includes theNorth Pole region in the middle of theNorthern Hemisphere and extends south to about60°N. The Arctic Ocean is surrounded byEurasia andNorth America, and the borders follow topographic features: theBering Strait on thePacific side and the Greenland Scotland Ridge on the Atlantic side. It is mostly covered bysea ice throughout the year and almost completely inwinter. The Arctic Ocean'ssurface temperature andsalinity vary seasonally as theice cover melts and freezes;[6] its salinity is the lowest on average of the five major oceans, due to lowevaporation, heavyfresh water inflow from rivers and streams, and limited connection and outflow to surrounding oceanic waters with higher salinities. Thesummer shrinking of the ice has been quoted at 50%.[1] The USNational 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 continuousdecline in sea ice extent.[7] 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%.[8]
The Thule Tradition lasted from about 200 BC to AD 1600, arising around the Bering Strait and later encompassing almost the entire Arctic region of North America. The Thule people were the ancestors of the Inuit, who now live inAlaska,Northwest Territories,Nunavut, Nunavik (northern Quebec), Labrador and Greenland.[11]
For much ofEuropean history, the northpolar regions remained largely unexplored and their geography conjectural.Pytheas ofMassilia recorded an account of a journey northward in 325 BC, to a land he called "Eschate Thule", where the Sun only set for three hours each day and the water was replaced by a congealed substance "on which one can neither walk nor sail". He was probably describing loose sea ice known today as "growlers" or "bergy bits"; his "Thule" was probablyNorway, though theFaroe Islands orShetland have also been suggested.[12]
Emanuel Bowen's 1780s map of the Arctic features a "Northern Ocean".
Earlycartographers were unsure whether to draw the region around the North Pole as land (as inJohannes Ruysch's map of 1507, orGerardus Mercator's map of 1595) or water (as withMartin Waldseemüller's world map of 1507). The fervent desire of European merchants for a northern passage, theNorthern Sea Route or theNorthwest Passage, to "Cathay" (China) caused water to win out, and by 1723 mapmakers such asJohann Homann featured an extensive "Oceanus Septentrionalis" at the northern edge of their charts.
The few expeditions to penetrate much beyond theArctic Circle in that era added only small islands, such asNovaya Zemlya (11th century) andSpitzbergen (1596), though, since these were often surrounded bypack-ice, their northern limits were not so clear. The makers ofnavigational charts, more conservative than some of the more fanciful cartographers, tended to leave the region blank, with only fragments of known coastline sketched in.
This lack of knowledge of what lay north of the shifting barrier of ice gave rise to a number of conjectures. In England and other European nations, themyth of an "Open Polar Sea" was persistent.John Barrow, longtime Second Secretary of theBritish Admiralty,promoted exploration of the region from 1818 to 1845 in search of this.
In the United States in the 1850s and 1860s, the explorersElisha Kane andIsaac Israel Hayes both claimed to have seen part of this elusive body of water. Even quite late in the century, the eminent authorityMatthew Fontaine Maury included a description of the Open Polar Sea in his textbookThe Physical Geography of the Sea (1883). Nevertheless, as all the explorers who travelled closer and closer to the pole reported, thepolar ice cap is quite thick and persists year-round.
The first surface crossing of the ocean was led byWally Herbert in 1969, in adog sled expedition from Alaska toSvalbard, with air support.[13] The first nautical transit of the north pole was made in 1958 by the submarineUSSNautilus, and the first surface nautical transit occurred in 1977 by theicebreakerNSArktika.
Since 1937,Soviet and Russian manneddrifting ice stations have extensively monitored the Arctic Ocean. Scientific settlements were established on the drift ice and carried thousands of kilometres byice floes.[14]
In August 2019, US President Donald Trump suggested buying Greenland.[15][16] He raised the idea firmly inDecember 2024, saying ownership of Greenland was necessary for the national security and economic interests of the United States.[17][18] He has said the use of force is not ruled out.[19][20][21] In a December 10, 2024, social media post, President-elect Trump referred to the prime minister of Canada as the governor of a purported 51st state.[22][23] Previously he had said that annexation of Canada might be preferable from a trade point of view[24][25][26] On February 1, 2025, he began a trade war.[27][28]
During a telephone call with new Canadian Prime Minister Mark Carney on March 28, 2025, Trump raised the idea of Canada becoming the 51st U.S. state and described his view of the advantages ofannexation. In various other comments, formal and informal, he has expressed a desire to control Canada's resources and theCanadian Internal Waters of the Arctic, commonly known as the Northwest Passage.
Abathymetric/topographic map of the Arctic Ocean and the surrounding lands.TheArctic region; of note, the region's southerly border on this map is depicted by a redisotherm, with all territory to the north having an average temperature of less than 10 °C (50 °F) in July.
The Arctic Ocean occupies a roughly circular basin and covers an area of about 14,056,000 km2 (5,427,000 sq mi), almost the size ofAntarctica.[29][30] The coastline is 45,390 km (28,200 mi) long.[29][31] It is the onlyocean smaller thanRussia, which has a land area of 16,377,742 km2 (6,323,482 sq mi).
The Arctic Ocean is surrounded by the land masses of Eurasia (Russia and Norway), North America (Canada and the U.S. state of Alaska), Greenland, andIceland.
The ocean's Arctic shelf comprises a number ofcontinental shelves, including the Canadian Arctic shelf, underlying theCanadian Arctic Archipelago, and theRussian continental shelf, which is sometimes called the "Arctic Shelf" because it is larger. The Russian continental shelf consists of three separate, smaller shelves: the Barents Shelf,Chukchi Sea Shelf andSiberian Shelf. Of these three, the Siberian Shelf is the largest such shelf in the world; it holds large oil and gas reserves. The Chukchi shelf forms the border between Russian and the United States as stated in theUSSR–USA Maritime Boundary Agreement. The whole area is subject to internationalterritorial claims.
The two major basins are further subdivided by ridges into theCanada Basin (between Beaufort Shelf of North America and theAlpha Ridge),Makarov Basin (between the Alpha and Lomonosov Ridges),Amundsen Basin (between Lomonosov andGakkel ridges), andNansen Basin (between the Gakkel Ridge and the continental shelf that includes theFranz Josef Land).
The crystalline basement rocks of mountains around the Arctic Ocean were recrystallized or formed during the Ellesmerian orogeny, the regional phase of the largerCaledonian orogeny in thePaleozoic Era. Regional subsidence in theJurassic andTriassic periods led to significant sediment deposition, creating many of the reservoirs for current day oil and gas deposits. During theCretaceous period, the Canadian Basin opened, and tectonic activity due to the assembly of Alaska caused hydrocarbons to migrate toward what is now Prudhoe Bay. At the same time, sediments shed off the rising Canadian Rockies built out the large Mackenzie Delta.
The rifting apart of thesupercontinentPangea, beginning in the Triassic period, opened the early Atlantic Ocean. Rifting then extended northward, opening the Arctic Ocean asmafic oceanic crust material erupted out of a branch of Mid-Atlantic Ridge. The Amerasia Basin may have opened first, with theChukchi Borderland moved along to the northeast by transform faults. Additional spreading helped to create the "triple-junction" of the Alpha-Mendeleev Ridge in theLate Cretaceousepoch.
Throughout theCenozoic 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 thePaleocene Epoch and theEocene 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.[48][49]
Distribution of the majorwater mass in the Arctic Ocean. The section sketches the different water masses along a vertical section fromBering Strait over the geographicNorth Pole toFram Strait. As thestratification is stable, deeper water masses are denser than the layers above.Density structure of the upper 1,200 m (3,900 ft) in the Arctic Ocean. Profiles of temperature and salinity for the Amundsen Basin, the Canadian Basin and the Greenland Sea are sketched.
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-calledhalocline, in which both salinity and temperature rise with increasing depth.
Because of its relative isolation from other oceans, the Arctic Ocean has a uniquely complex system of water flow. It resembles some hydrological features of theMediterranean Sea, referring to its deep waters having only limited communication through the Fram Strait with theAtlantic Basin, "where the circulation is dominated by thermohaline forcing".[50] The Arctic Ocean has a total volume of 18.07 × 106 km3, equal to about 1.3% of the World Ocean. Mean surface circulation is predominantly cyclonic on theEurasian side and anticyclonic in theCanadian Basin.[51]
Water enters from both the Pacific and Atlantic Oceans and can be divided into three unique water masses. The deepest water mass is called Arctic Bottom Water and begins around 900 m (3,000 ft) depth.[50] It is composed of the densest water in the World Ocean and has two main sources: Arctic shelf water and Greenland Sea Deep Water. Water in the shelf region that begins as inflow from the Pacific passes through the narrow Bering Strait at an average rate of 0.8Sverdrups and reaches theChukchi Sea.[52] During the winter, cold Alaskan winds blow over the Chukchi Sea, freezing the surface water and pushing this newly formed ice out to the Pacific. The speed of the ice drift is roughly 1–4 cm/s.[51] This process leaves dense, salty waters in the sea that sink over the continental shelf into the western Arctic Ocean and create a halocline.[53]
This water is met by Greenland Sea Deep Water, which forms during the passage of winter storms. As temperatures cool dramatically in the winter, ice forms, and intense vertical convection allows the water to become dense enough to sink below the warm saline water below.[50] Arctic Bottom Water is critically important because of its outflow, which contributes to the formation of Atlantic Deep Water. The overturning of this water plays a key role in global circulation and the moderation of climate.
In the depth range of 150–900 m (490–2,950 ft) is a water mass referred to as Atlantic Water. Inflow from theNorth Atlantic Current enters through the Fram Strait, cooling and sinking to form the deepest layer of the halocline, where it circles theArctic Basin counter-clockwise. This is the highest volumetric inflow to the Arctic Ocean, equalling about 10 times that of the Pacific inflow, and it creates the Arctic Ocean Boundary Current.[52] It flows slowly, at about 0.02 m/s.[50] Atlantic Water has the same salinity as Arctic Bottom Water but is much warmer (up to 3 °C [37 °F]). In fact, this water mass is actually warmer than the surface water and remains submerged only due to the role of salinity in density.[50] When water reaches the basin, it is pushed by strong winds into a large circular current called theBeaufort Gyre. Water in the Beaufort Gyre is far less saline than that of the Chukchi Sea due to inflow from large Canadian and Siberian rivers.[53]
The final defined water mass in the Arctic Ocean is called Arctic Surface Water and is found in the depth range of 150–200 m (490–660 ft). The most important feature of this water mass is a section referred to as the sub-surface layer. It is a product of Atlantic water that enters through canyons and is subjected to intense mixing on the Siberian Shelf.[50][54] As it is entrained, it cools and acts a heat shield for the surface layer on account of weak mixing between layers.[55][56]
However, over the past couple of decades a combination of the warming[57] and the shoaling of Atlantic water[58] are leading to the increasing influence of Atlantic water heat in melting sea ice in the eastern Arctic. The most recent estimates, for 2016–2018, indicate the oceanic heat flux to the surface has now overtaken the atmospheric flux in the eastern Eurasian Basin.[59] Over the same period the weakening halocline stratification has coincided with increasing upper ocean currents thought to be associated with declining sea ice, indicate increasing mixing in this region.[60] In contrast direct measurements of mixing in the western Arctic indicate the Atlantic water heat remains isolated at intermediate depths even under the 'perfect storm' conditions of theGreat Arctic Cyclone of 2012.[61]
Waters originating in the Pacific and Atlantic both exit through the Fram Strait between Greenland and Svalbard Island, which is about 2,700 m (8,900 ft) deep and 350 km (220 mi) wide. This outflow is about 9 Sv.[52] The width of the Fram Strait is what allows for both inflow and outflow on the Atlantic side of the Arctic Ocean. Because of this, it is influenced by theCoriolis force, which concentrates outflow to the East Greenland Current on the western side and inflow to theNorwegian Current on the eastern side.[50] Pacific water also exits along the west coast of Greenland and the Hudson Strait (1–2 Sv), providing nutrients to the Canadian Archipelago.[52]
As noted, the process of ice formation and movement is a key driver in Arctic Ocean circulation and the formation of water masses. With this dependence, the Arctic Ocean experiences variations due to seasonal changes in sea ice cover. Sea ice movement is the result of wind forcing, which is related to a number of meteorological conditions that the Arctic experiences throughout the year. For example, the Beaufort High—an extension of theSiberian High system—is a pressure system that drives the anticyclonic motion of the Beaufort Gyre.[51] During the summer, this area of high pressure is pushed out closer to its Siberian and Canadian sides. In addition, there is asea level pressure (SLP) ridge over Greenland that drives strong northerly winds through the Fram Strait, facilitating ice export. In the summer, the SLP contrast is smaller, producing weaker winds. A final example of seasonal pressure system movement is the low pressure system that exists over the Nordic and Barents Seas. It is an extension of theIcelandic Low, which creates cyclonic ocean circulation in this area. The low shifts to centre over the North Pole in the summer. These variations in the Arctic all contribute to ice drift reaching its weakest point during the summer months. There is also evidence that the drift is associated with the phase of the Arctic Oscillation andAtlantic Multidecadal Oscillation.[51]
On the sea ice of the Arctic Ocean temporary logistic stations may be installed, Here, aTwin Otter is refueled on the pack ice at 86°N, 76°43‘W.
Much of the Arctic Ocean is covered by sea ice that varies in extent and thickness seasonally. The mean extent of the Arctic sea ice has been continuously decreasing in the last decades, declining at a rate of currently 12.85% per decade since 1980 from the average winter value of 15,600,000 km2 (6,023,200 sq mi).[63] The seasonal variations are about 7,000,000 km2 (2,702,700 sq mi), with the maximum in April and minimum in September. The sea ice is affected by wind and ocean currents, which can move and rotate very large areas of ice. Zones of compression also arise, where the ice piles up to form pack ice.[64][65][66]
Icebergs occasionally break away from northernEllesmere Island, and icebergs are formed fromglaciers in western Greenland and extreme northeastern Canada. Icebergs are not sea ice but may become embedded in the pack ice. Icebergs pose a hazard to ships, of which theTitanic is one of the most famous. The ocean is virtually icelocked from October to June, and thesuperstructure of ships are subject toicing from October to May.[44] Before the advent of modern icebreakers, ships sailing the Arctic Ocean risked being trapped or crushed by sea ice (although theBaychimo drifted through the Arctic Ocean untended for decades despite these hazards).
The Arctic Ocean is contained in apolar climate characterized by persistent cold and relatively narrow annual temperature ranges. Winters are characterized by thepolar night, extreme cold, frequent low-level temperature inversions, and stable weather conditions.[67]Cyclones are only common on the Atlantic side.[68] Summers are characterized by continuousdaylight (midnight sun), and air temperatures can rise slightly above 0 °C (32 °F). Cyclones are more frequent in summer and may bring rain or snow.[68] It is cloudy year-round, with mean cloud cover ranging from 60% in winter to over 80% in summer.[69]
The temperature of the surface water of the Arctic Ocean is fairly constant at approximately −1.8 °C (28.8 °F), near thefreezing point ofseawater.
Thedensity of sea water, in contrast to fresh water, increases as it nears the freezing point and thus it tends to sink. It is generally necessary that the upper 100–150 m (330–490 ft) of ocean water cools to the freezing point for sea ice to form.[70] In the winter, the relatively warm ocean water exerts a moderating influence, even when covered by ice. This is one reason why the Arctic does not experience the extreme temperatures seen on theAntarctic continent.
There is considerable seasonal variation in how much pack ice of the Arctic ice pack covers the Arctic Ocean. Much of the Arctic ice pack is also covered in snow for about 10 months of the year. The maximum snow cover is in March or April—about 20–50 cm (7.9–19.7 in) over the frozen ocean.
The climate of the Arctic region has varied significantly during the Earth's history. During thePaleocene–Eocene Thermal Maximum 55 million years ago, when the global climate underwent a warming of approximately 5–8 °C (9–14 °F), the region reached an average annual temperature of 10–20 °C (50–68 °F).[71][72][73] The surface waters of the northernmost[74] Arctic Ocean warmed, seasonally at least, enough to support tropical lifeforms (thedinoflagellatesApectodinium augustum) requiring surface temperatures of over 22 °C (72 °F).[75]
Currently, the Arctic region is warming twice as fast as the rest of the planet.[76][77]
Endangered marine species in the Arctic Ocean includewalruses andwhales. The area has a fragileecosystem, and it is especially exposed toclimate change, because it warms faster than the rest of the world.Lion's mane jellyfish are abundant in the waters of the Arctic, and thebanded gunnel is the only species ofgunnel that lives in the ocean.
The political dead zone near the centre of the sea is also the focus of a mounting dispute between the United States, Russia, Canada, Norway, and Denmark.[82] It is significant for the globalenergy market because it may hold 25% or more of the world's undiscovered oil and gas resources.[83]
TheArctic ice pack is thinning, and a seasonal hole in theozone layer frequently occurs.[84] Reduction of the area of Arctic sea ice reduces the planet's averagealbedo, possibly resulting in global warming in a positive feedback mechanism.[66][85] Research shows that the Arctic may become ice-free in the summer for the first time in human history by 2040.[86][87] Estimates vary for when the last time the Arctic was ice-free: 65 million years ago when fossils indicate that plants existed there to as recently as 5,500 years ago; ice and ocean cores going back 8,000 years to thelast warm period or 125,000 during thelast intraglacial period.[88]
Warming temperatures in the Arctic may cause large amounts of freshmelt-water to enter the north Atlantic, possibly disrupting globalocean current patterns. Potentially severe changes in the Earth'sclimate might then ensue.[85]
As the extent of sea ice diminishes andsea level rises, the effect of storms such as theGreat Arctic Cyclone of 2012 on open water increases, as does possible salt-water damage to vegetation on shore at locations such as the MackenzieDelta as strongerstorm surges become more likely.[89]
Global warming has increased encounters between polar bears and humans. Reduced sea ice due to melting is causing polar bears to search for new sources of food.[90] Beginning in December 2018 and coming to an apex in February 2019,a mass invasion of polar bears into the archipelago ofNovaya Zemlya caused local authorities to declare a state of emergency. Dozens of polar bears were seen entering homes, public buildings and inhabited areas.[91][92]
The Permian–Triassic extinction event (theGreat Dying) may have been caused by release ofmethane fromclathrates. An estimated 52% of marinegenera became extinct, representing 96% of all marinespecies.
Sea ice, and the cold conditions it sustains, serves to stabilizemethane deposits on and near the shoreline,[93] preventing theclathrate breaking down and outgassing methane into the atmosphere, causing further warming. Melting of this ice may release large quantities of methane, a powerfulgreenhouse gas, into theatmosphere, causing further warming in a strongpositive feedback cycle and marine genera and species to become extinct.[93][94]
On 16 July 2015, five nations (United States, Russia, Canada, Norway, Denmark/Greenland) signed a declaration committing to keep their fishing vessels out of a 1.1 million square mile zone in the central Arctic Ocean near the North Pole. The agreement calls for those nations to refrain from fishing there until there is better scientific knowledge about the marine resources and until a regulatory system is in place to protect those resources.[99][100]
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^Drill cores were recovered from theLomonosov Ridge, presently at 87°N
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