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How Many Oceans Are There?

By Oishimaya Sen Nag September 16 2019

A map showing the oceans of the world.
A map showing the oceans of the world.

Oceans, large bodies of saline water, cover approximately 72% of the Earth’s surface. The oceans contain 97% of the water on Earth. Little is known about the origin of our planet’s oceans. It is estimated that they formed during the Hadean period and were responsible for the emergence of life on Earth. Historically, the world was thought to have four oceans: the Pacific, Atlantic, Indian, and Arctic. However, in many countries, the Southern (or the Antarctic) Ocean is also counted. Together, these five oceans of the world are responsible for influencing the climate and weather patterns on the planet. They also help in maintaining the carbon and water cycle that are vital to life on Earth. The oceans of the world host around 230,000 marine species. More species might be discovered if humans were to explore the greater depths of the oceans. Here, we present the five oceans of the world, their boundaries and dimensions, habitat and biodiversity, threats and other key features.

5. Arctic Ocean

The smallest and shallowest of the oceans of the world, the Arctic Ocean is located in the Northern Hemisphere’s Arctic north polar region. The Arctic Ocean has a roughly circular basin that is nearly completely enclosed by the continental landmasses of North America, Eurasia, Greenland, and several smaller islands. The area occupied by the ocean is about 14,056,000 square km, and its coastline extends for 45,390 km. The maximum recorded depth is found to be 18,456 feet. The Bering Strait connects the Arctic Ocean to the Pacific Ocean. The Greenland Sea and the Labrador Sea forms the connection between this ocean and the Atlantic Ocean. The countries bordering the Arctic Ocean are US, Canada, Iceland, Greenland, Norway, and Russia. Barrow and Prudhoe Bay in Alaska; Churchill, Nanisivik, and Inuvik in Canada; Nuuk in Greenland; Kirkenes, Vardø, and Longyearbyen in Norway; and a number of ports like Murmansk, Tiksi, and Pevek in Russia, all lie on the Arctic coast.

The Arctic Ocean is located in a polar climatic zone characterized by frigid year-round temperatures. Long hours of darkness engulf the ocean during winters and summers are characterized by continuous daylight. The marine habitat of the Arctic Ocean is a fragile ecosystem that is highly susceptible to slight disruptions in weather. Threatened species of whales and walruses inhabit the ocean. Plant life in the Arctic Ocean is scarce with the exception of abundant volumes of phytoplanktons. The Lion’s mane jellyfish and the banded gunnel are among the few species of marine creatures inhabiting the Arctic Ocean’s waters. The ocean bed also hosts petroleum and natural gas fields, polymetallic nodules, and placer deposits.

Like other oceans of the world, climate change threatens to adversely affect the marine ecosystem of the Arctic Ocean. As per research, the Arctic might become ice-free by 2040. This transformation would load the Arctic with large volumes of meltwater and affect the ocean currents prevailing in the region. These alterations would, in turn, cause a drastic change in global climate.

4. Southern Ocean

Encircling Antarctica, south of the 60° S latitude, is the Southern Ocean or the Antarctic Ocean. It is the southernmost of the oceans and the fourth largest of the five oceans of the world. Though the Southern Ocean does not have a landmass bordering it to the north, it is treated as a separate oceanic division due to the difference in water properties of the ocean south of the 60° S latitude. It is a deep ocean with depth ranging between 4,000 and 5,000 m across most parts. 

Researchers estimate that the Southern Ocean seabed is a storehouse of massive oil and gas fields, valuable minerals like gold, placer deposits, manganese nodules, and more. The icebergs of the Southern Ocean are treated as freshwater resources, sufficient to feed every person on Earth for a period of several months. The Southern Ocean is also one of the most dangerous ocean for ships. Choppy seas, storms, and iceberg interventions are common. The remoteness also prevents rescue missions from reaching the ships in need.

The Southern Ocean is home to unique species specially adapted to survive the frigid weather conditions. Penguins, orcas, whales, seals, colossal squids are some of the most notable species of the Southern Ocean. A large number of migratory birds can be spotted in the oceanic region and Antarctica. These include terns, gulls, albatrosses, skuas, petrels, etc. Several threats are experienced by the marine inhabitants of the Southern Ocean. The Antarctic ozone hole in the ozone layer above allows harmful UV rays to reach the marine habitat, reducing phytoplankton by as much as 15%. Unregulated fishing also reduces the fish stock in the ocean which disturbs the food chain and affects the survival of the other species in the chain.

3. Indian Ocean

The Indian Ocean occupies 68,556,000 square km area on the Earth’s surface. The Asian landmass borders the Indian Ocean to the north, Australia to the east, Africa to the west and the Southern Ocean and Antarctica to the south. 3,890 m is the average depth of the Indian Ocean, and its deepest point is Diamantina Deep. The depth in this region is 8,047 m.

The Indian Ocean region experiences a monsoon type of climate during the monsoon season. Cyclones are common during the summer season. This ocean is also the warmest ocean in the world. The warm tropical waters of the ocean support a great diversity of life. The abundance of phytoplanktons and aquatic flora supports a complex food chain. Thus, the Indian Ocean offers lucrative fishing grounds and fish from this ocean, especially tuna and shrimp are sold in worldwide markets. However, despite this great biodiversity, climate change is taking its toll on the Indian Ocean ecosystem. Overfishing in the waters is also disturbing the marine ecosystem.

2. Atlantic Ocean

The Atlantic Ocean spans an area of 106,4060,000 square km, about 20% of the Earth’s surface. The Atlantic Ocean is bounded by the landmasses of North and South America to the west and Asia and Africa to the east. The Arctic Ocean lies to its north, the Southern Ocean to its south, Pacific to the southwest and Indian Ocean to the southeast. The average depth of the Atlantic Ocean is 3,339 m and the Milwaukee Deep (8,380 m) in the Puerto Rico Trench, is its deepest known point.

Since the Atlantic Ocean is vast, its climate varies widely from the north to the south. Warm and cold ocean currents in the Atlantic also influence the climate of the coastal areas on the shores of the Atlantic. The Gulf Stream and the North Atlantic Drift are responsible for keeping large parts of the coast of north-western Europe and the British Isles warm when the coast of Newfoundland in Canada on the same latitude experiences extreme temperatures in winter.

The Atlantic Ocean has contributed significantly to the economy of many nations. Petroleum deposits on the Atlantic’s floor, precious stones, placer deposits, and polymetallic nodules are abundant. The Atlantic also hosts rich fishing resources with haddock, cod, mackerel, herring being the chief commercially important fish species.

Several rare and threatened species of marine life like sea turtles, whales, dolphins, manatees, seals, sea lions abound in the Atlantic. Frequent oil spills, municipal sewage pollution, industrial pollution, bycatch during irresponsible and outdated fishing activities all threaten the marine life in the Atlantic Ocean.

1. Pacific Ocean

The largest of the oceans of the world, the Pacific Ocean is bounded by the Arctic Ocean to the north, the Southern Ocean to the south, Australia, and Asia to the west and the Americas to the east. Spanning an area of 165.25 million square km, the Pacific Ocean accounts for one-third of the total surface area of the planet. The deepest point in the Pacific Ocean is the Mariana Trench (10,911 m) located in the western North Pacific.

Large parts of the Pacific remain unexplored due to its great depths. However, in the relatively shallow waters off the coast of Australia and New Zealand, petroleum and natural gas deposits have been discovered. Pearl extraction is also common in the Pacific waters. A large variety of fish like tuna, salmon, swordfish, herring, snapper, etc., abound in the Pacific waters.

Today, the Pacific Ocean and its marine life are not safe. A large number of highly polluted rivers from the countries of southeast Asia and east Asia drain into this ocean, filling the ocean with harmful toxins. Fertilizer and pesticide wash-off from agricultural fields, sewage, and industrial wastes all drain into the ocean via these rivers. Excess of oxygen depleting pollutants triggers hypoxia and creates dead zones in the ocean. Overfishing in the Pacific has also depleted its marine wealth greatly. A number of rare and threatened species have also been lost as bycatch.

5 Oceans of the World By Size

RankOceanSize (in sq km, estimated)
1Pacific 165,250,000

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