How Many Oceans Are There?

By Jesslyn Shields | How Stuff Works

Planet Earth, when viewed from space, has been described as a “blue marble.” This is, of course, because it’s covered in water. Our planet sustains life partially thanks to the 321,003,271 cubic miles (1,338,000,002 cubic kilometres) of salt water that continually circulates around and between the comparatively small bits of exposed land.

Oceans make up 70% of Earth’s surface, and almost 97% of global water is stored in them. Not only that, for much of the past 4 billion years, life on Earth has been doing its business almost exclusively in the ocean. You wouldn’t be breathing right now if it weren’t for the phytoplankton that make around 70% of the oxygen in the atmosphere.

As surrounded by water as we are, it’s strange that we know so little about the world oceans. For instance, we have yet to map over 85% of the ocean floor to the same resolution we’ve mapped the surface of Venus, we’ve only discovered about a third of the marine life lurking in the world’s oceans and we can’t account for most of the trillions of tons of plastic that’s ended up in the world’s oceans.

With all that we still don’t know about the oceans, how many oceans are there in the world?

How Many Oceans Are There In The World?

Humans have gotten into the habit of separating the one big, continuous, mysterious body of water that covers the globe into principle sectors that we call oceans. Historically, there were just four oceans, but we now recognize five different oceans: the Pacific Ocean, Atlantic Ocean, Arctic Ocean, Indian Ocean, and the recently added fifth ocean, the Southern Ocean.

The Atlantic, Indian and Pacific freeze together around Antarctica.

How Do We Separate The World’s Oceans?

There are no real barriers between the world’s oceans like there are with landmasses, mostly because bodies of water are often what we use to create geographical boundaries. Just like an island’s borders are drawn by water, continents mostly use oceans to describe their boundaries. There is only one global ocean, and yet we have to make distinctions between areas, for geography’s sake.

So, although the Atlantic Ocean isn’t technically a separate body of water from the Pacific Ocean, people call the Drake Passage — the narrow keyhole of water between Antarctica and Cape Horn at the tip of South America — the boundary between the two oceans. Although you might find videos online purporting to prove the waters of  two oceans don’t mix, there is no possible way to separate any of the world’s seawater.

The Newest Addition

The Southern Ocean surrounding Antarctica has been in name limbo for the better part of the past century. Before 1937, the body of water circling our planet’s southernmost continent was recognized by the International Hydrographic Organization (IHO), but its status was revoked in 1953.

In 1999, the National Oceanic and Atmospheric Administration (NOAA) decided that the Southern Ocean should be recognized as a separate body of water, but it took until 2021 for the IHO and the National Geographic Society to recognize it as separate from the Pacific Ocean.

The 5 Oceans of Planet Earth

All the oceans are pretty similar — after all, they’re all the same body of water. However, subtle differences in temperature, salinity and density exist between the oceans. For instance, the Atlantic Ocean is slightly saltier than the Pacific, due to a dizzying number of factors, from the way the water cycle works to the effects of hydrothermal vents.

Pacific Ocean

The Pacific Ocean is the largest and deepest of the five oceans, its waters covering more than 30% of the globe and holding more than half of the world’s above-ground water. The Pacific covers 60 million square miles (155 million square kilometres), which is larger than the area of all the continents combined. Challenger Deep, the deepest spot in any ocean anywhere on Earth, is in the Pacific Ocean’s ultra-deep Mariana Trench.

The Pacific Ocean was named by Ferdinand Magellan in 1520, who sailed through a particularly peaceful corner of the ocean and named it for its tranquil waters. Truth is, the Pacific stirs up some of the most ferocious storms on the planet and is home to the “Ring of Fire,” the most seismically and volcanically active spot in the world.

Atlantic Ocean

The Atlantic Ocean is the second largest ocean in the world. With an area of about 41 million square miles (106,460,000 square kilometres), it covers about 23% of the Earth’s surface. The Atlantic is much wider in some spots than others — in parts it is around 3,000 miles (4,800 kilometres) wide, but between Brazil and Liberia it’s only 1,770 miles (2,850 kilometres) wide. This narrowing and widening gives the Atlantic a distinctive “S” shape.

Along its margins, the Atlantic has several marginal seas that open into it. The Hudson Bay, the Caribbean Sea, the Mediterranean Sea and the English Channel are all shallow seas that feed into the Atlantic Ocean.

Indian Ocean

With an area of 27,243,000 square miles (70,560,000 square kilometres), the Indian Ocean is the third largest of the world’s oceans and the only ocean that is enclosed on three sides. Bordered by Africa, Asia and Australia, the Indian Ocean opens to the Southern Ocean, where it exchanges waters with the much colder body of water. In fact, there is no agreement among cartographers about exactly where the Indian Ocean ends and the Southern ocean begins, but it’s generally considered to be around the latitude 60 degrees S.

Because much of the Indian Ocean sits around the equator, it has the warmest ocean temperatures of any ocean.

Southern Ocean

The Southern Ocean is the fourth largest ocean in the world, as well as the most recently recognized. It has a total area of 7,848,300 square miles (20,327,000 square kilometres), and it has the greatest average depth of any ocean, with very few shallow areas.

Unlike most oceans, the Southern Ocean is separated from its neighbours by a current rather than by landmasses. The Antarctic Circumpolar Current (ACC) is the strongest ocean current on the planet, carrying up to 182 million cubic meters of water every second. Spinning from west to east around the continent of Antarctica, its flow separates the Southern Ocean from the saltier waters of the Atlantic, Pacific and Indian, carrying more than 100 times the flow of all the rivers on Earth.

Arctic Ocean

The Arctic Ocean is a tiny, shallow ocean, compared to its giant friends. At 5,427,000 square miles (14,056,000 square kilometres), it accounts for about 4% of the Earth’s surface area. The Arctic Ocean is the coldest of all the oceans, mostly because a large portion of it remains covered in ice year-round.

Starting in the 15^th century, the Arctic Ocean was a hot spot for sea exploration, as European explorers and merchants were eager to find a northern sea route between the Atlantic and Pacific Oceans so they could more easily trade with Asia. Many expeditions ended in disaster, but in 1906 the Norwegian explorer Roald Amundsen picked his way from the Atlantic to the Pacific by way of the Northwest Passage.

Now That’s Interesting

Earth’s oceans absorb around 26% of the carbon dioxide humans emit into the atmosphere.

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READ MORE: How Many of US Are Drinking Toxic Forever Chemicals?

Read more on Earth Science: How Many Continents Are There? Depends Whom You Ask

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