How many oceans exist on Earth?

Astronauts who have seen Earth from space often refer to it as a 'blue marble,' a reflection of how much water covers its surface. This water, totaling 321,003,271 cubic miles (1,338,000,002 cubic kilometers) of salt water, constantly circulates, nourishing life on our planet. But the question remains: how many oceans truly exist?

Despite the oceans' vast presence, we know remarkably little about them. For example, over 85% of the ocean floor remains unmapped with the same precision as the surface of Venus. We've only identified about a third of the marine species in our oceans, and we still can't trace most of the trillions of tons of plastic polluting these waters.

How Many Oceans Does Our Planet Have?

Humans have long divided the vast, continuous, and mysterious water that envelops the Earth into sections we call oceans. In the past, there were four oceans, but today we recognize five distinct ones: the Pacific, Atlantic, Arctic, Indian, and Southern Oceans.

The Pacific, Atlantic, and Indian Oceans all converge and freeze together around Antarctica.

How Are the World's Oceans Divided?

Unlike landmasses, there are no true boundaries separating the world's oceans. Instead, water often serves as the natural separator for geographic regions. Just as an island’s limits are defined by surrounding water, continents use oceans as natural borders to define their boundaries.

There is, in fact, only one global ocean, yet for the sake of geography, we make distinctions between different regions.

Although the Atlantic Ocean is part of the same global ocean as the Pacific, many consider the Drake Passage — the narrow body of water separating Antarctica from Cape Horn at the southern tip of South America — as the dividing line between these two oceans.

Though you may come across videos online claiming to show that the waters of two oceans don't mix, it's impossible to truly separate any of the Earth's oceans.

The 'Newest' Ocean

For much of the 20th century, the Southern Ocean that encircles Antarctica was in a sort of naming limbo. While the International Hydrographic Organization (IHO) acknowledged it before 1937, its recognition was withdrawn in 1953.

In 1999, the National Oceanic and Atmospheric Administration (NOAA) officially recognized the Southern Ocean as its own distinct body of water, but it wasn’t until 2021 that both the IHO and the National Geographic Society acknowledged it as separate from the Pacific Ocean.

The 5 Oceans of Planet Earth

All oceans are quite similar, considering they are essentially the same body of water. However, subtle differences in temperature, salinity, and density do exist across them.

For example, the Atlantic Ocean is somewhat saltier than the Pacific Ocean, due to a wide range of factors, including the water cycle and the influence of hydrothermal vents.

Pacific Ocean

The Pacific Ocean is the largest and deepest of all five oceans, spanning more than 30 percent of the Earth's surface and containing over half of the planet's surface water.

Covering an area of 60 million square miles (155 million square kilometers), the Pacific is larger than all the continents combined. Challenger Deep, located in the Pacific’s Mariana Trench, is the deepest point in any ocean on Earth.

In 1520, Ferdinand Magellan gave the Pacific Ocean its name after sailing through a particularly calm section, which he called Pacific for its serene waters.

Despite its peaceful name, the Pacific is home to some of the planet's most violent storms and the "Ring of Fire," a region known for its intense seismic and volcanic activity.

Atlantic Ocean

The Atlantic Ocean ranks as the second largest ocean in the world. Spanning an area of approximately 41 million square miles (106,460,000 square kilometers), it covers around 23 percent of the Earth's surface.

The width of the Atlantic varies greatly — in some areas, it stretches up to 3,000 miles (4,800 kilometers), while in other regions, such as between Brazil and Liberia, it narrows to just 1,770 miles (2,850 kilometers). This uneven expanse gives the Atlantic its characteristic "S" shape.

The Atlantic Ocean is bordered by several marginal seas, including the Hudson Bay, the Caribbean Sea, the Mediterranean Sea, and the English Channel. These shallow seas all feed into the vast Atlantic.

Indian Ocean

Covering an area of 27,243,000 square miles (70,560,000 square kilometers), the Indian Ocean is the third largest ocean, unique for being bordered by land on three sides. It stretches between Africa, Asia, and Australia, and connects to the Southern Ocean, where it mingles with much colder waters.

Cartographers do not have a universal consensus on where the Indian Ocean ends and the Southern Ocean begins, but it is commonly accepted to be around latitude 60 degrees S.

The Indian Ocean, located predominantly around the equator, experiences the warmest temperatures of any ocean.

Southern Ocean

The Southern Ocean, sometimes referred to as the Antarctic Ocean, is the fourth largest ocean and the most recently recognized. It covers an area of 7,848,300 square miles (20,327,000 square kilometers) and boasts the deepest average depth of any ocean, with very few shallow regions.

Unlike most of the world's oceans, the Southern Ocean is separated from its neighboring oceans by a current, rather than by landmasses.

The Antarctic Circumpolar Current (ACC) is the most powerful ocean current on Earth, transporting up to 182 million cubic meters of water per second. Flowing from west to east around Antarctica, it distinguishes the Southern Ocean from the saltier waters of the Atlantic, Pacific, and Indian Oceans, moving over 100 times the volume of all the Earth's rivers combined.

Arctic Ocean

The Arctic Ocean is relatively small and shallow compared to the other oceans. With an area of 5,427,000 square miles (14,056,000 square kilometers), it makes up about 4 percent of Earth's surface. It is the coldest ocean, mainly because much of it remains frozen throughout the year.

Beginning in the 15th century, the Arctic Ocean became a focal point for sea exploration, as European explorers and traders sought a northern sea route between the Atlantic and Pacific Oceans for easier access to Asian markets.

Although many expeditions ended in failure, in 1906, Norwegian explorer Roald Amundsen successfully navigated from the Atlantic to the Pacific through the Northwest Passage.