Officially, there is only one global ocean that covers 71% of the planet and contains 97% of the world’s water.
This global body of water is divided into either four or five distinct regions or ocean basins, depending on who you talk to.
Historically, there have been just four oceans – the Arctic, Pacific, Atlantic, and Indian.
The fifth ocean, known as the Southern or Antarctic Ocean, was only officially recognized in 2021, but some still struggle to accept its existence.
Although no boundaries separate one ocean from another, each one is different in terms of its biodiversity and topography.
Temperature and salinity also vary from one ocean to the next, creating a variety of habitats that provide food and shelter for the world’s marine creatures.
How Many Oceans Are There?
There are five oceans in the world, all of which join together to create a single, interconnected ocean.
The Pacific Ocean is the largest body of water in the world, covering over 30% of the world’s surface.
It’s also the deepest ocean, averaging 4,000 meters or 13,000 feet. The deepest point on Earth is Challenger Deep in the Mariana Trench, where the sea floor lies some 10,924 meters below sea level.
Stretching from Southern California to China, the Pacific Ocean also borders South America and Australia on its western coast.
Although cooler than the Atlantic and the Indian Oceans, the Pacific Ocean is still relatively warm, with a surface temperature of around 70 to 80℉ (21 to 27 °C).
The average temperature of the deep zone sits at approximately 38.3 °F (3.5 °C) and remains fairly constant throughout the year.
Marine Life in the Pacific Ocean
The world’s oceans are home to approximately 228,450 known species, with biologists discovering more every year. Scientists identified 1,500 new species in 2020 alone and estimate that could be between “500,00 and 2 million more that have not been identified.”
It contains many critical ecosystems that support a diversity of marine life.
Coral reefs are dotted throughout the ocean, forming a critical part of the food chain and providing a habitat for reef sharks, fish, and sea turtles.
Dugongs and manatees rely on the seagrasses meadows that flourish in the Pacific Ocean for food and as a safe place to breed.
Although various shark species call the Pacific Ocean home, the most dangerous predator is the orca. Capable of coordinating and orchestrating complex hunting strategies, orca are opportunistic predators capable of taking down prey much larger than themselves.
In addition to the orca, bull sharks, tiger sharks, and great whites all live in the Pacific Ocean, along with some of the largest shark species, including the whale shark and basking shark.
The Atlantic Ocean lies between Europe and Africa on the eastern side and North and South America on the west. It is the second largest ocean in the world, covering around 20% of the earth’s surface.
Shallower than the Pacific, the Atlantic has an average depth of 3,646 meters or 11,962 feet. Its deepest point is in the Puerto Rico Trench at Milwaukee Deep, where the sea floor drops to 27,493 feet (8,380 meters) below sea level.
The temperature of the Atlantic Ocean’s surface varies seasonally between 33°F and 85°F. Its deep zone ranges between 50 °F and68 °F, depending on the latitude.
The Atlantic Ocean has the highest salinity of any ocean in the world, with maximum surface salinities reaching “35.5 parts per thousand” in the northern region.
This large body of water plays a vital role in global weather patterns, with the North Atlantic Drift and Gulf Stream warming areas of north Western Europe and the British Isles and contributing to the cold temperatures around Newfoundland.
Marine Life in the Atlantic Ocean
With its dramatic underwater topography and wide-ranging water temperature, the Atlantic Ocean is home to numerous marine species, from minuscule crustaceans to giant whales.
The Mid-Atlantic Ridge is a mountain range that runs beneath the ocean’s surface. It is the world’s longest mountain range and provides a habitat for around 1,000 different species, including “birds, dolphins, and whales.”
Of all the fish species living in the North Atlantic Ocean, the Atlantic salmon is the most iconic. Preyed on by large predatory fish, toothed whales, and Greenland sharks, the Atlantic salmon is an important oceanic prey species and one extensively fished by humans.
The Atlantic Ocean also hosts numerous shark species, from the diminutive spined pygmy shark, to the 40-foot-long whale shark.
The Indian Ocean is the third largest ocean in the world and much warmer than other oceans. Temperatures in the Indian Ocean reach 82 °F and vary little throughout the year.
Although the average depth of the Indian Ocean is deeper than that of the Atlantic, its deepest point is over 1,000 feet shallower than the Milwaukee Deep.
For a long time, it was believed that the deepest point in the Indian Ocean was in the Java or Sunda Trench, but new data revealed that the Diamantina Trench is nearly 3,000 feet deeper at 26,400 feet.
Stretching from Bangladesh, India, Iran, and Pakistan in the north to the Southern Ocean in the south, the Indian Ocean connects four continents, Asia, Africa, Australia, and Antarctica.
As a result, it’s been an important trade route for thousands of years.
Marine Life in the Indian Ocean
Scientists believe there to be around 24,000 different species of plants and animals in the Indian Ocean, but there could be many more. This ocean remains virtually unexplored compared to other oceans, so many secrets are yet to be uncovered.
The Indian Ocean region has a range of habitats and aquatic flora, including seagrass meadows, coral reefs, dunes, and mangrove forests. Marine life thrives here, with dugongs grazing on seagrass while fish and sea turtles feed off the reefs.
Approximately 19 different species of sharks explore the warm tropical waters of the Indian Ocean, including Oceanic whitetips and silky sharks.
Approximately two-thirds of the world’s coral reef fish species live here, along with an abundance of sea cucumbers and mollusks.
Forming the northernmost section of our global ocean, the Arctic Ocean is the coldest yet shallowest of all the oceans.
At its deepest, it reaches just 18,210 feet and has an average depth of 4,468 feet (1361 m).
Temperatures in the Arctic Ocean are extremely cold but constant, averaging around −1.8 °C (28.8 °F).
The salinity in the Arctic Ocean is much lower than that of the Atlantic, as it receives lots of fresh water from rivers and streams. It also loses salt through evaporation.
Marine Life in the Arctic Ocean
The Arctic Ocean is an inhospitable place characterized by areas of ice cover and periods of continuous daylight. In the winter, temperatures plummet as low as −22°F (−30 °C), and the whole ocean is shrouded in darkness.
Despite these conditions, the Arctic Ocean supports a complex ecosystem teeming with life. Tiny plankton convert carbon dioxide into organic matter and become food for predatory fish and enormous. bowhead whales
Polar bears prowl the ice looking for seals, while Greenland sharks scavenge on the remains of decomposing carcasses some 2,500 feet below sea level. Dive even deeper, and you’ll discover “bottom-dwelling organisms like sea anemones, corals, and sponges.”
National Geographic may recognize the existence of the Southern Ocean, but the International Hydrographic Organization has yet to endorse it.
Part of the problem is that the Southern Ocean’s northern boundary is marked only by a current rather than a land mass.
The Antarctic Circumpolar Current flows from west to east around Antarctica, marking the end of the Southern Ocean and the beginning of the Atlantic, Pacific, and Indian oceans.
The Southern Ocean is over double the depth of the Arctic, averaging 10,728 feet (3,270 meters). Its deepest point is in the South Sandwich Trench, where the ocean floor drops to “nearly 24,400 feet (7,437 meters) below the sea surface.”
Almost as cold as the Arctic, the Southern Ocean has an average temperature of 2-4°C, and experiences some of the “strongest winds on Earth.”
Marine Life in the Southern Ocean
In 2000, the Census of Antarctic Marine Life (CAML) identified 15,500 different organisms, from microbes to whales, but the Antarctic Ocean is most famous for its populations of “emperor penguins and wandering albatrosses, blue whales and fur seals“.
Under the ice, “massive populations of phytoplankton” bloom, feeding the Antarctic krill that, in turn, provide sustenance for a wide range of fish species, penguins, seals, and whales.
Baleen whales, including the blue, humpback, and fin whale consume massive amounts of krill daily, and are thought to have eaten “around 430 million tonnes of krill per year before industrial whaling began in the early 20th century.”
Fish are also abundant in the Southern Ocean, with approximately 200 species surviving in its chilly waters. The Antarctic Ocean is also home to around 60% of the world’s seal population, including elephant seals, and Antarctic fur seals.
There may be only one world ocean, but each of its five regions or ocean basins is different. Greenland sharks and polar bears flourish in the Arctic Ocean, while dugongs and turtles prefer the warm tropical waters of the Indian Ocean.
Sea lions give the Atlantic Ocean a wide berth, preferring the chilly temperatures and strong winds of the Antarctic.
Each of our five world oceans offers a different environment for marine life to thrive. The Indian Ocean is warm, while the Atlantic is salty.
The Pacific Ocean provides life for deep-sea creatures such as sea cucumbers and snails, while the Arctic’s cold waters are perfect for the slow-moving Greenland shark.
Climate change, pollution, and overfishing endanger all our marine ecosystems, with scientists fearing that nearly every “marine species could face extinction by the end of the century.”
Nicky is a British adventurer and animal lover who spends her time exploring the natural world and writing about her experiences. Whether on horseback, underwater, running, hiking or just standing with a fishing rod in hand, she embraces everything her adopted home of South Africa has to offer.