By: Pratyush Bardoliwala
Look at a map of Earth and one fact immediately stands out: our planet is dominated by water. The ocean covers about 71% of Earth’s surface, influencing everything from climate and weather to marine ecosystems, food supplies and global trade. Although we commonly speak of five oceans, they are actually interconnected parts of one global ocean.
The five recognised oceans are the Pacific, Atlantic, Indian, Southern and Arctic oceans. Each has its own geography, depth, climate and marine environment. Some stretch across enormous distances, while others are relatively small but play an important role in Earth’s climate system.
There is also a remarkable amount that remains unknown beneath the surface. NOAA says less than 5% of the ocean has been explored. When it comes to actually seeing the deep-ocean seafloor, humans have visually observed less than 0.001%. Meanwhile, modern high-resolution mapping had covered 28.7% of the global seafloor as of April 2026. Mapping and exploration are different things, but both figures show just how much of the underwater world remains to be studied.
Pacific Ocean
The Pacific Ocean lies between Asia and Australia to the west and North and South America to the east. It stretches from the Arctic region in the north towards the Southern Ocean, covering an enormous area of open water and thousands of islands.
The Pacific is the largest and deepest of the five oceans. It covers more than 160 million square kilometres and contains the Mariana Trench. At Challenger Deep, the deepest known point in the world’s oceans, the seafloor lies about 10,935 metres below sea level. The average depth of the global ocean, by comparison, is about 3,682 metres.
Its importance extends far beyond its size. The Pacific influences global climate and weather, supports enormous marine ecosystems and provides important fishing grounds. It is also a major route for international shipping and connects many countries across Asia, Oceania and the Americas.
Atlantic Ocean
The Atlantic Ocean stretches between the Americas to the west and Europe and Africa to the east. It reaches towards the Arctic in the north and connects with the Southern Ocean in the south.
With an area of roughly 106 million square kilometres, the Atlantic is the world’s second-largest ocean by area. Its average depth is around 3,600 metres, although some parts descend more than 8,000 metres beneath the surface.
The Atlantic has played a major role in human history, connecting Europe, Africa and the Americas through centuries of exploration, migration and trade. It remains an important global shipping route today and supports extensive fisheries and diverse marine ecosystems.
Indian Ocean
The Indian Ocean lies between Africa to the west, Asia to the north, Australia to the east and the Southern Ocean to the south. For countries surrounding its waters, it is both a major geographical feature and an important economic and climatic force.
Covering roughly 70 million square kilometres, the Indian Ocean is the third-largest of the five oceans. Its waters reach considerable depths, with the deepest areas extending beyond 7,000 metres.
The Indian Ocean is particularly important to India and the wider South Asian region. Its waters are closely linked to the Indian monsoon, which influences rainfall across much of South Asia. It is also a major international shipping corridor, connecting the Middle East, Africa, South Asia, Southeast Asia and Australia.
Southern Ocean
The Southern Ocean surrounds Antarctica, forming a continuous body of water around the continent. It connects with the southern portions of the Atlantic, Pacific and Indian oceans and is known for its cold waters, powerful winds and strong currents.
The Southern Ocean covers roughly 20 million square kilometres, although its exact size can vary depending on how its boundaries are defined. Large areas are deep, and the region experiences some of the harshest marine conditions on the planet.
Despite its remote location, the Southern Ocean has a global influence. Its powerful currents help transport heat and nutrients around the planet and play an important role in Earth’s climate system. Its waters also support Antarctic wildlife, including penguins, seals and whales.
Arctic Ocean
The Arctic Ocean surrounds the North Pole and is bordered by parts of North America, Europe and Asia. It is the smallest of the five oceans and much of its surface is covered by sea ice for at least part of the year.
Covering approximately 14 million square kilometres, the Arctic is also the shallowest of the five oceans. Its average depth is around 1,200 metres, although some areas are considerably deeper.
Despite its size, the Arctic Ocean has an influence that reaches far beyond the polar region. Sea ice reflects sunlight back into space and plays a role in Earth’s climate system. The region also supports wildlife adapted to its extreme conditions, including polar bears, seals and walruses.
The five oceans may be divided by geographical boundaries, but they do not function as five completely separate bodies of water. Ocean currents constantly move water, heat and nutrients around the planet, linking these vast regions together.
Together, they influence the weather we experience, support marine food webs, provide resources and livelihoods, and carry a significant share of global trade. The ocean also plays a crucial role in regulating Earth’s climate.
Yet for all our dependence on it, much of the ocean remains beyond our direct view. Less than 5% has been explored, and the amount of the deep seafloor that humans have actually seen is tiny.
That makes the world’s oceans more than just geographical divisions on a map. They are enormous, interconnected environments containing landscapes, ecosystems and species that we are still working to understand.
And this is only the beginning.
In the next parts of this series, we can go deeper into each ocean, exploring its seas, islands, currents, marine life, trenches and extreme environments — gradually moving from the parts we know well to the parts that humans have barely seen.
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