The Indian Ocean
The Indian Ocean is the third-biggest ocean and by far the warmest. It is bordered by Africa to the west, Asia to the north, Australia to the east and the Southern Ocean to the south. People have been sailing across it for thousands of years, riding seasonal winds called monsoons that blow first one way and then the other.
- Surface area70.6 million km²Third biggest ocean
- Average depth3,741 mDeeper than the global ocean average
- Deepest pointJava Trenchapprox. 7,290 m, near Indonesia
- Surface tempUp to 28 °CThe warmest of the major oceans
- % of Earthapprox. 20%Of the planet's water surface
- Famous featureThe monsoonsSeasonal winds that shape the climate
Where the Indian Ocean fits in
Area in millions of km².
The Indian Ocean is two thirds the size of the Atlantic, but is the only one entirely in the warmer southern half of the world.
What is the Indian Ocean?
The Indian Ocean is the body of warm tropical water bordered by three continents: Africa, Asia and Australia. It is the only ocean named after a country (India) and the only one not connected to the Arctic. Its main seas include the Arabian Sea, the Bay of Bengal, the Andaman Sea, the Red Sea and the Persian Gulf.
The monsoon winds
The Indian Ocean is famous for its monsoons: seasonal winds that completely reverse direction twice a year. From May to September, the south-west monsoon blows from the ocean over India and Southeast Asia, bringing huge amounts of rain. From October to April, the north-east monsoon blows the other way, from the cool Asian continent over the ocean, with much drier weather.
The monsoon rains feed the rivers and crops of more than a billion people in India and Bangladesh. They have shaped the entire history and culture of the region. Without the monsoon, much of South Asia would be desert.
Wildlife of the Indian Ocean
The Indian Ocean is home to many unique species. The dugong (a gentle plant-eating sea mammal related to the elephant) lives in its warm shallow waters. Whale sharks (the biggest fish on Earth) gather off the coast of Western Australia and the Maldives each year. The Andaman Sea is dotted with thousands of small islands and is one of the best coral-reef regions in the world.
The ocean is also famous for its rare and beautiful islands: the Maldives, Seychelles, Mauritius, Reunion and Madagascar all sit in or around it.
Trade and history
The Indian Ocean was the heart of the world's trading network for centuries. Arab, Indian, Persian, Chinese, Malay and African merchants all sailed it long before Europeans arrived. Spices, silk, gold, ivory, slaves, ideas and religions all flowed across the Indian Ocean, linking three continents together. The Portuguese explorer Vasco da Gama was the first European to sail from Europe to India by sea, in 1498.
Deeper dive: the monsoon mechanism, the Indian Ocean Dipole and the Suez Canal
The monsoon is driven by the temperature difference between the Asian continent and the Indian Ocean. In summer the land heats up faster than the sea, creating low pressure over Asia that pulls in moist air from the ocean to the south. As this moist air rises over the mountains of India and Southeast Asia, it cools, condenses and dumps huge amounts of rain. In winter the land cools faster than the sea, the pressure reverses, and dry air flows from the land out over the ocean. Cherrapunji in north-east India holds the world record for annual rainfall thanks to monsoon air being forced up over the foothills of the Himalayas.
A less well-known but increasingly important climate pattern is the Indian Ocean Dipole, sometimes called the "Indian Niño". It is a periodic difference in surface temperatures between the western and eastern Indian Ocean. In a positive phase, the west is warmer than usual and the east is cooler, bringing drought to Indonesia and Australia and floods to East Africa. In a negative phase the opposite happens. The Dipole interacts with El Niño in the Pacific to influence weather across both ocean basins and as far away as southern Europe.
The Suez Canal in Egypt connects the Mediterranean Sea to the Red Sea and therefore to the Indian Ocean. Opened in 1869, it cut weeks off the journey between Europe and Asia by eliminating the need to sail all the way around Africa. The canal is still one of the most important shipping routes in the world, with approx. 12% of global trade passing through it. In 2021 the giant container ship Ever Given ran aground in the canal, blocking it for six days and disrupting global supply chains.
The biggest ocean is the Pacific. The second biggest is the Atlantic. The icy ones at the top and bottom of the world are the Arctic and the Southern.