Indian Ocean is the third largest ocean on earth. It comes behind pacific and Atlantic ocean in size and holds almost 20 percent of the water on the earth’s surface. It is the youngest and physically most complex ocean in the world and covers one fifth of the total ocean area in the world. Indian Ocean draws its boundaries with Asia to its north, Africa on its west, Australia to its east and Southern ocean and Antarctica to its south. Though all the world’s oceans are interconnected, the boundary between Indian Ocean at Atlantic Ocean is considered to be at 20⁰ east meridian which runs south from Cape Agulhas, and the boundary between Indian Ocean and Pacific Ocean is considered to be at 146⁰55’ east meridian.
The Indian Ocean has an estimated volume of about 292,131,000 cubic kilometres and it covers an area of around 73,556,000 square kilometres including the Red sea and the Persian Gulf. The northernmost point of the ocean is 30⁰ north of equator in the Persian Gulf. The ocean is more than 10000 kilometres wide between the southern tip of Africa and Australia. The ocean has large number of islands that dots the continental rims. The main island nations in Indian Ocean include Madagascar, Sri Lanka, Bahrain, Maldives, Mauritius, Seychelles and the archipelago of Indonesia. The average depth of the ocean is 3960 meters, and at its deepest point; the Sunda Deep of the Java trench, it is 7450 meters deep.
Compared to other oceans, Indian Ocean has very few marginal seas. The major seas are Red sea and Persian Gulf to the inland north, Arabian Sea, the gulfs of Aden and Oman to the North West, Andaman Sea and Bay of Bengal to the north east, and the Great Australian Bight odd the southern coast of Australia. Indian Ocean also differs from other oceans in many aspects as it is the only ocean landlocked in the northern region and has no connection to the Arctic waters.
The ocean floor of Indian Ocean is characterised by an inverted Y shaped mid oceanic ridge, this is formed because of the convergence of the African, Antarctica and Indian crustal plates in the Indian Ocean. This mid oceanic ridge divides the ocean into eastern, western, and southern basins, which are further subdivided into smaller basins by other ridges. The ocean has very narrow continental shelves compared to other oceans with an average width of around 200 kilometres.
Indian Ocean was formed almost 150 million years ago, when the southern super continent Gondwana started to breakup. The north east portion of gondwana, the Indian sub continent started to move up and collide with the Eurasia about 125 million years ago. Western movement of Africa, and splitting up of Australia from Antarctica started about 53 million years ago and Indian ocean as we see now took shape about 36 million years ago and hence making it one of the youngest oceans in the world.
There are many extinct submarine volcanoes that are conically shaped and often flat-topped, which rises up to 1000 meters above the ocean floor, they are found more often Seychelles and nearby regions. The ocean floor is characterised by basins with smooth flat plains with abyssal hills at the lower regions of the mid oceanic ridge. The Ganges, Indus, and the Zambezi rivers, all which flows to Indian ocean creates large canyons because of the sediment loads that they deposits at their joining points. The Ganges sediment cone is the widest and thickest sediment cone in the world.
The coasts of Indian Ocean are made up of several well defined coastal configurations. The coast lines is made up of estuaries, deltas, salt marshes, cliffs, mangrove swamps, coral reefs, lagoons, dunes and beaches. The sundarbans, situated in the lower parts of the Ganges river delta is the largest mangrove forest in the world. Coral reefs in either fringing, barrier or atoll forms are found abundant around all the islands in the tropic region and along the southern coasts of Bangladesh, Myanmar and eastern coasts of Africa.
Bordering countries and territories
French Southern and Antarctic Lands (FRA)
|United Arab Emirates|
Réunion Réunion (FRA)
Mayotte Mayotte (FRA)
| British Indian Ocean Territory (UK)|
Cocos (Keeling) Islands (AUS)
|Australasia||Ashmore and Cartier Islands (AUS)|
|Southern Indian Ocean||Heard Island and McDonald Islands (AUS)|
French Southern and Antarctic Lands (FRA)
The Indian Ocean is one of the warmest oceans in the world. The climate north of the equator is affected by the monsoon season. There are strong north east winds during October to April, and strong south and west winds prevail from May to October. The monsoon winds bring rains to the Indian subcontinent. The winds in the southern hemisphere regions of the Indian Ocean are far milder. Based on the atmospheric circulation, Indian Ocean can be subdivided into four latitudinal climatic zones; the monsoon zone, trade wind zone, Subtropical temperate zone, and subantarctic and Antarctic zone.
The monsoon zone extends north from 10⁰ south latitude. This region has the monsoon climate which is characterised by semi-annual reversing winds. The northwest parts of this region has dry climate with rainfall less than 10 inches per year, and the equatorial regions are the wettest with an average rainfall of more than 80 inches. The trade winds zone lies between 10⁰ and 30⁰ south latitudes. These regions are characterized by steady south easterly trade winds. The sub tropic temperate zone lies between 30⁰ and 45⁰ south latitudes. This region has light and variable prevailing winds in the northern region, and strong westerly winds in the southern region. The temperatures fall as we go down south in this region. The rainfall is moderate and uniformly distributed in this region. The sub Antarctic and Antarctic zone lies between 45⁰S latitude and the continent of Antarctica. This region experiences steady westerly winds and temperature between 6 to -4⁰C.
There are many large rivers that flow into Indian Ocean. The bigger ones include Zambezi, Indus, Ganges, Brahmaputra, and Irrawaddy rivers. The surface water salinity of Indian Ocean ranges between 32 to 37 parts per thousand, making it one of the saltiest oceans in the world. The salinity is highest in the Arabian ocean. Icebergs are found throughout the year at latitudes below 65⁰ S in Indian Ocean.
The ocean currents in the Indian Ocean are mainly controlled by the monsoon. There are two large circular currents in this ocean. The one in the northern hemisphere flows clockwise, and the one in the region south of equator flows anticlockwise. But the currents in the northern hemisphere get reversed during winter monsoon period. The underwater currents are mainly controlled by the inflows from Atlantic Ocean, Red sea, and Antarctic Ocean currents. The surface water temperature north of 20⁰S latitude is on an average 22⁰C. The surface water temperature drops quickly as we move far south below 40⁰ south latitude.
Indian Ocean is one of the key sea routes that connect Middle East, Africa, and East Asia with Europe and America. It is estimated that about 40 percent of the world’s offshore oil production is happening in the Indian Ocean. Offshore areas of Saudi Arabia, Iran, India and Western Australia have large reserves of hydrocarbons, and hence the ocean holds a key role in the heavy traffic of petroleum and related products from these oil fields of the Persian Gulf, and Indonesia. The major ports in Indian ocean includes Durban, Maputo and Djibouti along the African coast, Aden in Yemen, Karachi, Mumbai, Chennai and Kolkata in Indian sub continent, Colombo in Sri Lanka, and Melbourne, and Adelaide in Australia.
Marine and other resources
Life in Indian Ocean is limited because of the warm temperatures of the ocean which keeps the production of phytoplankton low. Marine life is very low in the ocean except in some places in the northern fringe and other few scattered pockets. Fishing is an important livelihood for people of all bordering countries. Countries such as Russia, Japan, South Korea and Taiwan also do fishing in the India Ocean, mainly the shrimp and tuna. The ocean is also home to many endangered marine species such as, seals, turtles, and whales.
The most valuable mineral resource in Indian Ocean is the oil and natural gas. Other minerals such as ilmenite, tin, zircon and chromite are also found in the near shore sand bodies. The ocean also has many biological resources. The shallow waters in the tropical regions of the ocean are idea locations for corals and other organisms that can build large coral reefs and coral islands. These marine structures give home to large thriving fauna of marine animals such as sponges, worms, crabs, sea urchins, star fish, and the reef fishes. The tropical coasts also have many mangrove forests that have many animals specific to that environment. These mangrove forests also help in stabilising the land along the coastal margin and act as a breeding ground for many offshore species.