Indian Ocean

Topic: Oceans: Hydrological Cycle, Relief of the Ocean Floor, Temperature and Salinity · NCERT: Class 6, Ch 2 "Oceans and Continents"; Class 7, Ch 2 "India and Her Neighbours"

Meaning

The Indian Ocean is the third-largest ocean on Earth and the only ocean named after a country (India). Asia closes it to the north, Africa lies to the west, Australia to the east and the Southern Ocean to the south.

• It matters because its shape drives India's monsoon.
• It is also a busy highway of world trade. About two-thirds of the world's oil shipments and half of its container traffic cross it.

Explanation

Position and parts

• North: Asia, with India in the middle.
• West: Africa.
• East: Australia.
• South: the Southern Ocean, which surrounds Antarctica south of about 60°S [2].
• Two arms of the sea lie on either side of the Indian Peninsula:
• the Arabian Sea to the west

• the Bay of Bengal to the east

• Seas, bays and gulfs are smaller parts of an ocean that land partly encloses. Examples are the Arabian Sea, the Bay of Bengal and the Gulf of Mannar.

• No natural line separates the oceans. They are all joined in one World Ocean, so their boundaries are drawn by agreement.

Why it has the monsoon (cause → process → result)

• Cause: Asia closes the ocean off to the north.
• The Indian Ocean does not reach the cold Arctic.

• A large landmass sits right next to warm tropical water.

• Summer:

• Land heats up faster than water.
• The hot land makes the air pressure over Asia fall.

• Moist winds blow in from the south-west. They bring the south-west monsoon (the seasonal rain-bearing wind).

• Winter:

• Land cools faster than water.
• The winds reverse and blow from the north-east.

Reversing currents

• Ocean currents in the northern Indian Ocean follow the monsoon winds.
• So these currents change direction with the seasons.
• No other ocean has currents that reverse like this.

A highway of world trade

• About two-thirds of the world's oil shipments and half of its container traffic cross the Indian Ocean.
• Chokepoints (narrow sea passages that a lot of shipping must squeeze through) guard its entry and exit:

Chokepoint	Connects	Lies between
Strait of Hormuz	Persian Gulf ↔ Gulf of Oman/Arabian Sea	Iran and Oman
Bab-el-Mandeb	Red Sea ↔ Gulf of Aden	Yemen and Djibouti/Eritrea
Strait of Malacca	Indian Ocean (Andaman Sea) ↔ South China Sea/Pacific	Malay Peninsula and Sumatra (Indonesia)

Where it occurs

• India's seas:
• Arabian Sea (west of the peninsula), which holds Lakshadweep. These are small coral islands and atolls (ring-shaped coral reefs). The capital is Kavaratti.
• Bay of Bengal (east of the peninsula), which holds the Andaman and Nicobar Islands. These are a large chain, part of a drowned mountain range, with some volcanic islands such as Barren Island. The capital is Sri Vijaya Puram (formerly Port Blair).

• Gulf of Mannar, a gulf that is part of the Indian Ocean.

• India's maritime reach:

• India has 1,382 islands [4][5].
• India's coastline was earlier given as 7,516.6 km. It has now been re-measured at 11,098.81 km by the National Hydrographic Office together with the Survey of India [4][5].
• The coast touches nine coastal states [5].

• About 95% of India's trade by volume and about 70% by value goes by sea [5].

• World:

• Persian Gulf and Strait of Hormuz (Iran–Oman).
• Red Sea, Gulf of Aden and Bab-el-Mandeb (Yemen–Djibouti/Eritrea).
• Andaman Sea and Strait of Malacca (Malay Peninsula–Sumatra), the link to the Pacific.
• In the south, it merges with the Southern Ocean. There the Antarctic Circumpolar Current (the world's largest ocean current, flowing west to east around Antarctica) links its waters with those of the Pacific and Atlantic [2].

Don't confuse with

• Pacific Ocean: the Pacific is the largest and deepest ocean and holds the Challenger Deep (about 10,935 m) [3]. The Indian Ocean is only third in size.
• Southern Ocean: it lies south of 60°S and is defined by the Antarctic Circumpolar Current [2]. The Indian Ocean is closed by land (Asia) to the north, but the Southern Ocean has no land to its north.
• Arabian Sea / Bay of Bengal: these are arms (parts) of the Indian Ocean, not separate oceans. The Arabian Sea is to the west (Lakshadweep), and the Bay of Bengal is to the east (Andaman and Nicobar).
• Atlantic Ocean: it is the second-largest ocean and is open to the Arctic in the north. The Indian Ocean is cut off from the Arctic, which is why it has the monsoon and reversing currents.

Prelims Hooks

• Oceans by size: Pacific > Atlantic > Indian > Southern > Arctic. The Indian Ocean is third.
• The only ocean named after a country is the Indian Ocean.
• Seasonal reversal of ocean currents happens only in the northern Indian Ocean, caused by the monsoon winds.
• Chokepoint pairs: Hormuz → Iran–Oman; Bab-el-Mandeb → Red Sea–Gulf of Aden; Malacca → Malay Peninsula–Sumatra.
• Trap: Lakshadweep (coral) is in the Arabian Sea, and Andaman and Nicobar (drowned mountain range, plus volcanic Barren Island) is in the Bay of Bengal.
• India has 1,382 islands, and its re-measured coastline is 11,098.81 km [4].

Mains Points

• Landlocked to the north, so it drives the monsoon (GS-I):
• Asia closes the ocean off, so land and sea heat up at different speeds.
• This creates the south-west monsoon in summer and north-east winds in winter, and makes the currents reverse.

• Farming and water supply across South Asia depend on this one fact.

• Strategic and economic weight (GS-III):

• Two-thirds of world oil shipments and half of container traffic pass through the ocean, squeezed through Hormuz, Bab-el-Mandeb and Malacca.

• About 95% of India's trade by volume goes by sea [5]. So any disruption at a chokepoint directly hurts India's energy and trade security.

• India's maritime reach and needs (GS-III):

• India's 1,382 islands and 11,098.81 km coastline [4] put India at the centre of the ocean that bears its name.
• The Andaman and Nicobar Islands sit near the Strait of Malacca, and Lakshadweep lies along Arabian Sea routes.
• This calls for sea-route security and port development.

Related concepts

• Distribution of land and water
• Five oceans
• Southern Ocean

Read more

• Oceans and continents: five oceans and the unequal hemispheres