Background: The Indian Ocean is the third largest of the world's five ocean basins (after the Pacific Ocean and Atlantic Ocean, but larger than the Southern Ocean and Arctic Ocean). Four critically important access waterways are the Suez Canal (Egypt), Bab el Mandeb (Djibouti-Yemen), Strait of Hormuz (Iran-Oman), and Strait of Malacca (Indonesia-Malaysia). The International Hydrographic Organization decided in 2000 to delimit a fifth world ocean basin, the Southern Ocean, which removed the portion of the Indian Ocean south of 60 degrees south latitude.

Area
Total: 70.56 million km²
Note: includes Andaman Sea, Arabian Sea, Bay of Bengal, Great Australian Bight, Gulf of Aden, Gulf of Oman, Mozambique Channel, Persian Gulf, Red Sea, Savu Sea, Strait of Malacca, Timor Sea, and other tributary water bodies
Comparative: almost seven times the size of the US

Coastline: 66,526 km

Climate: northeast monsoon (December to April), southwest monsoon (June to October); tropical cyclones occur during May/June and October/November in the northern Indian Ocean and January/February in the southern Indian Ocean

Elevation
Highest point: sea level
Lowest point: Java Trench -7,192 m unnamed deep
Mean depth: -3,741 m
Ocean zones: the ocean is divided into three zones based on depth and light level; sunlight entering the water may travel about 1,000 m into the oceans under the right conditions, but there is rarely any significant light below 200 m
Euphotic zone: the upper 200 m (656 ft) is also called 'sunlight' zone; only a small amount of light penetrates beyond this depth
Dysphotic zone: between 200 m (656 ft) and 1,000 m (3,280 ft), and also called the twilight zone; the intensity of light rapidly dissipates as depth increases, and photosynthesis is no longer possible
Aphotic zone: below 1,000 m (3,280 ft) and also called the midnight zone; sunlight does not penetrate to these depths

Natural hazards: occasional icebergs pose navigational hazard in southern reaches

Geography
Note: major chokepoints include Bab el Mandeb, Strait of Hormuz, Strait of Malacca, southern access to the Suez Canal, and the Lombok Strait