The Indian Ocean is the third-largest of the world's five oceanic divisions, covering 70,560,000 km2 (27,240,000 sq mi) or approximately 20% of the water area of Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by the Southern Ocean or Antarctica, depending on the definition in use. The Indian Ocean has large marginal or regional seas, including the Andaman Sea, the Arabian Sea, the Bay of Bengal, and the Laccadive Sea. Geologically, the Indian Ocean is the youngest of the oceans (being directly preceded by the Tethys Ocean, which fragmented into the Mediterranean Sea and the Indian Ocean only 20 million years ago), and it has distinct features such as narrow continental shelves. Its average depth is 3,741 m. It is the warmest ocean, with a significant impact on global climate due to its interaction with the atmosphere. Its waters are affected by the Indian Ocean Walker circulation, resulting in unique oceanic currents and upwelling patterns. The Indian Ocean is ecologically diverse, with important ecosystems such as coral reefs, mangroves, and seagrass beds. It hosts a significant portion of the world's tuna catch and is home to endangered marine species. The climate around the Indian Ocean is characterized by monsoons. The Indian Ocean has been a hub of cultural and commercial exchange since ancient times. It played a key role in early human migrations and the spread of civilizations. In modern times, it remains crucial for global trade, especially in oil and hydrocarbons. Environmental and geopolitical concerns in the region include climate change, overfishing, pollution, piracy, and disputes over island territories.
Etymology The Indian Ocean has been known by its present name since at least 1515, when the Latin form Oceanus Orientalis Indicus (lit. 'Indian Eastern Ocean') is attested, named after India, which projects into it. It was earlier known as the Eastern Ocean, a term that was still in use during the mid-18th century, as opposed to the Western Ocean (Atlantic) before the Pacific was surmised. The modern Hindi name for the Ocean is हिंद महासागर (Hind Mahāsāgar; lit. transl. Ocean of India). Conversely, Chinese explorers (e.g., Zheng He during the Ming dynasty) who traveled to the Indian Ocean during the 15th century called it the Western Oceans. In Ancient Greek geography, the Indian Ocean region known to the Greeks was called the Erythraean Sea. In traditional Indian geography, the ocean is historically called the Mahodadhi (Sanskrit: महोदधि, romanized: Mahōdadhi, lit. 'ocean, big sea'), divided into the two seas Purvapayodhi (Sanskrit: पूर्वपयोधि, romanized: Pūrvapayōdhi, lit. 'sunrise', referring to the Bay of Bengal) and Apara (Sanskrit: अपर, romanized: Apara, lit. 'sunset', referring to the Arabian Sea). Another name used for the Indian Ocean is Ratnakara (Sanskrit: रत्नाकर, romanized: Ratnākara, lit. 'one having jewels, mine of jewels, repository of jewels').
Geography
Extent and data The borders of the Indian Ocean, as delineated by the International Hydrographic Organization in 1953, included the Southern Ocean but not the marginal seas along the northern rim. In 2002 the IHO delimited the Southern Ocean separately, which removed waters south of 60°S from the Indian Ocean but included the northern marginal seas. Meridionally, the Indian Ocean is delimited from the Atlantic Ocean by the 20° east meridian, running south from Cape Agulhas, South Africa, and from the Pacific Ocean by the meridian of 146°49'E, running south from South East Cape on the island of Tasmania in Australia. The northernmost extent of the Indian Ocean (including marginal seas) is approximately 30°N in the Persian Gulf. The Indian Ocean covers 70,560,000 km2 (27,240,000 sq mi), including the Red Sea and the Persian Gulf but excluding the Southern Ocean, or 19.5% of the world's oceans. Its volume is 264,000,000 km3 (63,000,000 cu mi) or 19.8% of the world's oceans' volume; it has an average depth of 3,741 m (12,274 ft) and a maximum depth of 7,290 m (23,920 ft). All of the Indian Ocean is in the Eastern Hemisphere. The centre of the Eastern Hemisphere, the 90th meridian east, passes through the Ninety East Ridge. Within these waters are a number of islands. These include those controlled by surrounding countries, and independent island states and territories. Of the non-coastal islands, there are two broad clusters: one around Madagascar, and one south of India. A few other oceanic islands are scattered elsewhere.
Coasts and shelves In contrast to the Atlantic and Pacific, the Indian Ocean is enclosed by major landmasses and an archipelago on three sides and does not stretch from pole to pole, and can be likened to an embayed ocean. It is centered on the Indian Peninsula. Although this subcontinent has played a significant role in its history, the Indian Ocean has foremostly been a cosmopolitan stage, interlinking diverse regions by innovations, trade, and religion since early in human history. The active margins of the Indian Ocean have an average width (horizontal distance from land to shelf break) of 19 ± 0.61 km (11.81 ± 0.38 mi) with a maximum width of 175 km (109 mi). The passive margins have an average width of 47.6 ± 0.8 km (29.58 ± 0.50 mi). The average width of the slopes (horizontal distance from shelf break to foot of slope) of the continental shelves are 50.4–52.4 km (31.3–32.6 mi) for active and passive margins respectively, with a maximum width of 205.3–255.2 km (127.6–158.6 mi). In correspondence of the Shelf break, also known as Hinge zone, the Bouguer gravity ranges from 0 to 30 mGals that is unusual for a continental region of around 16 km thick sediments. It has been hypothesized that the "Hinge zone may represent the relict of continental and proto-oceanic crustal boundary formed during the rifting of India from Antarctica." Australia, Indonesia, and India are the three countries with the longest shorelines and exclusive economic zones. The continental shelf makes up 15% of the Indian Ocean. More than two billion people live in countries bordering the Indian Ocean, compared to 1.7 billion for the Atlantic and 2.7 billion for the Pacific (some countries border more than one ocean).
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