Indian Ocean

The Indian Ocean is bounded by Africa and the Arabian Peninsula to the west, Asia to the north, Australia and the Indonesian archipelago to the east, and the Southern Ocean to the south. Its exact limits at the Atlantic and Pacific connections depend on the boundary convention used. Encyclopaedia Britannica gives its area, excluding marginal seas, as about 70.56 million square kilometres, approximately one-fifth of the world's ocean area. It is the smallest of the three major oceans commonly listed as the Pacific, Atlantic and Indian.

Prominent northern marginal waters include the Red Sea, Persian Gulf, Arabian Sea and Bay of Bengal; the Andaman Sea lies farther east. The basin contains a system of mid-ocean ridges, plateaus and deep basins. One major tectonic feature is the Java Trench, part of the subduction zone south of Indonesia. The ocean's geological history is linked to the breakup of Gondwana and the movement of the Indian subcontinent toward Eurasia. These processes helped shape its ridges, islands and continental margins.

The Indian Ocean is distinctive among the major oceans because seasonal monsoon winds strongly affect circulation in its northern part. Surface currents north of roughly 10° south can reverse seasonally as the winds change, while patterns farther south are steadier. The Somali Current and currents in the Arabian Sea and Bay of Bengal form parts of this complex system. Long-term buoy observations in the northern Indian Ocean support research on weather, climate, fisheries and monsoon forecasting. Regional current behaviour can be nuanced: NOAA's Pacific Marine Environmental Laboratory has reported observations of Bay of Bengal surface flow to the left of surface winds, contrary to the commonly expected Ekman response.

The ocean borders many countries and island states and supports coastal communities, fisheries and marine habitats. Its routes connect ports across Africa, the Middle East, South Asia, Southeast Asia and Australia. UN Trade and Development (UNCTAD) notes that about 80 percent of the volume of international trade in goods is carried by sea, underscoring the wider importance of maritime transport; this is a global figure, not an Indian-Ocean-specific share. The region also contains coral reefs, mangroves, seagrass beds and open-ocean ecosystems. Their condition varies by location and is affected by pressures such as warming, pollution and fishing, making monitoring and sustainable management important.